Electrochemical Energy Storage Performance Research Articles

Effects of reduction method on reduced graphene oxide and its electrochemical energy storage performance

To enhance the application of reduced graphene oxide (rGO) in energy storage field, the effects of reduction method on rGO and its electrochemical energy storage performance were researched in this paper. Green and environmentally friendly reduction methods, such as l-ascorbic acid method (LAA), hydrothermal method and sodium borohydride method (NaBH4), were used to reduce the GO obtained by Hummers' method to rGO. The obtained samples were analyzed and characterized by Fourier transform Infrared spectroscopy, Ultraviolet-visible spectroscopy, X-ray diffraction, scanning electron microscope, Raman spectroscopy and N2 absorption and desorption. The obtained rGO samples were being assembled into symmetrical electrochemical super-capacitors with using organic solution as the electrolyte to characterize their electrochemical energy storage performance including cyclic voltammetry, galvanostatic charge and discharge, AC impedance and cycle life tests. The research results showed that the GO could all be changed into rGO via the reduction methods mentioned above, but the reduction degree and morphology structure of the obtained rGOs were quite different: the rGO obtained by LAA had a very smooth surface; the surface of rGO obtained by hydrothermal reduction method had wrinkles and formed a layered cross-linked structure; while the rGO obtained by NaBH4 showed severe agglomeration, forming obvious blocks. The electrochemical test results showed that the rGO obtained by hydrothermal reduction had the best electrochemical performance among the samples: its specific capacitance could reach 140 F g−1 (organic electrolyte) at a current density of 1 A g−1, moreover it had an energy density of 43.75 Wh kg−1 and a power density of 4500 W kg−1.

Recent Progress in Binder‐Free Electrodes Synthesis for Electrochemical Energy Storage Application

AbstractFabrication of binder‐free electrodes is an effective way to increase the performance of electrochemical energy storage (EES) devices, such as rechargeable batteries and supercapacitors. In traditional electrodes, the binder is usually electrochemically inert and has weak interactions and interfaces between binder and the active material, which increase “dead mass” and directly affect the performance of energy storage system. The binder‐free electrode can provide well‐designed electrode material structure enables well connection between active materials themselves and current collectors. In addition, without insulating binder, electron and electrolyte ions can transfer more efficiently within the electrode materials. Here, we reviewed research efforts in using various techniques involving chemical, physical and electrical methods to fabricate binder‐free electrodes. For every technique, we first briefly describe their principle and involved factors that influence the performance of as‐fabricated binder‐free electrodes and summarize advantages and disadvantages. Next, we reviewed several works which have used this technique to fabricate binder‐free electrodes. Further, the effect of well‐crafted structure design on the properties of energy storage performances including rate capability, and cycle stability was highlighted. Last, we offer our perspectives on the challenges and potential future research directions in this area. We hope this review can stimulate more research to design and synthesize the binder‐free materials for EES devices.

Plasma-assisted lattice oxygen vacancies engineering recipe for high-performing supercapacitors in a model of birnessite-MnO2

Defect engineering has been considered as an efficient strategy to enhance the electrochemical performance of transition metal oxides based energy storage devices. However, the electrochemical activity and stability were greatly determined by the defect located crystal and external environments, which dominate the electrochemical properties of its based electrode. Thus, regulating a defect engineering recipe becomes a vital and direct route to advance the performance of the electrode materials. Herein, a versatile recipe combining the mild H-plasma and O-plasma was demonstrated for prototypical birnessite-MnO2 to achieve the robust lattice oxygen vacancies in birnessite-MnO2 (LOV-MnO2), targeting to boost its electrochemical energy storage performance. Theoretical calculation reveals the facilitated ion intercalation and diffusion kinetics due to the lower energy barrier in the LOV-MnO2. The LOV-MnO2 demonstrates an exceptional electrochemical performance with a specific capacitance as high as 445.1 F g−1 (at the current density of 1 A g−1), and the diffusion-controlled capacitance contribution reaches unprecedented ~70% (at a scan rate of 5 mV s−1). Besides, the configured symmetrical supercapacitor device LOV-MnO2//LOV-MnO2 delivers remarkable performance with an energy density of 92.3 Wh kg−1 at a power density of 1100.3 W kg−1 with a widen working voltage of 2.2 V. An outstanding cyclic life of 92.2% capacitance retention was also achieved after 10,000 charge–discharge cycles. Such superior electrochemical performance suggests that the proposed defect engineering recipes here will aid in the future development of advanced electrode materials for electrochemical energy storage devices.

Highly Ordered TiO2 Nanotube Arrays with Engineered Electrochemical Energy Storage Performances.

Nanoscale engineering of regular structured materials is immensely demanded in various scientific areas. In this work, vertically oriented TiO2 nanotube arrays were grown by self-organizing electrochemical anodization. The effects of different fluoride ion concentrations (0.2 and 0.5 wt% NH4F) and different anodization times (2, 5, 10 and 20 h) on the morphology of nanotubes were systematically studied in an organic electrolyte (glycol). The growth mechanisms of amorphous and anatase TiO2 nanotubes were also studied. Under optimized conditions, we obtained TiO2 nanotubes with tube diameters of 70–160 nm and tube lengths of 6.5–45 μm. Serving as free-standing and binder-free electrodes, the kinetic, capacity, and stability performances of TiO2 nanotubes were tested as lithium-ion battery anodes. This work provides a facile strategy for constructing self-organized materials with optimized functionalities for applications.

Synthesis of Two-Dimensional Sr-Doped LaNiO3 Nanosheets with Improved Electrochemical Performance for Energy Storage.

Designing a novel, efficient, and cost-effective nanostructure with the advantage of robust morphology and outstanding conductivity is highly promising for the electrode materials of high-performance electrochemical storage device. In this paper, a series of honeycombed perovskite-type Sr-doped LaNiO3 nanosheets with abundant porous structure were successfully synthesized by accurately controlling the Sr-doped content. The study showed that the optimal LSNO-0.4 (La0.6Sr0.4NiO3-δ) electrode exhibited excellent electrochemical performance, which showed a high capacity of 115.88 mAh g−1 at 0.6 A g−1. Furthermore, a hybrid supercapacitor device (LSNO//AC) based on LSNO-0.4 composites and activated carbon (AC) showed a high energy density of 17.94 W h kg−1, a high power density of 1600 W kg−1, and an outstanding long-term stability with 104.4% capacity retention after 16,000 cycles, showing an excellent electrochemical performance and a promising application as an electrode for energy storage.

An enhanced electrochemical energy storage performance based on porous activated carbon and hard carbon derived from natural maple leaf

The recent development of the nanostructured electrode materials with a large porous carbon structure assures the next-generation material for the high-energy storage application. Herein, we report hard carbon (HC), and activated carbon (AC) materials from natural maple leaf derived. A facilely synthesized zinc chlorate presence and non-presence maple leaf were prepared for the pyrolysis temperature of 800 °C under the nitrogen atmosphere. Various analytical techniques investigated the as-prepared HC and AC samples. The HC and AC modified electrode performances were analyzed using cyclic voltammetry (CV) and galvanostatic charge/discharge in the presence of 6.0 M KOH electrolyte. The most efficient AC and HC performance derived from maple leaves shows the specific capacitance values of 217 F g−1 and 118 F g−1, respectively. The AC-modified electrode showed a promising candidate for high energy storage performance for a practical application.

Hierarchical Ni-Co-Mn hydroxide hollow architectures as high-performance electrodes for electrochemical energy storage.

In this study, hierarchical Ni–Co–Mn hydroxide hollow architectures were successfully achieved via an etching process. We first performed the synthesis of NiCoMn-glycerate solid spheres via a solvothermal route, and then NiCoMn-glycerate as the template was etched to convert into hierarchical Ni–Co–Mn hydroxide hollow architectures in the mixed solvents of water and 1-methyl-2-pyrrolidone. Hollow architectures and high surface area enabled Ni–Co–Mn hydroxide to manifest a specific capacitance of 1626 F g−1 at 3.0 A g−1, and it remained as large as 1380 F g−1 even at 3.0 A g−1. The Ni–Co–Mn hydroxide electrodes also displayed notable cycle performance with a decline of 1.6% over 5000 cycles at 12 A g−1. Moreover, an asymmetric supercapacitor assembled with this electrode exhibited an energy density of 44.4 W h kg−1 at 1650 W kg−1 and 28.5 W h kg−1 at 12 374 W kg−1. These attractive results demonstrate that hierarchical Ni–Co–Mn hydroxide hollow architectures have broad application prospects in supercapacitors.

Recent progress in conductive polymers for advanced fiber-shaped electrochemical energy storage devices

Conductive polymers endow fiber-shaped electrodes and devices with excellent mechanical and electrochemical performance for energy storage in future wearable electronics.

High-performance ultracapacitor electrodes realized by 3-dimensionally bicontinuous block copolymer nanostructures with enhanced ion kinetics

Exceptional electrochemical energy-storage performances are demonstrated with three-dimensionally bicontinuous carbon nanostructures with interconnected, size-tunable macro-channels derived from block copolymer self-assembly.

Coffee-derived activated carbon from second biowaste for supercapacitor applications

The electrochemical energy storage performance of activated carbons (ACs) obtained from coffee-derived biowastes was assessed. ACs were obtained from spent coffee ground second waste, after polyphenol extraction, by means of a hydrothermal process followed by physical or chemical activation. The resulting materials exhibited microporous structures with a total specific area between 585 and 2330 m2·g−1. Scanning electron microscopy (SEM) revealed a highly porous microstructure in the case of the chemically activated carbons, while physical activation led to a cracked micro-sized morphology. The electrochemical properties of the materials for supercapacitor applications were investigated in 1 M Na2SO4. After chemical activation, the coffee-derived material displayed a capacitance of 84 F·g−1 at 1 A·g−1 in a 1.9 V voltage window, with 70% capacitance retention at 10 A·g−1 and 85% retention after 5000 cycles of continuous charge-discharge. This work demonstrates how coffee secondary biowaste can be conveniently activated to perform as electrochemical energy storage material, contributing to its revalorization and reinsertion in a circular economy.

High performance Li-ion hybrid capacitors with micro-sized Nb14W3O44 as anode

Niobium tungsten oxides (Nb-W-O) have been verified as promising Li storage anodes because of their similar working voltage and cycling stability to Li4Ti5O12 but higher specific capacity than the latter. However, the phase and microstructural evolutions of a designated Nb-W-O compound during sintering as well as its possible application in Li-ion hybrid capacitors have not been reported. In this work, micro-sized phase pure Nb14W3O44 is obtained by sintering a solvothermal-derived precursor at about 1050 °C, which as a Li-ion insertion host exhibits not only high reversible specific capacity up to 226 mAh g−1 at 0.04 A g−1, but outstanding rate capability (137 mAh g−1 at 6 A g−1) and cycle stability (74.2% capacity retention at 2 A g−1 after 1000 cycles). Such an excellent rate capability enables the Nb14W3O4 anode highly matchable to the capacitive cathode and yields high energy densities of 64.6 and 29.2 Wh kg−1 at 198.9 and 14,576 W kg−1, respectively, in Li-ion hybrid capacitors, along with a high capacity retention of 83.9% after 3,000 cycles at 1 A g−1. With these excellent electrochemical energy storage performances and a high packing density, the micro-sized Nb14W3O44 can be a very promising anode material for both Li-ion batteries and Li-ion hybrid capacitors towards high energy-power outputs.

Simultaneously Crafting Single‐Atomic Fe Sites and Graphitic Layer‐Wrapped Fe3C Nanoparticles Encapsulated within Mesoporous Carbon Tubes for Oxygen Reduction

AbstractThe rational design and facile synthesis of 1D hollow tubular carbon‐based materials with highly efficient oxygen reduction reaction (ORR) performance remains a challenge. Herein, a simple yet robust route is employed to simultaneously craft single‐atomic Fe sites and graphitic layer‐wrapped Fe3C nanoparticles (Fe3C@GL NPs) encapsulated within 1D N‐doped hollow mesoporous carbon tubes (denoted Fe‐N‐HMCTs). The successional compositional and structural crafting of the hydrothermally self‐templated polyimide tubes (PITs), enabled by Fe species incorporation and acid leaching treatment, respectively, yields Fe‐N‐HMCTs that are subsequently exploited as the ORR electrocatalyst. Remarkably, an alkaline electrolyte capitalizing on Fe‐N‐HMCTs achieves excellent ORR activity (onset potential, 0.992 V; half‐wave potential, 0.872 V), favorable long‐term stability, and strong methanol tolerance, outperforming the state‐of‐the‐art Pt/C catalyst. Such impressive ORR performances of the Fe‐N‐HMCTs originate from the favorable configuration of active sites (i.e., atomically dispersed Fe‐Nx sites and homogeneously incorporated Fe3C@GL NPs) in conjunction with the advantageous 1D hollow tubular architecture containing adequate mesoporous surface. This work offers a new view to fabricate earth‐abundant 1D Fe‐N‐C electrocatalysts with well‐designed architecture and outstanding performance for electrochemical energy conversion and storage.

Self-supported transition metal oxide electrodes for electrochemical energy storage

Electrode materials are of decisive importance in determining the performance of electrochemical energy storage (EES) devices. Typically, the electrode materials are physically mixed with polymer binders and conductive additives, which are then loaded on the current collectors to function in real devices. Such a configuration inevitably reduces the content of active species and introduces quite some undesired interfaces that bring down the energy densities and power capabilities. One viable solution to address this issue is to construct self-supported electrodes where the active species, for example transition metal oxides (TMOs), are directly integrated with conductive substrates without polymer binders and conductive additives. In this review, the recent progress of self-supported TMO-based electrodes for EES devices including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), aluminum-ion batteries (AIBs), metal-air batteries, and supercapacitors (SCs), is discussed in great detail. The focused attention is firstly concentrated on their structural design and controllable synthesis. Then, the mechanism understanding of the enhanced electrochemical performance is presented. Finally, the challenges and prospects of self-supported TMO-based electrodes are summarized to end this review.

Redox-additive electrolyte–driven enhancement of the electrochemical energy storage performance of asymmetric Co3O4//carbon nano-onions supercapacitors

For efficient energy storage, Co3O4@nickel foam exhibiting a plate-like (p-Co3O4) and grass-like (g-Co3O4) nanostructure were prepared as binder-free supercapacitor electrode materials. The electrochemical performance of the electrodes was tested using a redox-additive electrolyte (RAE). The homogeneously grown grass-like nanostructure (g-Co3O4) exhibited superior electrochemical performance to those with the plates-like structure (p-Co3O4) in a KOH electrolyte. In addition, the electrochemical performance of g-Co3O4 was improved using an RAE in a 3 M KOH solution. Remarkably, the specific capacitance of g-Co3O4 (1560 F g−1) was increased to 6580 F g−1, approximately 4-fold just by varying the RAE concentration in KOH. Carbon nano-onion (CNO) in the form of multi-layer fullerene was introduced as a negative electrode material. Owing to the more favorable morphology and properties of CNO such as exohedral structure, small diameter, high electrical conductivity, and relatively easy aqueous media dispersion than activated carbon and graphene, the as-fabricated asymmetric Co3O4//CNO supercapacitor delivered a high energy density of 42.5 Wh kg−1 and a high power density of 12.8 kW kg−1.

Pores for Thought: Reconstructing 3D, Multi-Phase Electrode Microstructures with Periodic Boundaries Using Generative Adversarial Networks for Battery Design

The microstructure of porous electrodes significantly impacts the performance of electrochemical energy storage (EES) devices [1,2]. Thus, their morphological optimisation is vital for developing the next generation of EES technologies [3]. Recent improvements in 3D imaging techniques have allowed the characterisation of porous electrodes at a nanoscale [4]. However, a variety of challenges remain, including how to extract the key metrics or “essence” of the microstructure with which synthetic volumes with equivalent properties can be generated.This work implements a machine learning technique called deep-convolutional generative adversarial networks (GANs) to generate 3D synthetic realisations of n-phase electrode microstructures (Figure 1 (a)). The same network architecture is successfully applied to generate two very different three-phase microstructures: a Li-ion cathode and a SOFC anode. GANs implicitly capture the probability distribution function that fully defines the microstructure [5] into a low dimensional space, which is crucial for the follow-up process of optimisation. A statistical comparison between the real and synthetic data is performed in terms of the morphological properties (volume fraction, surface area, triple phase boundary) and transport properties (relative diffusivity), as well as the two-point correlation function. The results show excellent agreement between both datasets and they are also visually indistinguishable.The impact of this work lies in the ability to obtain a fully differentiable function that constitutes a “virtual representation” of the electrode microstructure. We show that with these virtual representations, it is possible to implement physical simulations based on which we can design an optimised porous microstructure. Furthermore, we introduce the possibility of generating spatially periodic microstructures with the same microstructural properties as the real tomographic data (Figure 1 (b)). These periodic microstructures have the potential to significantly reduce the simulated volume required to be considered “representative" and therefore massively reduce the computational cost of the electrochemical simulations necessary to predict the performance of a particular microstructure during optimisation. Keywords : Electrode microstructure, machine learning, generative adversarial networks, optimisation[1] G. Wei, C. Jia, J. Liu and C. Yan, Journal of Power Sources 220, 185 (2012).[2] H. Moussaoui, J. Laurencin, Y. Gavet, G. Delette, M. Hubert, P. Cloetens, T. Le Bihan and J. Debayle, Computational Materials Science. 143, 262 (2018).[3] N. Ni, S.J. Cooper, R. Williams, N. Kemen, D.W. McComb, and S.J. Skinner, ACS Applied Materials and Interfaces. 8(27), 17360 (2016).[4] F.L.E. Usseglio-Viretta, A. Colclasure, A.N. Mistry, K.P.Y. Claver, F. Pouraghajan, D.P. Finegan, T.M.M. Heenan, D. Abraham, P.P. Mukherjee, D. Wheeler, P. Shearing, S.J. Cooper and K. Smith, Journal of The Electrochemical Society. 165, A3403 (2018).[5] A. Gayo-Lombardo, L. Mosser, N.P. Brandon, S.J. Cooper, npj Computational Materials (2020) (Pre-print arXiv https://arxiv.org/abs/2003.11632) Figure 1

Vertically Aligned ZnO/MnO2/Pedot Core-Shell Electrode in 3-D Nano-Architecture for High Energy-Power Density Pseudocapacitive Electrochemical Energy Storage

Electrochemical capacitors have emerged as the favored energy storage technology in diverse applications like hybrid electric vehicles, portable electronics, communication and smart grids. The key challenge is to increase the energy density alongside the high power density. The structured carbons based electrical double layer capacitors are common but fail to meet this requirement. The Faradaic charge storage mechanism based pseudo-capacitors offer enticing opportunities to bridge the energy and power density functionality gap between the battery and supercapacitors. One approach is to use conducting polymers (CPs), poly 3,4-ethylenedioxythiophene (pedot), polypyrrole and polyaniline etc wherein Faradaic processes are visualized as doping-dedoping of counter ions across vast interface with electrolyte. The other approach is to utilize reversible redox process exhibited by transition metal oxides (TMO) such as RuO2, MnO2 NiO, V2O5 etc which due to multivalent cation states and fast ions/electron kinetics can exhibit high charge storage capability. TMOs could have specific capacitance > 1000 Fg-1 but low electrical conductivity and low cycle stability are the main impediments. Conducting polymers have high electrical conductivity, but have poor mechanical strength and cyclic ability. Most past researches have tried to overcome these deficiencies in TMOs and ECPs by forming composite with carbon nanotubes, graphene etc. In this work we have investigated the metal oxide and conducting polymer composite electrode created in a specific nano-architecture that takes advantage of synergy of their potent properties coupled with the short ion diffusion paths and efficient electron exchange during redox processes.By hierarchical integration, supercapacitor electrodes in the 3-dimensional core-shell nanostructure have been designed based on ZnO nanorods at the core, redox active MnO2 layer and surface electro-polymerized pedot conducting polymer as shell. The vertically aligned ZnO nanorods array were hydrothermally grown over flexible graphite sheets to form the core template (Fig 1a). The ZnO nanorods were decorated with a thin ~120 nm layer of MnO2 nanoflakes by KMnO4+MnSO4 solution dip process to form an initial shell nanostructure. A microporous 250 nm thin layer of pedot was molecularly formed by insitu electro-pulsed polymerization over MnO2 surface to create a bi-layer shell (Fig 1b). The pedot shell with controlled porosity was achieved by short 10 ms high current (4 mA.cm-2) pulsed polymerization in aqueous solution of edot monomer, LiClO4 dopant and sodium dodecyl sulfate (SDS) surfactant. The ZnO / MnO2/ pedot core-shell nanostructure electrode shortens the ion diffusion path for fast ionic transport and renders large electroactive sites due to vast surface area. Pedot shell facilitates electronic transfer and ZnO core and imparts structural stability beside large surface area. The electrochemical energy storage performance of ZnO core, ZnO/MnO2 and ZnO/MnO2/Pedot core-shell electrodes was analyzed by cyclic voltammetry (CV), impedance spectroscopy (EIS), charge-discharge (CD) and long term cyclic tests in a three-electrode cell with Pt sheet as counter and Ag/AgCl as reference electrode in aqueous 1M sodium sulfate mediumThe Raman spectra analysis shows MnO2 shell forms in birnessite Mn(IV) state uniformly over ZnO nanorods. The pedot is highly conjugated (ClO4 ions) with sufficient micro-porosity for MnO2 to access electrolyte (LiClO4) and possible Li-ion incursion in pedot and MnO2. CV analysis establishes redox behavior of ZnO-MnO2 core-shell and with pedot shell further increase in areal capacitance >1090 F.g-1 with near rectangular CV plots (Fig 2a). The scan rate dependent study of surface charge and ion diffusion limitation shows that pedot layer mitigates poor electronic conduction in MnO2 shell and provided diffusive pathways for the ions thus enhancing capacitive properties (Fig 2b). This is further affirmed from the Nyquist plots showing nonexistent Warburg region indicating inconsequential diffusion limitation and the near vertical imaginary impedance indicating high pseudocapacitance. The 1.0- 3.0 mA cm-2 CD plots of ZnO/MnO2/pedot core-shell electrodes are triangular with minimal resistive drop and ~91% Coulomb efficiency. The ZnO/MnO2/core-shell shows energy density of 25.6 Wh kg-1 and power density 2.6 kW kg-1 and a significantly improved rate capability is realized with added pedot shell as evidenced by power density 20.8 kW.kg-1 corresponding to energy density of 37.9Wh.kg-1 .The cyclic stability tested over 6000 CD cycles show the usual capacitance fading for 900 cycles and highly stable performance thereafter and perhaps beyond 6000 cycles as the CD plots were in triangular without any change in resistive drops (Fig 2c). The supercapacitor device based on two symmetrical ZnO/MnO2/core-shell electrodes was similarly investigated. This paper will report on the significant research findings on the synergistic electrochemical action of nano MnO2 with molecularly integrated microporous pedot over ZnO nanorod array in a 3-dimensional nanoarchitecture Figure 1

Solvothermal synthesis of CuFeS2 nanoflakes as a promising electrode material for supercapacitors

The present work describes the electrochemical energy storage performance of CuFeS2 (Chalcopyrite), which is well known for its high electrical conductivity, natural abundance, and low cost. The laboratory synthesis method for CuFeS2 nanoflakes by facile one step solvothermal method is successfully accomplished. The as-synthesized CuFeS2 nanoflakes are subjected to both Physical and chemical characterization, as well as electrochemical characterization. CuFeS2 sample has been coated over carbon cloth substrate for the fabrication of flexible electrode for supercapacitor. The Cu1+ and Fe3+ ions offer a synergistic contribution in the redox mechanism and substantiate an eminent electrochemical performance for supercapacitor. Galvanometric Charge Discharge (GCD) profile of CuFeS2 electrode in three electrode system manifests a high specific capacitance of 219 F g−1 at 1 A g−1 in an aqueous medium of 2 M KOH electrolyte with the potential range of -0.5 to 0.5 V. Further in two electrode system, the symmetric supercapacitor based on CuFeS2 electrode exhibits a high specific capacitance of 120 F g−1 at a current density of 1 A g−1 in aqueous 2 M KOH electrolyte. The symmetric supercapacitor based on CuFeS2 electrode delivers a maximum specific energy of 16 Wh Kg−1 at a specific power of 1146 W kg−1with a capacitive retention of 94% over 6000 cycles. These factors inclusively promote CuFeS2 as a promising electrode material for supercapacitor application.

Washnut Seed-Derived Ultrahigh Surface Area Nanoporous Carbons as High Rate Performance Electrode Material for Supercapacitors

Abstract Hierarchical porous carbon materials with high surface area and large porosity derived from biomass are desired for the sustainable development of low-cost electrode materials for advanced energy storage devices. Here, we report the electrochemical supercapacitance performance of washnut seed-derived nanoporous carbon materials in aqueous electrolyte (1 M H2SO4) on a three-electrode system. Potassium hydroxide (KOH) activation of the pre-carbonized Washnut seed powder at high temperatures (800–1000 °C) under nitrogen atmosphere yielded nanoporous carbons with hierarchical micro- and mesoporous structure with well-developed porosity. The surface areas and pore volumes are found in the range of 2005 to 2185 m2 g−1 and 1.370 to 2.002 cm3 g−1, respectively. The as-prepared materials showed outstanding electrochemical energy storage performance achieving a high specific capacitance of 288.7 F g−1 at a current density of 1 A g−1 followed by a high rate capability sustaining 67.2% capacitance even at a high current density of 50 A g−1 with only a small capacity loss (<2%) after 10,000 charging/discharging cycles. This work demonstrates novel insights into low-cost high-performance carbon materials design using natural biomass for the sustainable development of electrode materials for advanced supercapacitor applications.

Electrochemical Impedance Spectroscopy Study of Metal Hydride Electrodes Using a Porous Model: Effect of Thermal Pretreatment and Titanium Incorporation

The aim of this work was to study the influence of titanium and thermal pretreatments on the electrochemical performance of Zr1−xTixCr0.7Mo0.3Ni alloys used as anodic active materials in Ni-MH batteries to improve their electrochemical energy storage performance. It was observed that the substitution of Zr by Ti produced new responses in electrochemical impedance spectroscopy (EIS) diagrams. EIS spectra were adjusted employing a fitting methodology through a model for a porous electrode where the physical meanings of parametric figures and time constants were emphasized. Changes in the system response with the electrode state of charge (SOC) were also studied, and new functional relations between time constant values and SOC were found. The results give new evidence supporting the fact that certain crystallographic phases (such as cubic center body phases) have a helpful influence on the diffusion process, while other phases (such as the hexagonal titanium phase) contribute negatively to it.

Cu2O/Cu@C nanosheets derived from one novel Cu (II) metal-organic framework for high performance supercapacitors

Unique nanostructures could lead to extraordinary electrochemical energy storage performance. Cu2O/Cu@C nanosheets were successfully synthesized from one novel Cu (II) metal-organic framework (Cu-MOF) with a three-dimensional structure, which was assembled by Cu (II), 4-(pyridine-4-yl) phthalic acid and 1,4-bis (benzoimidazo-1-ly) benzen. The Cu (II) was in-situ reduced to form Cu2O/Cu nanoparticles by calcination, which were homogeneously anchored onto carbon sheets. The Cu2O/Cu@C nanosheets exhibit a high specific surface area (336.3 m2 g−1) and large total pore volume (3.41 cm3 g−1), which inherit the original morphology and structure of the Cu-MOF. The nanosheets possess a specific capacitance of 665 F g−1 at a current density of 0.5 A g−1, which is higher than that of Cu-MOF (320 F g−1). Meanwhile, the capacitance retention remains 53.5% with the increasing current density from 0.5 to 5 A g−1, and 82.5% after 5000 cycles at a current density of 0.5 A g−1, which indicate their outstanding rate capability and cycling stability. Further, the as-assembled Cu2O/Cu@C//AC asymmetric supercapacitor achieves the maximum energy density of 38.6 Wh kg−1 at the power density of 466.5 W·kg−1. These excellent electrochemical performances indicate that the Cu2O/Cu@C nanosheets have potential applications in energy storage.