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Self-healability is essential for supercapacitors to improve their reliability and lifespan when powering the electronics. However, the lack of a universal healing mechanism leads to low capacitive performance and unsatisfactory intelligence. Here, we demonstrate a multi-responsive healable supercapacitor with integrated configuration assembled from magnetic Fe3O4@Au/polyacrylamide (MFP) hydrogel-based electrodes and electrolyte and Ag nanowire films as current collectors. Beside a high mechanical strength, MFP hydrogel exhibits fast optical and magnetic healing properties arising from distinct photothermal and magneto-thermal triggered interfacial reconstructions. By growing electroactive polypyrrole nanoparticles into MFP framework as electrodes, the assembled supercapacitor exhibits triply-responsive healing performance under optical, electrical and magnetic stimuli. Notably, the device delivers a highest areal capacitance of 1264 mF cm−2 among the reported healable supercapacitors and restores ~ 90% of initial capacitances over ten healing cycles. These prominent performance advantages along with the facile device-assembly method make this emerging supercapacitor highly potential in the next-generation electronics., Self-healing property is important for supercapacitors when powering the electronics, but designing devices that possess a universal healing mechanism remains challenging. Here, the authors achieve an optically, electrically, and magnetically-responsive self-healing device with integrated configuration.

Emerging wearable electronics require stretchable energy storage devices to achieve energy autonomy for future commercialization. Stretchable microsupercapacitors (SMSCs) with neutral multivalent electrolytes are desired to increase the specific capacitance while addressing the safety concerns of using acidic/organic electrolytes near the human body. Ti3C2Tx MXene nanosheets exhibit attractive electrochemical properties for various energy storage applications, yet few MXene SMSCs with neutral electrolytes were reported. Herein, a two-step contraction process was developed for fabrication of MXene SMSCs with high specific capacitance. After thermal shrinkage and solvent-induced contraction, an elastomer-infiltrated MXene (e-MXene) device with miniaturized dimensions and interdigitated electrodes was obtained. Upon incorporating an acidic gel electrolyte, the e-MXene SMSC demonstrated high areal capacitance (CA, 127.9 mF cm−2), high rate performance (64.0% retention from 10 to 200 mV s−1), and high mechanical stability under 50% strain for 3000 cycles (91.6% preservation). Furthermore, the e-MXene SMSC with neutral multivalent electrolyte demonstrated high CA of 61.4 and 51.7 mF cm−2 under 0% and 50% strains, respectively. Compared with the literature, our e-MXene SMSC with acidic electrolyte showed superior energy density (5.4 μW h cm−2 at 0.15 mW cm−2), and the SMSC with neutral multivalent electrolyte demonstrated high electrochemical performance (3.1 μW h cm−2 at 0.03 mW cm−2) together with ensured user safety.

Two-dimensional (2D) Ti3C2Tx MXene has shown great potential in the energy storage field, and its performance strongly depends on the intercalation of cations. Therefore, engineering its interlayer...

Gel electrolytes are important components in flexible solid-state supercapacitors. An urgent need exists for gel electrolytes that can store abundant electrolyte ions and provide high ionic conductivity, with performance characteristics similar to the liquid electrolyte, enabling high-power capability for devices. Herein, we have reported a general and scalable strategy toward various high-performance gel electrolytes including the first freeze of chemical cross-linked poly(vinyl alcohol) followed by infusing with different electrolytes (acid, neutral, and alkaline). The engineering not only endows robust electrolyte ion retention ability and outstanding ion migration rate but also strengthens the mechanical properties for gel electrolytes. As a proof of application, we demonstrate that an all-in-one supercapacitor with a H2SO4 gel electrolyte can deliver excellent rate capability (58.2% retention under the 50-fold increase in current densities), high areal capacitance (644.4 mF cm–2), and long operating ...

A conceptually new approach has been developed for the fabrication of magnetite (Fe3O4)‐decorated carbon nanotubes (M‐CNTs) for negative electrodes of electrochemical supercapacitors. M‐CNTs were prepared by an ultrasonic‐assisted chemical synthesis method, which involved dispersion of functionalized CNTs in water, Fe3O4 formation on the CNTs surface, and particle extraction through liquid‐liquid interface (PELLI). Palmitic acid was found to be an efficient new extractor for PELLI. The slurries produced after drying and redispersing M‐CNTs and slurries obtained using PELLI were used for electrode fabrication. The electrodes prepared using PELLI showed superior performance due to reduced particle agglomeration. Testing results provided an insight into the influence of Fe3O4/CNTs mass ratio on the capacitance and capacitance retention at high charge‐discharge rates. A capacitance of 5.82 F cm−2 (145.4 F g−1) was achieved in Na2SO4 electrolyte using electrodes with high active mass of 40 mg cm−2 and ratio of active mass to current collector mass of 0.6. Good electrochemical performance was achieved at low impedance. The capacitance of the negative M‐CNTs electrodes was comparable with capacitance of advanced positive MnO2‐CNTs electrodes, which was beneficial for the fabrication of asymmetric devices. The asymmetric device has been fabricated, which showed promising performance in a voltage window of 1.6 V.

A carefully designed energy storage smart window (ESSW) was successfully demonstrated with transparent-to-dark electrochromic behavior and improved pseudocapacitive performance that constructed by Mo-doped WO3 film electrode and MnO2 nanoflake film electrode. These two electrodes were all synthesized by facile electrodeposition method which is simple, economic and easy-to-production. The proposed ESSW could change its color between transparent and dark with over 60% optical modulations in all visible bands (420–800 nm), which is satisfactory to the applications toward energy saving. Also, the areal capacitance of the ESSW reaches 19.1 mF cm−2 with working voltage window of 2.0 V so that just one single ESSW could power an LED bulb for more than 90 s. The complementary electrochromic behavior of the two electrodes guarantees the commendable electrochromic performance of the proposed ESSW, and the well-matched working potentials and areal capacitances of the asymmetric electrodes improve the pseudocapacitive performance. Such ESSW could have widely future applications toward energy saving and storing fields.

Zinc cobaltite (ZnCo2O4) is an emerging electrode material for supercapacitors due to its rich redox reactions involving multiple oxidation states and different ions. In the present work, potato chip-like 0D interconnected ZnCo2O4 nanoparticles (PIZCON) were prepared using a solvothermal approach. The prepared material was characterized using various analytical methods, including X-ray powder diffraction and scanning electron microscopy. The possible formation mechanism of PIZCON was proposed. The PIZCON electrode material was systematically characterized for supercapacitor application. The areal capacitance of PIZCON was 14.52 mF cm−2 at 10 µA cm−2 of current density, and retention of initial capacitance was 95% at 250 µA cm−2 following 3000 continuous charge/discharge cycles. The attained measures of electrochemical performance indicate that PIZCON is an excellent supercapacitor electrode material.

Metal organic frameworks (MOFs) with numerous potential pseudocapacitive sites are quite appealing to supercapacitors with high specific and areal capacitances. However, MOFs suffer from a low conductivity nature, resulting in a mediocre electrochemical performance. Herein, we propose a template-growth strategy of MOF to enhance both specific and areal capacitances of MOF as the electrode material for supercapacitor. As the loading mass of MOF increases from 2 to 5 mg, the specific capacitance also increases from 937 to 2387 Fg−1 (431 to 1098 Cg−1) and areal capacitance 1.87 to 11.94 Fcm−2 (0.86 to 5.49 Ccm−1). Accordingly, a hybrid MOF//AC supercapacitor can deliver a maximum energy density of 67 Wh kg−1 and a maximum power density of 6000 W kg−1. These results point to a way to fabricate MOF electrode of supercapacitor with high specific and areal capacitance, which leads them to a more practical future.

With the rapid improvement of the global economy, the role of energy has become even more vital in the 21st century. In this regard, energy storage/conversion devices have become a major, worldwide research focus. In response to this, we have prepared two-dimensional (2D)-hierarchical sheet-like ZnCo2O4 microstructures for supercapacitor applications using a simple hydrothermal method. The 2D-hierarchical sheet-like morphologies with large surface area and smaller thickness enhanced the contact area of active material with the electrolyte, which increased the utilization rate. We investigated the electrochemical performance of sheet-like ZnCo2O4 microstructures while using Cyclic voltammetry (CV), Galvanostatic charge-discharge (GCD), and Electrochemical impedance spectroscopy (EIS) analysis. The electrochemical results demonstrated that the ZnCo2O4 electrode possesses 16.13 mF cm&minus, 2 of areal capacitance at 10 &micro, A cm&minus, 2 of current density and outstanding cycling performance (170% of capacitance is retained after 1000 cycles at 500 &micro, 2). The high areal capacitance and outstanding cycling performance due to the unique sheet-like morphology of the ZnCo2O4 electrode makes it an excellent candidate for supercapacitor applications.

• Flexible supercapacitor is fabricated by electrodeposition of PANI. • Areal capacitance of 5120 mF.cm−2 in 1M H2SO4 at 100 100 mA.cm−2 is achieved. • 1.6% decrement in specific capacitance after 1000 cycles in PVA/H2SO4.

Three-dimensional (3D) microsupercapacitors (MSC) have been spotlighted, because they overcome limited areal capacitance of two-dimensional planar MSCs. Specially, 3D printing technology offers numerous advantages to generate 3D electrodes for MSCs, which includes time-saving, cost-effective manufacturing, and realization of tailorable complex electrode designs. In this paper, we report novel hierarchical 3D designs of conductive 3D electrodes for MSC by digital light processing (DLP)-based 3D printing. Photocurable composite resin with silver nanowires was optimized for DLP printing for the hierarchical design of high aspect ratio in 3D electrodes. The hierarchical 3D electrodes showed unique patterns on the structure corresponding to stacking of layers in the direction of 3D printing. The fabricated 3D MSCs demonstrated low electrical resistance to be used as feasible MSC electrodes. Energy storage from silver redox reactions was demonstrated in hierarchical 3D electrodes designed with mechanically durable 3D octet trusses.

Because of the poor specific capacitance of transparent and flexible supercapacitors reported recently, exploring electrode materials with high electrochemical properties for such devices is still ...

Excellent self-healability is considered as a critical element for next-generation flexible/wearable energy-storage devices. However, realizing superior electrochemical performances remains a big challenge for such devices because self-healability intrinsically offsets their basic energy-storage functions. Here we demonstrate that the conflict can be effectively addressed for a supercapacitor via rationally designing its device configuration at a molecular level. The capacitor is fabricated by in situ integrating polyaniline (PANI) and H2SO4 solution into a single network comprising the copolymer of vinylimidazole and hydroxypropyl acrylate (PVH). The all-in-one configuration combines fast charge-carrier transportation, good structural durability and excellent self-healability. Consequently, the resulting capacitor delivers a high specific areal capacitance and rate capability superior to its counterparts, but also maintains ultra-long cycling life even after breaking/healing 10 times. This example of configuration engineering offers a new and promising avenue to design self-healable energy-storage devices with outstanding performances.

Areal capacitance, that is, electric capacitance per unit of surface area, is an important physical quantity, especially in electrochemistry and in colloid chemistry. In handbooks and in scientific papers, the symbol C which normally denotes capacitance is also used for areal capacitance, although capacitance and areal capacitance are two different physical quantities, which have different units (F, and F/m2, respectively), and different numerical values. Using the same name and symbol for two different physical quantities is misleading, especially when the both quantities appear in the same text. The present author postulates that the term “areal capacitance” and the symbol Ξ (with corresponding subscript when applicable) are always used when areal capacitance is meant, to clearly distinguish it from capacitance. The rationale for such a name and symbol is discussed.

In this work, we have mainly investigated the electrochemical properties of Bi 2 SiO 5 and Bi 2 O 2 CO 3 . They have the different layer structures and the areal capacitance (10.1 mF cm − 2 ) of Bi 2 O 2 CO 3 electrode is 2.9 times higher than that (2.6 mF cm − 2 ) of Bi 2 SiO 5 one at 0.1 mA cm − 2 . After 4000 cycles, 84% and 81% capacitances are retained for Bi 2 O 2 CO 3 and Bi 2 SiO 5 electrodes, respectively. Because Bi 2 O 2 CO 3 has a lower BET area (3.634 m 2 g − 1 ) and a higher electrical resistance (5.231 Ω cm 2 ) than Bi 2 SiO 5 (35.13 m 2 g − 1 , 2.022 Ω cm 2 ), their different electrochemical properties have been mainly attributed to the different fine layer structures. For Bi 2 O 2 CO 3 , the anion layers and cation layers are completely separated and the unobstructed passageways form, which would favour to get in and out for ions and improve the capacitance. For Bi 2 SiO 5 , the newly-formed Bi O Si bonds can improve conductivity, but there is no passageway between the anion layers and cation layers, which does not favour for the getting in and out of ions. This study demonstrates that fine layer structure has a significant influence on the electrochemical properties.

Ni Foam substrate directly serves as the Ni source for the final Ni-Co oxide product with a Cu assisted chemical method. Especially, after shaking off top layer of Ni-Co oxide grown on Ni Foam, the sample unexpectedly exhibits a greatly enhanced areal capacitance from 4.17 to 11.44 F cm −2 (1 mA cm −2 ). Finer structures including oxide nanotubes are interestingly found underneath the top layer, which may account for this extraordinary phenomenon.

Herein, a simple and green two-step electrochemical method was used to prepare nanoflake-like CuO\Cu microparticles on Nickel Foam (NiF) for supercapacitor applications. First, Cu microparticles were plated on NiF through a simple immersion method. Next, the Cu/NiF electrode was electrochemically oxidized in KOH solution to CuO/Cu/NiF. The effect of KOH electrolyte concentration on the electro-oxidation of Cu/NiF was also investigated. FESEM studies show that the surface morphology of CuO/Cu is highly porous, consisting of Cu interconnected microparticles on which islands of CuO have grown. The CuO/Cu/NiF electrode exhibited a high areal capacitance of 0.31 F cm−2 at a scan rate of 10 mV s−1 with excellent stability over 1000 voltammetric cycles. The results in this study show the potential application of CuO/Cu/NiF as a low-cost high-performance positive electrode in Supercapacitors.

Most advances towards flexible supercapacitors (SCs) have been focused on porous carbon materials. However, the poor flexibility and low areal capacitance impede their industrial application. While carbon cloth is generally regarded as improper electrode material due to its poor electrochemical performance, here, we demonstrate the capacitance of carbon cloth can be boosted to three orders of magnitude higher (2900 mF cm-2) with a simple high-temperature annealing process. The improvement stems from ultramicropores effects in the range of 0.46–0.64 nm besides superhydrophilicity and high specific surface area. Remarkably, direct implementation for flexible solid-state SCs (SSCs) provides areal capacitance and energy density for the stack of 920 mF cm-2 and 128 μW h cm-2, respectively. In addition, these devices are bendable, durable and easy to be any dimensions, hence, holding great promise for large-scale production of flexible electronics.

Wood carbon (WC)-derived thick electrode design has recently received increasing interest because of its high energy density at the device level. Herein, a facile, low-cost, and efficient strategy by surface engineering to synthesize ultrathick electrodes of quasi-solid-state symmetric supercapacitors (SSCs) based on activated wood-carbon (AWC) monoliths is presented. The AWC as a freestanding ultrathick electrode shows an impressive areal capacitance of 6.85 F cm−2 at 1 mA cm−2 and 4.55 F cm−2 at 20 mA cm−2. Furthermore, a quasi-solid-state SSC assembled by two identical AWC monoliths delivers an excellent energy density of 0.23 mW h cm−2 (4.59 W h kg−1 and 0.77 W h L−1) at 500 mW cm−2 (9.9 mW kg−1 and 2500 W L−1) while maintaining a capacitance retention of 86% after 10 000 cycles. The remarkable electrochemical performance is associated with the structural integrity of natural wood, the introduction of oxygen-containing functional groups, and the ultrathick electrode design, which significantly enhance electroactive material loading and device integration.

The effect of substrate surface roughening on the capacitance of Ni(OH)2/NiOOH nanowall array samples produced via chemical bath deposition for 2, 4, 6, 24 and 48 h on an as-received stainless steel substrate and the same substrate after sandblasting has been investigated. Symmetric cells were subjected to 120,000 charge-discharge cycles to access changes in their capacitance. Specific capacitances were derived from cyclic voltammetry and charge-discharge cycling under a three electrode setup. Substrate roughening significantly increases the capacitance of symmetric cells and film stability since film exfoliation does not occur to the same degree as on the as-received substrate. Interestingly, films deposited on a roughened substrate for 6, 24 and 48 h also exhibit self-recovery of capacitance, which could be related to an electrodissolution-electrodeposition effect. With the use of a roughened substrate, the thinnest film gives the highest specific capacitance, 1456 F g−1, whilst the thickest one shows the highest areal capacitance, 235 mF cm−2, after 20,000 cycles. These results reveal the promise of surface roughening toward increasing the capacitance and stability of Ni(OH)2/NiOOH films.

Two-dimensional carbon-based nanomaterials have demonstrated great promise as electrode materials for electrochemical energy storage. However, there is a trade-off relationship between energy storage and rate capability for carbon-based energy storage devices because of the incrementing ion diffusion limitations, especially for thick electrodes with high mass loading. Herein, we report the cross-linked microporous carbon nanosheets enabling high-energy and high-rate supercapacitors. The as-fabricated microporous carbon nanosheets exhibit an extraordinary thickness-independent electrochemical performance. With the thickness of 15 μm, the as-fabricated carbon nanosheet electrode possesses areal/volumetric/gravimetric capacitance of 895 mF cm

Poly(3,4-ethylenedioxythiophene) (PEDOT) is known for compact morphology owing to dense growth, which limits its electrochemical capacitive properties. In this work, we have facilitated the dispersed growth of PEDOT by incorporating graphene oxide (GO) nanosheets, thus forming the PEDOT/GO hybrids via a facile electropolymerization route, in which GO nanosheets act as substrates with large specific area to load PEDOT coatings. The impact of electropolymerization modes and parameters on the supercapacitive properties of PEDOT/GO hybrids is studied in detail. Electrochemical measurements indicate that GO incorporation remarkably enhances the supercapacitive properties of PEDOT electrode. Among numerous preparation conditions, galvanostatically prepared electrode using 1 mA cm−2 presents the optimal supercapacitive properties, delivering an areal capacitance of 109.3 mF cm−2 at 0.5 mA cm−2 and retaining 95.1% of initial capacitance after 10,000 cycles. Such an electrode preserves the curly morphology of GO nanosheets and gives rise to more dispersed distribution for PEDOT coatings.

Typical functionalization treatment by strong acid is used to introduce functional groups into/onto the multiwall carbon nanotubes (MWCNTs), to enhance the desired redox activity for electrochemical applications. The influence of various functional groups on the redox of MWCNT has been studied in recent years. Different functional groups on MWCNT can be removed selectively using different thermal annealing temperatures. By this method, it is recognized that carboxyl, anhydride, and phenol groups play essential roles in the redox reaction. A designed carboxyl/anhydride-rich defective MWCNT is fabricated with a superior specific areal capacitance of 34.55 mF/cm2. These results provide more information for the study of the MWCNTs' electrochemical applications toward supercapacitors and batteries.

Flexible, high-performance miniature supercapacitors that offer reliable energy storage and output are desirable for use in portable and wearable electronics. Herein, we developed micro-supercapacitors with three-dimensional electrodes by printing assembly of graphene. By controlling the microstructures and macroscopic architectures of the graphene electrodes, superior electrochemical performance was achieved; especially, we demonstrated an advancement to address the limitation of areal capacitance. The unique three-dimensional graphene structure also provides this new class of micro-supercapacitors with exceptional mechanical flexibility. With these remarkable features, facile integration of the micro-supercapacitor array into flexible printed circuits was demonstrated. This printing assembly approach will pave the way to explore energy storage systems with diverse structures and extended functionalities.

In this paper, hierarchical WO 3 nanofibers are synthesized on a flexible carbon cloth by a facile hydrothermal route. The as-prepared products as supercapacitor electrodes show high discharge areal capacitance (1716.92 mF cm −2 at 2 mA cm −2 ) and cycling stability (20.9% loss after 6000 repetitive cycles at 10 mA cm −2 ). These superior performances of hierarchical WO 3 structures indicate their promising applications in supercapacitor electrode materials.

Hierarchical structure design can greatly enhance the unique properties of primary material(s) but suffers from complicated preparation process and difficult self-assembly of materials with different dimensionalities. Here we report on the growth of single carbon tubular nanostructures with hierarchical structure ( h CTNs) through a simple method based on direct conversion of carbon dioxide. Resorting to in-situ transformation and self-assembly of carbon micro/nano-structures, the obtained h CTNs are blood-like multichannel hierarchy composed of one large channel across the h CTNs and plenty of small branches connected to each other. Due to the unique pore structure and high surface area, these h CTN-based flexible supercapacitors possess the highest areal capacitance of ∼320 mF cm −2 , as well as good rate-capability and excellent cycling stability (95% retention after 2500 cycles). It was established that this method can control the morphology, size, and density of h CTNs and effectively construct h CTNs well anchored to the various substrates. Our work unambiguously demonstrated the potential of h CTNs for large flexible supercapacitors and integrated energy management electronics.

High specific-capacity pseudocapacitive transition-metal-hydroxide (TMH) materials are desirable for future high performance transparent supercapacitors, but have been rarely reported previously. The successful synthesis of TMH materials with desired nanostructures is a key factor for their transparency. Here, Ni(OH)2 nanosheet transparent film (NNS-TF) was developed simply through a gas-liquid diffusion method. The nanostructures were enwrapped in graphene shells (NNS@Gr-TF) for using as transparent electrodes. The unique encapsulation structures build up rapid three-dimensional electron and ion transport pathways together with the underlying ITO layer. The specific areal capacitance (18.9 mF/cm2 at 0.1 mA/cm2) was greatly improved, at least a thousand times higher than the reported value for transparent devices based on planer CVD graphene, and ten times as that for 3D micro-structured graphene membrane.

A simple and controllable strategy has been developed to fabricate CoMoO4 microplates/CoMoO4 microprisms (CMCMs) structures on Ni foam via a facile, cost-effective, two-step hydrothermal route. The as-grown 3D architecture exhibited excellent areal capacitance of 4.33 F cm−2 at a galvanostatic charge-discharge current density of 50 mA cm−2 (6 A g−1) and outstanding cycle performance with only 2.8% degradation over 6500 cycles in the 3 M KOH solution. The asymmetric all-solid-state supercapacitors based on activated carbon (AC) and CMCMs exhibited much better electrochemical performance than the symmetric counterpart, showing an areal capacitance of 95.22 mF cm−2 at the current density of 12 mA cm−2 and excellent cycling stability with 92.27% of the initial capacitance after 5000 cycles. These results may provide useful guidelines for materials selection and configuration designs for the novel energy storage devices based on CoMoO4 components and substrates.

In this work, commercial Ni foams are directly oxidized into Ni@Ni(OH)2 foams in a mild NH4NO3 solution at 80 °C. When used as binder-free electrodes, these Ni@Ni(OH)2 electrodes demonstrate a high areal capacitance of 6.4 F/cm2 at a current density of 2.5 mA/cm2, or 1.62 F/cm2 at a high current density of 30 mA/cm2. Nevertheless, they show a poor cycling ability with 70.4% (or 42%) capacitance retention after 2000 (or 5000) cycles at 30 mA/cm2. This kind of electrodes has a promising application in low-cost, high-performance supercapacitor, if an effective strategy is found to improve their cycling ability.

Volumetric and areal energy densities are the key performance metrics for electrochemical supercapacitors (EC) used in portable storage devices, whereas mechanical flexibility and potential for direct integration with conventional cloths are the primary requirements for wearable usage. Herein, highly scalable, versatile EC electrodes are presented based on the spontaneously assembled hydrogel-hybrids of graphene and polyaniline (PANI). Our hydrogel-hybrids exhibit areal capacitance of 853 mF cm−2 (at 1 mA cm−2) with superb cycling stability (95.2% retention after 5000 cycles), which can be readily increased up to 2.2 F cm−2 by the multistacking of electrodes without sacrificing charging-discharging rate capability. Control of hydration level (water

Few-layer graphene sheet-passivated porous silicon (PSi) as an outstanding electrochemical double-layer supercapacitor electrode was demonstrated. The PSi matrix was formed by electrochemical etching of a doped silicon wafer and was further surface-passivated with few-layer graphene sheets by a Ni-assisted chemical vapor deposition process where a wide range of porous PSi structures, including mesoporous, macroporous, and hybrid porous structures were created during the graphene growth as temperature increases. The microstructural and graphene-passivation effects on the capacitive performance of the PSi were investigated in detail. The hybrid porous PSi electrode, optimized in terms of capacitive performances, achieves a high areal capacitance of 6.21 mF/cm2 at an ultra-high scan rate of 1000 mV/s and an unusual progressing cyclic stability of 131% at 10,000 cycles. Besides mesopores and macropores, micropores were introduced onto the surfaces of the passivating few-layer graphene sheets with a KOH activation process to further increase the functioning surface area of the hierarchical porous PSi electrode, leading to a boost in the areal capacitance by 31.4% up to 8.16 mF/cm2. The present designed hierarchical porous PSi-based supercapacitor proves to be a robust energy storage device for microelectronic applications that require stable high rate capability. Electronic supplementary material The online version of this article (10.1186/s11671-018-2646-7) contains supplementary material, which is available to authorized users.

Herein, a facile and available electrochemical activation approach has been developed to markedly boost the capacitive performance of carbon fiber paper (CFP). The activated CFP could deliver a significant areal capacitance of 1.56 F cm−2 at a high current density of 5 mA cm−2 with excellent rate capability and cycling performance.

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Layered hierarchical CoMoO 4 nano-structured arrays grown on nickel foam were designed and synthesized by a two-step hydrothermal method following by annealing. With the increase in the nearly three times loading mass of active materials, the specific capacitance of the layered hierarchical CoMoO 4 nano-structured arrays only shows a slight loss compared with the single-layer CoMoO 4 nano-structured arrays, which dramatically improved the areal capacitance from 2.47 to 6.79 F cm −2 . Also, the layered hierarchical CoMoO 4 nano-structured arrays showed 94.8% capacitance retention after 2500 cycles, which is mainly due to the well-designed layered hierarchical structure and good conductivity.

Traditional stretchable supercapacitors, possessing a thin electrode and a 2D shape, have limited areal specific areal capacitance and are incompatible with 3D wearables. To overcome the limitations of 2D stretchable supercapacitors, it is highly desirable to develop 3D stretchable supercapacitors with higher mass loading and customizable shapes. In this work, a new 3D stretchable supercapacitor inspired by a honeycomb lantern based on an expandable honeycomb composite electrode composed of polypyrrole/black-phosphorous oxide electrodeposited on carbon nanotube film is reported. The 3D stretchable supercapacitors possessing device-thickness-independent ion-transport path and stretchability can be crafted into customizable device thickness for enhancing the specific areal energy storage and integrability with wearables. Notably, a 1.0 cm thick rectangular-shaped supercapacitor shows enhanced specific areal capacitance of 7.34 F cm-2 , which is about 60 times higher than that of the original 2D supercapacitor (120 mF cm-2 ) at a similar discharge rate. The 3D supercapacitor can also maintain a capacitance ratio of 95% even under the reversible strain of 2000% after 10 000 stretch-and-release cycles, superior to state-of-the-art stretchable supercapacitors. The enhanced specific areal energy storage and the customizablility in shapes of the 3D stretchable supercapacitors show immense promise in a wide range of applications in stretchable and wearable electronics.

In the present work, we report on the use of organized TiO2 nanotube (NT) layers with a regular intertube spacing for the growth of highly defined α-Fe2O3 nano-needles in the interspace. These α-Fe2O3 decorated TiO2 NTs are then explored for Li-ion battery applications and compared to classic close-packed (CP) NTs that are decorated with various amounts of nanoscale α-Fe2O3. We show that NTs with tube-to-tube spacing allow uniform decoration of individual NTs with regular arrangements of hematite nano-needles. The tube spacing also facilitates the electrolyte penetration as well as yielding better ion diffusion. While bare CP NTs show a higher capacitance of 71 μAh cm−2 compared to bare spaced NTs with a capacitance of 54 μAh cm−2, the hierarchical decoration with secondary metal oxide, α-Fe2O3, remarkably enhances the Li-ion battery performance. Namely, spaced NTs with α-Fe2O3 decoration have an areal capacitance of 477 μAh cm−2, i.e. they have nearly ~8 times higher capacitance. However, the areal capacitance of CP NTs with α-Fe2O3 decoration saturates at 208 μAh cm−2, i.e. is limited to ~3 times increase.

Stretchable energy storage devices are required to fit for stretchable electronic devices, forming a fully stretchable system for comfortable and body-attachable electronic devices. Herein, highly stretchable micro-supercapacitors are fabricated by designing wave-shaped hybrid multiwalled carbon nanotubes/polyaniline electrodes. As-fabricated stretchable devices exhibit a large areal capacitance of 44.13 mF cm−2 and offer a power density of 0.07 mW cm−2 at an area energy density of 0.004 mW h cm−2. Owing to the designed wavy electrode structure, the electrochemical performances of the stretchable micro-supercapacitors are almost invariably under different stretching stations ranging from 5% to 40%. By fabricating stretchable micro-supercapacitors arrays, a red light-emitting diode can be easily lighted under different conditions including stretching, twisting, crimping, and winding. All these results confirm the outstanding stability and mechanical strength of stretchable micro-supercapacitors, demonstrating its potential application in skin-patchable electronics or portable/wearable devices.

Hierarchical Ni(OH)2@CoMoO4 nanoflake composite on Ni foam was successfully constructed by electrodepositing Ni(OH)2 onto CoMoO4 nanoflake and investigated as binder-free electrodes for supercapacitor. The composite shows a large areal capacitance of 5.23[Formula: see text]F[Formula: see text]cm[Formula: see text] at current density of 8[Formula: see text]mA[Formula: see text]cm[Formula: see text], and a capacitance retention of 82.5% after 1000 cycles. The high electrochemical performances can be attributed to the hierarchical nanoflakes structure and the synergetic effect between Ni(OH)2 nanosheets and CoMoO4 nanoflakes. This work demonstrates that Ni(OH)2@CoMoO4 nanoflake composite is highly desirable for application as advanced electrochemical electrode material.