Layered H2Ti6O13‐Nanowires: A New Promising Pseudocapacitive Material in Non‐Aqueous Electrolyte

Layered H₂Ti₆O₁₃‐nanowires are prepared using a facile hydrothermal method and their Li‐storage behavior is investigated in non‐aqueous electrolyte. The achieved results demonstrate the pseudocapacitive characteristic of Li‐storage in the layered H₂Ti₆O₁₃‐nanowires, which is because of the typical nanosize and expanded interlayer space. The as‐prepared H₂Ti₆O₁₃‐nanowires have a high capacitance of 828 F g^?1 within the potential window from 2.0 to 1.0 V (vs. Li/Li⁺). An asymmetric supercapacitor with high energy density is developed successfully using H₂Ti₆O₁₃‐nanowires as a negative electrode and ordered mesoporous carbon (CMK‐3) as a positive electrode in organic electrolyte. The asymmetric supercapacitor can be cycled reversibly in the voltage range of 1 to 3.5 V and exhibits maximum energy density of 90 Wh kg^?1, which is calculated based on the mass of electrode active materials. This achieved energy density is much higher than previous reports. Additionally, H₂Ti₆O₁₃//CMK‐3 asymmetric supercapacitor displays the highest average power density of 11 000 W kg^?1. These results indicate that the H₂Ti₆O₁₃//CMK‐3 asymmetric supercapacitor should be a promising device for fast energy storage.     

Metal‐Ion (Fe,V, Co,and Ni)‐Doped MnO2 Ultrathin Nanosheets Supported on Carbon Fiber Paper for the Oxygen Evolution Reaction

Manganese dioxides (MnO₂) are considered one of the most attractive materials as an oxygen evolution reaction (OER) electrode due to its low cost, natural abundance, easy synthesis, and environmental friendliness. Here, metal‐ion (Fe, V, Co, and Ni)‐doped MnO₂ ultrathin nanosheets electrodeposited on carbon fiber paper (CFP) are fabricated using a facile anodic co‐electrodeposition method. A high density of nanoclusters is observed on the surface of the carbon fibers consisting of doped MnO₂ ultrathin nanosheets with an approximate thickness of 5 nm. It is confirmed that the metal ions (Fe, V, Co, and Ni) are doped into MnO₂, improving the conductivity of MnO₂. The doped MnO₂ ultrathin nanosheet/CFP and the IrO₂/CFP composite electrodes for OER achieve a low overpotential of 390 and 245 mV to reach 10 mA cm^?2 in 1 m KOH, respectively. The potential of the doped composite electrode for long‐term OER at a constant current density of 20 mA cm^?2 is much lower than that of the pure MnO₂ composite electrode.     

Ultralight and Binder‐Free All‐Solid‐State Flexible Supercapacitors for Powering Wearable Strain Sensors

Flexible energy storage devices play a pivotal role in realizing the full potential of flexible electronics. This work presents high‐performance, all‐solid‐state, flexible supercapacitors by employing an innovative multilevel porous graphite foam (MPG). MPGs exhibit superior properties, such as large specific surface area, high electric conductivity, low mass density, high loading efficiency of pseudocapacitive materials, and controlled corrugations for accommodating mechanical strains. When loaded with pseudocapacitive manganese oxide (Mn₃O₄), the MPG/Mn₃O₄ (MPGM) composites achieve a specific capacitance of 538 F g^?1 (1 mV s^?1) and 260 F g^?1 (1 mV s^?1) based on the mass of pure Mn₃O₄ and entire electrode composite, respectively. Both are among the best of Mn₃O₄‐based supercapacitors. The MPGM is mechanically robust and can go through 1000 mechanical bending cycles with only 1.5% change in electric resistance. When integrated as all‐solid‐state symmetric supercapacitors, they offer a full cell specific capacitance as high as 53 F g^?1 based on the entire electrode and retain 80% of capacitance after 1000 continuous mechanical bending cycles. Furthermore, the all‐solid‐state flexible supercapacitors are incorporated with strain sensors into self‐powered flexible devices for detection of both coarse and fine motions on human skins, i.e., those from finger bending and heart beating.     

Facile Synthesis of Hematite Quantum‐Dot/Functionalized Graphene‐Sheet Composites as Advanced Anode Materials for Asymmetric Supercapacitors

For building high‐energy density asymmetric supercapacitors, developing anode materials with large specific capacitance remains a great challenge. Although Fe₂O₃ has been considered as a promising anode material for asymmetric supercapacitors, the specific capacitance of the Fe₂O₃‐based anodes is still low and cannot match that of cathodes in the full cells. In this work, a composite material with well dispersed Fe₂O₃ quantum dots (QDs, ≈2 nm) decorated on functionalized graphene‐sheets (FGS) is prepared by a facile and scalable method. The Fe₂O₃ QDs/FGS composites exhibit a large specific capacitance up to 347 F g^?1 in 1 m Na₂SO₄ between –1 and 0 V versus Ag/AgCl. An asymmetric supercapacitor operating at 2 V is fabricated using Fe₂O₃/FGS as anode and MnO₂/FGS as cathode in 1 m Na₂SO₄ aqueous electrolyte. The Fe₂O₃/FGS//MnO₂/FGS asymmetric supercapacitor shows a high energy density of 50.7 Wh kg^?1 at a power density of 100 W kg^?1 as well as excellent cycling stability and power capability. The facile synthesis method and superior supercapacitive performance of the Fe₂O₃ QDs/FGS composites make them promising as anode materials for high‐performance asymmetric supercapacitors.     

A Self‐Branched Lamination of Hierarchical Patronite Nanoarchitectures on Carbon Fiber Cloth as Novel Electrode for Ionic Liquid Electrolyte‐Based High Energy Density Supercapacitors

The developments of rationally designed binder‐free metal chalcogenides decorated flexible electrodes are of paramount importance for advanced energy storage devices. Herein, binder‐free patronite (VS₄) flower‐like nanostructures are facilely fabricated on a carbon cloth (CC) using a facile hydrothermal method for high‐performance supercapacitors. The growth density and morphology of VS₄ nanostructures on CC are also controlled by varying the concentrations of vanadium and sulfur sources along with the complexing agent in the growth solution. The optimal electrode with an appropriate growth concentration (VS₄‐CC@VS‐3) demonstrates a considerable pseudocapacitance performance in the ionic liquid (IL) electrolyte (1‐ethyl‐3‐methylimidazolium trifluoromethanesulfonate), with a high operating potential of 2 V. Utilizing VS₄‐CC@VS‐3 as both positive and negative electrodes, the IL‐based symmetric supercapacitor is assembled, which demonstrates a high areal capacitance of 536 mF cm^?2 (206 F g^?1) and excellent cycling durability (93%) with superior energy and power densities of 74.4 µWh cm^?2 (28.6 Wh kg^?1) and 10154 µW cm^?2 (9340 W kg^?1), respectively. As for the high energy storage performance, the device stably energizes various portable electronic applications for a long time, which make the fabricated composite material open up news for the fabrication of fabrics supported binder‐free chalcogenides for high‐performance energy storage devices.     

A Low‐Cost,Self‐Standing NiCo2O4@CNT/CNT Multilayer Electrode for Flexible Asymmetric Solid‐State Supercapacitors

The demand for a new generation of flexible, portable, and high‐capacity power sources increases rapidly with the development of advanced wearable electronic devices. Here we report a simple process for large‐scale fabrication of self‐standing composite film electrodes composed of NiCo₂O₄@carbon nanotube (CNT) for supercapacitors. Among all composite electrodes prepared, the one fired in air displays the best electrochemical behavior, achieving a specific capacitance of 1,590 F g^?1 at 0.5 A g^?1 while maintaining excellent stability. The NiCo₂O₄@CNT/CNT film electrodes are fabricated via stacking NiCo₂O₄@CNT and CNT alternately through vacuum filtration. Lightweight, flexible, and self‐standing film electrodes (≈24.3 µm thick) exhibit high volumetric capacitance of 873 F cm^?3 (with an areal mass of 2.5 mg cm^?2) at 0.5 A g^?1. An all‐solid‐state asymmetric supercapacitor consists of a composite film electrode and a treated carbon cloth electrode has not only high energy density (≈27.6 Wh kg^?1) at 0.55 kW kg^?1 (including the weight of the two electrodes) but also excellent cycling stability (retaining ≈95% of the initial capacitance after 5000 cycles), demonstrating the potential for practical application in wearable devices.     

High‐Performance Ultrathin Flexible Solid‐State Supercapacitors Based on Solution Processable Mo1.33C MXene and PEDOT:PSS

MXenes, a young family of 2D transition metal carbides/nitrides, show great potential in electrochemical energy storage applications. Herein, a high performance ultrathin flexible solid‐state supercapacitor is demonstrated based on a Mo_1.33C MXene with vacancy ordering in an aligned layer structure MXene/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) composite film posttreated with concentrated H₂SO₄. The flexible solid‐state supercapacitor delivers a maximum capacitance of 568 F cm^?3, an ultrahigh energy density of 33.2 mWh cm^?3 and a power density of 19 470 mW cm^?3. The Mo_1.33C MXene/PEDOT:PSS composite film shows a reduction in resistance upon H₂SO₄ treatment, a higher capacitance (1310 F cm^?3) and improved rate capabilities than both pristine Mo_1.33C MXene and the nontreated Mo_1.33C/PEDOT:PSS composite films. The enhanced capacitance and stability are attributed to the synergistic effect of increased interlayer spacing between Mo_1.33C MXene layers due to insertion of conductive PEDOT, and surface redox processes of the PEDOT and the MXene.     

Synthesis of MnO2 Nanoparticles Confined in Ordered Mesoporous Carbon Using a Sonochemical Method

A sonochemical method has been successfully used in order to incorporate MnO₂ nanoparticles inside the pore channels of CMK‐3 ordered mesoporous carbon. Modification of the intrachannel surfaces of CMK‐3 to make them hydrophilic enables KMnO₄ to readily penetrate the pore channels. At the same time, the modification changes the surface reactivity, enabling the formation of MnO₂ nanoparticles inside the pores of CMK‐3 by the sonochemical reduction of metal ions. The resultant structures were characterized by X‐ray diffraction (XRD), nitrogen adsorption, and transmission electron microscopy (TEM). CMK‐3 with 20 wt.‐% loading of MnO₂ inside CMK‐3 delivered an improved discharge performance of 223 mA h g^–1 at a relatively high rate of 1 A g^–1. Almost no decrease in specific capacity is observed for the second cycle, and a discharge capacity of more than 165 mA h g^–1 is retained after 100 cycles. This is attributed to the nanometer‐sized MnO₂ formed inside CMK‐3 and the high surface area of the mesopores (3.1 nm) in which the MnO₂ nanoparticles are formed.     

Metal–Organic Framework (MOF) Derived Electrodes with Robust and Fast Lithium Storage for Li‐Ion Hybrid Capacitors

Hybrid metal–organic frameworks (MOFs) demonstrate great promise as ideal electrode materials for energy‐related applications. Herein, a well‐organized interleaved composite of graphene‐like nanosheets embedded with MnO₂ nanoparticles (MnO₂@C‐NS) using a manganese‐based MOF and employed as a promising anode material for Li‐ion hybrid capacitor (LIHC) is engineered. This unique hybrid architecture shows intriguing electrochemical properties including high reversible specific capacity 1054 mAh g^?1 (close to the theoretical capacity of MnO₂, 1232 mAh g^?1) at 0.1 A g^?1 with remarkable rate capability and cyclic stability (90% over 1000 cycles). Such a remarkable performance may be assigned to the hierarchical porous ultrathin carbon nanosheets and tightly attached MnO₂ nanoparticles, which provide structural stability and low contact resistance during repetitive lithiation/delithiation processes. Moreover, a novel LIHC is assembled using a MnO₂@C‐NS anode and MOF derived ultrathin nanoporous carbon nanosheets (derived from other potassium‐based MOFs) cathode materials. The LIHC full‐cell delivers an ultrahigh specific energy of 166 Wh kg^?1 at 550 W kg^?1 and maintained to 49.2 Wh kg^?1 even at high specific power of 3.5 kW kg^?1 as well as long cycling stability (91% over 5000 cycles). This work opens new opportunities for designing advanced MOF derived electrodes for next‐generation energy storage devices.     

Remarkable Improvements in Volumetric Energy and Power of 3D MnO2 Microsupercapacitors by Tuning Crystallographic Structures

Transition‐metal oxides as faradaic charge‐storage intermediates sandwiched between conductor and electrolyte are key components to store/deliver high‐density energy in microsupercapacitors for many applications in miniaturized portable electronics and microelectromechanical systems. While the conductor facilitating their electron transports, they generally suffer from a switch of rate‐determining step to their sluggish redox reactions in pseudocapacitive energy storage, during which poor cation accessibility and diffusion leads to high internal resistances and lowers volumetric capacitance and rate performance. Here it is shown that the faradaic processes in a model system of MnO₂ can be radically boosted by tuning crystallographic structures from cryptomelane (α‐MnO₂) to birnessite (δ‐MnO₂). As a result of greatly enhanced Na⁺ accessibility and diffusion, 3D layered crystalline δ‐MnO₂ microelectrodes exhibit volumetric capacitance as high as ≈922 F cm^?3 (≈1.5‐fold higher than α‐MnO₂, ≈617 F cm^?3) and excellent rate performance. This enlists δ‐MnO₂ microsupercapacitor to deliver ultrahigh stack electrical powers (up to ≈295 W cm^?3) while maintaining volumetric energy density much higher than that of thin‐film lithium battery.     

Nitrogen‐Doped Carbon Networks for High Energy Density Supercapacitors Derived from Polyaniline Coated Bacterial Cellulose

Bacterial cellulose (BC) is used as both template and precursor for the synthesis of nitrogen‐doped carbon networks through the carbonization of polyaniline (PANI) coated BC. The as‐obtained carbon networks can act not only as support for obtaining high capacitance electrode materials such as activated carbon (AC) and carbon/MnO₂ hybrid material, but also as conductive networks to integrate active electrode materials. As a result, the as‐assembled AC//carbon‐MnO₂ asymmetric supercapacitor exhibits a considerably high energy density of 63 Wh kg^?1 in 1.0 m Na₂SO₄ aqueous solution, higher than most reported AC//MnO₂ asymmetric supercapacitors. More importantly, this asymmetric supercapacitor also exhibits an excellent cycling performance with 92% specific capacitance retention after 5000 cycles. Those results offer a low‐cost, eco‐friendly design of electrode materials for high‐performance supercapacitors.     

All‐Solid‐State Asymmetric Supercapacitors with Metal Selenides Electrodes and Ionic Conductive Composites Electrolytes

All‐solid‐state flexible asymmetric supercapacitors (ASCs) are developed by utilization of graphene nanoribbon (GNR)/Co_0.85Se composites as the positive electrode, GNR/Bi₂Se₃ composites as the negative electrode, and polymer‐grafted‐graphene oxide membranes as solid‐state electrolytes. Both GNR/Co_0.85Se and GNR/Bi₂Se₃ composite electrodes are developed by a facile one‐step hydrothermal growth method from graphene oxide nanoribbons as the nucleation framework. The GNR/Co_0.85Se composite electrode exhibits a specific capacity of 76.4 mAh g^?1 at a current density of 1 A g^?1 and the GNR/Bi₂Se₃ composite electrode exhibits a specific capacity of 100.2 mAh g^?1 at a current density of 0.5 A g^?1. Moreover, the stretchable membrane solid‐state electrolytes exhibit superior ionic conductivity of 108.7 mS cm^?1. As a result, the flexible ASCs demonstrate an operating voltage of 1.6 V, an energy density of 30.9 Wh kg^?1 at the power density of 559 W kg^?1, and excellent cycling stability with 89% capacitance retention after 5000 cycles. All these results demonstrate that this study provides a simple, scalable, and efficient approach to fabricate high performance flexible all‐solid‐state ASCs for energy storage.     

Multifunctional Carbon for Electrochemical Double‐Layer Capacitors

Multifunctional carbon materials are prepared for application as an active electrode material in an electrochemical capacitor displaying both charge storage and binder properties. The synthesis of the materials involves the functionalization of high surface area Black Pearls 2000 carbon black by a covalent attachment of polyacrylic acid. The polyacrylic acid polymer is formed by atom transfer radical polymerization using 1‐(bromoethyl)benzene groups initially bonded to the carbon by spontaneous grafting from the corresponding diazonium ions. The grafting of 1‐(bromoethyl)benzene and polyacrylic acid is confirmed by thermogravimetric analysis, Fourier transform infrared spectroscopy, energy‐dispersive X‐ray spectroscopy, and nitrogen gas adsorption isotherm. The composite electrode films prepared from the modified carbon are more hydrophilic and have better wettability in an aqueous electrolyte than the one prepared with the unmodified carbon. The modified electrodes also show a higher specific capacitance (≈140 F g^?1), a wider working potential window (1.5 V) and excellent specific capacitance retention upon cycling (99.9% after 5000 cycles) in an aqueous 0.65 m K₂SO₄ electrolyte. Moreover, a relatively high specific capacitance (≈90 F g^?1) is maintained at a scan rate of 1000 mV s^?1 with the polyacrylic‐acid‐modified carbon electrode.     

Layered Silicon‐Based Nanosheets as Electrode for 4 V High‐Performance Supercapacitor

Silicon‐based materials have shown great potential and been widely studied in various fields. Unlike its unparalleled theoretical capacity as anodes for batteries, few investigations have been reported on silicon‐based materials for applications in supercapacitors. Here, an electrode composed of layered silicon‐based nanosheets, obtained through oxidation and exfoliation, for a supercapacitor operated up to 4 V is reported. These silicon‐based nanosheets show an areal specific capacitance of 4.43 mF cm^?2 at 10 mV s^?1 while still retaining a specific capacitance of 834 µF cm^?2 even at an ultrahigh scan rate of 50 000 mV s^?1. The volumetric energy and power density of the supercapacitor are 7.65 mWh cm^?3 and 9312 mW cm^?3, respectively, and the electrode can operate for 12000 cycles in a potential window of 4 V at 2 A g^?1, while retaining 90.6% capacitance. These results indicate that the silicon‐based nanosheets can be a competitive candidate as the supercapacitor electrode material.     

Interfacial Approach toward Benzene‐Bridged Polypyrrole Film–Based Micro‐Supercapacitors with Ultrahigh Volumetric Power Density

2D soft nanomaterials are an emerging research field due to their versatile chemical structures, easily tunable properties, and broad application potential. In this study, a benzene‐bridged polypyrrole film with a large area, up to a few square centimeters, is synthesized through an interfacial polymerization approach. As‐prepared semiconductive films exhibit a bandgap of ≈2 eV and a carrier mobility of ≈1.5 cm² V^?1 s^?1, inferred from time‐resolved terahertz spectroscopy. The samples are employed to fabricate in‐plane micro‐supercapacitors (MSCs) by laser scribing and exhibit an ultrahigh areal capacitance of 0.95 mF cm^?2, using 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ([EMIM][BF₄]) as an electrolyte. Importantly, the maximum energy and power densities of the developed MSCs reach values up to 50.7 mWh cm^?3 and 9.6 kW cm^?3, respectively; the performance surpassing most of the 2D material‐based MSCs is reported to date.     

Engineering MoS2 Nanosheets on Spindle‐Like α‐Fe2O3 as High‐Performance Core–Shell Pseudocapacitive Anodes for Fiber‐Shaped Aqueous Lithium‐Ion Capacitors

Fiber‐shaped aqueous lithium‐ion capacitors (FALICs) featured with high energy and power densities together with outstanding safety characteristics are emerging as promising electrochemical energy‐storage devices for future portable and wearable electronics. However, the lack of high‐capacitance fibrous anodes is a major bottleneck to achieve high performance FALICs. Here, hierarchical MoS₂@α‐Fe₂O₃ core–shell heterostructures consisting of spindle‐shaped α‐Fe₂O₃ cores and MoS₂ nanosheet shells on a carbon nanotube fiber (CNTF) are successfully fabricated. Originating from the unique core/shell architecture and prominent synergetic effects for multi‐components, the resulting MoS₂@α‐Fe₂O₃/CNTF anode delivers a remarkable specific capacitance of 2077.5 mF cm^?2 (554.0 F cm^?3) at 2 mA cm^?2, substantially outperforming most of the previously reported fibrous anode materials. Further density functional theory calculations reveal that the MoS₂@α‐Fe₂O₃ nano‐heterostructure possesses better electrical conductivity and stronger adsorption energy of Li⁺ than those of the individual MoS₂ and α‐Fe₂O₃. By paring with the self‐standing LiCoO₂/CNTF battery‐type cathode, a prototype quasi‐solid‐state FALIC with a maximum operating voltage of 2.0 V is constructed, achieving impressive specific capacitance (253.1 mF cm^?2) and admirable energy density (39.6 mWh cm^?3). Additionally, the newly developed FALICs can be woven into the flexible textile to power wearable electronics. This work presents a novel effective strategy to design high‐performance anode materials for next‐generation wearable ALICs.     

Ultrathin MnO2/Graphene Oxide/Carbon Nanotube Interlayer as Efficient Polysulfide‐Trapping Shield for High‐Performance Li–S Batteries

Ultrathin MnO₂/graphene oxide/carbon nanotube (G/M@CNT) interlayers are developed as efficient polysulfide‐trapping shields for high‐performance Li–S batteries. A simple layer‐by‐layer procedure is used to construct a sandwiched vein–membrane interlayer of thickness 2 µm and areal density 0.104 mg cm^?2 by loading MnO₂ nanoparticles and graphene oxide (GO) sheets on superaligned carbon nanotube films. The G/M@CNT interlayer provides a physical shield against both polysulfide shuttling and chemical adsorption of polysulfides by MnO₂ nanoparticles and GO sheets. The synergetic effect of the G/M@CNT interlayer enables the production of Li–S cells with high sulfur loadings (60–80 wt%), a low capacity decay rate (?0.029% per cycle over 2500 cycles at 1 C), high rate performance (747 mA h g^?1 at a charge rate of 10 C), and a low self‐discharge rate with high capacity retention (93.0% after 20 d rest). Electrochemical impedance spectroscopy, cyclic voltammetry, and scanning electron microscopy observations of the Li anodes after cycling confirm the polysulfide‐trapping ability of the G/M@CNT interlayer and show its potential in developing high‐performance Li–S batteries.     

Ternary Hybrids of Amorphous Nickel Hydroxide–Carbon Nanotube‐Conducting Polymer for Supercapacitors with High Energy Density,Excellent Rate Capability,and Long Cycle Life

The utilization of Ni(OH)₂ as a pseudocapacitive material for high performance supercapacitors is hindered by its low electrical conductivity and short cycle life. A coaxial ternary hybrid material comprising of amorphous Ni(OH)₂ deposited on multiwalled carbon nanotubes wrapped with conductive polymer (poly (3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate)) is demonstrated. A thin layer of disordered amorphous Ni(OH)₂ is deposited by an effective “coordinating etching and precipitating” method, resulting in an ultrahigh specific capacitance of 3262 F g^?1 at 5 mV s^?1 and excellent rate capability (71.9% capacitance retention at 100 mV s^?1). More importantly, the polymer layer prevents the degradation of the nanostructure and dis­solution of Ni ion during repeated charge–discharge cycling for 30 000 cycles, a phenomenon which often plagues Ni(OH)₂ nanomaterials. Using the ternary Ni(OH)₂ hybrid and the reduced graphene oxide/carbon nanotube hybrid as the positive and negative electrodes, respectively, the assembled asymmetric supercapacitors exhibit high energy density of 58.5 W h kg^?1 at the power density of 780 W kg^?1 as well as long cycle life (86% capacitance retention after 30 000 cycles). The ternary hybrid architecture design for amorphous Ni(OH)₂ can be regarded as a general approach to obtain pseudocapacitive materials for supercapacitors with both high energy density, excellent rate capability, and long cycle life.     

Ultrahigh‐Performance Pseudocapacitor Electrodes Based on Transition Metal Phosphide Nanosheets Array via Phosphorization: A General and Effective Approach

In this study, a general and effective phosphorization strategy is successfully demonstrated to enhance supercapacitor performance of various transition metals oxide or hydroxide, such as Ni(OH)₂, Co(OH)₂, MnO₂, and Fe₂O₃. For example, a 3D networked Ni₂P nanosheets array via a facile phosphorization reaction of Ni(OH)₂ nanosheets is grown on the surface of a Ni foam. The Ni foam‐supported Ni₂P nanosheet (Ni₂P NS/NF) electrode shows a remarkable specific capacitance of 2141 F g^?1 at a scan rate of 50 mV s^?1 and remains as high as 1109 F g^?1 even at the current density of 83.3 A g^?1. The specific capacitance is much larger than those of Ni(OH)₂ NS/NF (747 F g^?1 at 50 mV s^?1). Furthermore, the electrode retains a high specific capacitance of 1437 F g^?1 even after 5000 cycles at a current density of 10 A g^?1, in sharp contrast with only 403 F g^?1 of Ni(OH)₂ NS/NF at the same current density. The similar enhanced performance is observed for Ni₂P powder, which eliminates the influence of nickel foam. The enhanced supercapacitor performances are attributed to the 3D porous nanosheets network, enhanced conductivity, and two active components of Ni²⁺ and P^δ? with rich valences of Ni₂P.     

The Role of Sulfur in Solution‐Processed Cu2ZnSn(S,Se)4 and its Effect on Defect Properties

Understanding the electrically active defects in kesterite Cu₂ZnSn(S,Se)₄(CZTSSe) is critical for the continued development of solar cells based on this material, but challenging due to the complex nature of this polycrystalline multinary material. A comparative study of CZTSSe alloys with three different bandgaps, made by introducing different fractions of sulfur during the annealing process, is presented. Using admittance spectroscopy, drive level capacitance profiling, and capacitance‐voltage profiling, the dominant defect energy level present in the low sulfur content device is determined to be 0.134 eV above the valence band maximum, with a bulk defect density of 8 × 10¹⁴ cm^?3, while the high sulfur content device shows a deeper defect energy level of 0.183 eV and a higher bulk defect density, 8.2 × 10¹⁵ cm^?3. These findings are consistent with the current density–voltage characteristics of the resulting solar cells and their external quantum efficiency. It suggests that as the sulfur content increases, the bandgap of the absorber is enlarged, leading to an increasing open‐circuit voltage (V_oc), that is accompanied by stronger recombination due to the higher defect density of the sulfur‐rich absorber. This is reflected in large V_oc deficit and poor carrier collection of the high sulfur content device.