A rational preparation strategy of phase tuned MoO_(3) nanostructures for high-performance all-solid asymmetric supercapacitor

In this work,phase and morphology-tuned MoO_(3) nanostructures are synthesized through a novel modified co-precipitation method,and their electrochemical properties are investigated.For the first time,such a simple surfactant-assisted synthesis process aided by minor temperature variations is reported which results in phase transition of the nanoparticles from h-MoO_(3) nano-rods to a-MoO_(3) nano-flakes.The nanostructures thus developed are highly porous and crystalline with significantly large specific surface area as compared to previous literature.The theoretical bandgap energy of the optimized sample calculated using Perdew-Zunger local density approximation(LDA) is in good agreement with the experimental findings.An overall structural,morphological,and surface-behavioural analysis predicts the electrochemical superiority in 2D a-MoO_(3).The cyclic voltammetry and galvano-potentiometry measurements of 2D a-MoO_(3) in the potential window of-0.6 V to +0.2 V present the highest pseudosupercapacitive response with a maximum specific capacitance of 829 F g^(-1)at 2 A g^(-1)as compared to h-MoO_(3) (452 F g^(-1)) and h@a-MoO_(3) (783 F g^(-1)).Thus,the MoO_(3) 2D nanostructures synthesized through our novel synthesis technique display excellent specific capacitance as compared to previous reported data.Additionally,a-MoO_(3) exhibits a galvanostatic charging-discharging cyclic stability of about 91%after 2000 cycles,indicating that it can serve as an excellent electrode material for supercapacitors.A solid-state asymmetric supercapacitor device is successfully constructed using a-MoO_(3) which can light up 4 red LEDs for 10 s.The specific energy density of the device reaches a maximum value of 36.3 W h kg^(-1)at the power density of 50 W kg^(-1).

Synthesis of high-performance nickel hydroxide nanosheets/gadolinium doped-α-MnO_(2) composite nanorods as cathode and Fe_(3)O_(4)/GO nanospheres as anode for an all-solid-state asymmetric supercapacitor

The wide use of manganese dioxide(MnO_(2))as an electrode in all-solid-state asymmetric supercapacitors(ASCs)remains challenging because of its low electrical conductivity.This complication can be circumvented by introducing trivalent gadolinium(Gd)ions into the MnO_(2).Herein,we describe the successful hydrothermal synthesis of crystalline Gd-doped MnO_(2) nanorods with Ni(OH)_(2) nanosheets as cathode,which we combined with Fe_(3)O_(4)/GO nanospheres as anode for all-solid-state ASCs.Electrochemical tests dem on strate that Gd dopi ng sign ifica ntly affected the electrochemical activities of the MnO_(2),which was further enhanced by introducing Ni(OH)_(2).The GdMnO_(2)/Ni(OH)_(2) electrode offers sufficient surface electrochemical activity and exhibits excellent specific capacity of 121.8 mA h g^(-1),at 1A g^(-1),appealing rate performance,and ultralong lifetime stability(99.3%retention after 10,000 discharge tests).Furthermore,the GdMnO_(2)/Ni(OH)_(2)//PVA/KOH//Fe_(3)O_(4)/GO solid-state ASC device offers an impressive specific energy density(60.25 W h kg^(-1))at a high power density(2332 W kg^(-1)).This investigation thus shows its large potential in developing novel approaches to energy storage devices.

Zeolitic imidazolate framework-67 derived Al-Co-S hierarchical sheets bridged by nitrogen-doped graphene:Incorporation of PANI derived carbon nanorods for solid-state asymmetric supercapacitors

Metal sulfides have been widely enticed as battery-type electrodes in supercapacitor devices because of their maximal theoretical capacitance.Nevertheless,their lower conductivity and ion transport kinetics can largely restrict their rate performance,hence the practical usage in fields of demanding high power devices.Therefore,the design of new electrodes with higher energy and power densities remains a highly challenging task.To the best of our knowledge,a novel hierarchical composite of Al-CoS_(2) on nitrogendoped graphene(NG)is prepared based on a zeolite imidazole framework using a simple and scalable hydrothermal process.In this hybrid,ultrathin Al-CoS_(2) nanosheet arrays are vertically orientated on the NG framework to limit self-aggregation,hence increasing the electrical property and cycle stability of composite.It is investigated that the Al/Co feeding ratio plays a crucial role in controlling the obtained hierarchical structure of Al-Co-S sheets and their electrode performance.Also,Al^(3+) can influence remarkably the morphology and electrochemical property of the resultant graphene composite.An effective synergism is noticed between the redox Al-CoS_(2) and NG resulting in fast electron transfer and chargingdischarging processes.Surprisingly,when the as-developed composite is utilized as a positive electrode at an applied current density of 1 A/g,a specific capacitance of 1915.8 F/g is attained with ultra-long cycle stability(96%,10,000 cycles)and an excellent retention rate(~89%).As a consequence,when a solid-state asymmetric supercapacitor(ASC)device is made by combining an Al-CoS_(2) @NG hybrid with a negative electrode made of polyaniline(PANI)derived carbon nanorods(PCNRs),it demonstrates remarkable specific capacitance(188 F/g),energy density(66.9 Wh/kg),and cyclic stability of 92%after 10,000 cycles.This may open the pathway for the application of the next-generation supercapacitors in the future.

Efficient conversion of lignin waste and self-assembly synthesis of C@MnCo_(2)O_(4)for asymmetric supercapacitors with high energy density

Lignin waste from the papermaking and biorefineries industry is a significantly promising renewable resource to prepare advanced carbon materials for diverse applications,such as the electrodes of supercapacitors;however,the improvement of their energy density remains a challenge.Here,we design a green and universal approach to prepare the composite electrode material,which is composed of lignin-phenolformaldehyde resins derived hierarchical porous carbon(LR-HPC)as conductive skeletons and the self-assembly manganese cobaltite(MnCo_(2)O_(4))nanocrystals as active sites.The synthesized C@MnCo_(2)O_(4)composite has an abundant porous structure and superior electronic conductivity,allowing for more charge/electron mass transfer channels and active sites for the redox reactions.The composite shows excellent electrochemical performance,such as the maximum specific capacitance of~726 mF cm^(-2)at 0.5 mV s^(-1),due to the significantly enhanced interactive interface between LR-HPC and MnCo_(2)O_(4)crystals.The assembled all-solid-state asymmetric supercapacitor,with the LR-HPC and C@MnCo_(2)O_(4)as cathode and anode,respectively,exhibits the highest volumetric energy density of 0.68 mWh cm^(-3)at a power density of 8.2 mW cm^(-3).Moreover,this device shows a high capacity retention ratio of~87.6%at 5 mA cm^(-2)after 5000 cycles.

A novel polyaniline/mesoporous carbon nano-composite electrode for asymmetric supercapacitor

A novel nano-composite of polyaniline/mesoporous carbon（PANI/CMK-3） was prepared with mesoporous carbon（CMK-3） serving as the support.Electrochemical asymmetric capacitors have been successfully designed by using PANI/CMK-3 composite and CMK-3 as positive and negative electrode,respectively.The results showed that the discharge capacity of the asymmetric capacitor could reach 87.4 F/g under the current density of 5 mA/cm^2 and cell voltage of 1.4 V.The energy density of the asymmetric capacitor was up to 23.8 Wh/kg with a power density of 206 W/kg.Furthermore,PANI/CMK-3-CMK-3 asymmetric capacitor using this PANI/CMK-3 nano-composite could be activated quickly and possess high charge-discharge efficiency.

Facile synthesis of high electrical conductive CoP via solid-state synthetic routes for supercapacitors

Co-P precursor was prepared by a mechanical alloying method and then is controlled to synthesis of CoP phase through an annealing method. The optimal conditions of ball milling and annealing temperature are investigated. The CoP exhibits higher electrical conductivity than graphite and cobalt oxide, showing excellent pseudocapacitive properties due its high electrical conductivity which can result in a fast electron transfer in high rate charge-discharge possess. The as-obtained CoP electrode achieves a high specific capacitance of 447.5 Fig at 1 Aug, and displays an excellent rate capability as well as good cycling stability. Besides, the asymmetric supercapacitor (ASC) based on the CoP as the positive electrode and activated carbon (AC) as the negative electrode was assembled and displayed a high rate capability (60% of the capacitance is retained when the current density increased from 1 Aug to 12 Aug), excellent cycling stability (96.7% of the initial capacitance is retained after 5000 cycles), and a superior specific energy of 19 Wh/kg at a power density of 350.8 W/kg. The results, suggest that the CoP electrode materials have a great potential for developing high-performance electrochemical energy storage devices. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

High-Performance Flexible Asymmetric Supercapacitor Based on CoAl-LDH and rGO Electrodes

A flexible asymmetric supercapacitor(ASC)based on a Co Al-layered double hydroxide(Co Al-LDH)electrode and a reduced graphene oxide(r GO) electrode was successfully fabricated. The Co Al-LDH electrode as a positive electrode was synthesized by directly growing Co Al-LDH nanosheet arrays on a carbon cloth(CC)through a facile hydrothermal method, and it delivered a specific capacitance of 616.9 F g^(-1)at a current density of1 A g^(-1). The r GO electrode as a negative electrode was synthesized by coating r GO on the CC via a simple dipcoating method and revealed a specific capacitance of110.0 F g^(-1)at a current density of 2 A g^(-1). Ultimately,the advanced ASC offered a broad voltage window(1.7 V)and exhibited a high superficial capacitance of1.77 F cm^(-2)at 2 m A cm^(-2)and a high energy density of0.71 m Wh cm^(-2)at a power density of 17.05 m W cm^(-2),along with an excellent cycle stability(92.9% capacitance retention over 8000 charge–discharge cycles).

High-performance self-assembly MnCo2O4 nanosheets for asymmetric supercapacitors

In this study,MnCo2O4 nanosheets were proposed to be utilized as an electrode material for supercapacitors.A two-step hydrothermal method with post-annealing treatment was employed in preparation of the nanostructures.MnCo2O4 electrode delivered a high specific capacitance of 2000 F g^-1 at 0.5 A g^-1,remarkable high-rate capability of 1150 F g^-1 at 20 A g^-1,and an excellent cycling stability of 92.3%at 5 A g^-1 after 5000 cycles.It is found that a three-electrode supercapacitor based on MnCo2O4 exhibits a promising electrochemical performance,better than the other similar materials,benefited from the synergistic effects of MnCo2O4 nanosheets.In fact,the self-assembly of nanosheets structure with high specific surface area and mesoporous structure can potentially enhance the electrochemical performance of supercapacitors.

KOH activated carbon derived from biomass-banana fibers as an efficient negative electrode in high performance asymmetric supercapacitor

Here we demonstrate the fabrication, electrochemical performance and application of an asymmetric supercapacitor (AS) device constructed with ss-Ni(OH)(2)/MWCNTs as positive electrode and KOH activated honeycomb-like porous carbon (K-PC) derived from banana fibers as negative electrode. Initially, the electrochemical performance of hydrothermally synthesized ss-Ni(OH)(2)/MWCNTs nanocomposite and K-PC was studied in a three-electrode system using 1 M KOH. These materials exhibited a specific capacitance (Cs) of 1327 Fig and 324 F/g respectively at a scan rate of 10 mV/s. Further, the AS device i.e., ss-Ni(OH)(2)/MWCNTs// K-PC in 1 M KOH solution, demonstrated a Cs of 156 F/g at scan rate of 10 mV/s in a broad cell voltage of 0-2.2 V. The device demonstrated a good rate capability by maintaining a Cs of 59 F/g even at high current density (25 A/g). The device also offered high energy density of 63 Wh/kg with maximum power density of 5.2 kW/kg. The AS device exhibited excellent cycle life with 100% capacitance retention at 5000th cycle at a high current density of 25 A/g. Two AS devices connected in series were employed for powering a pair of LEDs of different colors and also a mini fan. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Bimetallic NiCo2S4 Nanoneedles Anchored on Mesocarbon Microbeads as Advanced Electrodes for Asymmetric Supercapacitors

Bimetallic Ni–Co sulfides are outstanding pseudocapacitive materials with high electrochemical activity and excellent energy storage performance as electrodes for high-performance supercapacitors.In this study,a novel urchin-like NiCo2S4@mesocarbon microbead(NCS@MCMB) composite with a core–shell structure was prepared by a facile two-step hydrothermal method.The highly conductive MCMBs offered abundant adsorption sites for the growth of NCS nanoneedles,which allowed each nanoneedle to fully unfold without aggregation,resulting in improved NCS utilization and efficient electron/ion transferin the electrolyte.When applied as an electrode material for supercapacitors,the composite exhibited a maximum specific capacitance of 936 Fg-1 at 1 Ag-1 and a capacitance retention of 94% after 3000 cycles at 5 Ag-1,because of the synergistic effect of MCMB and NCS.Moreover,we fabricated an asymmetric supercapacitor based on the NCS@MCMB composite,which exhibited enlarged voltage windows and could power a light-emitting diode device for several minutes,further demonstrating the exceptional electrochemical performance of the NCS@MCMB composite.

In-situ growth of nanowire WO_(2.72) on carbon cloth as a binder-free electrode for flexible asymmetric supercapacitors with high performance

For the first time,WO_(2.72) nanowires were in-situ grown on carbon cloth by a simple solvothermal reaction.The nanowire WO_(2.72)/carbon cloth(NW WO_(2.72)/CC) electrode showed good electrochemical performance with specific capacitance(C_s) reaching up to 398 F g^(-1) at a current density of 2 A g^(-1).The capacitance of 240 F g^(-1) was retained at a high current density of 16 A g^(-1).To further evaluate the energy storage performance,flexible asymmetric supercapacitors(FASC_s) were fabricated using the activated carbon/carbon cloth(AC/CC) as negative electrode and NW WO_(2.72)/CC as positive electrode,respectively.The FASC_s delivered a high energy density of 28 Wh kg^(-1) at a power density of 745 W kg^(-1) and 13 Wh kg^(-1) even at a high power density of 22.5 k W kg^(-1).More impressively,81% of the specific capacitance of the FASC_s was retained after 10,000 cycles,indicating excellent cycle stability.This work indicates the NW WO_(2.72)/CC holds a great potential for application in energy storage devices.

Porous NiCo_2O_4 nanowires supported on carbon cloth for flexible asymmetric supercapacitor with high energy density

Recently, binary metal oxides have been considerably researched for energy storage since it can provide higher electrical conductivity and electrochemical activity than single components. Besides, rational arrays structure design can effectively enhance the utilization of active material. In this article, we synthesis a porous NiCo_2O_4 nanowires arrays, which were intimate contact with flexible carbon cloth（CC）by a facile hydrothermal reaction and calcination treatment. The rational array structures of NiCo_2O_4 facilitate the diffusion of electrolyte and effectively increase the utilization of active material. The asobtained NiCo_2O_4@CC electrode exhibits a high capacitance of 1183 mF cm^（-2） and an outstanding capacitance retention of 90.4% after 3000 cycles. Furthermore, a flexible asymmetric supercapacitor（ASC）using NiCo_2O_4@CC as positive electrode and activated carbon cloth（ACC） as negative electrode was fabricated, which delivers a large capacitance of 750 mF cm^（-2）（12.5 F cm^（-3））, a high energy density of 0.24 mWh cm^（-2）（3.91 mWh cm^（-3））, as well as excellent cycle stability under different bending states.These remarkable results suggest that as-assembled NiCo_2O_4@CC//ACC ASC is a promising candidate in flexible energy storage applications.

High energy density performance of hydrothermally produced hydrous ruthenium oxide/multiwalled carbon nanotubes composite: Design of an asymmetric supercapacitor with excellent cycle life

Hydrous ruthenium oxide(h-Ru O) nanoparticles and its composite with multiwalled carbon nanotubes(h-Ru O/MWCNT) were synthesized by a simple hydrothermal method and proved to have potential application as hybrid supercapacitor material.The h-Ru Oand h-Ru O/MWCNT were characterized for their physico-chemical properties by PXRD,BET surface area,Raman,SEM-EDS and TEM techniques.The electrochemical performance of the materials were investigated,specific capacitance(Cs) of h-Ru Oand hRu O/MWCNT estimated by their cyclic voltammetric studies were found to be 604 and 1585 F/g respectively at a scan rate of 2 m V/s in the potential range 0–1.2 V.Further,this value was found to be nearly three times higher than that of pure h-Ru O.An asymmetric supercapacitor(AS) device was fabricated by employing h-Ru O/MWCNT as the positive electrode and activated carbon as the negative electrode.The device exhibited Cs of 61.8 F/g at a scan rate of 2 m V/s.Further,the device showed excellent long term stability for 20,000 cycles with 88% capacitance retention at a high current density of 25 A/g.

Application of spherical Ni(OH)_2/CNTs composite electrode in asymmetric supercapacitor

The composite electrodes consisting of carbon nanotubes and spherical Ni(OH)2 are developed by mixing nickel hydroxide, carbon nanotubes and carbonyl nickel powder together in 8:1:1 ratio. A maximum capacitance of 311 F/g is obtained for an electrode prepared with the precipitation process. In order to enhance energy density, an asymmetric type pseudo-capacitor/electric double layer capacitor is considered and its electrochemical properties are investigated. Values for the specific energy and maximum specific power of 25.8 W·h/kg and 2.8 kW/kg, respectively, are demonstrated for a cell voltage between 0 and 1.6 V. By using the modified cathode of a Ni(OH)2/carbon nanotube composite electrode, the asymmetric supercapacitor exhibits high energy density and stable power characteristics.

Engineered NiCo-LDH nanosheets- and ZnFe_(2)O_(4) nanocubes-decorated carbon nanofiber bonded mats for high-rate asymmetric supercapacitors

In this work,we have prepared the hierarchically nanostructured core–shell NiCo layered double hydroxide(NiCo-LDH)nanosheets-and ZnFe_(2)O_(4) nanocubes-decorated polyacrylonitrile(PAN)/pitch-based carbon nanofibers(PPCNs)webs(NiCo-LDH@PPCNs as cathode and ZnFe_(2)O_(4)@PPCNs as anode materials)with the bonded network structure by a facile and scalable hydrothemal method.Herein,the low-cost pitch with lower softening point(~90℃)as co-precursor was utilized to produce the PAN/pitch-based carbon nanofibers(PPCNs)with enhanced electrical conductivity.The obtained PPCNs with pitch content of 30%(PP30CNs)electrode material delivered higher specific capacitance(~67 F g^(-1))than that(~48 F g^(-1))of the PAN-based carbon nanofibers(PCNs)at 1 A g^(-1),due to the increased electrical conductivity and lower interfacial charge transfer resistance(RCT)of~0.16 U.Further,the NiCo-LDH-decorated PP30CNs(NiCoLDH@PP30CNs)as cathode material showed superior specific capacitance of 1162 F g^(-1) at 1.0 A g^(-1) and ultra-high retention rate of 91.56%at 10 A g^(-1).The ZnFe_(2)O_(4)@PP30CNs as anode material also showed higher specific capacitance of 282 F g^(-1) at 1 A g^(-1) and good rate capability with capacitance retention of 56.73%at 10 A g^(-1).The as-fabricated asymmetric NiCo-LDH@PP30CNs//ZnFe_(2)O_(4)@PP30CNs hybrid supercapacitor device delivered a specific capacitance of~98 F g^(-1) at 1 A g^(-1) and excellent capacitance retention of~88%after 5000 charge–discharge cycles.

Construction of Desirable NiCoTe_(2) Nanosheet Arrays on a Carbon Cloth Substrate as a Positive Electrode Material for a High-Performance Asymmetric Supercapacitor

Nickel–cobalt tellurides are deemed as promising electrode materials for energy storage devices due to their superior conductivity and theoretical specific capacitance.Here,NiCoTe_(2)was successfully fabricated on carbon cloth by facile electrodeposition and hydrothermal synthesis,which can directly serve as a binderless electrode.The NiCoTe_(2)with interconnected nanosheet arrays on a conductive carbon substrate showed a high specific capacitance(924 F/g at 1 A/g)and robust longterm cycling stability(89.6%retention after 5000 cycles).In addition,the assembled NiCoTe_(2)//activiated carbon hybrid supercapacitor achieved a high energy and power density with a short charging time(42.26 Wh/kg at a power density of 760.96 W/kg).This work provides a novel idea to produce bimetallic nickel–cobalt telluride nanosheet array electrodes for high-performance hybrid supercapacitors.

3D hierarchical oxygen-deficient AlCoNi-(oxy)hydroxides/N-doped carbon hybrids enable efficient battery-type asymmetric supercapacitor

Polynary transition-metal layered hydroxides are promising energy materials owing to their unique architecture,impressive theoretical capacities,and adjustable compositions.Regulating the dimensional morphology and active sites/redox states are the keys to electrochemical performance enhancement.Distinguish from the reported mono-metal or binary-metal configurations,a new ternary-metal AlCoNi-LTH is coanchored onto a highly graphitized porous N-doped carbon matrix to develop superior 3D hierarchical microporous functional energy hybrids AlCoNi-LTHs/NAC.The constructed hybrids possess superior structural durability,good electrical conductivity,and rich active sites due to the strong interfacial conjunction and favorable synergistic effect between the doped porous carbon and AlCoNi nanosheets.Consequently,the AlCoNi-LTHs/NAC hybrids demonstrate high conductivity,reasonable specific surface area,and superior specific capacitance,and the assembled hybrid battery-type supercapacitor reveals an ideal energy density of 72.6 Wh kg^(-1)at a power density of 625 W kg^(-1),which is superior to the reported devices.This strategy opens a platform to rationally design polynary transition-metal layered hydroxides and their hybrids for efficient supercapacitors.

High-performance flexible all-solid-state asymmetric supercapacitors based on binder-free MXene/cellulose nanofiber anode and carbon cloth/polyaniline cathode

The search for wearable electronics has been attracted great efforts,there is an ever-growing demand for all-solid-state flexible energy storage devices.However,it is a challenge to obtain both positive and negative electrodes with excellent mechanical strength and match positive and negative charges to achieve high energy densities and operate voltages to satisfy practical application requirements.Here,flexible MXene(Ti_(3)C_(2)Tx)/cellulose nanofiber(CNF)composite film negative electrodes(MCNF)were fabricated with a vacuum filtration method,as well as positive electrodes(CP)by combining polyaniline(PANI)with carbon cloth(CC)using an in-situ polymerization method.Both positive and negative free-standing electrodes exhibited excellent electrochemical behavior and bendable/foldable flexibility.As a result,the all-pseudocapacitance asymmetric device of MCNF//CP assembled with charge-matched between anode and cathode achieves an extended voltage window of 1.5 V,high energy density of 30.6 Wh·kg^(−1)(1211 W·kg^(−1)),86%capacitance retention after 5000 cycles,the device maintains excellent bendability,simultaneously.This work will pave the way for the development of all-pseudocapacitive asymmetric supercapacitors(ASC)with simultaneously preeminent mechanical properties,high energy density,wide operating voltage window.

Newly Design Porous/Sponge Red Phosphorus@Graphene and Highly Conductive Ni2P Electrode for Asymmetric Solid State Supercapacitive Device With Excellent Performance

Supercapacitors have attracted much attention in the field of electrochemical energy storage.However,material preparation,stability,performance as well as power density limit their applications in many fields.Herein,a sponge-like red phosphorus@graphene(rP@rGO)negative electrode and a Ni2P positive electrode were prepared using a simple one-step method.Both electrodes showed excellent performances(294 F g^−1 and 1526.6 F g^−1 for rP@rGO and Ni2P,respectively),which seem to be the highest among all rP@rGO-and Ni2P-based electrodes reported so far.The asymmetric solid-state supercapacitor was assembled by sandwiching a gel electrolyte-soaked cellulose paper between rP@rGO and Ni2P as the negative and positive electrodes.Compared to other asymmetric devices,the device,which attained a high operating window of up to 1.6 V,showed high energy and power density values of 41.66 and 1200 W kg−1,respectively.It also has an excellent cyclic stability up to 88%after various consecutive charge/discharge tests.Additionally,the device could power commercial light emitting diodes and fans for 30 s.So,the ease of the synthesis method and excellent performance of the prepared electrode materials mat have significant potential for energy storage applications.

Superhydrophilic nickel hydroxide ultrathin nanosheets enable high-performance asymmetric supercapacitors

Superhydrophilic surfaces have been applied for supercapacitor;however,during energy storage reaction,how the wettability affects the process of electrochemical reaction specifically is still unclear.Herein,we demonstrate superhydrophilic surface for promotion of electrochemical reactions by liquid affinity and further explain the mechanism,where the transition of the wettability state caused by the change in surface free energy is the main reason for the obvious increase in specific capacitance.Through citric acid assistance strategy,an intrinsically hydrophobic Ni(OH)_(2)thick nanosheets(HNHTNs,16 nm)can be transitioned into superhydrophilic Ni(OH)_(2)ultrathin nanosheets(SNHUNs,6.8 nm),where the water contact angle was 0°and the surface free energy increased from 8.6to 65.8 mN·m^(-1),implying superhydrophilicity.Compared with HNHTNs,the specific capacitance of SNHUNs is doubled:from 1230 F·g^(-1)(HNHTNs)to 2350 F·g^(-1)(2A·g^(-1))and,even at 20 A·g^(-1),from 833 F·g^(-1)(HNHTNs)to 1670 F·g^(-1).The asymmetric capacitors assembled by SNHUNs and activated carbon show 52.44 Wh·kg^(-1)at 160W·kg^(-1)and excellent stability with~90%retention after5000 cycles(~80%retention after 9500 cycles).The promotion of electrochemical performances is ascribed to the change of surface wettability caused by surface free energy,which greatly increase affinity of electrode to the surrounding liquid environment to reduce the interface resistance and optimize the electron transport path.