Preparation of Eco-Friendly High-Performance Manganese Dioxide Supercapacitors by Linear Sweep Voltammetry

In this paper,the non-polluting,non-toxic,and eco-friendly material-MnO_(2)electrodes were deposited on three-dimensional porous nickel(Ni)foam by linear sweep voltammetry,and the entire electrodeposition process did not require sintering of the material,which was fast and convenient while avoiding unnecessary energy consump-tion and thus was environmentally friendly.Scanning electron microscopy(SEM)and transmission electron microscopy were used to examine the surface and microscopic characteristics of each sample(TEM).Chronoam-perometry(CA),cyclic voltammetry(CV),galvanostatic charge/discharge(GCD),and electrochemical impedance spectroscopy(EIS)were then used to determine the electrochemical characteristics of the manufactured samples.The result suggests that the MnO_(2)-sv80 electrode sample at a scan rate of 80 mV/s^(−1)has excellent performance for the supercapacitor electrode.The specific capacitance was as high as 531.4 F g^(−1)at a current density of 1 A g^(−1)and remained at 223.2 F g^(−1)at an ultra-high current density of 20 A g^(−1),with capacitance retention of 42%.

Manganese doping to boost the capacitance performance of hierarchical Co_(9)S_(8)@Co(OH)_(2) nanosheet arrays

Transition metal sulfides(TMSs)have been regarded as greatly promising electrode materials for supercapacitors because of abundant redox electroactive sites and outstanding conductivity.Herein,we report a self-supported hierarchical Mn doped Co_(9)S_(8)@Co(OH)_(2) nanosheet arrays on nickel foam(NF)substrate by a one-step metal–organic-framework(MOF)engaged approach and a subsequent sulfurization process.Experimental results reveal that the introduction of manganese endows improved electric conductivity,enlarged electrochemical specific surface area,adjusted electronic structure of Co_(9)S_(8)@Co(OH)_(2) and enhanced interfacial activities as well as facilitated reaction kinetics of electrodes.The optimal Mn doped Co_(9)S_(8)@Co(OH)_(2) electrode exhibits an ultrahigh specific capacitance of 3745 F g^(-1) at 1 A g^(-1)(5.618 F cm^(-2) at 1.5 mA cm^(-2))and sustains 1710 F g^(-1) at 30 A g^(-1)(2.565 F cm^(-2) at 45 mA cm^(-2)),surpassing most reported values on TMSs.Moreover,a battery-type asymmetric supercapacitor(ASC)device is constructed,which delivers high energy density of 50.2 Wh kg^(-1) at power density of 800 W kg^(-1),and outstanding long-term cycling stability(94%capacitance retention after 8000 cycles).The encouraging results might offer an effective strategy to optimize the TMSs for energy-storage devices.

Binary ionic liquid electrolyte design for ultrahigh-energy density graphene-based supercapacitors

Although room temperature ionic liquids(ILs)have emerged as potential next-generation electrolytes for their wide electrochemical stability window(ESW),the trade-off between this window and viscosity has hindered their widespread use in energy storage devices.Here,we present for the first time that such a trade-off can be balanced by mixing two ILs with the common anion([NTf_(2)]^(-))but different cations([EMIM]^(+) and[N1114]^(+))together.The[EMIM]cation-based IL possesses low viscosity while the[N1114]cation-based IL exhibits wide ESW.Since the concentrations of each IL in the mixtures can result in different electrolyte properties,we demonstrate a systematic approach by exploring the properties of various concentration combinations.In addition,the corresponding cell voltage of their resulting graphene supercapacitors(SCs)accompanied based on the interaction between the binary ionic liquid and the electrodes,and the associated electrochemical performance were studied to determine the optimum electrolyte system for the highest SC energy density.The well-balanced viscosity/ESW trade-off is achieved in binary IL consisting 50 vol%[EMIM][NTf_(2)]and 50 vol%[N1114][NTf_(2)]as evident from the extraordinary electrode specific capacitance of 293.1 F g^(-1) and the ultrahigh SC energy density of 177 Wh kg^(-1),which approaches that of a lithium-ion battery.

Facile synthesis of NiMn2S4 nanoflakes on nickel foam for high-performance aqueous asymmetric supercapacitors

Supercapacitors display promising electrochemical performance with high power density and excellent cycle stability.However,their low energy density limits their advancement in a broader range of applications.To enhance their energy density,we proposed self-assembled spinel NiMn2S4nanoflakes grown on nickel foam which we successfully prepared by a facile hydrothermal method.The NiMn2S4electrode delivers a high capacitance of 2096.7 F g^(-1)at 1.0 A g^(-1),with an exceptional rate capability(~720.6 F g^(-1)at a very high current density of 100 A g^(-1))and good cycle stability(~85.1%retention of the initial capacitance after 7000 cycles with the Coulombic efficiency around 100%).The as-fabricated asymmetric supercapacitors based on NiMn2S4nanoflakes//active carbon demonstrate an energy density of 73.6 W h kg^(-1)at 800.5 W kg^(-1)and adequate cycling performance of~84.6%capacitance retention at 15 A g^(-1)after 10000 cycles.The results reveal that the nanostructured NiMn2S4is an excellent electrode material for high-performance energy storage applications.

Construction of Frame-Structured Flexible MXene Film Electrode to Achieve High Areal Capacitance Micro-Supercapacitor

Two-dimensional MXene-based film materials as flexible electrodes have been widely studied in wearable microsupercapacitors(MSCs).However,the existence of strong van derWaals interactions leads to serious self-stacking ofMXene layers,resulting in poor ionic dynamics and loss of active sites,which causes MXene film electrodes to exhibit low capacitance and poor rate performance in practical studies.To solve this,a frame-structured hybrid film(labeled as CN-MX hybrid film)is constructed by introducing intercalating agents(nanometer g-C_(3)N_(4))into MXene layers.In this unique hybrid film,the g-C_(3)N_(4)nanoparticles rationally occupy the interspace between MXene layers so as to alleviate layer stacking,thus effectively expanding the electrochemically active surface and promoting proton transfer.Synergistic pseudocapacitance inducted by g-C_(3)N_(4)surface groups,consequently,the CN-MX hybrid film electrode achieves an enhanced capacitive capability.In the three-electrode system,this frame-structured film electrode exhibits an ultra-high areal capacitance of 1932.8 mF cm^(−2).The assembled symmetry flexible MSC device based on CN-MX hybrid film can achieve an energy density of 2.28μWh cm^(−2)at 0.075 mW cm^(−2),as well as a superior cyclic stability with 90.4%retention after 700 cycles in alternating 90o bending and releasing states,revealing its potential in practical 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.

Porous and free-standing Ti3C2Tx-RGO film with ultrahigh gravimetric capacitance for supercapacitors

MXene-based electrode materials exhibit favorable supercapacitor performance in sulfuric acid due to praised pseudocapacitance charge storage mechanism.However,self-stacking of conventional MXene electrodes severely restricts their electrochemical performance,especially at high loading.Herein,a flexible cross-linked porous Ti3C2Tx-MXene-reduced graphene oxide(Ti3C2Tx-RGO)film is skillfully designed and synthesized by microscopic explosion of graphene oxide(GO)at sudden high te mperature.The generated chamber structure between layers could hold a few of electrolyte,leading to a close-fitting reaction at interlayer and avoiding complex ions transmission paths.The Ti3C2Tx-RGO film displayed a preferable rate performance than that of pure Ti3C2Tx film and a high capacitance of 505 F/g at 2 mV/s.Furthermore,the uniform intralayer structure and unique energy storage process lead to thicknessindependenct electrochemical performances.This work provides a simple and feasible improvement approach for the design of MXene-based electrodes,which can be spread other electrochemical systems limited by ions transport,such as metal ions batteries and catalysis.

Design of soil moisture distribution sensor based on high-frequency capacitance

In order to obtain accurate real-time soil moisture data and the spatial distribution of soil moisture,the soil moisture measurement methods based on high-frequency capacitance edge field effect were analyzed,the structure of probe was studied,and a multi-channel soil moisture sensor was designed.Moreover,with the established two-dimensional trace planar capacitance probe model and the method of the finite element analysis,relationship between the structure of sensor probe and electric field intensity was studied and capacitance of the probe trace amount planar capacitance model was analyzed,the most optimal structure of sensor probe was determined.Design parameters of the probe which can achieve optimal sensitivity and detection range are:outer diameter 40 mm and inner diameter 38.4 mm for the probe copper ring electrode,axial length 20 mm and axial spacing 10 mm.The sensor is suitable for measuring the moisture of different type of soil.Moreover,the features of the profile soil moisture sensor were experimentally explored.The measurement accuracy reached±1.31%with better stability and consistency.Sensor probes can be assembled according to the measurement depth and used to measure soil moisture of different crop root zone.

Characterization of porous cobalt hexacyanoferrate and activated carbon electrodes under dynamic polarization conditions in a sodium-ion pseudocapacitor

We report here the activated carbon and cobalt hexacyanoferrate composite,which is applied as the electrode materials in symmetric supercapacitors containing a 1.0 M Na_(2)SO_(4) aqueous electrolyte.This novel material combines high specific surface area and electrochemical stability of activated carbon with the redox properties of cobalt hexacyanoferrate,resulting in maximum specific capacitance of 329 F g^(-1) with large voltage working window of 2.0 V.Electrochemical studies indicated that cobalt hexacyanoferrate introduces important pseudocapacitive properties accounting for the overall charge-storage process,especially when I<0.5 A g^(-1).At lower gravimetric currents(e.g.,0.05 A g^(-1))and up to 1.0 V,the presence of cobalt hexacyanoferrate improves the specific energy for more than 300%.In addition,to better understanding the energy storage process we also provided a careful investigation of the electrode materials under dynamic polarization conditions using the in situ Raman spectroscopy and synchrotron light Xray diffraction techniques.Interesting complementary findings were obtained in these studies.We believe that this novel electrode material is promising for applications regarding the energy-storage process in pseudocapacitors with long lifespan properties.

Reduced graphene oxide-modified Ni Co-phosphates on Ni foam enabling high areal capacitances for asymmetric supercapacitors

NiCo-phosphates can deliver high specific capacitances and high electrochemical activities as pseudocapacitive electrode material for supercapacitors.In this study,The NiCo-phosphates@reduced graphene oxide(NCPO@rGO)composite is directly loaded on Ni foam by a simple one-step hydrothermal process.The conductive rGO sheets provides continuous electron pathways between NCPO flowers and Ni foam,allowing active electrochemical reactions throughout the whole electrode.This can solve the difficulty of low active material utility and small areal capacitances in the Ni foam-supported electrodes.At the same time,the rGO sheets creates large amount of mesopores within the electrode,which can ensure a highly open structure for electrolyte attachment and ion transport.Because of the positive effect of rGO in improving charge transfe r,the NiCo-phosphates can be fully involved in the electrochemical reactions with high utility,ensuring high specific capacitances(1416.7 F g^(-1)at 1 A g^(-1))and high-rate performances.Specially,the areal capacitance of the NCPO@rGO electrode can reach as large as 3.69 F cm^(-2)at 1 A g^(-1),which is among the highest ones in Ni foam supported electrodes.An asymmetric supercapacitor is then fabricated by NCPO@rGO as the positive material with attractive energy densities and power densities,further proving its excellent electrochemical performance.

Novel hierarchical yolk-shell α-Ni(OH)_(2)/Mn_(2)O_(3) microspheres as high specific capacitance electrode materials for supercapacitors

For high performance supercapacitors, novel hierarchical yolk-shell α-Ni(OH)_(2)/Mn_(2)O_(3) microspheres were controllably synthesized using a facile two-step method based on the solvothermal treatment. The unique α-Ni(OH)_(2) based yolk-shell microstructures decorated with numerous interconnected nanosheets and the heterocomposition features can synergistically enhance reactive site exposure and electron conduction within the microspheres, facilitate charge transfer between electrolyte and electrode materials, and release structural stress during OH− chemisorption/desorption. Moreover, the Mn2O3 sediments distributed over the α-Ni(OH)_(2) microspheres can serve as an effective protective layer for electrochemical reactions. Consequently, when tested in 1 mol·L^(−1) KOH aqueous electrolyte for supercapacitors, the yolk-shell α-Ni (OH)_(2)/Mn_(2)O_(3) microspheres exhibited a considerably high specific capacitance of 2228.6 F·g^(−1) at 1 A·g^(−1) and an impressive capacitance retention of 77.7% after 3000 cycles at 10 A·g^(−1). The proposed α-Ni(OH)_(2)/Mn_(2)O_(3) microspheres with hetero-composition and unique hierarchical yolk-shell microstructures are highly promising to be used as electrode materials in supercapacitors and other energy storage devices.

Novel 2D/2D NiCo_(2)O_(4)/ZnCo_(2)O_(4)@rGO/CNTs self-supporting composite electrode with high hydroxyl ion adsorption capacity for asymmetric supercapacitor

The energy storage device has been urgently studied and developed to meet the increasing demand for energy and sustainable development.Due to the excellent conductivity of graphene and high performance of ZnCo_(2)O_(4)and NiCo_(2)O_(4),we design a self-supporting electrode based on vertically grown twodimensional/two-dimensional(2D/2D)NiCo_(2)O_(4)/ZnCo_(2)O_(4)hierarchical flakes on the carbon-based conductive substrate(NiCo_(2)O_(4)/ZnCo_(2)O_(4)@graphene/carbon nanotubes,NZ@GC).The density functional theory calculations indicate that the high OH-adsorption capacity of the NiCo_(2)O_(4)/ZnCo_(2)O_(4)nanosheets can significantly enhance the electrochemical reaction activity.NZ@GC shows a high capacitance of 1128.6 F g^(-1)at 1 A g^(-1).The capacitance retains 84.0%after 6000 cycles even at 10 A g^(-1).A hybrid supercapacitor is fabricated using NZ@GC and activated carbon,exhibiting a large energy density of 50.8 W h kg^(-1)at the power density of 800 W kg^(-1).After 9000 charge/discharge cycles,the supercapacitor still has 86.1%capacitance retention.The NZ@GC film has showed the potential as promising electrodes in high efficiency electrochemical energy storage devices.

Walnut septum-derived hierarchical porous carbon for ultra-high-performance supercapacitors

The conversion of biomass waste into eco-nomical and high-performance energy storage devices receives significant attention.Herein,a facile and green method to prepare porous active carbon from walnut sep-tum is applied to the electrode materials of supercapacitors.The effect of chemical etching reagent(KOH)on the microstructure and specific capacitance of the porous car-bon are explored.The modified BC-2.0,with a KOH/walnut septum mass ratio of 2∶1,exhibits large specific surface area of 1003.9 m^(2)·g^(-1)with hierarchical micro-mesoporous structures.BC-2.0 reveals a superior specific capacitance of 457 F·g^(-1)at 1 A·g^(-1).The flexible sym-metric supercapacitor in gel electrolyte(KOH/PVA)exhi-bits considerable synergetic energy-power output performance.The results indicate that walnut septum is a better precursor to obtain activated carbons relative to other biomass carbon sources.The large mesoporosity after activation effectively boosts the electrochemical properties of supercapacitor.Consequently,the walnut septum has potential to be a superior electrode material for supercapacitors.

High-performance aqueous asymmetric supercapacitors based on the cathode of one-step electrodeposited cracked bark-shaped nickel manganese sulfides on activated carbon cloth

In this work,we report a high-performance self-standing supercapacitor electrode of mixed nickel manganese sulfides (NMSs)with a cracked-bark shape grown by one-step electrochemical deposition on activated carbon cloth (ACC).The electrode possesses outstanding electrochemical properties,including a high specific capacitance of up to 3142.8 F g^(-1)at 1.0 A g^(-1),the high-rate performance (~1206.8 F g^(-1)at 60.0 A g^(-1)),and cycle stability (~92.3%capacitance retention after 8000 cycles at8 A g^(-1)).An asymmetric supercapacitor assembled using NMSs on ACC as the cathode,activated carbon on carbon cloth as the anode and 1.0 mol L;KOH as the electrolyte delivers a high energy density of 111.2 W h kg^(-1)at 800.0 W kg^(-1)and the prominent cycling performance of~93.2%capacitance retention after 10000 cycles at 5 A g^(-1)with the Columbic efficiency of around 100%during these 10000 cycles.The high performance and facile preparation indicate that the NMSs on ACC hold a huge potential as the electrode for supercapacitors.

N,P-codoped porous carbon derived from chitosan with hierarchical N-enriched structure and ultra-high specific surface Area toward high-performance supercapacitors

In this work,a facile"carbonization-activation"strategy is developed to synthesize N,P-codoped hierarchical porous carbon.Phosphoric acid is innovatively introduced during the hydrothermal process to achieve in-situ P doping as well as create abundant pores,and the employment of sodamide is of vital importance to simultaneously serve as activating agent and N-source to succeed a high-level N doping.Thus,the obtained samples exhibit a unique three-dimensional hierarchical structure with an ultra-high specific surface area(3646 m^(2)g^(-1))and ultra-high N-doping level(9.81 at.%).Computational analyses confirm that N,P co-doping and higher N content can enhance active sites and widen potential differences of carbon materials to improve their capacitance.The as-prepared carbon materials demonstrate superior electrochemical performances,such as an ultra-high capacitance of 586 Fg^(-1)at 1 Ag^(-1),a superior rate capability of 409 Fg^(-1)at 20 Ag^(-1),and excellent long-term stability of 97%capacitance retention after10,000 cycles in 6 M KOH.Moreover,an assembled symmetric supercapacitor delivers a high energy density of 28.1 Wh kg^(-1)at the power density of 450 W kg^(-1)in 1 M Na_(2)SO_(4),demonstrating a great potential for applications in supercapacitors.

Paper‑like Polyphenylene Sulfide/Aramid Fiber Electrode with Excellent Areal Capacitance and Flame‑Retardant Performance

In this paper,an aramid chopped fiber,so-called(ACF)/polyphenylene sulfide(PPS)composite,containing multi-walled carbon nanotubes(MWCNT),and in situ polymerized polypyrrole(PPy)was designed and fabricated,to be applied as a paper based electrode.The ACF/PPS/MWCNT-PPy electrode features highly porous paper-like structure with excel-lent electrochemical activity,rendering it a high areal capacitance of~3205 mF cm^(-2) at a current density of 5 mA cm^(-2).After 5000 charge-discharge cycles,the areal capacitance still maintains 93%and 70%at high current densities of 20 and 80 mA cm^(-2),respectively.Moreover,the ACF/PPS/MWCNT-PPy electrode displays over 50%the areal capacitance and maintains it's mechanical stability after annealing at 300℃.The UL-94 test reveals that the highest V-0 flame-retardant performance can be achieved.All these results suggest that the ACF/PPS/MWCNT-PPy composite is a promising material to be used as electrode for supercapacitor with high energy-storage capability and noninflammability.

PVA-assisted hydrated vanadium pentoxide/reduced graphene oxide films for excellent Li^(+)and Zn^(2+)storage properties

Low-cost,high safety and environment-friendly aqueous energy storage systems(ESSs)are huge potential for grid-level energy storage,but the(de)intercalation of metal ions in the electrode materials(e.g.vanadium oxides)to obtain superior long-term cycling stability is a significant challenge.Herein,we demonstrate that polyvinyl alcohol(PVA)-assisted hydrated vanadium pentoxide/reduced graphene oxide(V_(2)O_(5)·n H_(2)O/r GO/PVA,denoted as the VGP)films enable long cycle stability and high capacity for the Li^(+)and Zn^(2+)storages in both the VGP//Li Cl(aq)//VGP and the VGP//Zn SO4(aq)//Zn cells.The binderfree VGP films are synthesized by a one-step hydrothermal method combination with the filtration.The extensive hydrogen bonds are formed among PVA,GO and H_(2)O,and they act as structural pillars and connect the adjacent layers as glue,which contributes to the ultrahigh specific capacitance and ultralong cyclic performance of Li^(+)and Zn^(2+)storage properties.As for Li^(+)storage,the binder-free VGP4 film(4mg PVA)electrode achieves the highest specific capacitance up to 1381 F g^(-1)at 1.0 A g^(-1)in the three-electrode system and 962 F g^(-1)at 1.0 A g^(-1)in the symmetric two-electrode system.It also behaves the outstanding cyclic performance with the capacitance retention of 96.5%after 15000 cycles in the three-electrode system and 99.7%after 25000 cycles in the symmetric two-electrode system.As for Zn^(2+)storage,the binder-free VGP4 film electrode exhibits the high specific capacity of 184 m A h g^(-1)at 0.5A g^(-1)in the VGP4//Zn SO4(aq)//Zn cell and the superb cycle performance of 98.5%after 25000 cycles.This work not only provides a new strategy for the construction of vanadium oxides composites and demonstrates the potential application of PVA-assisted binder-free film with excellent electrochemical properties,but also extends to construct other potential electrode materials for metal ion storage cells.