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Nitrogen-doped Bernal graphene has several advantages, including improved electrical conductivity, enhanced stability and better compatibility with electrolytes. This article presents the synthesis of few-layer pristine graphene and nitrogen-doped Bernal graphene (CVDNG) through the Low-pressure chemical vapor deposition approach and its application for flexible supercapacitors. A novel hot lamination-assisted approach is employed to transfer the graphene on the desired substrates, enabling the reusability of copper. Raman mapping is utilized to analyze the characteristic bands and statistical distribution of Bernal stacking in CVDNG. The doping in graphene is confirmed through the X-ray photoelectron spectroscopy suggesting the content of pyrrolic-N (73.38%), pyridinic-N (20.28%) and graphitic-N (6.38%) in the CVDNG. Cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy are performed by sandwiching the polyvinyl alcohol-sodium perchlorate based hydrogel membrane between two symmetrical supercapacitor electrodes. CVDNG symmetrical supercapacitor device delivers an enhanced areal capacitance of 26.75 mF cm−2 with a high energy density of 2.14 mWh cm−2 with a power density of 72 mW cm−2 at 0.05 mA cm−2. The device shows excellent flexibility by retaining 91.1% of its capacitance at extreme bending (180° angle) conditions and excellent specific capacitance retention (90.6%) after 10,000 charge-discharge cycles. [Display omitted] • Nitrogen-doped Bernal graphene through the LPCVD approach for flexible supercapacitors. • A novel PMMA free approach to transfer the graphene, enabling the reusability of copper. • NaClO 4 -PVA based quasi-solid-state hydrogel membrane electrolyte. • The device shows excellent flexibility by retaining 91.1% of its capacitance at extreme bending (180° angle) conditions. • Excellent specific capacitance retention (90.6%) after 10,000 charge-discharge cycles. [ABSTRACT FROM AUTHOR]

Ti 3 C 2 T x has attracted great attention as negative electrode material of supercapacitors owing to its high metallic conductivity, abundant surface terminations, and suitable potential range. However, the inevitable restacking of two-dimensional nanosheets dramatically restrain the electrochemical performances of individual Ti 3 C 2 T x electrodes. In this work, interface-induced in-situ growth strategy was developed to construct W 18 O 49 /Ti 3 C 2 T x heterostructures through a simple solvothermal reaction. The optimized W 18 O 49 /Ti 3 C 2 T x hybrid electrode delivered a high specific capacitance of 472.6 F g−1 at 1 mV s−1 and retained 73.3% of its initial capacitance under 100-fold scan rate. The asymmetric supercapacitor assembled with W 18 O 49 /Ti 3 C 2 T x negative electrode and RuO 2 @CC positive electrode exhibited a high energy density of 29.6 Wh kg−1 and maximum power density of 7.0 kW kg−1. In sum, the designed negative electrode materials look promising for future use in high-energy-density supercapacitors. [Display omitted] • W 18 O 49 /Ti 3 C 2 T x heterostructure is constructed by an interface-induced in-situ growth strategy. • W 18 O 49 /Ti 3 C 2 T x electrode exhibits remarkable improved specific capacitance of 472.6 F g−1. • This study provides an efficient way to rational designation of for high energy density supercapacitors. [ABSTRACT FROM AUTHOR]

Whether or not specific ion effects determine the charge storage properties of aqueous graphene and graphite-based supercapacitors remains a highly debated topic. In this work we present a multiscale quantum mechanics – classical molecular dynamics (QMMD) investigation of aqueous mono- and divalent salt electrolytes in contact with fully polarizable charged graphene sheets. By computing both the electrochemical double layer (EDL) and quantum capacitance we observe a constant electrode specific capacitance with cationic radii and charge. Counterintuitively, we determine that a switch in the cation adsorption mechanism from inner to outer Helmholtz layers leads to negligible changes to the EDL capacitance, this appears to be due to the robust electronic structure of the graphene electrodes. However, the ability of ions (such as K+) with a relatively low hydration free energy to penetrate the inner Helmholtz plane and adsorb directly on the electrode surface is found to slow their diffusion parallel to the interface. Ions in the outer Helmholtz layer are found to have higher diffusivity at the surface due to their position in ion channels between water layers. Our results show that surface effects such as the surface polarization and the partial dehydration and local structuring of ions on the surface underpin the behaviour of cations at the interface and add a vital new perspective on trends in ion mobilities seen under confinement. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper reports the capacitive behavior of N-enriched carbon nanofiber/MnO 2 /carbon nanofibers with a triple layer structure (N-rich C@MnO 2 @C) prepared by continuous electrospinning. N-functional groups were introduced into the upper (or lower) or middle layer of the triplex and the structures and electrochemical properties of each are compared. N-functional groups introduced into the lower (or upper) layer induce a high surface area, numerous pyrrolic-N, high electrical conductivity, and low contact angle in N-rich C@MnO 2 @C composites. The optimized material provides a specific capacitance of 201 Fg−1 (1 mAcm−2) with more than 84% specific capacitance retention in a symmetric two-electrode cell configuration using a 6 M KOH electrolyte. In addition, it shows a maximum energy density of 24.8 and 13.41 Whkg−1 at power densities of 400 and 10,000 Wkg−1 with excellent cycling stability (95% capacity retention after 10,000 cycles at 1 mAcm−2). An assembled asymmetric device, consisting of optimized N-rich C@MnO 2 @C as the positive electrode and C@MnO 2 @C as a negative electrode, delivers a high energy density of 41 Whkg−1 at a power density of 400 Wkg−1. This material has excellent potential as an electrode for constructing high-voltage asymmetric supercapacitors in aqueous electrolytes. [Display omitted] [ABSTRACT FROM AUTHOR]

After being undervalued for a long-time, the potential use of lignins have gained interest as a source of wealth from waste. Despite the complexity of lignins chemical structure, its high carbon content compared to cellulose and sugars makes lignin a very promising precursor for the development of nanocarbons for broad range applications, including supercapacitors for energy storage. High performing supercapacitors have been made using dimensionally different nanocarbon entities (zero-to three), such as carbon nanoparticles, carbon nanodots, carbon fibers, and carbon nanosheets with modular and interconnected pore structures, which are prepared from lignins of various types with and without use of templates, porogens and chemical agents. Control of physicochemical and electrochemical properties in such nanocarbons remains the key for their high energy density, flexibility, and long-term stability. To this end, nanocarbons conductivity, porosity and surface areas are controlled by various synthesis approaches while detailed adjustment of pore structure, pore width and pore distribution have been made to improve electrolyte access, ions confinement, and transportation. To compare performances of nanocarbons made from different lignin types, we must do meaningful investigations on the lignin's structure, composition, and purity to understand how their structure-property relationships are influenced by pyrolysis, carbonization and activation methods/conditions used. In this review, a clear overview of the lignins structure, classification, and properties is presented, wherein we compared the structure-property-performance relationships of nanostructured carbons from lignins for improvement of supercapacitor device performances with recent advances. Separation processes of lignin from wood, steps involved in preparing dimensionally different nanocarbon entities (zero -to three), and electrolytes for the fabrication of sustainable and flexible supercapacitor devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Defect and interface engineering on heterostructured electrode materials is an effective approach to improve the electrochemical performance of supercapacitors and water-splitting. Herein, we have prepared MXene nanosheets-tagged hetero atom-doped graphitic carbons wrapped CoSe 2 (MXe-F,N- g CW-CoSe 2) polyhedral heterostructure electrode material, and further investigated kinetic and thermodynamic factors that affect on defect and interface engineering to facilitate efficient electron and ionic path and promote the electrochemical active sites. The composites exhibit excellent hydrogen evolution reaction (HER) performances of the Tafel slope of 84.2 mV dec−1 and 94.5 mV dec−1 in 1 M KOH and 0.5 M H 2 SO 4 , respectively. It also shows a high specific capacity of 403.4C g−1 at 1 A g−1 and the thus-assembled MXe-F,N- g CW-CoSe 2 //AC hybrid supercapacitor revealed an energy density of 44.2 Wh kg−1 at a power density of 851.3 W kg−1 with superior stability of ∼94% after 10,000 cycles. [Display omitted] [ABSTRACT FROM AUTHOR]

Developing electrochemical energy storage that enables simultaneously delivering high areal, volumetric, and gravimetric performance is a grand fundamental and technological challenge. It is straightforward but problematic to make electrodes thicker and denser for high areal and volumetric performance while sustaining a high level of gravimetric performance. The insufficient charge transports in these electrodes with high mass loading and electrode density could severely degrade the energy storage performance. Herein, we developed an energy-efficient fast sintering method (e.g. , Spark Plasma Sintering) to fabricate a structural cathode with a high electrode density (2.0–2.3 g cm−3) and high mass loading (70–100 mg cm−2). The vertically aligned carbon networks and anisotropic pore channels in the ultrathick electrodes (300–500 μm) are designed and tailored for efficient charge transports throughout the whole thickness. As a result, the sintered structural electrodes perform high areal (8.6 mAh cm−2), volumetric capacity (246 mAh cm−3), uncompromised gravimetric performance (164 mAh g−1) at normal current (<2 mA cm−2), and stable cycling with a capacity retention of 84% after 200 cycles under a current density of 4.5 mA cm−2. [Display omitted] [ABSTRACT FROM AUTHOR]

Supercapacitors exhibit fast charging/discharging ability and have attracted considerable attention within the automotive, aerospace, and telecommunication industries. Porous carbons, prized for their high electrical conductivity and high surface area, have been attractive candidates for supercapacitor electrodes. Moving to thick electrodes is one strategy to further increase energy density due to a higher volume fraction of active material. However, thick electrodes suffer from sluggish charged species transport, which is why thin electrodes are currently favored. In this work, we investigate the use of computational optimization and additive manufacturing to design and fabricate thick porous electrodes with improved performance. Electrode performance was maximized by designing their morphologies via topology optimization and printing by projection micro stereolithography (PμSL) using commercial resin (PR48). The PR48 resin was then pyrolyzed (PR48-P) to create the final conductive electrode. The optimized PR48-P electrodes exhibited 99% improvement in capacitance compared to control electrodes printed with cubic lattice morphologies. To further improve performance, we formulated a resin combining graphene oxide (GO) and trimethylolpropane triacrylate (TMPTA). Electrodes printed with 3 wt% GO in TMPTA exhibited improved capacitance retention after pyrolysis compared to the PR48-P electrodes. This work demonstrates the benefits of using topology optimization to design electrodes and material development to improve functional properties of 3D printable electrodes. [Display omitted] • 3D printing of complex shaped electrodes by projection micro stereolithography. • Topology optimization is used to design porous electrodes with optimal energy density. • Adding graphene oxide into photocurable resin improves the capacitance retention of supercapacitors. [ABSTRACT FROM AUTHOR]

Promoting and enhancing the transport rate of multivalent electrolyte ions in the pores of electrode is central for constructing high-performance electrochemical devices. Herein, waxberry-like porous carbon with nanosheets packaged by spherical carbon particles is produced by adjusting separation of hydrophilic and hydrophobic parts of carbon source precursors. The carbon particles maintain their original morphology after KOH activation at high temperature, forming tunable pores (pore volume: 0.9386 cm3 g−1) on the surface of stacked nanosheet layers. Benefiting from the synergistic effect of structural features, an interfacial transport of aqueous zinc ions within the carbon electrodes is achieved, endowing the assembled zinc-ion hybrid supercapacitors (ZHSCs) with excellent energy storage performances, including high capacity (122.3 mAh g−1 at 0.1 A g−1), high energy density (97.78 Wh kg−1), large power density (8000 W kg−1), and cycling stability up to 10,000 cycles with capacity retention of 98%. Moreover, the ZHSCs show superior low-temperature performance and operability (78.27 mAh g−1 at −30 °C and three-time cycling stability between −20 and 20 °C without performance degradation). This work presents a new prospect on design and development of aqueous rechargeable zinc-ion energy storage devices that are available for a range of environmental conditions. [Display omitted] • Waxberry-like carbon particles were prepared via one-step hydrothermal carbonization. • Excellent energy storage performances were achieved at various conditions tested. • Cycling stability of 10,000 cycles with capacity retention over 98% was attained. • The assembled zinc-ion hybrid supercapacitors showed reliable performances at −20 °C [ABSTRACT FROM AUTHOR]

The specific surface area (SSA) and pore structure are two critical factors that determine the energy storage performance of carbon-based supercapacitors. However, for biobased carbon electrodes, it is difficult to simultaneously control the pore structures and achieve high SSA. Herein, highly porous carbons (HPCs) with ultrahigh SSA and controllable pore structures are produced through hydrogel-controlled carbonization and activation process for glucose. Polyacrylamide (PAM) is used as the pore-forming agent, and pore structures can be regulated by controlling the content of PAM. The highest SSA of the HPCs reaches 3381 m2 g−1 with a 60% PAM content. Compared with the sample without PAM, the specific capacitance of HPCs-60 shows a 63% increase, reaching 441 F g−1 at a current density of 0.25 A g−1. Moreover, a KOH/PVA symmetric supercapacitor assembled from HPCs-60 not only exhibits an excellent energy density (10.9 Wh kg−1 at a power density of 125 W kg−1) but also has high cycling stability (∼10% loss over 20,000 cycles) and good flexibility. The as-prepared supercapacitors can provide stable power supplies for multiple electronic devices, indicating that the HPCs have enormous potential for use in high-performance electrochemical energy storage devices. Highly porous carbons with ultrahigh specific surface areas and controllable pore structures were obtained by hydrogel-controlled carbonization and activation of glucose. [Display omitted] [ABSTRACT FROM AUTHOR]

Self-discharge, which refers to voltage depression when a power source is removed, is a crucial issue for supercapacitors (SCs). Self-discharge results in Coulombic efficiency loss and energy dissipation, and thus restricts the charge storage performance of SCs. A cost-effective and facile strategy for addressing self-discharge is newly developed in this work. It is found that self-discharge involves charge redistribution and Faradaic side reactions, which are closely associated with the pore size of activated carbon electrodes. Importantly, the pore size distribution (and thus self-discharge) can be controlled by the binder type. Specifically, a binder that maintains high macropore and mesopore fractions can effectively mitigate self-discharge. The fundamental reasons for this finding are examined. The effects of the charging rate, holding time at the full charging voltage, operation temperature, and charging cutoff voltage on the self-discharge of SCs prepared using various binders are investigated. The data reveal that binder selection also influences SC reliability in terms of the aging rate at elevated temperature and high voltage, leakage current, and gas evolution during operation. [Display omitted] • Self-discharge has long been an issue that restricts application of supercapacitors. • Electrode self-discharge involves charge redistribution and Faradaic side reactions. • A proper pore size distribution control of carbon electrode mitigates self-discharge. • A cost-effective strategy related to binder selection suppresses self-discharge. • Charging rate, temperature, and voltage all affect self-discharge rate. [ABSTRACT FROM AUTHOR]

Portable electronic devices require high-performance miniaturised electronic components, preferably produced at low cost. In most line-powered applications, alternating current (AC) line filters are used to filter AC lines to direct current (DC) signals, making filtering capacitors a key necessity in modern electronic devices. Currently, aluminium electrolytic capacitors (AECs) are commonly used, which are bulky and have narrow electrochemical performance. Thus, replacing AECs with a compact capacitor design is highly desirable for future portable electronic devices but simultaneously very demanding. Here, we report the fabrication of an electrochemical capacitor with an electrode based on vertically aligned carbon nanostructures produced by a green plasma-enabled deposition technique. These capacitors delivered a high capacity of 1145 μF with a phase angle close to −80° at 100 Hz in a lab-scale two-electrode set-up. A prismatic prototype capacitor fabricated by stacking 10 pairs of electrodes (2.5 × 3.5 cm2) showed one of the lowest equivalent series resistance values, about 5.8 mΩ, with a high capacitance of ∼12 mF at 100 Hz. This performance delivered at the lab scale and in industrial-relevant environments suggests such electrochemical capacitors represent a suitable alternative to conventional AECs for high-frequency filtering applications. [Display omitted] • Eco-friendly plasma-designed vertical carbon nanostructures as binder-free electrodes. • Supercapacitor with excellent high-frequency capacitive response and line-filtering properties. • Design of a prototype with an ultra-high capacitance value of 12 mF at 100 Hz. • A facile supercapacitor design opens future directions to replace conventional filtering devices. [ABSTRACT FROM AUTHOR]

The development of flexible supercapacitors (SCs) with high energy density, excellent deformation and cycling stability has great meaning for flexible electronic. Herein, polyaniline array@carbon nanotubes/partially reduced graphene oxide hybrid fiber (PANI@CNT/PRGO) was rationally designed and fabricated. The PANI array were vertically and uniformly grown on CNT/PRGO fiber by controlling the nucleation sites on the fiber. This unique structure enabled the ion to rapid diffusion and the electron to fast transport and sufficient utilization of active sites. The strong interfacial interaction between PANI and CNT/PRGO fiber can reduce the risk of PANI shedding from the fiber during mechanical deformation and long-term cycling. As a consequence, a fiber-shaped SC fabricated by PANI@CNT/PRGO fiber can deliver high volumetric capacitance of 50.2 F cm−3 at a current density of 60 mA cm−3 with 62.5% capacitance retention at 2000 mA cm−3. More encouragingly, the device not only possesses outstanding flexibility and deformation stability (Retention 96.6% after 2000 bending cycles) but also owns prominent long-term stability (Retention 95.8% after 20,000 cycles). Furthermore, the device can yield an outstanding energy density up to 6.97 mWh cm−3. This findings may carve out a new path for regulating the nucleation sites to control the distribution of nanomaterials on graphene fiber, thus obtain hybrid fiber electrodes with outstanding electrochemical performances. [Display omitted] [ABSTRACT FROM AUTHOR]

Fe 3 O 4 is considered as an appealing anode material for constructing high-energy-density asymmetric supercapacitors owing to its high theoretical capacitance, large potential window, natural abundance and eco-friendliness. However, the dilemma of inadequate practical capacitance, low rate performance and unsatisfactory cycling stability of Fe 3 O 4 -based electrode materials significantly plagues their progress in supercapacitor applications. To well utilize the advantage of Fe 3 O 4 , herein, Fe 3 O 4 @onion-like carbons (OLCs) with covalently interconnected and few-shelled graphitic coatings were synthesized in a size-controllable manner from uniform-sized monodispersed nanoparticles of Fe 3 O 4 @oleic acid ligands. The ultrasmall-sized Fe 3 O 4 nanoparticles with a good size uniformity enable a high electrochemical activity and a pseudocapacitive-dominated electrochemical behavior. Meanwhile, the efficient ion/electron transportations are facilitated by the structural advantages including covalently interconnected graphitic layers, conformal and seamless graphitic coating with ultrathin thickness, and hierarchical pores. As a result of the synergistic cooperation of these merits, the Fe 3 O 4 @OLCs hybrid structure exhibits a high specific capacitance of 686.1 F g−1 at 1 A g−1 and a high rate capability with 71.3% capacitance retention at 10 A g−1, superior to most of the reported Fe 3 O 4 -based electrode materials. An asymmetric supercapacitor device assembled based on Fe 3 O 4 @ OLCs shows a high energy density of up to 63.1 Wh kg−1, which is still maintained as high as 39.1 Wh kg−1 at a high power density of 1.49 kW kg−1. Moreover, a high cycling stability (more than 80% of initial capacitance remained after 10,000 cycles) is obtained. This study offers a novel strategy for preparing high-performance Fe 3 O 4 /carbon hybrid structures for asymmetric supercapacitor applications. [Display omitted] • A size-controllable synthesis of covalently interconnected Fe 3 O 4 @OLCs hybrid structures was developed. • The ultrasmall Fe 3 O 4 size and graphitic structural advantages result in high capacitance and rapid ion/electron transfer. • The hybrid structure exhibits a high specific capacitance of 686.1 F g−1 with a high rate performance. • The asymmetric supercapacitor shows a high energy density of 63.1 Wh kg−1 and a good cycling stability. [ABSTRACT FROM AUTHOR]

Enhancing the electrochemical performance while maintaining excellent mechanical properties of carbon nanofiber-based flexible electrodes remains a significant challenge, which blocks their potential application in advanced energy storage and conversion. Herein, taking advantage of the thermal stability difference between polyacrylonitrile and polypyrrolidone, we report a simple strategy to fabricate N-doped porous carbon nanofiber membranes with inter-fiber cross-linked structures via eccentric coaxial electrospinning combined with carbonization processes. During carbonization processes, the obstacles of large contact resistance are removed and sufficient contacts among electrospun nanofibers are formed, endowing the carbon nanofiber membranes with outstanding electrical conductivity (25.4 S cm−1) and flexibility in various forms. Further, NiCo 2 O 4 nanoneedles are in-situ decorated onto the prepared carbon nanofiber membranes to construct hybrid electrodes for improving capacitance. The hybrid electrodes (NiCo 2 O 4 @NPCNFs) achieve a competitive specific capacitance (capacity) of 1474.2 F g−1 (245.4 mAh g−1) at the current density of 0.5 A g−1, as well as good rate performance (78.0% capacitance retention at a current density of 10 A g−1). In addition, the assembled asymmetric supercapacitors exhibit a high energy density of 53.0 Wh kg−1. This study paves a promising way toward carbon nanofiber-based electrodes for application in energy storage systems. [Display omitted] • According to the different thermal stabilities of the polymers, cross-linked electrospun carbon nanofibers are prepared. • Design eccentric core-shell nanofibers to facilitate the outflow of the melting core to form abundant crosslinking points. • The novel carbon nanofiber membranes render robust flexibility and high electrical conductivity. • The assembled flexible supercapacitor can supply power stably and continuously even under severe bending states. [ABSTRACT FROM AUTHOR]

Electrochemical supercapacitors (ECs) have increased large attention in recent years due to their faster charging and discharging process, large specific capacity, and high power density. Herein, we designed the preparation of carbon quantum dots (CQDs), and N-/S-doped CQDs, encapsulated within graphene sheets via a lemon-juice-derived sustainable route for high-performance positive electrode material in supercapacitor application. The as-prepared electrodes revealed an unusual battery-type behavior due to the presence of large number of O-/N-/S-containing functional groups within the graphitic network of the CQDs-graphene composite, which enhances the redox-active sites. The specific capacities were obtained for CQDs, N-doped, and S-doped CQDs at 284, 181, and 125 mAh/g at 1 A/g current density. The S-doped CQDs delivered 94.5% capacitance retention over 10,000 cycles with 98% Coulombic efficiency. The real-time symmetric supercapacitor was constructed using as-prepared S-doped CQDs with an operated potential window of 1.4 V. The constructed symmetric supercapacitor shows high specific capacity, energy, and power densities of 21.7 mAh/g (55.7 F/g at 1 A/g), 15.2 Wh/kg, and 700 W/kg, respectively. The outstanding electrochemical results are based on the easy formation of heteroatom doped S and N-CQDs to enhance the better electronic/ionic motion. [Display omitted] • N-/S-doped CQDs encapsulated graphene sheets is prepared using lemon-juice. • As-prepared electrodes revealed an unusual battery-type behavior. • Large number of O-/N-/S- functional groups enhances the redox-active sites. • The heteroatom doped S,N-CQDs enhance better electronic/ionic motion. [ABSTRACT FROM AUTHOR]

The effect of surface functionalization on the carbon walls-ionic liquid (IL) interactions is analyzed by combining differential scanning calorimetry (DSC) and Raman spectroscopy. Four mesoporous carbons (L meso ~ 9.0 nm) with a gradually increasing oxygenated surface functionality have been soaked with the 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide ([EMIm+][FSI−]) IL at filling ratios R ≈ 0.8 (almost complete pore fullness) and R ≈ 1.2 (fully filled pores with excess liquid). The low temperature behavior of the IL molecules confined in mesopores depends on their distribution between two populations: i) located close to the pore center, or ii) near the pore walls. In the surface clean material soaked with R ≈ 0.8, the molecules in the proximity of the pore center are involved in freezing/melting, whereas the species located in the vicinity of the pore walls are involved in a glass transition upon cooling, followed by cold crystallization and melting upon heating. When applying the functionalized carbon hosts, all the species located near the pore surface freeze already upon cooling, owing to their aggregation to the walls through the formation of hydrogen bonds with the surface oxygenated functionality. The amount of [EMIm+][FSI−] exhibiting exclusively freezing/melting can be as well enhanced by completely filling the pores (R ≈ 1.2) to strengthen the IL-IL and IL-carbon interactions. The information derived from this study is crucial for designing an optimal porous carbon-IL system intended to be implemented in e.g., electrochemical capacitors (ECs) operating at low temperature. [Display omitted] [ABSTRACT FROM AUTHOR]

Despite the advantages of fiber-shaped supercapacitors (FSCs) in powering wearable electronics, the low energy density dramatically hinders their practical application. Asymmetric configuration design especially with pseudocapacitive materials is an effective solution due to the extended voltage window and large pseudocapacitance. In this paper, a flexible asymmetric FSC is designed, which uses carbon fiber (CF) as the substrate, multi-layer alternating Ni–Al layered double hydroxide/mono-dispersed carbon nanotube (CNT) coaxial layer ([Ni–Al LDH-x/CNT-y]@CF) as the positive electrode material, and tremella-derived activated carbon@CF (TDC-z) as negative electrode material. The 3D Ni–Al LDH/CNT network can realize high-quality loading, rapid electron transfer, effective ion diffusion, and mechanical stress release. The obtained [Ni–Al LDH-2/CNT-2]@CF composite has a large specific capacitance of 1800 F g−1 and high capacity retention of 65.8% at a current density of 10 A g−1. Based on that, the resulting Ni–Al LDH-2/CNT-2]@CF//TDC-800@CF achieves a remarkable energy density of 35.6 Wh kg−1, a power density of 7531.90 W kg−1, and superior cycling stability of 124.8% over 5000 cycles at a current density of 10 A g−1. These encouraging results indicate that our hybrid FSC has clear potential as a wearable/flexible energy storage device. Schematic diagram of the preparation of [Ni-Al LDH-x/CNT-y]@CF fiber electrode and its capacitor properties. [Display omitted] [ABSTRACT FROM AUTHOR]

Lasers offer a versatile means towards the single-step, binder-free synthesis of three-dimensional graphene-like porous networks, providing an enticing alternative over energy intensive, multi-step traditional synthesis protocols creating unwanted waste streams. Here, we report on a novel laser-assisted method for the one-step preparation of the electrode component, not solely the active material, based on the simultaneous synthesis of turbostratic graphene-like structures on a carbon precursor and its transfer/deposition on the selected current collector. The performance of the graphene-based electrodes was electrochemically evaluated for both electric double layer capacitor (EDLC) and zinc-ion hybrid capacitor (ZIC) configurations. The performance of the EDLC devices was found to be superior to that of the current state-of-the-art devices prepared by laser-grown graphene. The ZIC exhibited higher areal energy density than the symmetric devices by one order of magnitude. The devices showed very low equivalent series resistance, good rate performance and high long-term cycling stability. Notably, the EDLC with the KOH electrolyte demonstrated an unexpected ∼20% increase in capacitance during the stability test of 10,000 cycles. This result was attributed to the substantial increase of oxygen content of the graphene electrodes, which act as sites for redox activity. [Display omitted] [ABSTRACT FROM AUTHOR]

Owning a highly symmetric geometry, fullerenes are popular building blocks in nanoarchitectonics. The successful preparation of fullerene superstructures with various sizes and dimensions forms the basis for their applications. However, the lack of porosity and the limited electrical conductivity of most fullerene superstructures prevent their applications in energy-related fields such as supercapacitors. Herein, hybrid crystals with a crossed-tubular morphology and a hexagonal close packed (hcp) lattice were constructed by fullerene C 60 and its derivative, [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM), through a modified liquid-liquid interfacial precipitation method. Subsequent calcination can greatly improve the porosity of this hybrid crystals and produce mesoporous carbon with an increased BET surface area nearly 30 times (from 13.91 to 432.41 m2 g−1), which exhibited a good performance as an electrode material in supercapacitor with a capacitance retention rate of 87.3% after 2000 cycles and specific capacitances of ∼213 F g−1 at 5 mV s−1 and ∼158 F g−1 at 1 A g−1, respectively. Compared to the crystals formed solely by fullerenes, the presence of PCBM lowered the calcination temperature and induced self-doping of oxygen. In addition, rough surfaces could be produced on the superstructures by solvent etching, which increased as well the performance of the material in supercapacitor. Our work provided a new strategy to engineer fullerene-derived functional materials for applications in energy storage and expanded the knowledge on the factors regulating their performance when using as electrode materials in supercapacitors. [Display omitted] [ABSTRACT FROM AUTHOR]

High-performance multifunctional electromagnetic (EM) materials exhibit great potential for development, and have attracted extensive attention from the scientific field. Generally, the dielectric "genes", including conductive networks, interfaces, and defects, are the pivotal factors that determine their performance. Herein, multifunctional Ti 3 C 2 T x @polyaniline decorated MWCNT (TPMC) nanocomposites, containing generous dielectric "genes", were synthesized via the electrostatic self-assembly method. Thanks to the regulation of internal dielectric "genes", TPMC exhibited a tunable EM wave absorption (EMA) and EM interference (EMI) shielding performance. TPMC achieved a maximum reflection loss (RL) of −54.7 dB and an effective absorption bandwidth (EAB) of nearly 6 GHz at 1.5 mm. Moreover, the complete conductive networks endowed TPMC with a reliable EMI shielding capability. It exhibited a maximum EMI shielding effectiveness (SE) of 34 dB, and meanwhile, displayed an absorption-dominated green shielding performance. Furthermore, owing to the integration of the "genes", TPMC showed a high coulomb efficiency (∼98%) and excellent cycling stability (exceeded 95% retation after 8000 cycles), indicating a great potential as outstanding supercapacitor electrode material. This work provides a promising strategy for controlling the EM pollution and alleviating the energy issues. The Dielectric "genes" are the key core to regulate the multifunction of TPMC, which include defects, interfaces, functional groups and conductive networks. By regulating and patching the dielectric "genes" of TPMC, the multifunctional integration of EM wave absorption, EMI shielding and charge storage can be achieved. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of advanced coal-based functional nanomaterials is of great significance for clean and effective utilization of coal resources. Herein, we report novel coal-based ultra-fine carbon nanosheets (UCNSs) prepared by chemical oxidation of bituminous coal with a high yield of 40.0 wt%. UCNSs show a lamellar size of 10–20 nm, mainly composed of 63.5 at.% carbon, 5.1 at.% nitrogen, and 31.4 at.% oxygen. The structural merits of suitable size distribution, enriched functional groups, and highly conjugated core enable the UCNSs showing a tri-functional reinforcement for carbon nanofibers prepared by electrospinning and carbonization. Thanks to the strong cross-linking effect and formation of entire conductive networks, the UCNS-embedded carbon nanofiber fabrics show 32.6 and 1.5 times improved mechanical strength and electrical conductivity, respectively, than the one without UCNSs. What's more, the exposed edges of UCNSs act as active sites for ultrafast capacitive energy storage, leading to the free-standing fabric with significantly improved capacitance and rate performance (191.2 F g−1 at 1 A g−1, 113.5 F g−1 at 50 A g−1) for aqueous supercapacitors. This work may provide a new thought for high-efficient and high-value-added utilization of coal resources. Ultra-fine carbon nanosheets with a high yield of 40.0 wt% were prepared through liquid-phase oxidation of bituminous coal, showing tri-functional (mechanical/electrical/electrochemical) reinforcement for carbon nanofiber fabrics. [Display omitted] • Ultra-fine carbon nanosheets with a high yield of 40 wt% were prepared from coal. • The inlaid UCNSs show tri-functional reinforcement for carbon nanofiber fabrics. • Exposed edges enable an ultra-fast pseudocapacitive energy storage ability. [ABSTRACT FROM AUTHOR]

Scrupulously designed porous carbon nanostructures with high pore volumes and surface area can store a large amount of charge through EDLC behaviour. In this report, polymer-derived honeycomb-like carbon nanostructures (HCNs) have been prepared, taking nano-spherical silica as a template, PVDF as a carbon source, and PMMA as a pore-forming agent. The as-prepared material offers a higher specific capacitance of 578.80 Fg-1 in a basic (6 M KOH) solution. A PVDF/PVP composite membrane has been developed as a separator to fabricate a coin-cell device. The addition of redox-active species [0.1 M K 3 (Fe(CN) 6)3-] with the electrolyte substantially enhanced the supercapacitance properties. The oxidized HCNs (HCN ox) have been prepared, and it shows enhanced supercapacitance performance (3328 Fg-1) in redox-active species added 6 M KOH compared to HCNs (913 Fg-1). An asymmetrical coin cell device is fabricated using HCNs as cathode, HCNox as the anode, and PVDF/PVP as separator in redox-active added 6 M KOH. The fabricated asymmetric coin-cell device offers an energy density of 260.18 Wh Kg−1 and a power density of 935.91 W kg−1. The enhanced performance of the supercapacitor device is the concerted effect of HCNs, HCNox, and redox-active added electrolyte, as well as the PVDF/PVP composite separator. [Display omitted] • Non-solvent Induced Phase Separation method is followed to synthesize HCNs for supercapacitor application. • Highly porous carbon nanostructure has been carved out from a solid matrix. • Low electrolyte flooding and maximum specific capacitance (578.80 Fg-1) is obtained. • Asymmetric device delivers Energy Density of 260.18 W hrKg−1 at Power Density of 935.91 kW kg−1. • Polyvinylidine fluoride/Polyvinylpyrrolidone separator is fabricated by Vapour Induced Phase Separation method, PVP holds electrolyte properly. [ABSTRACT FROM AUTHOR]

The logical design and engineering of bimetallic oxide nanomaterials with porous carbon materials have had a significant impact on the development of high-performance electrode materials for energy storage devices in recent years. The vertical and uniform building of porous multimetal nanomaterials on the surface of nanoscale carbon fibers is difficult but not impossible. We present a self-templated metal-organic framework (MOF)-based strategy for the synthesis and assembly of bimetallic oxides/nanoporous carbon nanostructures (Ni–Fe–O/NPC) on porous carbon nanofibers (PCNFs). The vertical alignment of Ni–Fe–O/NPC at PCNFs favors a fast redox reaction by shortening the ion/electrode diffusion path at the electrode-electrolyte interface and helps enhance the overall electrochemical performance. As a freestanding electrode for supercapacitors, it has a high specific capacitance of 1419 F g−1 at 1 A g−1 and good cycling life with capacitance retention of approximately 88.5% after 10,000 cycles. The Ni–Fe–O/NPC@PCNFs-400//Fe 2 O 3 /NPC@PCNFs asymmetric supercapacitor (ASC) achieves a high energy density of 41.3 Wh kg−1 at a power density of 892.2 W kg−1 with a long cycle of life (20,000 cycles) and a high rate capability (78.6%), indicating its potential applications. [Display omitted] • MOF-derived metallic oxides on PCNFs as free-standing electrode materials for ASC. • Tetragonal rodlike Ni–Fe–O/NPC@PCNFs is successfully grown using Ni–Fe-MOF@PCNFs. • Vertical alignment of Ni–Fe–O/NPC at PCNFs provides sufficient redox-active sites. • The assembly of Ni–Fe–O/NPC@PCNFs//Fe 2 O 3 /NPC@PCNFs as an ASC delivers high energy density. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) printing has stood out as a reliable technology to construct carbon microlattice electrodes for supercapacitors (SCs) in the field of custom areal electrochemical performance needed. The complex structural parameters of 3D-printed (3DP) electrodes make customization of the 3DP electrodes low efficient and time-consuming. Herein, we integrate machine learning (ML) to deeply unravel the influence of typical structural parameters of 3DP electrodes made of graphene and carbon nanotubes (CNTs). The dependence of areal performance on electrode structures was established through selecting only 9 experimental points combined with random forest (RF) algorithm, where the valuable information and the hidden correlations were quickly extracted. By using the as-established model, the electrodes with desired performance could be printed based on structural parameters directly selected from the model, offering an essentially improved performance for target performance. Specifically, the areal performance could be tuned from 0.032 to 1.6 F cm−2, covering an extremely large range. Moreover, the electrochemical surface area (ECSA) and finite element analysis (FEA) were employed to analyze the dependence of areal performance on structural parameters, agreeing well with the model information. The idea proposed in this work could largely increase the efficiency of developing new electrode architectures for desired performance. [Display omitted] A machine learning framework is established to develop a prediction model between structural parameters and areal capacitance of 3DP electrodes. The well-fitted machine learning model constructed by random forest indicated that the feature importance is geometric area > electrode thickness > gap distance. Based on this model, the customization of areal capacitance could be realized, fulfilling the diverse requirements of actual applications. • 3D printing exhibits huge advantages in fabricating customized supercapacitors. • Machine learning model is established to guide 3D printing supercapacitors with desired performance. • Structural parameters influence areal capacitance by regulating electrochemical surface area and current distribution. [ABSTRACT FROM AUTHOR]

Mechanically strong and electrically conducting fibers, particularly those with high specific capacitances, are promising fiber-shaped electrodes for fiber- and textile-based energy storage devices like fiber-shaped supercapacitors (FSCs). However, a high loading of fillers or bridging agents is commonly required to fabricate fiber electrodes with good mechanical strength, which compromises electrical conductivity and energy storage performance. Herein, an easily scalable wet-spinning strategy is reported to fabricate multifunctional Ti 3 C 2 T x MXene/carbon nanotubes (MXene/CNT) hybrid fibers from a harmonious mixture of MXene and CNT in water and using acetic acid as a coagulation bath. The hybrid fiber achieved high strength (61 ± 7 MPa), good conductivity (1142.08 ± 40.04 S cm−1) and excellent energy storage performance (∼295 F g−1 at 5 mV s−1) at a very low CNT content of ∼1 wt%. When CNT loading increased to ∼9 wt%, the maximum strain at broken reached 161 ± 19 MPa and conductivity further increased to 1715 ± 22 S cm−1. The excellent mechanical performance allows hybrid fibers to be knitted into textiles for energy storage textiles. The assembled FSCs exhibit energy and power densities of ∼6.08 mW h cm−3 and ∼6440 mW cm−3, respectively. The excellent performance of MXene/CNT fiber and good feasibility for scalable production will open up new opportunities for the development of wearable and textile-based devices in the near future. [Display omitted] • Large scale wet-spinning of MXene/CNT fibers with great fiber performance. • CNTs infiltrated between MXene flakes and constructed good connection between MXene flakes. • The excellent mechanical properties allow hybrid fibers to be weave into fabrics for energy storge applications. [ABSTRACT FROM AUTHOR]

The mismatch in kinetics and capacity of electrodes restricts the further improvement of lithium-ion capacitors (LICs). In specific, carbon cathode with a high specific capacity plays a crucial role in achieving the high energy density of LICs devices. Herein, the ordered-disordered hybrid carbon structure was designed and different anions storage behaviors were revealed. Benefiting from this novel method, the specific capacity of carbon cathode reached 130.1 mAh g−1 at 0.1 A g−1 in the range of 2–4.6 V with anions adsorption and intercalation mechanism. Moreover, the specific capacity still stabilized at 62.3 mAh g−1 even after 500 cycles at 5.0 A g−1 (vs. 17.6 mAh g−1 of commercial activated carbon). When assembled into dual-carbon LICs with the modified anode, the energy density was as high as 231.5 Wh kg−1 at a power density of 40.6 W kg−1, which was much superior to the present LICs devices. The energy density was still maintained at 86.2 Wh kg−1 at 5.0 A g−1 after 1000 cycles. The improved carbon cathode tactic by regulating the anions storage behavior provides a new approach for high-performance LICs. [Display omitted] • Ordered-disordered hybrid carbon with improved anions storage performance was achieved. • The electrochemical characteristics of anions at different voltage was revealed. • High energy density dual-carbon LICs was assembled (231.5 Wh kg−1 at 40.6 W kg−1). [ABSTRACT FROM AUTHOR]

Polymer gel electrolytes have been actively employed in exploiting solid-state supercapacitors. However, the access to tiny pores of electrode materials is hindered by the sticky nature and sluggish ion transport of polymers. Consequently, supercapacitors usually present much lower capacitance in gel electrolytes than in liquid electrolytes. Here, we develop a molten-salt-directed mesopore engineering to design carbon nanotubes that are highly accessible to gel electrolytes. The rich mesopores, 12–15 nm in diameter and cross-linked, drastically facilitate the infilling of gel electrolytes into carbon nanotubes, leading to robust capacitive performance. Such mesoporous carbon nanotubes exhibit a high capacitance of 195.2 F g−1 in polyvinyl alcohol electrolyte and an ion diffusion coefficient of 2.8 × 10−7 cm2 s−1, close to that in liquid electrolyte. Additionally, solid-state supercapacitors based on mesoporous carbon nanotubes exhibit a short relaxation time of 39 ms and a capacity retention of 93% over 10000 cycles, thus demonstrating their great potential in practical applications. [Display omitted] • An efficient mesopore engineering strategy is developed in molten-salt medium. • Three synthetic routes have been designed to create different porous structure. • The mesoporous carbon nanotubes greatly promote the infilling of gel electrolyte. • The mesoporous carbon nanotubes exhibit a high capacitance in gel electrolyte. • The assembled solid-state supercapacitor shows a short relaxation time of 39 ms. [ABSTRACT FROM AUTHOR]

The rational design of the pore structure of carbon materials is of great significance for solving the low specific capacitance and poor rate performance of supercapacitors. Herein, we propose a multiple heteroatom-doped three-dimensional (3D) interconnected carbon material obtained from the self-assembly of biomass derivatives including chitosan and sodium lignosulfonate with the assistance of boric acid. The amino group of chitosan protonated by boric acid can form electrostatic adsorption and hydrogen bonding with the sulfonic acid group of sodium lignosulfonate to form a carbon network structure. Boric acid also acts as a template, and in combination with KOH activation, further promotes the formation of the hierarchical porous structure, resulting in the as-prepared carbon possessing a high specific surface area of 2700.65 m2 g−1. As the electrode material in 6 M KOH electrolyte, it manifests a decent specific capacitance of 332 F g−1 at 1 A g−1 in the three-electrode system, while the symmetric electrode achieves a high energy density of 17.7 W h kg−1 at 166.4 W kg−1. Moreover, the contribution rate of the fast and slow kinetic process, as well as the fast diffusion of electrolyte ions are deeply revealed through the ultrafast charge/discharge and the ion diffusion kinetics analysis, respectively. The symmetric electrode in PVA/KOH gel electrolyte maintains 97% capacitance retention and 100% Coulombic efficiency over 10000 cycles, indicating excellent cycling stability. [Display omitted] • Sodium lignosulfonate and chitosan realize the self-assembly assisted by boric acid. • The carbon materials possess heteroatoms‐doped 3D-interconnected porous structure. • The electrode materials exhibit high specific capacitance and energy density. • The electrochemical properties are analyzed by two kind of kinetics analysis. [ABSTRACT FROM AUTHOR]

Although water-soluble redox based supercapacitors (SCs) had attractive supercapacitor characteristics, they still suffered from problems of low operating voltages and unsatisfactory energy density. Herein, it was reported that the oxygen defect modulated copper oxide on flexible carbon fiber (denoted as CuO x /CF) achieved a broad potential range of up to 3.0 V in 1 M Na 2 SO 4 contained 0.05 M K 4 [Fe (CN) 6 ]/K 3 [Fe (CN) 6 ] electrolyte. Oxygen defects in CuO x /CF improved charge transfer efficiency, adjust [Fe (CN) 6 ]3−/4− ions diffusion and stimulated more pseudocapacitive behavior, which demonstrated by electrochemical characterization and theoretical calculation results. It is noteworthy that the 3.0 V high voltage water-soluble CuO x /CF based symmetric supercapacitor yielded a maximum energy density of 53.1 Wh kg−1 at a power density of 1950 W kg−1 and exceptionally remarkable cycling durability of 98.9%. This work presented a viable strategy for constructing wide-voltage flexible supercapacitor devices. [Display omitted] • Introduced defect engineering successfully increased specific capacitance of CuO x /CF symmetric supercapacitor. • The water-soluble redox electrolytes broaden the voltage window and improved ionic conductivity. • DFT theoretical calculation analysis was performed for the contribution of oxygen vacancies modulated copper oxide for the energy storage. [ABSTRACT FROM AUTHOR]

Despite low cost and high theoretical specific capacitances, nickel-based compounds still suffer from poor conductivity, limited redox active sites and sluggish ion and charge transfer for their applications in flexible supercapacitors (FSCs). The rational structural control of nickel-based compound electrodes is vital but very challenging. Herein, a series of flower-like nickel-based compound electrodes are grown on carbon cloth (CC) by a general synthetic method, including Ni(OH) 2 /CC, NiS 2 /CC, NiO/CC and Ni 2 P/CC hybrid electrodes. The formation mechanism of such flower-like structure is investigated in-depth. Benefiting from the fibrous structure of flexible carbon cloth and flower-like porous structure of NiS 2 , the NiS 2 /CC hybrid electrodes are more accessible for the electrolyte ions, which facilitates their electrochemical kinetics and capacitive performances. The maximum specific capacitance of the NiS 2 /CC electrode is 1166.3 F/g at 0.4 A/g. Moreover, flexible asymmetric supercapacitors (FASCs) are assembled using NiS 2 /CC and activated carbon/CC (AC/CC) as positive and negative electrodes, respectively. Such FASCs exhibit an energy density of 34.1 Wh/kg at a power density of 561.3 W/kg, a long lifetime stability (96% retention after 8,000 cycles), and excellent mechanical stability. These superior electrochemical characteristics make the flower-like porous NiS 2 /CC hybrid a good candidate for next-generation flexible and high-performance electrode in FSCs. A series of flower-like nickel-based electrodes are developed as high performance free-standing electrodes for flexible supercapacitors (FSCs). The flower-like porous structure, high specific surface area and porous structure can render electrolyte ions free access to electrodes and provide abundant active sites for redox reactions, thereby promoting their capacitive performances. The assembled FSCs exhibit an energy density of 34.1 Wh/kg (51.1 μWh/cm2) at a power density of 561.3 W/kg (841.2 μW/cm2), 96% capacitance retention after 8,000 cycles and excellent mechanical stability. [Display omitted] [ABSTRACT FROM AUTHOR]

The rational design of flexible, portable, and wearable fiber-based electrodes via selective hybridization of materials has motivated researchers to focus on the advancement of miniaturized energy-storage systems with excellent efficacy. Here, we introduce a novel Joule-heating approach for manufacturing hybridized fibers consisting of bark-like NiO as a faradaic shell decorated over electrically treated graphene fibers (EGFs@NiO) as a capacitive core for high-performance hybrid supercapacitors. Each Joule-heating process was conducted for a very short period (∼100 s) to achieve highly restored graphitic structures with a reduced internal resistance of GFs to expedite the electrochemical kinetics and successful hybridization of EGFs with NiO for promoting redox reactions. Moreover, an all-solid-state hybrid supercapacitor was constructed using EGFs@NiO as a positive electrode and chemically reduced GF (CGF) as a negative electrode; the supercapacitor exhibited a volumetric capacitance of 838.3 F cm−3 (volumetric capacity: 139.7 mAh cm−3), wide operating window of 1.5 V, and volumetric energy density of 34.49 mWh cm−3 at a power density of 374.97 mW cm−3. The energy efficiency of the process was evaluated based on the ratio of the volumetric capacitance of the device to the process time, and the proposed supercapacitor outperformed the recently reported asymmetric/hybrid supercapacitors based on the conventional manufacturing process. Thus, this work contributes to the development of fast, scalable, and cost-effective techniques for fabricating wearable electrodes for real-time applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Rational design of the pore structure and surface heteroatoms modification of the carbonaceous-based electrodes is essential for high performance energy storage. Herein, a N, S co-doped porous carbon nanotubes with hierarchically hollowed and trunk-branched nanotube structure based on polypyrrole was fabricated via simple soft template polymerization and activation. The 3D interconnected structure with uniformly distributed active sites can form intimate contact interface and interconnected channels, thus facilitate the electron transfer and electrolyte infiltration. Therefore, the N, S co-doped branched carbon reveals a large specific capacitance (420.6 F g−1 at 0.5 A g−1), good rate capability (287.2 F g−1 at 30 A g−1) and superior cyclic stability (99.32% capacitance retained after 12000 cycles) in supercapacitor. Moreover, this N, S co-doped branched carbon nanotubes also exhibits a high specific capacity (905 mAh g−1 at 0.1 A g−1) and rate capability (461 mAh g−1 at 12.8 A g−1) as LIBs anode. Additionally, full LIBs battery configured by aNSC-2.5//LiFePO 4 can achieve an energy density of 2112 W h kg−1 anode (424 W h kg−1 cathode). This simple, well-controlled and easy-scalable porous carbon fabrication strategy can be applied in the many practical fields. [Display omitted] • Interconnected 3D branched N, S co-doped porous carbon nanotubes are prepared. • Branched and rough structure can be adjusted by modifying soft template morphology. • Heteroatom dopant and porous carbon nanotubes enhance the electrolyte infiltration. • Branched carbon nanotubes facilitate tight contact interface and electron transfer. • Branched carbon shows high rate capability and stability in supercapacitor and LIBs. [ABSTRACT FROM AUTHOR]

Rechargeable aqueous zinc-based hybrid supercapacitors (ZHSC) are widely used because of their safety, high capacity, cost-effectiveness, and environmental friendliness. However, the serious dendrite growth, low cycle life, and poor safety of zinc metal anodes greatly hinder their practical application. Additionally, the lack of excellent cathode materials also restricts further development of high-efficiency aqueous ZHSC. Herein, we report a novel persimmon-branch biomass carbon-based material with a naturally graded pore structure. Persimmon branch activated carbon (PBAC) was used as the cathode, and the anode was constructed using a zinc foil coated with one-step carbonized persimmon branch carbon (PBC). A new type of high-performance ZHSC was assembled using the porous structure of a carbon-based material and Cu2+-electrolyte additive. The hierarchical pore structure endowed the activated carbon with excellent electric double-layer capacitance characteristics as well as superb zinc ions storage ability. The artificial carbon-coated zinc metal anodes could homogenize the electric fields, and the Cu2+ from the electrolyte induced zinc metal deposition, which improved the cycle stability of the ZHSC. Therefore, the assembled ZHSC (PBAC 4 |ZnSO 4 +CuSO 4 |PBC@Zn) exhibited excellent electrochemical performance, high discharge capacity (182.8 mAh g−1), good rate performance (51.4 mAh g−1 at 10 A g−1), high energy density (27.1 W h kg−1 at 5 kW kg−1 based on the weight of the active material) and demonstrated a long cycle life with 73.8% capacitance retention after 3000 cycles at 5 A g−1 high current density. [Display omitted] [ABSTRACT FROM AUTHOR]

It is a critical challenge to build electrochemical energy storage devices with both high energy density and remarkable power density. Although zinc ion hybrid supercapacitors (Zn-ion HSCs) with battery-type cathode and capacitor-type anode have attracted widespread attention, cathode materials possessing high stability and good electrical conductivity are still worth pursuing. Herein, Na+ pre-intercalated δ-MnO 2 nanoflakes (Na 0.11 MnO 2) were grown on three-dimensional graphene (3DG) by a facile electrodeposition method. Benefiting from the in situ growth of MnO 2 on high-crystallinity graphene and Na+ pre-intercalation in layered δ-MnO 2 , the Na 0.11 MnO 2 /3DG electrode shows a superior specific capacitance of 1240 F g−1 at the current density of 0.2 A g−1 and excellent cycling stability with 90% capacitance retention after 9000 cycles in 2 M ZnSO 4 /0.2 M MnSO 4 aqueous electrolyte. Moreover, the assembled Na 0.11 MnO 2 /3DG//AC Zn-ion HSCs device delivers superb energy density of 74.3 Wh kg−1 and high power density of 9.6 kW kg−1, as well as satisfactory cycling lifespan with 83% capacitance retention after 5000 cycles. This work may pave a way for rational design of layer-structured MnO 2 cathode in aqueous energy storage devices with both high energy and power densities. A novel layered Na 0.11 MnO 2 /3DG cathode was fabricated by in-situ growth of Na+ pre-intercalated MnO 2 on 3DG. When combining with AC anode to assemble a Zn-ion HSC, the device manifests desirable energy density and superior power output simultaneously. [Display omitted] • Na+ pre-intercalated MnO 2 nanoflakes on 3D graphene were successfully fabricated as cathodes for Zn-ion HSCs. • Pre-intercalation of Na+ ions into δ-MnO 2 stabilizes the layered structure and facilitates diffusion of electrolyte ions. • Na 0.11 MnO 2 /3DG//AC Zn-ion HSCs achieves high energy density and power density at the same time. [ABSTRACT FROM AUTHOR]

Bimetallic nanostructures within carbon-based materials can overcome the fundamental limits of energy materials, which cannot be obtained using a single material. However, their synthesis involves time-consuming and complex processes that cause phase/interface segregation and non-uniformly distributed metal elements. Herein, we report a facile combustion-driven synthesis for bimetallic Ag–Bi nanoparticle (NP)-anchored carbon nanotube (CNT) electrodes. One-step combustion wave passing through freestanding films comprising Ag 2 O and Bi powders, nitrocellulose layers within CNTs enables high-density thermochemical reactions in seconds. The rapid heating-cooling rates induce the formation of liquefied Ag–Bi and trapping of metastable Ag–Bi phases at the carbon surfaces, thereby synthesizing homogeneously mixed bimetallic Ag–Bi NPs anchored on the CNTs, along with smaller diameters (∼20 nm) and high distribution density. A supercapacitor electrode employing them exhibits outstanding specific capacitance and retention (1372-1093 Fg-1 at 2-5 mVs−1, and 101.3% of the stabilized capacitance after 10,000 cycles at 100 mVs−1). This was attributed to the large active site surface area from the small diameters and high distribution density of the bimetallic Ag–Bi NPs by low surface energy, and highly stable adhesion to the CNTs. The synthesis strategy can be extended to a scalable fabrication method of various multi-metallic nanostructures for versatile electrochemical electrodes and catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

Flexible supercapacitors (SCs) based on carbon nanomaterials are one of the promising energy storage devices for wearable electron devices. However, their low energy density and cycle stability severely restrict further practical applications. The development of unique capacitor electrodes is expected largely to overcome these challenges. Herein, vertical 3D diamond/graphite (DG) composite films are directly grown on carbon cloth (CC) using a microwave plasma chemical vapor deposition (MPCVD) technique. Thin, straight nanosheets, consisted of diamond as core and graphite as shell, are interlaced with each other to form a 3D porous structure. As a binder- and additive-free electrode material, the DG/CC electrodes are used to construct electrical double layer capacitors (EDLCs) in diluted H 2 SO 4 solution and pseudocapacitors (PCs) using Fe(CN) 6 3−/4- redox electrolytes. Both EDLCs and PCs exhibit large specific capacitance and high capacitance retention. When assembled as all-solid-state flexible symmetric SCs, they offer high full-cell capacitances of 30.4 and 143.6 mF cm−2 at 10 mV s−1 for EDLCs and PCs, respectively. The power densities are 6.3 μW cm−2 and 3.0 mW cm−2 for EDLCs and PCs, together with their energy densities of 3.7 and 86.2 μWh cm−2, respectively. As flexible SCs, the specific capacitance can be completely recovered for EDLCs and has only about 6.7% loss for PCs even after the U-shape bending state. Such vertical 3D porous DG films are thus promising for the construction of high-performance battery-like SCs for an intelligent wearable energy supplier. [Display omitted] • Vertical 3D diamond/graphene composite films were synthesized on carbon cloth to construct battery-like flexible SCs. • In-situ electrochemical anodic polarization treatment remarkably enhanced the electrochemical performance. • High energy densities with large power densities were obtained in the battery-like SCs. [ABSTRACT FROM AUTHOR]

Conversion of CO 2 and CH 4 greenhouse gases (GHGs) into high-value products using cleaner, sustainable, and renewable-energy-electrified processes is a critical step towards the ultimate decarbonization of our economy and society. Here, we demonstrate an industry-relevant, scalable, plasma-electrified roll-to-roll process to produce vertical graphenes (VGs) for energy storage and syngas from the GHG feedstock with a one-round conversion efficiency of ∼80%. The growth temperature of VGs from an appropriate mixture of CO 2 and CH 4 is reduced from the expected 700 °C to only 300 °C due to the effective dissociation of CH 4 caused by reactive plasma-generated oxygen-containing species. A new pilot-scale process is developed to fabricate highly-branched VGs from CH 4 + CO 2 gas mixture on a large area (10 × 100 cm2) nickel foil under plasmas generated by a roll-to-roll linear microwave antenna. The analysis of gaseous products and carbon mass flow reveals that most of the GHG mix is effectively converted into the high-value syngas (CO and H 2). Our results demonstrate the integrated re-carbon (re-use of GHGs), up-carbon (conversion of GHG into high-value carbon-based products, HVCBPs), and de-carbon (using the electrification to reduce process-related carbon emissions while producing HVCBPs for clean energy storage) approach that is environmentally benign, scalable, and industry-relevant. Widespread adoption of similar re-carbon – up-carbon – de-carbon process cycles at industry-relevant scales will significantly enhance the production of active nanocarbon materials for diverse applications, while contributing to the achievement of the ultimate zero-carbon-emissions global targets. [Display omitted] • Integrated approach for circular carbon economy: re-carbon - up-carbon - de-carbon. • Dominant greenhouse gases (CO 2 +CH 4) converted to vertical graphene (VG) and syngas. • Roll-to-roll fabrication of branched VGs at industry-relevant scale (10 × 100 cm2). • Low VG growth temperature (300 °C) by optimum mix of CO 2 and CH 4 in the plasma. • Plasma-specific mechanism of low-temperature VG growth by O-enhanced CH 4 cracking. [ABSTRACT FROM AUTHOR]

Graphene-based foams were widely applied as electrode (or substrate) in energy storage devices. However, many efforts were spent on exfoliation, purification and fabrication process as the graphene-based materials were mostly fabricated by the assembly of GO nanosheets. In this work, a novel top-down strategy was presented to directly fabricate the GO/graphite foam from graphite paper. Under a controllable intercalation/expansion method, the graphite layers were partly expanded (and oxidized) and cross-linked by the coplanar GO/graphite heterostructure. The expanded GO parts endowed the electrode high surface area and pseudocapacitance, while the coplanar unexpanded graphite parts supported the electrode with hierarchical nanostructure and superior conductive network. The synergistic effect with GO and graphite greatly enhanced the electrochemical performance of the heterostructure electrodes. This method suggests an alternative to revisit the electrode production made from graphite and GO, which could greatly simplify the production flow of graphene-based electrodes. The graphene-based foam was produced by a controlled intercalation/expansion method. [Display omitted] [ABSTRACT FROM AUTHOR]

Wood with vertically aligned tracheids has many potential applications in energy storage. Carbonized wood inherits the previous tracheid structure and has good electrical conductivity, which provides favorable conditions for its application in self-supporting electrodes of supercapacitors. However, problems such as low specific surface area, low space utilization, and hydrophobicity limit the development of wood-derived carbon (WC) as an electrode material. Here, to improve the specific surface area and tracheid space utilization of WC, a porous carbon skeleton (PCS) was simply and efficiently constructed in its interior by using glucose and sodium chloride templates, and then potassium hydroxide etching treatment was used to further improve the specific surface area and hydrophilicity of the PCS, resulting in an etched porous carbon skeleton (E-PCS). The prepared E-PCS@WC electrode had an excellent area/volumetric specific capacitance of 7.29 F cm−2/145.8 F cm−3, and the supercapacitor exhibited a high volumetric capacitance and volumetric energy density of 34.99 F cm−3 and 4.86 mWh cm−3 at a power density of 2.5 mW cm−2. The supercapacitor constructed from this electrode exhibited good cycling stability with a retention rate of 98.5% over 20,000 cycles at a current density of 50 mA cm−3. This research will provide new ideas and a scientific basis for the design, construction and application of new green energy storage devices. [Display omitted] • A porous carbon skeleton was constructed inside the wood tracheid. • The hydrophilicity of the electrode was effectively improved by KOH etching. • The E-PCS@WC electrode has excellent specific capacitance of 145.8 F cm−3 • The E-PCS@WC//E-PCS@WC SC delivered a remarkable energy density of 4.86 mWh cm−3 • This strategy can be used as a platform for high-performance electrode. [ABSTRACT FROM AUTHOR]

Electrochemical exfoliation has been identified as a promising top-down method for obtaining high-quality graphene from graphite. However, conventional anodic exfoliation introduces undesirable oxidation and defects in resultant graphene while cathodic exfoliation eliminates that issue but is time and energy intensive. Herein we report a versatile and rapid fabrication approach for gentle (<1 h ultrasonication) cathodic exfoliation of graphite using only 0.05 M K 2 SO 4 in a polyvinyl alcohol (PVA)-based aqueous gel medium as electrolyte. The few-layer graphene obtained via this route demonstrates high quality (I D /I G ratio of 0.07) and minimal oxidation (3.02 at% oxygen). This gel-exfoliated graphene is found to be particularly suitable for micro-supercapacitors (MSCs) achieving a stable working voltage of 1.2 V in aqueous gel electrolyte, good rate capability, high capacitance of 13.7 F cm−3 at 10 mV s−1 and energy density of 2.74 mW h cm−3. Importantly, gel-exfoliated graphene is also compatible with ionogel electrolyte, achieving a high voltage of 3.4 V and resulting in competitive energy density of 14.5 mW h cm−3, outperforming most reported graphene-based MSCs. The MSCs show excellent long cycling performance retaining nearly 100% capacitance over 10,000 cycles. We also demonstrate the mechanical flexibility and integration of the MSCs connected in series and parallel for powering future microscale flexible electronics. [Display omitted] [ABSTRACT FROM AUTHOR]

Triple-layered boron-containing carbon nanofibers (CNFs) with hollow channels (PPMPB) are fabricated via step-by-step electrospinning for high-performance freestanding supercapacitors. Polyacrylonitrile (PAN)-based CNFs in the first layer are chosen as the support layer material because of their excellent chemical stability and electrospinnability. The well-developed hollow channels provided fast ion diffusion in the second layer of PAN/poly(methyl methacrylate) (PMMA)-based CNFs. The surface boron functional groups constituting the third layer contribute to the pseudo-capacitance. The symmetric supercapacitor of the PPMPB electrodes delivers a maximum specific capacitance of 180 Fg−1 at 1 mAcm−2, a high energy density of 22.38 Whkg−1 at a power density of 400 Wkg−1, and an excellent retention rate of 96% after 10,000 cycles in aqueous solution. The excellent electrochemical performance is attributed to the unique sandwich nanostructure with a three-layer structure, in which the factors representing the electrochemical properties of each layer do not interfere with each other. Therefore, a moderate amount of boron and the high surface area of the triple-layer structured PPMPB can be fully utilized as an excellent conductive network and electroactive sites, which is expected in a high-performance supercapacitor electrode. [Display omitted] • Triple-layered boron-containing CNFs were fabricated by step-by-step electrospinning. • The CNFs in the first layer provide active adsorption sites for EDLC. • Hollow core present in the interlayer serves as an excellent conductive network. • A moderate amount of boron in the third layer is utilized as the electroactive site. • Symmetric PPMPB(20) electrode showed good rate capability and long cycle life. [ABSTRACT FROM AUTHOR]

Biomass-based porous carbon is a very promising electrode material for supercapacitors, but adverse leakage current and self-discharge has hindered its practical applications. Herein, high-performance armor-wearing biomass-based porous carbon (NP-RHPC) was prepared with finely adjustable surface properties and micro-structure using rice husk as carbon source and coal pitch as chemical modification reagent. The synergetic effect of the stable biochar skeleton and the pitch carbon armor ensures NP-RHPC has low leakage current and self-discharge, long cyclic stability, and good rate performance. The leakage current and open circuit voltage attenuation rate of NP-RHPC are lower than those of N-RHPC without pitch carbon armor and the commercial capacitor carbon of YP-50F. The synthesized NP-RHPC has ideal specific capacitance of 209.2 F g−1 and the capacitance retention rate is up to 95.0% over 20,000 cycles at a high current density of 1.0 A g−1, which is higher than that of N-RHPC. This impressively long-term cyclic performance of NP-RHPC can be ascribed to the excellent electrical conductivity and especially the reduction of the unstable oxygen-containing groups. This study provides insights for the rational design of high-performance armor-wearing biomass-based porous carbon electrode material towards the advanced application of biomass and coal pitch in energy storage. A high-performance armor-wearing biomass-based porous carbon electrode material was prepared with finely adjustable surface properties and micro-structure using biochar as stable skeleton and pitch carbon as armor, which can effectively suppress the leakage current and self-discharge and increase the cyclic stability and rate performance of supercapacitors. [Display omitted] • A high-performance armor-wearing biomass-based porous carbon electrode material (NP-RHPC) was prepared with finely adjustable surface properties and micro-structure. • The synergetic effect of the stable biochar skeleton and the pitch carbon armor ensures NP-RHPC has low leakage current and self-discharge, long cyclic stability, and good rate performance. • The possible suppression mechanism of self-discharge for NP-RHPC was proposed. [ABSTRACT FROM AUTHOR]

Understanding of the electrode/electrolyte interface interaction is crucial to electrochemical energy storage devices. In aqueous electrochemical double-layer capacitors (supercapacitors), the energy density is limited by the narrow voltage window, which is dominated by water dissociation. However, molecular-level understandings of the operating voltage window are still ambiguous because of the lacks of accurate description of this electric double layer structure and the clear picture of the adsorption structure of interfacial water molecules during electrochemical process, which makes it difficult to improve electrochemical performance. We focus on the typical graphene/aqueous electrolyte interface and employ Ab inito molecular dynamics simulations to accurately describe the electrified interface in simulation cells. Thus, a fundamental relationship between the asymmetric response of interfacial water molecules to applied electrode potentials and operating voltage window has been revealed. It is found that the response for orientation of the interfacial water molecules to varied potentials affects their adsorption structure, and the adsorption behavior determines the practical EDL region. Moreover, our calculations show that nitrogen dopants effectively adjust adsorption behavior of interfacial water molecules and thus broaden the negative voltage window. Our work provides new insights into the operating voltage window in electrochemical double-layer capacitors and efficient strategies for broadening voltage window. Ab inito molecular dynamics simulation studies to reveal the fundamental relationship between the adsorption structure of interfacial water molecules and voltage window in graphene and nitrogen doped graphene-based electrode/electrolyte EDL structure. [Display omitted] [ABSTRACT FROM AUTHOR]

Designing SnO 2 /carbon composites is an effective strategy to improve the conductivity and buffer the volume expansion of SnO 2. However, it remains a challenge to combine SnO 2 and carbon materials tightly as a stable integration. Herein, a facile and versatile strategy of Sn/SnO 2 nanodots anchored tightly into carbon nanofibers (CNFs) with the decoration of graphene quantum dots (GQDs) for high performance supercapacitor is reported. Through a simple electrospinning and carbonization reduction process, a novel multidimensional carbon skeleton of GQD/CNF effectively improves the conductivity, and importantly, abundant Sn–O–C covalent bonds are constructed to anchor SnO 2 nanodots tightly into GQD/CNF, suppressing SnO 2 aggregation and facilitating electron/ion transfer kinetics. Consequently, as self-supporting and binder-free electrode material, Sn/SnO 2 /GQD/CNF displays high specific capacitance of 168.6 mA h g−1 (1349 F g−1) at 1 A g−1 with excellent rate capability (88.9% retention at 20 A g−1). Furthermore, a flexible solid-state asymmetric supercapacitor based on Sn/SnO 2 /GQD/CNF and GQD/CNF achieves a high energy density of 32.3 W h kg−1 at a power density of 800 W kg−1 with remarkable flexibility and cycling stability (86.1% retention after 5000 cycles). The excellent electrochemical performances demonstrate that this novel carbon skeleton anchored active materials shows great potential for electrochemical energy storage applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Pseudocapacitive micro-supercapacitors (MSCs) have been regarded as miniaturized electrochemical energy storage devices with prominent features for seamless integrating wearable electronic devices. However, the electrochemical performance remains challenging due to the low voltage of aqueous electrolyte. Herein, we constructed aqueous pseudocapacitive MSCs (PPy@rGO-MSCs) with a high operation voltage of 1.6 V using hybrid polypyrrole (PPy) and reduced graphene oxide (PPy@rGO) nanosheets working in 20 M LiCl gel electrolyte. The pseudocapacitive MSCs with interdigital planar geometry were manufactured by one-step mask-assisted filtration on a flexible substrate. The as-fabricated PPy@rGO-MSCs in 20 M LiCl electrolyte showed higher areal capacitance of 44.5 mF/cm2 and improved areal energy density of 15.8 μWh/cm2, in comparison with the cell in 20 M LiTFSI electrolyte (35.7 mF/cm2, 12.7 μWh/cm2). Additionally, PPy@rGO-MSCs exhibited excellent mechanical flexibility with 97% of initial capacitance retention at a bending angle of 180°, and superior integrated modular to boost voltage and current output. This work demonstrates that 2D pseudocapacitive materials hold a great chance for constructing high-performance MSCs. The aqueous pseudocapacitive MSCs with a high operation voltage of 1.6 V are demonstrated based on 2D polypyrrole/graphene hybrid nanosheets working in 20 M LiCl gel electrolyte, showing high energy density, excellent flexibility and superior integration. [Display omitted] [ABSTRACT FROM AUTHOR]

Transition metal sulfides (TMSs) have become promising candidates as electrode materials in energy storage fields thanks to the high theoretical capacity. However, their application is hindered by depressed electrical conductivity and poor cycling performance. Herein, we proposed a ZIF-67 derived, nitrogen-doped, graphene-coated and carbon nanotubes-interlinked 3D Co 3 S 4 /C conductive network (N–Co 3 S 4 -GN/CNT) for high-performance supercapacitors. Through controlling the mass ratio of ZIF-67, melamine and g-C 3 N 4 , various microstructures with determined electrochemical performance could be achieved. The nanocomposites synthesized with the ingredient mass ratio of 2: 1: 1 (NCSC-211) were proven to have the most excellent comprehensive electrochemical properties. In the NCSC-211 nanostructure, multi-layer graphene function as conductive shells for improved cycling performance by alleviating pulverization caused by volume change, thick CNTs act as conductive bridges and agglomeration spacers that increase electron conductivity and provide more active sites for redox reaction and doped-nitrogen offer enhanced wettability to electrolyte and faster electron transfer. The NCSC-211 electrode displayed specific capacitance of 1158 F g−1 at 1 A g−1, rate capability of 86% at 10 A g−1 and extraordinary cycling stability with 97.2% capacitive retention after 4000 cycles. Furthermore, the assembled asymmetric supercapacitor NCSC-211//activated carbon exhibited energy density of 43.73/37.69 Wh kg−1 at power density of 800/8000 W kg−1 and capacity retention of 95.3% after 5000 cycles at 5 A g−1. The designing strategy of in-situ grown instead of additional added conductive phase that fully-covered and strongly-interlinked network nanostructure may pave the road towards TMSs in synthesizing energy storage materials by compensating their intrinsic drawbacks. The N–Co 3 S 4 -GN/CNT 3D interlinked conductive network nanostructures were rationally designed and successfully synthesized as electrode materials for supercapacitors. The NCSC-211 electrode exhibited the most comprehensive electrochemical performance especially long cycle life, which thanks to the in-situ grown multi-layer graphene shells as well as thick carbon nanotubes bridges and spacers. [Display omitted] • Construction of N–Co 3 S 4 -GN-CNT 3D interlinked conductive network nanostructure. • The graphene and carbon nanotubes are in-situ grown instead of additional synthesized and further composited. • Tightly-coated graphene conductive shells restrain volume expansion of Co 3 S 4 nanoparticles. • Strongly-interlinked CNTs conductive bridges and agglomeration spacers increase electrical conductivity and active sites. • Extraordinary cycling stability with 97.2% capacitance retention after 4000 cycles for cobalt sulfide electrode materials. [ABSTRACT FROM AUTHOR]

Designed porous structure coupling with proper functional groups are of great importance in enhacing Zn-ion hybrid supercapacitors (ZIHSs) and the long-term cycling life. Herein, a biomass-derived three-dimensional (3D) porous carbon (LSPC-2) with lotus like network structure and oxygen containing groups was prepared by using lotus husk as precursor via a combination utilization of hydrothermal and KOH activation. The as assembled Zn//LSPC-2 ZIHSs exhibit remarkable overall performance, including a high specific capacity of 212 mA h g−1 at 0.1 A g−1, an impressive energy density of 124 Wh kg−1 at 34 W kg−1, and an exceptionally long cycle life (with 97% capacitance retention after 10,000 cycles at 10 A g−1). These outstanding characteristics primarily result from the unique 3D carbon frame structure, rich in C O functional groups and large specific surface area, providing a concise mass transfer pathway, rapid kinetics, enhanced conductivity, and enlarged Zn2+ adsorption sites. Charge-discharge process mechanism studies show that the reversible chemical adsorption of Zn2+ occur on the C O and COOH functional groups, thereby markedly augmenting the pseudocapacitance contribution. [Display omitted] • The 3D network porous carbon was designed and prepared by lotus house. • Lotus house based porous carbons was firstly used as the cathode for ZIHSs. • For ZIHSs, LSPC-2 showed a high capacity of 212 mA h g−1 at 0.1 A g−1. • The storge mechanism of LSPC-2 for ZIHSs was investigated by Ex-characterizations. [ABSTRACT FROM AUTHOR]

Herein, we present pore architecture-tailorable porous carbons through a time-adjustable hydrothermal reaction and subsequent KOH chemical activation method. Accordingly, platanus spiky (Ps) fruits, taro (T) roots, and green bell peppers (Pp) biowaste substrates were utilized as sustainable precursors to construct novel hierarchical porous carbons (HPCs) with highly interconnected porous frameworks and smart micro/meso/macroporous architecture for supercapacitors. The heterogeneous feedstocks were pre-carbonized under hydrothermal conditions for different hold durations (12 h, 24 h, 36 h) at 200 °C. The optimized Ps-24h material exhibits a high capacitance of 371.6 F g−1 at 1 A g−1 in an aqueous Na 2 SO 4 electrolyte and an outstanding rate performance (94% capacitance retention after 10,000 charge-discharge cycles). Surprisingly, the specific gravimetric capacitance of HPCs can be significantly manipulated by establishing a high-performance redox electrolytic system. In particular, the tailored Ps-24h-based electrode delivers a superior capacitance of 843 F g−1 at 1 A g−1 with an exceptional rate capability (64.7% capacitance retention from 1 to 20 A g−1 in K 3 [Fe(CN) 6 ]/Na 2 SO 4 electrolyte). Consequently, the as-integrated Ps-24h//Ps-24h symmetric supercapacitor device with a working voltage of 1.8 V presents enhanced energy/power outcomes (63.8 W h kg−1/900.2 W kg−1) with remarkable long-term cyclic durability (90.4% capacitance retention after 15,000 cycles) in a redox electrolytic system. An eco-benign time-adjustable thermochemical strategy was adopted to form hydrochar-based HPCs from heterogeneous platanus spiky fruits, taro roots, and green bell pepper waste substrates. The effect of the hydrothermal reaction hold time on key characteristics was found to be of significant influence. The achievable Ps-24h material displays a high specific surface area (1801.74 m2 g−1), large total pore volume (⁓ 1.212 cm3 g−1), and prominent micro/meso/macropore structure. With these advantages, the optimized Ps-24h electrode realizes the combined EDLC-like behavior and Faradaic pseudocapacitance mechanism. The constructed Ps-24h//Ps-24h symmetric supercapacitor device reveals an outstanding charge storage performance, yielding a high specific energy density of 63.8 W h kg−1 at a specific power density of 900.2 W kg−1 and sustaining 90.4 % of its initial capacitance after 15,000 charge-discharge cycles. [Display omitted] • Time-adjustable hydrothermal approach to construct hydrochar-based HPCs. • The retention time affects the development of hierarchical porosities. • The achievable Ps-24h HPCs display prominent micro/meso/macroporous architecture. • The Ps-24h approaches combined EDLC-like behavior and Faradaic pseudocapacitance. • The Ps-24h//Ps-24h symmetric supercapacitor yields 63.8 W h kg−1 at 900.2 W kg−1. [ABSTRACT FROM AUTHOR]

Carbons derived from pyrolysis and activation of waste biomass are attracting much attention as components of energy technologies, such as batteries, supercapacitors and fuel cells. This experimental study focuses on the production of a high-surface-area biochar (LAC) obtained from the treatment of lignin-rich waste of a biodigester plant, by applying KHCO 3 as an activating agent. The pyrolysis-activation conditions were set by following the process by thermogravimetric analysis and by checking the purity and porosity of the resulting carbon by several analytical techniques. The best pyrolysis condition provided a microporous carbon featuring up to 1840 m2 g−1, which was demonstrated at a 25 g biodigestate batch-scale. Moreover, the production process was critically analyzed by means of life cycle assessment to identify environmental hotspots and thus derive recommendations for process optimization. The impact of substance- and energy-recovery and the use of renewable energy sources on the sustainability of the product was demonstrated in several scenarios, complemented by benchmarking and an outlook regarding further optimization needs. In the best case scenario, the global warming potential of the proposed biochar could be reduced to 15.9 kg CO 2 -eq per kg of LAC. The activating agent KHCO 3 was dominant in almost all environmental impact categories, hence, a theoretical recovery process for this substance was suggested and evaluated via life cycle assessment. [Display omitted] • High-surface-area biochar (LAC) is produced from lignin-rich digestate waste. • One-step pyrolysis-activation with KHCO 3 provides a microporous carbon with 1840 m2 g−1. • Environmental impacts of the production process are analyzed by life cycle assessment. • Global warming potential is 15.9 kg CO 2 -eq per kg LAC in the best-case scenario. [ABSTRACT FROM AUTHOR]