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The design and preparation of a reduced graphene oxide (rGO) paper electrode with a reinforced concrete structure is an effective strategy to improve the mechanical properties of flexible electrodes. Therefore, PEDOT:PSS is added as a binder, toughening and conductive agent. CNTs, with good mechanical properties, are added to enhance the strength. Fe2O3 nanoparticles are added to increase the energy storage. According to these assumptions, we successfully prepared a flexible hydrophilic paper electrode with rGO nanosheets, PEDOT:PSS, CNTs and Fe2O3 nanoparticles by a constant temperature vacuum drying method. In addition, the assembled symmetrical supercapacitor exhibits a high capacitance of 1924 mF cm−3 at 1 mA cm−3, an excellent energy density of 35.6 W h kg−1 (at 166 W kg−1) and a remarkable cycle stability of 98.2% retention over 10 000 cycles at 1 mA cm−2. [ABSTRACT FROM AUTHOR]

In order to solve the problem of low energy density of previous cement-based supercapacitors, the capacitor performance was optimized in four aspects: positive electrode performance, positive and negative capacity matching, and electrolyte performance. The effects of electrodeposition solution ratio and scan rate on the electrochemical properties of nickel–cobalt double hydroxide were investigated. The microscopic morphology and elements of nickel–cobalt double hydroxide were analyzed by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The optimized nickel–cobalt double hydroxide electrode demonstrates an excellent areal capacitance of 10.53 F cm−2 and excellent cycling stability (106% capacitance retention after 10 000 cycles) at a current density of 1 mA cm−2. In this paper, an electrode made of activated carbon was used as the negative electrode and the loading of activated carbon was strictly controlled to better match the high specific capacitance of the nickel–cobalt double hydroxide electrode. An optimally proportioned cementitious-polymer electrolyte was selected as the electrolyte for the supercapacitor. The three-step optimized supercapacitor exhibits a high areal capacitance of 1.442 F cm−2, good cycle retention (69.4%), and a remarkable energy density of 0.444 mW h cm−2 (0.75 mW cm−2). This paper is expected to provide a new way to mitigate the issue of "curtailed light" and to construct large-scale buildings integrating light, electricity, and energy storage. [ABSTRACT FROM AUTHOR]

Manganese dioxide is attractive for energy storage but still needs to be combined with highly conductive materials to improve its electrochemical properties. In this paper, δ-MnO2/GNS composites with three-dimensional structures were synthesized by anchoring hydrangea-like δ-MnO2 on graphene substrates. Physicochemical analysis shows that δ-MnO2 is uniformly anchored on the graphene surface, and adjacent hydrangea-like δ-MnO2 self-assembles to build a three-dimensional conductive network, and this special structure not only provides abundant surface active sites but also more fast channels for electron transport during electrochemical reactions. The optimized composite (δ-MnO2/GNS-1.8) exhibited excellent electrochemical performance with a high specific capacitance of 326.6 F g−1 at a current density of 0.2 A g−1 and a cycling performance of 97.1%. Asymmetric supercapacitors assembled with δ-MnO2/GNS and activated carbon (AC) exhibited energy densities up to 42.2 W h kg−1 at a power density of 196.8 W kg−1. Hydrangea-like δ-MnO2 anchored on GNS has great potential for application as a high-performance supercapacitor electrode material. [ABSTRACT FROM AUTHOR]

Biomass-derived carbon materials are being increasingly utilized in various fields. This paper reports a facile synthesis method for O/N co-doped hierarchical porous carbon, utilizing the inherent pore structure and high heteroatom content of sesame meal. The O/N co-doped hierarchical porous carbon (SC-120) exhibits a hierarchical pore structure and abundant surface functional groups, the specific surface area reached 1743 m2 g−1, and the O and N element contents were measured at 10.87% and 1.95% respectively. In the three-electrode system, the specific capacitance of SC-120 reached 358.6 F g−1 at a current density of 0.5 A g−1, and a specific capacitance of 262.5 F g−1 is maintained even at a high current density of 30 A g−1. Constructed using SC-120 as the electrode, the symmetrical supercapacitor exhibits a high energy density of 9.23 W h kg−1 at a power density of 100 W kg−1 and excellent cyclic stability of 93.58% capacitance retention rate after 7500 charge–discharge testing. Additionally, SC-120 demonstrates potential for electromagnetic interference shielding, attaining an efficiency of 33.18 dB and a shielding effectiveness of 99.59% within the X-band frequency range of 8.2–12.4 GHz. [ABSTRACT FROM AUTHOR]

Na3(VOPO4)2F (NVOPF) is an ideal cathode for high-energy-density sodium ion batteries (SIBs), due to its impressive output voltage and stable structure. However, the high production costs and complex operation processes associated with conventional synthetic methods impede its commercial applications. Herein, a simple but efficient method for large-scale low-cost synthesis of NVOPF at low temperatures is proposed. The optimal sample obtained at a suitable pH delivers a high discharge capacity of 119.6 mA h g−1 at 0.2C and remarkable cycling performance with a decay rate of merely 0.0043% per cycle over 1400 cycles at 1C. Coin-type full cells composed of NVOPF and commercial hard carbon achieve a distinguished energy density of 426.2 W h kg−1 calculated based on the cathode material. Most importantly, 2.1 A h soft-pack batteries with 100 mm in length and 60 mm in width were assembled based on the as-synthesized kilogram-scale NVOPF, which can stably cycle at 1C for 400 cycles with a capacity retention of 93.2% and an average coulombic efficiency of 99.96%. Moreover, the soft-pack battery exhibits fascinating performance in a wide temperature range, including superior rate capability at −20 °C (86.4% at 5C compared to 1C) as well as stable cycling performance at 50 °C (72.5% capacity retention after 400 cycles at 1C). This paper proposes a low-temperature co-precipitation method for synthesizing NVOPF, which significantly reduces the cost of production and contributes a solution for the industrial-scale production of NVOPF. [ABSTRACT FROM AUTHOR]

This paper reported an easy synthesis of MnCo2S4 (MCS) nanosheets using a one-pot solvothermal method for high performance supercapacitor electrode material applications. The obtained ultrathin MCS nanosheets with a thickness of approximately 10 nm are coated on a graphite paper substrate without a binder using the 3D printing technique to form supercapacitor electrodes. The electrochemical performance of the MCS electrode was studied by CV, GCD, EIS measurements in a 6 M KOH electrolyte using a three electrode system. As a result, the MCS electrode material exhibits a higher specific capacity of 2203.6 F g−1 at a current density of 3 A g−1 along with an excellent cycling stability of 93% after 5000 charge–discharge cycles. Furthermore, the symmetric supercapacitor is fabricated using a two-electrode system with synthesized MCS nanosheets and exhibits an outstanding energy density and power density of 96 W h kg−1 and 1857 W kg−1, respectively. These results demonstrate the potential of the MCS nanosheets as an efficient electrode material for next generation supercapacitors. [ABSTRACT FROM AUTHOR]

Inexpensive fabrication with the scalable design of environmentally friendly supercapacitors is highly desirable for portable and wearable electronics. In this context, the role of an electrolyte on two-dimensional (2D) materials such as WS2 nanosheet-based electrodes is important for the rational design of an efficient, stable, and environmentally friendly supercapacitor. In this paper, high-quality and ultrathin 2D WS2 nanosheets are synthesized by an easy, fast, and scalable LiI-assisted liquid phase exfoliation method. The synthesized WS2 nanosheets are then employed as an electrode material in combination with 1-butyl-3-methylimidazolium chloride (BMIC) and polyvinyl alcohol (PVA) gel electrolyte to fabricate a solid-state supercapacitor. The effect of different concentrations of BMIC on the 2D WS2 nanosheet-based electrodes is investigated in a symmetric supercapacitor. An optimum concentration of BMIC in PVA gel provides the best performance due to the low viscosity and high conductivity of the gel electrolyte, resulting from the H bonding alteration inside the PVA matrix. High voltage supercapacitors with a large electrochemically stable window (up to ±4 V), and higher capacitance (5 F g−1) and specific energy density are fabricated using 0.5 M BMIC in the PVA gel electrolyte. The fabricated solid-state devices show 100% specific capacitance retention up to 8000 cyclic charge–discharge cycles. Electrochemical impedance spectroscopy and Kelvin probe force microscopy are employed to investigate the enhanced performance and stability of 0.5 M BMIC in PVA gel electrolyte in combination with a WS2-based electrode. [ABSTRACT FROM AUTHOR]

A Ni-rich quaternary layered material, LiNi0.88Co0.06Mn0.03Al0.03O2, demonstrates great potential as a cathode candidate for Lithium-ion batteries with high energy density. Nevertheless, the pristine LiNi0.88Co0.06Mn0.03Al0.03O2 generally suffers from severe side reactions and transformation of the surface layer to a spinel structure during cycling. In the paper, a simple but efficient approach was taken to enhance the electrochemical properties of LiNi0.88Co0.06Mn0.03Al0.03O2 by covering with the conductive polymer polyaniline (PANI), which could protect the cathode against the continuous corrosion of electrolyte. The PANI coated cathode with the optimal covering amount of 1.0 wt% delivered a specific capacity of 132.7 mA h g−1 at a high rate of 5C and 122.9 mA h g−1 at −30 °C with a rate of 1C, while the corresponding discharging capacities of only 100.2 mA h g−1 and 85.5 mA h g−1 were respectively obtained for the pristine cathode. In addition, the 1 wt% PANI coated LiNi0.88Co0.06Mn0.03Al0.03O2 also exhibited outstanding cycling stability with 92.0% capacity retention after 200 cycles at 45 °C, much better than that (82.1%) of the pristine cathode. The simple covering technology using low cost raw materials endows the modification with potential practical application value. [ABSTRACT FROM AUTHOR]

A series of B, N and O-co-doped samples, CPFP-3/1, CPFP-2/1 and CPFP-1/1, with spherical morphological features have been synthesized by carbonization of a polymer obtained by co-condensation of 1,4-phenylenediamine/formaldehyde/phloroglucinol (PFP) in the presence of tetraethyl orthosilicate. Boric acid (H3BO3) has been used here as an external doping agent to introduce B into the frameworks. To distinguish the properties of the B-doped samples from their undoped counterpart, another sample has been synthesized without the addition of H3BO3 (CPFP-1/0). The materials have been thoroughly characterized by powder X-ray diffraction, nitrogen adsorption/desorption studies, scanning electron microscopy and X-ray photoelectron spectroscopy. All the samples possess a high specific surface area and are predominantly microporous in nature. The electrochemical behaviour of the samples has been studied thoroughly using cyclic voltammetry, galvanostatic charge/discharge studies and impedance spectroscopy in 1 M H2SO4 electrolyte. The specific capacitances of all the samples are high with the values improving as the number of B-atoms (total heteroatoms) increases from CPFP-1/0 to CPFP-3/1, CPFP-2/1 and CPFP-1/1 introducing pseudocapacitive behaviour. CPFP-1/1 with 1 : 1 doping of the polymer with H3BO3 is the best performer showing a specific capacitance of 977 F g−1 at 1 A g−1 and 700 F g−1 at 30 A g−1 with a high discharge time. It has a notable specific energy density of 110 W h kg−1 at a specific power of 449 W kg−1 at 1 A g−1, performance-wise bridging the gap between supercapacitors and batteries. Additionally, beyond the potential window of supercapacitance (0–0.9 V), at higher voltage the material shows water splitting activity through the oxygen evolution reaction. [ABSTRACT FROM AUTHOR]

Strategically engineering composite materials holds considerable importance in research for enhancing their electrochemical characteristics for application in advanced energy storage devices. Within this context, we explored the potential of a heterostructured material as an electrode for high-performance battery-type electrodes for supercapatteries, individually evaluating the material's components. We synthesized MCM-41, functionalized-MCM-41, ZIF-8, and a ZIF-8@NH-MCM-41 heterostructured material and examined their individual physicochemical characteristics to gain insights into their collective properties when combined. X-ray diffraction patterns confirmed the successful preparation of a heterostructure, while spectroscopic analyses indicated the possible chemical interactions of these materials. Also, nitrogen adsorption–desorption isotherms suggested a new porous architecture for the ZIF-8@NH-MCM-41 material, making it suitable and highly interesting for resolving storage issues. The ZIF-8@NH-MCM-41 material exhibited a high specific capacity (356.11 mA h g−1) with excellent retention. When used to create an asymmetric supercapacitor, the heterostructure showed an energy density of 7.7 W h kg−1 at a power density of 495 W kg−1 at 1 A g−1. Even after 1000 cycles at 8 A g−1, the material demonstrated excellent stability showing its potential for future applications. Thus, this work demonstrates the potential of a heterostructured material for application in high-performance supercapacitors, providing a viable route forward for energy storage applications. [ABSTRACT FROM AUTHOR]

Herein, a simple in situ hydrothermal carbonization (HTC) approach has been used to synthesize different ratios of carbon-incorporated nickel cobaltite nanocomposites, denoted as NiCo2O4/C (Dx) (where x = 1, 2, 5, and 10, representing the molar ratio of dextrose to nickel precursor). The prepared nanomaterials were further characterized using XRD, SEM, TEM, Raman, FT-IR, BET, and XPS techniques and subsequently subjected to supercapacitor (SC) studies using 3 M KOH as the electrolyte. In the three-electrode SC studies, NiCo2O4/C (D2) showed a superior specific capacitance of 736 F g−1 at 1 A g−1 in comparison with pure NiCo2O4 (307 F g−1) and carbon nanospheres (CNS, 52 F g−1), with appreciable cycling stability, retaining about 85% of capacity up to 1000 cycles. Furthermore, in the two-electrode SC studies for NiCo2O4/C (D2) at 1 A g−1, the asymmetric configuration exhibited twice the energy density (20.3 W h kg−1) and power density (406 W kg−1) compared to the symmetric configuration, due to the hybrid EDLC–pseudocapacitive mechanism. In contrast, the symmetric configuration showed lower energy density (13.5 W h kg−1) and power density (213 W kg−1) owing to pseudocapacitive behavior alone. This noted synergistic enhancement effect on the supercapacitor performance of the NiCo2O4/C (D2) nanocomposite can be ascribed to the incorporation of optimal carbon content into NiCo2O4 to facilitate more electroactive sites for charge storage compared to pure NiCo2O4 and CNS. This kind of tuning of the carbon ratios in the metal oxide/carbon nanocomposites through the in situ HTC approach and tailoring the symmetric/asymmetric SC device configurations will efficiently deliver a promising SC in the near future. [ABSTRACT FROM AUTHOR]

All-solid-state lithium–sulfur batteries (ASSLSBs) have gained significant attention due to their high energy density and excellent safety characteristics. However, the practical application of these batteries is hindered by interfacial issues between the solid electrolyte and electrode. The instability of this interface during charge–discharge cycles arises from side effects of the electrolyte and anode, as well as poor solid–solid contact. In this study, we employ first principles calculations to analyze the chemical stability at the interface between the Li1/2La1/2TiO3 (LLTO) electrolyte and the Li anode, with a focus on strategies to address this issue and stabilize the cathode–electrolyte interface. We systematically investigate various physicochemical properties at the LLTO‖Li and LLTO‖LiIn2 interfaces, including electron conductivity, work function, chemical stability, and Li+ diffusion across the interface. Our findings demonstrate that LLTO‖LiIn2 exhibits enhanced long-term storage capabilities for ASSLSBs while reducing overall costs. Alloying lithium anodes with In atoms weakens electron injection into the electrolyte within the anode, thereby reducing chances of electrolyte reduction and improving charge–discharge performance. Additionally, a lower Li+ diffusion barrier is observed at the LLTO‖LiIn2 interface which promotes efficient Li+ transport. This work provides valuable theoretical insights for developing effective interface engineering strategies between electrolytes and anodes. [ABSTRACT FROM AUTHOR]

Transition metal chalcogenides are considered to be the most promising battery-type cathodes to construct hybrid supercapacitors. The rational design and construction of multi-anion-based heterojunctions with multi-interface structures, such as sulfoselenide and oxyselenide, are significant and necessary. In this work, a bimetallic sulfoselenide–selenite heterojunction, (Ni,Co)(Se,S)2/(Ni,Co)SeO3, was facilely synthesized by a simple one-pot hydrothermal method using NiCo–LDH as a template. The rough surface of the nanosheet array provides more active sites and the multi-interface optimizes the electronic structure for electrochemical reactions. As a battery-type cathode for supercapacitors, the optimized (Ni,Co)(Se,S)2/(Ni,Co)SeO3-1 exhibits a high specific capacitance of 7.61 F cm−2 at a current of 2 mA cm−2. In addition, the assembled HSC device provides a high energy density of 0.59 mW h cm−2 at a power density of 1.44 mW cm−2 and displays a capacitance retention rate of 84.38% after 5000 charge/discharge tests. These results demonstrate a green, safe and simple method to prepare bimetallic sulfoselenide–selenite heterojunctions from LDH-based templates as high-capacity battery-type materials for hybrid supercapacitors. [ABSTRACT FROM AUTHOR]

Carbon-based materials/metal hydroxide composite materials are one type of the most promising electrode materials for improving the performance of supercapacitors. They have the advantages of low cost, controllable morphology, high theoretical capacity, and excellent stability. In this study, nickel hydroxide nanosheets were grown vertically on the surface of carbon nanotubes (Ni(OH)2@CNTs) by a wet chemical method at low temperatures. The unique spatial configuration provides a larger specific surface area and exposes more electrochemically active sites, which is more conducive to improving electrochemical performance. The prominent conductivity of carbon nanotubes can quickly transfer electrons and improve the electrochemical cycling stability of the composite. The Ni(OH)2@CNTs composite exhibits excellent electrochemical performance with a specific capacitance of 1234 F g−1 at a current density of 1 A g−1 under a three-electrode system. In addition, an asymmetric supercapacitor (ASC) assembled using Ni(OH)2@CNTs as a cathode material shows an energy density of 65.63 W h kg−1 at a power density of 752.39 W kg−1 and a capacity retention rate of 85.9% after 10 000 cycles at a current density of 2 A g−1. The results indicate that Ni(OH)2@CNTs has prospects for application as a cathode material in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

The performance of electrochemical supercapacitors is greatly affected by electrodes, which are considered one of the most significant components. This article sheds light on manganese dioxide (MnO2)-incorporated poly(methyl methacrylate) (PMMA) membranes as electrodes for supercapacitor applications. The interaction between MnO2 and PMMA is justified by Fourier transform infrared spectroscopy. The surface morphology of MnO2@PMMA membranes was observed using scanning electron microscopy and atomic force microscopy. Techniques such as cyclic voltammetry and electrochemical impedance spectroscopy indicated that a 7.5 wt% MnO2@PMMA membrane exhibited the highest electrochemical performance. GCD tests revealed that the 7.5 wt% MnO2@PMMA membrane showed a maximum specific capacitance of 361 F g−1 at a current density of 125 mA g−1 with a maximum energy density of 144 W h kg−1 and maximum power density of 1135 W kg−1. The membrane displayed 87% capacitance retention after 5000 cycles. The fabricated interdigital microsupercapacitor device revealed the highest specific capacitance of 528 mF g−1 at a current density of 0.15 mA g−1 with a maximum energy density of 47 mW h kg−1 and maximum power density of 400 mW kg−1. [ABSTRACT FROM AUTHOR]

Copper oxide (CuO) is considered a promising material for pseudocapacitor electrodes in supercapacitors. In this study, binder-free CuO/Ni7S6 composite electrode materials were prepared on nickel foam using a two-step electrodeposition method. The test results show that the CuO/Ni7S6-1:1–20 composite material has the best electrochemical performance. It displays an areal capacitance of 8644.3 mF cm−2 at a current density is 1 mA cm−2. The assembled CuO/Ni7S6-1:1–20‖PVDF/KOH‖CuO/Ni7S6-1:1–20 devices can reach a maximum energy density (Ea) and power density (Pa) of 112.5 μW h cm−2 and 4200 μW cm−2 respectively while retaining 58.3% of their initial capacitance after 3000 charge/discharge cycles. Two devices connected in series can power an LED lamp for up to 15 minutes. The results demonstrate that CuO/Ni7S6 materials have significant potential for application in supercapacitors. [ABSTRACT FROM AUTHOR]

Pseudocapacitors (PCs) have attracted research interest not only due to their superior performance in energy storage devices, but also to bridge the performance gap between batteries and electrostatic double-layer capacitors. Nevertheless, the storage of charges within PCs greatly depends on the electrode materials. Recent studies have found redox organic materials to be highly advantageous over conventional inorganic electrode materials due to their improved cycling stability augmented with electrochemical reversibility. In this work, we report a new organic electrode material, i.e., 2-((3,4-dihydroxyphenethyl)amino)naphthalene-1,4-dione (NQ-DP) composed of core naphthoquinone (NQ) and functionalised on the periphery with a dopamine (DP) neurotransmitter subunit. Following the fabrication of the electrode on toray carbon paper (CP), NQ-DP/CP displayed efficient pseudocapacitor performance for the three-electrode system with a very good specific capacitance of 177.9 F g−1 at a scan rate of 5 mV s−1 measured with cyclic voltammetry (CV), and 160.8 F g−1 at a current density of 0.5 A g−1 measured using galvanostatic charge–discharge (GCD) studies. Moreover, symmetric and asymmetric two electrode devices were fabricated using NQ-DP/CP electrode materials, which displayed a good specific capacitance of 43.4 F g−1 and 65.9 F g−1 at a current density of 0.5 A g−1 (GCD), respectively. NQ-DP/CP devices demonstrate an excellent capacitance retention percentage of >90% for over 5000 continuous charge–discharge cycles. Importantly, the NQ-DP/CP electrode displays an energy density of 6.0 W h kg−1 and 2.6 W h kg−1 at power densities of 0.6 kW kg−1 and 6.3 kW kg−1, respectively, in the symmetric cell combination. Energy densities of 9.0 W h kg−1 and 5.5 W h kg−1 were obtained at power densities of 1.0 kW kg−1 and 7.4 kW kg−1, respectively, in the asymmetric cell combination. Overall, the organic electrode architecture design and synthesis based on NQ and DP results in an outstanding pseudocapacitor energy storage device performance, and may open new routes for the production of high performance supercapacitors in the future. [ABSTRACT FROM AUTHOR]

Poly(vinyl alcohol)–phosphoric acid–phosphomolybdic acid hydrate (PVA–H3PO4–PMo12, PPP) and poly(vinyl alcohol)–phosphoric acid–sodium molybdate (PVA–H3PO4–Na2MoO4, PPM) are synthesized to form an asymmetric gel polymer electrolyte (GPE) system PPP‖PPM. PPM and PPP GPEs worked on the sides of the positive and negative electrodes respectively to fabricate a carbon paper (CP) supercapacitor. The influence of PMo12-to-PVA and Na2MoO4-to-PVA mass ratios on the ionic conductivity of GPEs is discussed. The maximum ionic conductivity of PPP‖PPM can reach 36.43 mS cm−1 which is 5 times that of PVA-H3PO4. Both the Na2MoO4 electrolyte and the PMo12 electrolyte exhibit reversible redox activity and provide excellent pseudo-capacitance to improve the capacitance performance. Accordingly, the asymmetric PPP‖PPM GPE has the highest specific capacitance of 170.03 mF cm−2 and an energy density of 236.15 mW h m−2 at 0.5 mA cm−1 when compared with 23.80 mF cm−2 and 32.06 mW h m−2 for the PP GPE. In addition, it shows outstanding cycling stability with an 80% capacitance retention ratio at 0.5 mA cm−2 after 1000 charge per discharge cycles. Density functional theory calculations are used to investigate the interaction between electrolytes and electrodes. The enhancement of the electrochemical performance of the GPE is assigned to the reversible faradaic reaction associated with the redox PMo12 (Mo(V)/Mo(VI)) and Na2MoO4 (Mo(VI)/Mo(V)) in the asymmetric GPE system. [ABSTRACT FROM AUTHOR]

Defect engineering is an effective strategy to improve the electrochemical and electrocatalytic properties of transition metal oxide-based electrode materials. In this work, NH4+ ion intercalated MnO2 nanoflowers (C-A-MnO2) were prepared from hydrothermally synthesized manganese dioxide (MnO2) using a simple temperature-controlled method, in which oxygen vacancies on/inside the C-A-MnO2 nanoflowers were generated by the reduction of Mn4+ species by NH4+ ions. The electrical conductivity and electrochemical properties were improved by modulating the content of oxygen vacancies. In addition, the intercalation of NH4+ ions further enlarged the layer spacing of MnO2, obtaining a larger specific surface area, exposing more active sites, and shortening the electron/ion transport paths. The specific capacitance of the 1 M-A-MnO2 samples exhibited a significant enhancement (from 182.2 F g−1 to 252.2 F g−1 at a current density of 0.5 A g−1). An ASC device (1 M-A-MnO2//La-MoO3/GQD) with an operating voltage of 1.9 V was assembled. The energy density of the device was 66.66 W h kg−1 at a power density of 475 W kg−1. 1 M-A-MnO2 also exhibited excellent cycling stability with 94.3% capacitance retention after 8000 cycles. Meanwhile, it exhibited a low overpotential (361 mV at 10 mA cm−2) and Tafel slope (61 mV dec−1) as the oxygen evolution reaction (OER) electrocatalyst. Thus, this work provides valuable insights for rational intercalation of NH4+ ions for controlled synthesis of supercapacitor electrode materials and OER catalysts. [ABSTRACT FROM AUTHOR]

Transition metal oxides (TMOs) have excellent electrochemical properties. However, they are commonly associated with short cycle lives, agglomeration, and lower electrical conductivity. To ameliorate these drawbacks, porous rod-shaped CuO@Co3O4 has been synthesized through calcination with optimized oxidation temperature by using CuCo-MOF-74 as a template. Due to the porous structure, the CuO@Co3O4 electrode significantly increases the contact area with the electrolyte and greatly improves the reaction kinetics. As a result, the CuO@Co3O4 electrode exhibits excellent electrochemical performance with a specific capacitance of 545.5 F g−1 at a current density of 1 A g−1. The capacitance retention at 10 A g−1 was 88.7% after 10 000 cycles. Furthermore, an asymmetric supercapacitor (SC) has been assembled with CuO@Co3O4 as the positive electrode and commercial reduced graphene oxide (RGO) as the negative electrode, and the device has exhibited an energy density of 38.2 W h kg−1 at a power density of 1268.3 W kg−1. Impressively, the capacitance retention remained 83.2% even after 10 000 cycles at a high current density of 10 A g−1. This performance has demonstrated the potential of CuO@Co3O4 as an anode material for SCs. [ABSTRACT FROM AUTHOR]

Electrolytes play a significant role in improving the stability and specific capacity of supercapacitors; however, they have gained less attention compared to the designing of electrode materials. This study presents the supercapacitor application of novel Prussian blue analog (PBA)-based fabricated electrodes in different electrolytes. PBA was derived by the ligand substitution of sodium pentacyanonitrosyl ferrate(III) dihydrate followed by precipitation with cobalt salt to yield cobalt pentacyano(methylaniline)ferrate(II) (CoPCF). The fabricated electrode exhibited specific capacity of 390, 233, 175, and 83 mA h g−1 in 3 M KOH, 1 M NaOH, 1 M LiOH, and 1 M KNO3 at 1 A g−1 with capacity retention of 88.80%, 89.95%, 92.42%, and 90.80%, respectively, after 1000 continuous charge–discharge cycles. Furthermore, a solid-state asymmetric supercapacitor (ASC) device was fabricated using a PVA/KOH polymer gel electrolyte that exhibited a specific capacity of 56 mA h g−1 with a specific energy density of 71 W h kg−1 and a specific power density of 2560 W kg−1 at a current density of 1 A g−1, with excellent capacity retention of 93% over 2000 continuous (dis)charge cycles. These results demonstrated that the introduction of organic ligands in the framework of PBAs along with the selection of the right electrolyte is an effective strategy in the development of high-capacity and stable supercapacitor electrodes. [ABSTRACT FROM AUTHOR]

Vanadium nitride is a typical pseudocapacitive material that has attracted much attention among electrode materials as a result of its high theoretical capacity and wide voltage window. Nevertheless, its poor rate capability, cycling stability, and dissolution in alkaline electrolytes have restricted its practical applications. In this work, these problems are addressed by utilizing melamine-assisted pyrolysis and a dual-carbon composite strategy. A structurally controllable clustered shuttle vanadium-MOF is selected as the precursor. By subjecting it to high-temperature pyrolysis, melamine-derived carbon is coated on the surface of the vanadium-MOF, resulting in the formation of vanadium nitride-doped carbon electrode materials. Interestingly, they have a capacity of 407.5 F g−1 at a current density of 0.5 A g−1, with a capacity retention of 82.02% and a Coulombic efficiency of 80.59% after 10 000 cycles at a current density of 3 A g−1. When assembled into a device, the device shows a power density of 775 W kg−1 and an energy density of 39.29 W h kg−1. It is worth noting that the energy density reaches 15.82 W h kg−1 when the maximum power density of 3, 875 W kg−1 is attained. These anode materials have broad applications in energy storage systems, providing an innovative approach to developing new materials. [ABSTRACT FROM AUTHOR]

Rare earth element doped bimetallic oxides are a new technology for improving the electrochemical performance of electrode materials. In this study, 0.5% La-NiMoO4 flower-like structured nanomaterials were directly grown on nickel-based surfaces through a fast and simple room temperature stirring method. The characterization methods such as SEM and TEM confirmed that the prepared product has a three-dimensional nanoflower-like structure, and also demonstrated that the prepared 0.5% La-NiMoO4 nanoflower material was successfully doped with rare earth elements. We also conducted electrochemical tests on the material, and the results showed that at a reaction time of 16 h, the 0.5% La-NiMoO4 flower-like structure exhibited excellent electrochemical performance. At a current density of 2 A g-1, the specific capacitance was 2100 F g-1. After 5500 cycles of charging and discharging at a current density of 1 A g-1, the capacitance retention rate was 99.8%. A 0.5% La-NiMoO4/Ni//Fe2O3/Ni asymmetric supercapacitor device was assembled using 0.5% La-NiMoO4 as the positive electrode and Fe2O3 as the negative electrode. At a current density of 15 A g-1 and a working window voltage of 1.8 V, the power density of the asymmetric device was 8000 W kg-1 (energy density 56.5 W h kg-1). At a current density of 5 A g-1, the device underwent 5000 cycles of charge and discharge, and the capacitance retention rate was 89.5%. The 0.5% La-NiMoO4 electrode material prepared in this study through a simple, fast, environmentally friendly method exhibits good electrochemical performance, making it a potential electrode material for development. [ABSTRACT FROM AUTHOR]

In this paper, a hierarchical CuNi2O4@SnS@rGO nanocauliflower-like structure was grown on Ni foam for the first time via a novel two-step synthesis. Through a hydrothermal method, SnS@rGO was prepared and after this a facile and commendable electrodeposition process was used for fabricating CuNi2O4 on it. The hierarchical CuNi2O4@SnS@rGO/NF is a promising electrode material for building up an impressive supercapacitor. The morphology and structure of the prepared samples were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption, energy dispersive spectroscopy (EDS), elemental mapping analysis, field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). N2 adsorption tests showed that the specific surface area of CuNi2O4@SnS@rGO/NF (295.82 m2 g−1) is much higher than that of SnS@rGO/NF (168.53 m2 g−1). The electrochemical properties of the modified electrodes have been studied in detail at various scan rates using cyclic voltammetry, galvanostatic charge–discharge (GCD) analysis, and electrochemical impedance spectroscopy (ESI). As a result, the nanocauliflower-like structure of CuNi2O4@SnS@rGO/NF exhibits a high specific capacitance of 1061 F g−1 and the specific capacity of 177 A h g−1 at a current density of 1 A g−1. The specific capacitance of CuNi2O4@SnS@rGO/NF is more than the capacitance of the individual modified electrodes and shows good stability during long-term cycling with perfect cycling stability up to 3000 cycles and a high energy density of 688 W h kg−1 at a power density of 3892 W kg−1 in a KOH (3 mol L−1) electrolyte. Also, a CuNi2O4@SnS@rGO/NF//AC asymmetric supercapacitor was assembled, which displayed excellent electrocapacitive performance. The flexible asymmetric supercapacitor exhibits high energy density (589 W h kg−1), and long cycle life (86.7% of capacitance retention after 3000 cycles). [ABSTRACT FROM AUTHOR]

A simple and template-free method for the fabrication of modified pulp fiber (PF)–polyacrylamide (PAM)–graphene (RGO) composite electrodes was developed. The pulp fiber–graphene electrodes decorated with polyacrylamide were synthesized via a facile vacuum-filtration process, and further optimized through different mass ratios. Benefiting from the porous structure and large amounts of hydrophilic groups in the paper fiber, the PF–PAM–RGO composite electrode demonstrated good hydrophilic property and ion transport capacity within the electrode. After adding the polyacrylamide molecule (PF–RGO), the PF–PAM–RGO composite electrode exhibited good mechanical properties and capacitance performance due to PF–RGO hydrogen bonding. Moreover, the PF–PAM–RGO composite electrode displayed a high area specific capacitance of 498.4 mF cm−2 with a mass of 2.32 mg cm−2 (specific capacitance of 214.8 F g−1) at 0.2 mA cm−2. The assembled PF–PAM–RGO composite electrode showed a good cycling stability (92.36% capacitance retention after 8000 charging/discharging cycles) and mechanical flexibility (87.65% capacitance retention after 500 bending/unbending cycles). Remarkably, the flexible device could achieve superior energy density of 80.59 μWh cm−2 and high power density of 2549.83 μW cm−2. [ABSTRACT FROM AUTHOR]

All-solid-state fluoride-ion batteries (FIBs) with a high theoretical energy density have attracted considerable attention due to their enhanced safety features and superior capacity. The selection of solid electrolyte materials with enhanced fluoride-ion conductivity is crucial for the successful implementation of high fluoride-ion energy storage in realistic scenarios. In this study, heterogeneous solid fluoride-ion electrolytes with different ratios of (LaF3)1−x(PbF2)x are investigated. In contrast to other research efforts focusing on the development of single-phase, single-lattice-defect solid-state electrolytes, the (LaF3)1−x(PbF2)x material incorporates two phases with different defects, namely fluoride vacancies and mobile fluoride ions. This unique combination of defects results in a significant enhancement in conductivity while maintaining their coexistence. The crystal gaps are filled by the orthorhombic phase, which is conductive, resulting in a reduction of the contact resistance due to the uniform distribution of the three crystal phases and the heterointerface between the hexagonal phase and the cubic phase. The multi-component electrolyte (LaF3)0.4(PbF2)0.6 exhibits the best performance among the samples tested. The electrolyte exhibits a high fluoride-ion conductivity, with a value of 2.78 × 10−4 S cm−1 at 120 °C and 6.37 × 10−6 S cm−1 at room temperature. The electronic conductivity is negligible with a value of 5.48 × 10−8 S cm−1. Furthermore, the electrolyte has an electrochemical stability window of 1.85 V vs. Sn/Sn2+. Due to its favorable electrochemical properties, this material has considerable potential as a solid-state fluoride-ion electrolyte. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries are widely used in electronic devices due to their high energy density and long cycle life. However, the use of flammable organic solvents in electrolytes leads to frequent safety problems. Therefore, ensuring the safety of lithium-ion batteries has become an essential and urgent research topic. In this study, vinyl tris(2-methoxyethoxy)silane (VTMS) and triethyl phosphite (TEPi), serving as flame retardant additives, were employed to systematically explore the synergistic flame retardant effect and elucidate the underlying mechanism between them. Additionally, an assessment was conducted to examine the impact of their incorporation on the performance of the battery. The results indicate that the introduction of a combination of VTMS and TEPi led to the formation of a uniform and compact char layer under elevated temperatures, in contrast to the use of either additive alone. Incorporating 5 wt% of VTMS and TEPi enhances the thermal stability of the LiCoO2 electrode, resulting in discharge capacity exceeding 145 mA h g−1 for Li‖LiFePO4 and 315 mA h g−1 for Li‖natural graphite half cells, respectively, at a current density of 0.5C. Moreover, their utilization facilitates the generation of the solid electrolyte interphase (SEI) film. This study offers a novel perspective for investigating flame-retardant electrolytes in lithium-ion batteries. [ABSTRACT FROM AUTHOR]

An organic–inorganic hybrid is a promising electrode material for aqueous batteries due to its larger potential in improving electrochemical performance. Herein, we designed and prepared a naphthoquinone@FeOx(OH)/iron foam (NQ@FeOx(OH)/IF) hybrid electrode as a highly-efficient anode in Ni/Fe batteries via combining electro-deposition of FeOx(OH) and in situ hydrothermal growth of naphthoquinone. The as-prepared hybrid electrode materials present a 2D nanosheet morphology of FeOx(OH) and a branch/band-like structure of NQ, with the formation of NQ–FeOx(OH) interfaces. Such an interface structure is revealed to have more electron active sites, with increased electron delocalization caused by the aromatic ring structure, thereby enhancing the transport of the electrons in the electrode materials. Thus, a superior electrochemical performance of the NQ@FeOx(OH)/IF electrode was received, with a large areal capacity of ∼2.23 mA h cm−2 and a favorable rate capability of 1.09 mA h cm−2 at 40 mA cm−2. Besides, the NQ@FeOx(OH)/IF anode was coupled with the NiCo2O4 cathode to assemble a Ni/Fe battery, as a result, an admirable energy density of 235.2 W h kg−1 and a maximum power density of 5.4 kW kg−1 were obtained. The study on high-performance NQ@FeOx(OH)/IF electrode materials paves the way to design and synthesize better iron-based materials for Ni/Fe batteries. [ABSTRACT FROM AUTHOR]

For energy-related applications such as solar cells, catalysts, thermo-electrics, lithium-ion batteries, graphene-based materials, supercapacitors, and hydrogen storage systems, nanostructured materials have been extensively studied because of their advantages of high surface to volume ratios, favorable transport properties, tunable physical properties, and confinement effects resulting from their nanoscale dimensions. Due to their high energy and power densities, supercapacitors are potential power storage technologies. In this case, carbon nanomaterials, in particular carbon nanotubes, graphene, mesoporous carbon, and their hybrids, have received extensive research interest as effective electrode materials for supercapacitors because of their distinctive hierarchical structure, excellent electrical and mechanical properties, and large specific surface area. Lithium-ion batteries (LIBs) have been receiving extensive attention because of their high specific energy density. In LIBs, graphite is the most commonly used anode material; however, lithium-ion intercalation in graphite is limited, hindering the battery charge rate and capacity. Recently, nanowire/graphene hybrids have been developed for the enhancement of the LIB performance; therefore, we present a new approach of hydrothermally growing uniform nanowires on a graphene aerogel to further improve the performance. This nanowire/graphene aerogel hybrid not only exhibited the large surface area of graphene aerogels but also increased the specific surface area for electrode–electrolyte interaction. Therefore, this new nanowire/graphene aerogel hybrid anode material can enhance the specific capacity and charge–discharge rate. There is enormous interest in the use of graphene-based materials for energy storage. Graphene-based materials have great potential for application in supercapacitors owing to their unique two-dimensional structure and inherent physical properties, such as excellent electrical conductivity and large specific surface area. In recent years, the development of different organic and inorganic nanostructured materials such as nanocarbons, metal oxides (W18O49 and Co3O4), metal sulphides (MoS2 and WS2), graphene nanosheets, and conducting polymers has enabled the fabrication of high-performance devices. MoS2, a typical layered transition-metal dichalcogenide material, has attracted significant attention for application in heterogeneous catalysis, lithium ion batteries and electrochemical energy storage systems considering its unique layered structure and electronic properties. Thus, transition metal dichalcogenide nanomaterials have shown important research progress in the field of energy conversion and storage. [ABSTRACT FROM AUTHOR]

Transparent conducting oxides (TCOs) play an important role in advanced energy harvesting and storage systems, as well as cutting-edge display technology. In this study, we successfully synthesized antimony-doped tin oxide nanoparticles (Sb–SnO2 (ATO)) employing the sol–gel technique, a well-established and facile method. The resulting ATO powder was meticulously analysed utilizing scanning electron microscopy and X-ray diffraction to reveal the intricate aspects of its crystallite phase and morphological structure. Our findings elucidated that elevating the calcination temperature led to enhanced crystallinity and increased crystallite size, while preserving the tetragonal structure. The electrochemical investigations were performed employing the ATO nanoparticles prepared at temperatures of 500 °C and 1100 °C using an electrochemical workstation. The in-depth analysis of the electrochemical performance of the ATO samples demonstrated their desirable capacitance behaviour, signifying the potential suitability of ATO nanostructures as electrode materials for supercapacitors. Notably, the highest capacitance value of 1064 F g−1 was attained from the cyclic voltammetry (CV) curves at a scan rate of 2 mV s−1 for the ATO nanoparticles prepared at 1100 °C. At a current density of 10 mA cm−2, the ATO-based electrode exhibited an energy density of 21 W h kg−1 and a power density of 390 W kg−1, making it crucial for electrochemical devices. The outstanding capacitance retention of 90% was observed even after 3000 cycles in 3 M KOH electrolyte, in the potential window ranging from −0.2 to 0.55 V. The novel supercapacitor electrode in this study displayed an outstanding specific capacitance, exceptional stability, elevated power density, and reduced impedance, showcasing its promising practical utility. These encouraging results signify a pioneering approach for the synthesis of cost-effective ATO materials through an environmentally benign sol–gel process, paving the way for their prospective utilization in high-performance supercapacitors. [ABSTRACT FROM AUTHOR]

Supercapacitors often deliver a significantly high-power density with a long cycling life but low energy density. An exceedingly promising approach is to construct asymmetric supercapacitors (ASCs) reconciling the compromise between power density and energy density. However, ASCs combining transition metal oxides (TMOs) and activated carbon (AC) struggle to improve energy density due to a vast difference in their specific capacitance. To cross this hurdle, we first proposed a new strategy to construct the ASCs with α-MoO3 as the anode and conductive polymer polypyrrole (PPy) as the cathode. The remarkable features of α-MoO3, including its layered structure and ultra-high specific capacitance, along with the stability and fast charge–discharge ability of PPy, have contributed significantly to the augmentation of power density and energy density in ASCs. Taking advantage of these bright features, the operation voltage for α-MoO3//PPy is effectively expanded to 2.0 V, exhibiting a high energy density of 25.9 W h kg−1 at 1538 W kg−1. Furthermore, the energy density presented a remarkable recovery rate, reaching 91.04% of its initial state after undergoing full rate tests. These conclusions reveal that the construction of α-MoO3//PPy can effectively enhance the energy density and power density of supercapacitors. [ABSTRACT FROM AUTHOR]

LiFe1−xMnxPO4 with elevated energy density is becoming the next-generation olivine-type cathode. However, its long cycling stability and delivered capacities are far from perfect, chiefly induced by its intrinsically poor ionic/electrical conductivities, sluggish electrode kinetics and notable Jahn–Teller effects upon charge/discharge cycles. Aimed at overcoming these barriers, we herein propose an efficient synergistic fluorine (F)/indium (In) dual doping strategy. As confirmed from the XRD Rietveld refinement results, the doped electronegative F can interact with Mn, thereby shortening Mn–O bond lengths, strengthening the covalent bonding nature and inhibiting the Jahn–Teller distortion/Mn dissolution, whereas the In doping helps to increase the electronic conductivity of particle cathodes, and opens up the crystal lattice spacing for expediting Li+ diffusion. As a proof-of-concept demonstration, the developed F/In-doped LiFe0.5Mn0.5PO4 cathodes exhibit less adverse phase variations, showing a maximum output capacity of 158.5 mA h g−1 at 0.1C, a capacity retention ratio over 86.7% after 500 cycles, and a markedly improved Mn discharge plateau capacity and capacity retention rate (at 2C). This work may not only shed new light on understanding the anion/cation co-doping effects for LiFe1−xMnxPO4, but also offer an applicable concept to design other high-energy-density electrode species. [ABSTRACT FROM AUTHOR]

Recently, many studies have been done on MXene (2D titanium carbide) for energy storage applications. It possesses outstanding features like hydrophobicity, conductivity, and particularly strong surface redox reactivity, which are essential for energy storage applications. Despite these exceptional properties, MXene's electrochemical performance is significantly impacted by certain deficiencies, such as the inability to assemble MXene sheets. To prevent MXene sheets from restacking, the spaces between them must be filled with an appropriate material. Metal-organic frameworks (MOFs) for electrochemical applications have also been extensively studied. Due to their high crystallinity, porous structure, and substantial surface area, MOFs find diverse applications, but their efficacy as electrode materials is hindered by a lower specific capacity and charging/discharging rate. Addressing these limitations, combining MOFs with suitable materials is preferred for enhanced performance. This study suggests an innovative approach: a composite between Cu-BTC MOF and N-MXene. By shortening both the ion/electron diffusion pathways and improving the electroactive sites, the prevention of MXene sheet restacking was achieved, leading to exceptional specific and rate capacity in the composite with MOFs. The Cu-BTC/N-MXene-decorated electrode exhibited energy and power density reaching approximately 65.23 W h kg-1 and 923 W kg-1 in a two-electrode (real device) configuration. Cu-BTC/N-MXene//N-MXene retained 99% of its capacity and a coulombic efficiency of 92% after 8000 alternate GCD cycles. The findings of this investigation highlight the significant potential of employing the innovative electrode material Cu-BTC/N-MXene for supercapattery applications. [ABSTRACT FROM AUTHOR]

In order to push the energy density limit of supercapacitors (SCs), the strategy of developing heterostructure composites is feasible. Currently, MXenes with favorable physicochemical properties are promising electrode materials for energy storage systems. Herein, by electrostatic assembly, negatively charged NiCo2S4 nanoflowers were uniformly anchored onto the surface of positively charged Ti3C2Tx substrates to form a hierarchical Ti3C2Tx@NiCo2S4 heterostructure, which was then assembled into a 3D porous hydrogel by a hydrothermal graphene oxide (GO)-gelation self-convergence process at low temperatures. The resultant 3D hierarchical Ti3C2Tx@NiCo2S4–reduced graphene oxide (RGO) heterostructure hydrogel displayed an ultrahigh specific capacitance of 717.1 F g−1 at 1 A g−1, in comparison to that of the Ti3C2Tx–RGO hydrogel (155.5 F g−1). As a result, the heterostructure hydrogel was then used as electrodes to construct a SC device, which exhibited a high energy density (73.86 W h kg−1 at 300.1 W kg−1 and 42.97 W h kg−1 at 7111.7 W kg−1), and a remarkable cycling stability (retention of 98.5% of the capacitance after 10 000 cycles at 10 A g−1). This study highlights the unique potential of the 3D MXenes-based heterostructure hydrogel as a favorable electrode material for SCs. [ABSTRACT FROM AUTHOR]

Lithium–sulfur (Li–S) batteries have gained significant attention as promising candidates for next-generation energy storage systems due to their high theoretical energy density. However, their commercialization has been limited due to serious polysulfide dissolution. Herein, we synthesized polyaniline-coated Ni–Co Prussian blue nanocubes (NCP@PANi) for Li–S battery separator modification using a simple coprecipitation and in situ oxidation polymerization method. The synergistic catalytic effect of Ni and Co bimetallics enhanced the cathodic reaction kinetics. In addition, the coating of PANi on the NCP surface further improved the electrical conductivity and adsorption of polysulfides. The sulfur/ketjen black cathode (S/KB) using the modified separator exhibited an initial discharge specific capacity of 1443.1 mA h g−1 at 0.1C. Even at a high sulfur loading of 3.1 mg cm−2, it exhibited an initial capacity of 713.9 mA h g−1 at 0.5C and maintained 431.3 mA h g−1 after 300 cycles. Overall, the NCP@PANi modified separator effectively inhibited the polysulfide shuttling and thus improved the electrochemical performance. This study provides valuable insights into separator modification for Li–S batteries. [ABSTRACT FROM AUTHOR]

Although bimetallic oxide electrodes have excellent physical and chemical properties, as well as a high theoretical capacity, their low energy density and poor cycling stability restrict their application in supercapacitors (SCs). This study demonstrates an effective method for enhancing the conductivity and capacitance performance of NiMoO4 by inducing oxygen vacancies. The electrochemical performance of Ov-NiMoO4 nanoneedles soaked in NaBH4 solution was significantly superior to that of untreated NiMoO4 electrodes, exhibiting excellent electrochemical properties. Moreover, the density functional theory (DFT) calculations further indicate that the material possesses a higher electron transmission rate. An asymmetric supercapacitor (ASC) based on NiMoO4 was prepared, using Ov-NiMoO4@Ni foam (NF) as the positive electrode and activated carbon as the negative electrode. These findings could further expand the applications of transition metal-based materials and provide an effective approach for the study of ASCs. [ABSTRACT FROM AUTHOR]

Multi-component metal sulfide heterostructures possess a modulated electronic structure, abundant active sites and various morphology features, which are kinetically beneficial for fast electron/ion transport to enhance the energy storage performance. Herein a novel NiMoS4@Co9S8/Ni3S2 core–shell heterostructure is designed and constructed, which consists of Co9S8/Ni3S2 heterogeneous hollow nanotubes as the core and NiMoS4 nanospheres as the shell. The hierarchical NiMoS4@Co9S8/Ni3S2 array has the merits of each component and exhibits excellent electrochemical performance due to the synergistic effect. When examined as the supercapacitor electrode, an area specific capacitance of 9.61 F cm−2 was provided at a current density of 2 mA cm−2. In addition, the assembled asymmetric supercapacitor device achieves superior properties regarding high energy density of 0.44 mW h cm−2 at a power density of 2.30 mW cm−2 and good durability with 82.67% capacitance retention over 5000 cycles. This work sheds light on the design and construction of multi-component heterostructure with well-defined hollow core–shell morphology, which is an effective strategy to fabricate electrode materials for high performance energy storage devices. [ABSTRACT FROM AUTHOR]

Niobium tungsten oxide has become one the promising electrode materials for supercapacitors due to its high ion diffusion coefficient, multiple redox pairs and structural stability, however, extremely low inherent electrical conductivity limits its rate capability. The study reports the synthesis of a W3Nb14O44/biomass carbon (BC) composite by introducing serine and histidine-functionalized and boron-doped graphene quantum dots (SHB-GQDs). Here, ammonium tungstate and niobium oxalate combined with SHB-GQDs to form a water-soluble SHB-GQD-Nb/W complex, sucked into rambutan peel, freeze-dried and annealed. The introduction of SHB-GQD realizes the construction of the W3Nb14O44 nanocrystals with a (4 × 4)-sheer structure, more exposed high-index crystal faces and small size (22 ± 0.18nm), oxygen vacancies and graphene electron trap. The integration of these multiple structure engineering improves the inherent electronic conductivity and expands the safe voltage window (2.1 V) and leads to outstanding supercapacitor performance. The W3Nb14O44-SHB-GQD/BC electrode offers a high capacitance of 535 F g−1 at 1 A g−1 (312 mA h g−1), which is more than the theoretical capacity of W3Nb14O44 in lithium ion batteries (293.56 mA h g−1). The symmetrical supercapacitor exhibits a high capacitance of 457 F g−1 at 1 A g−1, an energy density of 70 W h Kg−1 at 525 W Kg−1 and 95.6% capacitance retention after 10 000-cycle at 10 A g−1. It shows a broad prospect for applications in wearable electronics. [ABSTRACT FROM AUTHOR]

In this paper, natural dictyophora has been used as a precursor to synthesize nitrogen-doped porous carbon microspheres (PCMS) by hydrothermal carbonization and subsequent KOH activation at different temperatures (650–850 °C). This unique structure of PCMS is conducive to the penetration and mobility of ions. The PCMS were characterized using different analysis technologies and their capacitive performance was investigated. The results indicate that the PCMS activated at 750 °C (PCMS-750) exhibited the highest specific capacitance, 380 F g−1, at the current density of 1 A g−1. The excellent electrochemical performance can be attributed to the structure of novel porous microspheres and effective N self-doping. The symmetric supercapacitor device based on the PCMS-750 electrodes exhibited high energy density (27.50 W h kg−1 at a power density of 899.9 W kg−1) and excellent cycle stability (94.1% after 10 000 cycles). Such a high-performance shows that the PCMS-750 electrodes will be a potential candidate for energy storage. [ABSTRACT FROM AUTHOR]

The design and development of composite materials with novel structures is one of the effective ways to enhance the electrochemical properties of supercapacitors. In this paper, a one-step electrodeposition method is used to adjust the morphology and structure of CoMnS nanomaterials by changing the amount of CS2. CoMnS nanomaterials with unique flower-like structures are reasonably prepared, which promotes the flow of electron transfer and improves the electrochemical behavior. It is worth noting that when the amount of CS2 is 4 mmol, the specific capacitance of CoMnS-4 reaches 3469.5 F g−1 at 1 A g−1, and the specific capacitance is still 2830.5 F g−1 (maintaining 81.56%) until the high current density reaches 20 A g−1. After 10 000 cycles, it shows excellent cycle stability (maintaining 95.78% at 20 A g−1). The CoMnS-4//AC asymmetric supercapacitor device has an excellent energy density of 85.91 W h kg−1 when the power density is 800 W kg−1, which shows it's great application value. [ABSTRACT FROM AUTHOR]

An aligned carbon-nanotube array has been identified as an ideal candidate for super-capacitor devices due to its high specific surface, regular pore structures and highly efficient ion transfer paths. However, poor mechanical strength and super hydrophobicity greatly impede its applications in the manipulation of the energy storage device. In this paper, we fabricate a robust flexible solid-state supercapacitor (FSC) device by using a silk fibroin incorporated 3D aligned carbon nanotube array (CNTA) composite matrix. We thoroughly investigate the effect of a silk fibroin scaffold as well as its carbonization product on the electrochemical properties of the composite devices. Compared with pure CNTA-based FSC devices, the mechanical strength as well as hydrophilicity of the CNTA@silk fibroin (CNTA@SF) composites are greatly enhanced. Meanwhile there is neither damage of the aligned structure of CNTA nor sacrifice of the volumetric capacitance of the device. Additionally, further carbonization of the CNTA@SF composites can generate a pyridine-type nitrogen doped CNTA (CNTA@C) hybrid thus further enhancing the electrochemical capacitance while still maintaining the original flexibility and hydrophilicity. The charge transfer resistance (Rct) of the CNTA@C-based device decreases about 40% (from 3 Ω to 1.8 Ω) and the volumetric specific capacitance increases to about 60% higher (from 126.8 mF cm−3 to 197.4 mF cm−3) compared with the initial. Meanwhile, excellent cyclic stability (2.9 mA cm−3, 10 000 cycles with a loss of less than 1%), good rate performance (from 0.58–5.8 mA cm−3, volumetric specific capacitance Cv retention stays at around 80%) as well as high energy density of 0.018 mW h cm−3 (with the power density of 0.46 mW cm−3) were successfully derived. Our approach thus reveals a new kind of robust 3D platform based on a carbon nanotube array and silk fibroin which has great potential for the design of biocompatible FSC devices as well as implantable electronics in the future. [ABSTRACT FROM AUTHOR]

Electrodes for commercially viable supercapacitors (SCs) require an active material mass loading of >10 mg cm−2; however, increasing the mass loading or electrode thickness typically deteriorates the electron and mass transfer and thus results in inferior specific capacitance, rate capability, and cycling stability. Herein, we develop a monolithic carbon membrane-based hybrid electrode (Co@CPE) with ultrahigh mass loading carbon-coated Co nanoparticles (>20 mg cm−2) by direct carbonization of Co2+-adsorbed Pleurotus eryngii (PE). During carbonization, the PE precursor is converted into a carbon membrane matrix with a layered porous structure, good conductivity and excellent structural integrity, whereas the adsorbed Co2+ ions are in situ converted into carbon-encapsulated Co nanoparticles that are firmly and evenly distributed on a carbon membrane matrix. The optimal Co@CPE-1000 electrode has a high areal capacitance of 5.04 F cm−2 at 2 mA cm−2. Due to the high mass loading, the symmetric SC assembled by the Co@CPE-1000 electrode has a high specific capacitance of 2.81 F cm−2 at 2 mA cm−2 and an energy density as high as 190 μW h cm−2. Notably, the symmetric SC exhibits an ultra-long cycle life, with a retention rate of 113% after 40 000 cycles. This work presents a feasible and effective strategy for the development of monolithic carbon membrane-based hybrid electrodes with high active mass loading for achieving practically viable SCs with excellent electrochemical performance. [ABSTRACT FROM AUTHOR]

MXenes have gained significant recognition due to their outstanding electrical conductivity, abundant surface functional groups, and distinctive two-dimensional layered structure. However, restacking of nanoflakes hinders the electrochemical performance of Ti3C2Tx-based supercapacitors. Herein, a Ti3C2Tx/VN composite is fabricated using a one-step in situ nitriding method. The presence of VN within the Ti3C2Tx nanoflakes results in an increased interlayer spacing, providing additional electrochemically active sites for charge storage. In addition, the Ti3C2Tx nanosheets form a continuous metallic skeleton that suppresses the formation of soluble salts from VN during charging and discharging resulting in better cycling stability. As the negative electrode in supercapacitors, Ti3C2Tx/VN demonstrates an outstanding specific capacity of 382.1 F g−1 at a current density of 1 A g−1 and exceptional cycling endurance, retaining 93.5% of its capacity after 5000 cycles. An asymmetric supercapacitor comprising Co3O4 and Ti3C2Tx/VN as the positive and negative electrodes, respectively, shows high energy and power densities of 69.1 W h kg−1 (1 A g−1) and 7.6 kW kg−1 (8 A g−1). The results reveal a promising strategy to design composite anodes with high energy and power densities for supercapacitors. [ABSTRACT FROM AUTHOR]

In this study, we successfully prepared a polypyrrole conductive matrix (PPY) covered manganese nickel oxide (MnNi2O4) nanocomposite via co-precipitation and a chemical oxidative polymerization route. The structural morphology of the as-prepared electrode materials was studied using FTIR, XRD, SEM, and XPS analysis. The specific surface area of the prepared MnNi2O4/PPY composite was found to be 68.40 m2 g−1, which facilitated the active migration of electrolyte ions. Supercapacitor measurements on the as-synthesized materials were performed through cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) measurements. From three electrode measurements, the MnNi2O4/PPY composite delivered a specific capacitance (Csp) of 304 F g−1 at a current density of 1 A g−1. The charge storage contribution analysis of the MnNi2O4/PPY composite electrode showed 62.2% diffusion-controlled behavior and 37.8% surface-controlled behavior. The suitability of these composites was extensively studied as a positive electrode material for asymmetric supercapacitors in a widened operating voltage window of 1.6 V. Furthermore, the assembled MnNi2O4/PPY//AC asymmetric device had an energy density of 35.9 W h kg−1 at a power density of 802.9 W kg−1. These results open up promising applications of these materials in advanced energy storage. [ABSTRACT FROM AUTHOR]

Developing low-cost electrodes for energy storage devices with high energy and power densities remains a daunting problem. Herein, interconnected porous carbon is created using the Phyllanthus emblica (amla, also known as Indian gooseberry) fruit as a precursor and KOH as an activating agent by a simple carbonization method combined with chemical activation. The activated amla-derived carbon (AAC) has a large specific surface area (up to 1661 m2 g−1) and a hierarchical porous structure with mesopores. Furthermore, the large interlayer spacing (0.367 nm) and the residual elements (N and O) in the porous carbon structure substantially enhance the conductivity and reaction activity. The AAC showed a high reversible capacity of 295 mA h g−1 at 100 mA g−1, as well as remarkable rate properties and good cycling life stability (210 mA h g−1 after 1500 cycles at 1000 mA g−1) with 99.8% coulombic efficiency, when evaluated as an electrode material for potassium ion batteries. The AAC electrode in a symmetric supercapacitor device exhibited a remarkable specific energy of 57.5 W h kg−1 at a specific power of 300 W kg−1 in an organic electrolyte (1 M TEABF4/AN) with a wide voltage window of 0.0–3.0 V. Moreover, it retained a specific energy of 25 W h kg−1 even at a high specific power of 3000 W kg−1, indicating its high-rate capability. Furthermore, it exhibited an excellent efficiency of 97.3% over 10 000 charge–discharge cycles. [ABSTRACT FROM AUTHOR]

Exploiting high-performance carbonaceous materials from biomass for supercapacitor (SC) electrodes has attracted extensive attention. In this research, hierarchical porous carbon electrodes derived from sorghum have been explored for the construction of symmetrical supercapacitors. A facile carbonization/activation strategy has been employed to synthesize porous carbon with a large specific surface area (∼1271 m2 g−1), an interconnected hierarchical pore structure, and heteroatom doping such as N, O, P, and S. The supercapacitors show a high specific capacitance of ∼483 F g−1 at 1 A g−1, a high energy density of 96.54 W h kg−1 at a power density of 1200 W kg−1 and cycle stability with capacitance retention of 97.5% after 10 000 charge/discharge cycles. This work presents a promising strategy for fabricating biomass-derived porous carbon with high energy density and low loss for commercial application in energy storage systems. [ABSTRACT FROM AUTHOR]

Design and development of promising electrode materials for supercapacitors has been a vital topic of current research focus. Here, we report the supercapacitive performance of the strontium titanate–graphene quantum dot–polyaniline heterohybrid. The synthesis strategy involves a sequential sol–gel synthesis of strontium titanate, followed by hydrothermal aided interface formation with graphene quantum dots (GQD) and polyaniline (PANI) deposition by chemical oxidative polymerization. A high specific capacitance of 2134 F g−1 could be observed in 1 M H2SO4 electrolyte at a current density of 1 A g−1. The Ragone plot for the symmetric cell reveals an energy density of 16.2 W h kg−1 at a power density of 4533.7 W kg−1. The 97.7% retention of specific capacitance demonstrated at higher current densities ensures high rate capability. Further, the device demonstrated a capacitance retention of 80% at 10 A g−1 after 10000 galvanostatic charge–discharge cycles. Low interfacial charge transfer resistance as evidenced by impedance spectroscopy analysis and high performance could be attributed to the synergistic interaction at the interface. [ABSTRACT FROM AUTHOR]

The fabrication of polymetallic selenide nanomaterials as supercapacitor electrode materials via a convenient and efficient design route has become the center of attention in energy storage research. However, the design and synthesis of such materials still does not address the major challenges of optimal energy storage. Herein, we present the synthesis of high-performance selenated polymetallic amorphous Co/Mo–MnSex supercapacitor electrodes with metal MOFs as precursors. The morphology and capacitance of the electrodes are improved by changing the structure of Co/Mo–MOF through ion doping and hydrothermal selenization. At a current density of 1 A g−1, the Co/Mo–MnSex electrode material exhibits an ultrahigh specific capacitance of 3679 F g−1. In particular, the combined hybrid supercapacitor (HBS) has an excellent energy density of 141.3 W h kg−1 at a power density of 496 W kg−1 and even 79.7 W h kg−1 at a power density of 15 105.3 W kg−1. It can light up light strips 0.5 and 1.0 m in length. In addition, the superb cycling stability of the electrode material can be corroborated by its retention rate of 96.0% after 35 000 cycles. This work synthesized excellent supercapacitor electrode materials through a facile and novel method and provides insights into the design of MOF-based polymetallic materials. [ABSTRACT FROM AUTHOR]

Li–O2 batteries, which involve the reversible formation and decomposition of Li2O2, attract extensive concern for their extremely high theoretical energy density. As main sites for redox reactions, the ability of air electrodes to accommodate discharge products and resist passivation is indispensible for battery performance. Therefore, electrodes with a rational architecture and effective catalysts should be designed to improve the electrochemical performance of Li–O2 batteries. In this paper, Co–N-reduced graphene oxide (rGO) materials are synthesized as catalysts for Li–O2 batteries by simple carbonization of graphene oxide (GO) supported ZIF-67 nanocrystals. The relationship between carbonization time and morphology of the catalysts, and thus affect the electrochemical performance are investigated in order to improve the catalytic activity of the air electrode. With tailored deposition sites and morphology of the discharge products, the air electrode exhibits a significant enhancement in specific capacity and cycling capability. A specific capacity of 3304 mA h gactive materials−1 is acquired for the Co–N-rGO-7 h electrode. By controlling the discharge depth to 500 mA h g−1, the electrode delivers improved performance with stable discharge–charge profiles over 30 cycles. [ABSTRACT FROM AUTHOR]

As an emerging high-power density energy storage device, supercapacitors are limited in their development by electrode materials. Transition metal nitrides have attracted widespread attention in supercapacitors due to their high electrical conductivity and considerable capacity. Among them, vanadium nitride features a high theoretical capacity and excellent electrical conductivity, nevertheless, its solubility problem in alkaline electrolytes has always hindered the practical application of vanadium nitride. Herein, a universal method is reported for the preparation of vanadium nitride quantum dot composites by solvothermal methods and in situ substitution. Using the stable ZIF-8 dodecahedral structure, vanadium ions are riveted to the structure of the metal–organic framework by in situ substitution; after high-temperature annealing, it retains the dodecahedral structure of ZIF-8 and forms hollow nanocages. This hollow structure generates more active sites and ameliorates the reaction kinetics of the vanadium nitride material. It has a capacity of 278 F g−1 at a current density of 0.5 A g−1. Interestingly, a capacity retention rate of 82.23% can be achieved after 20 000 cycles at a current density of 3 A g−1. In addition, the assembled device exhibits a coulombic efficiency of 97.35%, a power density of 775 W Kg−1, and an energy density of 49.8 W h kg−1. This good electrochemical performance, especially the enhanced cycling stability, should be attributed to the effective solution to solve the dissolution problem of vanadium nitride in electrolytes. In conclusion, the proposed method is simple and easy to implement and has a broad utilization value and application prospects in energy conversion and storage systems. [ABSTRACT FROM AUTHOR]