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An environmentally friendly hydrogel based on gelatin has been investigated as a gel polymer electrolyte in a symmetric carbon-based supercapacitor. To guarantee the complete sustainability of the devices, biomaterials from renewable resources (such as chitosan, casein and carboxymethyl cellulose) and activated carbon (from coconut shells) have been used as a binder and filler within the electrode, respectively. The electrochemical properties of the devices have been compared by using cyclic voltammetry, galvanostatic charge/discharge curves and impedance spectroscopy. Compared to the liquid electrolyte, the hydrogel supercapacitors show similar energy performance with an enhancement of stability up to 12,000 cycles (e.g., chitosan as a binder). The most performant device can deliver ca. 5.2 Wh/kg of energy at a high power density of 1256 W/kg. A correlation between the electrochemical performances and charge storage mechanisms (involving faradaic and non-faradaic processes) at the interface electrode/hydrogel has been discussed.

MgH2-based hydrogen storage materials are promising candidates for solid-state hydrogen storage allowing efficient thermal management in energy systems integrating metal hydride hydrogen store with a solid oxide fuel cell (SOFC) providing dissipated heat at temperatures between 400 and 600 °C. Recently, we have shown that graphite-modified composite of TiH2 and MgH2 prepared by high-energy reactive ball milling in hydrogen (HRBM), demonstrates a high reversible gravimetric H storage capacity exceeding 5 wt % H, fast hydrogenation/dehydrogenation kinetics and excellent cycle stability. In present study, 0.9 MgH2 + 0.1 TiH2 +5 wt %C nanocomposite with a maximum hydrogen storage capacity of 6.3 wt% H was prepared by HRBM preceded by a short homogenizing pre-milling in inert gas. 300 g of the composite was loaded into a storage tank accommodating an air-heated stainless steel metal hydride (MH) container equipped with transversal internal (copper) and external (aluminium) fins. Tests of the tank were carried out in a temperature range from 150 °C (H2 absorption) to 370 °C (H2 desorption) and showed its ability to deliver up to 185 NL H2 corresponding to a reversible H storage capacity of the MH material of appr. 5 wt% H. No significant deterioration of the reversible H storage capacity was observed during 20 heating/cooling H2 discharge/charge cycles. It was found that H2 desorption performance can be tailored by selecting appropriate thermal management conditions and an optimal operational regime has been proposed.

ZnO nanoparticles were successfully in situ synthesized in the form of PEO–COO− modified ZnO by a three-step method, based on which the solid polymer electrolytes (SPEs), based on polyethylene oxide (PEO) with excellent electrochemical performance, were prepared. The evolution of the electrochemical and mechanical performances of the SPEs with the ZnO content (0–5 wt.%) was investigated in detail. The mechanical property of the SPEs demonstrated a Λ-shaped change trend as increasing the ZnO content, so that the highest value was acquired at 3 wt.% ZnO. The SPE containing 3 wt.% ZnO had the most outstanding electrochemical performance, which was significantly better than that containing directly-added ZnO (2 wt.%). Compared with the latter, the ion conductivity of the former was improved by approximately 299.05% (1.255 × 10−3 S·cm−1 at 60 °C). The lithium-ion migration number was improved from 0.768 to 0.858. The electrochemical window was enhanced from 5.25 V to 5.50 V. When the coin cell was subject to the cycling (three cycles in turn from 0.1 C to 3 C, and subsequent fifty cycles at 1 C), the 68.73% specific capacity was retained (106.8 mAh·g−1). This investigation provides a feasible approach to prepare the SPEs with excellent service performance.

Graphene has presented promising features for application in lithium ion batteries(LIBs) due to its superior electronic conductivity and high surface area. It has been successfully used for modifying cathode materials to meet the increasing demand for LIBs with longer cycle life. However, the improving effect of graphene on cycling stability is still unclear, which restricts its further application in LIBs. Herein, graphene coated hollow sphere-like structure LiNi0.5Mn1.5O4(LNMO) was designed and the improvement mechanism of graphene coating on LNMO's cycling stability was investigated. The results show that graphene coating not only contributes to suppress structural deformation from mechanistic reaction and extend solid-solution reaction, but also helps protect electrode from corrosion by the products from electrolyte decomposition and suppress the generation of surface defects, especially at high temperature. Owing to graphene coating, graphene coated LNMO can deliver a discharge capacity of 91 mAh g−1 with high capacity retention of 82.5% after 1000 cycles under 20C and 83.8 mAh g−1 with 94.5% capacity retention after 100 cycles under 2C at 55 °C. This work deeply explores the effect of graphene coating on cycling stability from crystal stability and surface stability, which will help a wider application of graphene in energy storage field.

In the present work, we described the synthesis and characterization of the ternary Cu2O/CuS/ZnS nanocomposite using a facile two-step wet chemical method for blue LED-light-induced photocatalytic hydrogen production. The concentrations of the ZnS precursor and reaction time were essential in controlling the photocatalytic hydrogen production efficiency of the Cu2O/CuS/ZnS nanocomposite under blue LED light irradiation. The optimized Cu2O/CuS/ZnS nanocomposite exhibited a maximum photocatalytic hydrogen evolution rate of 1109 µmolh−1g−1, which was remarkably higher than Cu2O nanostructures. Through the cycle stability it can be observed that the hydrogen production rate of the Cu2O/CuS/ZnS nanocomposite decreased after 4 cycles (1 cycle = 3 h), but it remained at 82.2% of the initial performance under blue LED light irradiation. These reasons are mainly attributed to the introduction of CuS and ZnS to construct a rationally coupled reaction system, which enables the synergistic utilization of photogenerated carriers and the increased absorption of visible light for boosting blue LED-light-driven photocatalytic hydrogen evolution.

Highlights The Zn/MnO2 cell with inorganic colloidal electrolyte demonstrates unprecedented durability over 1000 cycles.For the cathode, the presence of the protective film can inhibit the dissolution of manganese element and the formation of irreversible by-products.For the anode, it can reduce the corrosion and de-solvation energy, inhibit the growth of dendrite and irreversible by-products. Supplementary Information The online version contains supplementary material available at (10.1007/s40820-021-00595-6)., Zinc-ion batteries (ZIBs) is a promising electrical energy storage candidate due to its eco-friendliness, low cost, and intrinsic safety, but on the cathode the element dissolution and the formation of irreversible products, and on the anode the growth of dendrite as well as irreversible products hinder its practical application. Herein, we propose a new type of the inorganic highly concentrated colloidal electrolytes (HCCE) for ZIBs promoting simultaneous robust protection of both cathode/anode leading to an effective suppression of element dissolution, dendrite, and irreversible products growth. The new HCCE has high Zn2+ ion transference number (0.64) endowed by the limitation of SO42−, the competitive ion conductivity (1.1 × 10–2 S cm−1) and Zn2+ ion diffusion enabled by the uniform pore distribution (3.6 nm) and the limited free water. The Zn/HCCE/α-MnO2 cells exhibit high durability under both high and low current densities, which is almost 100% capacity retention at 200 mA g−1 after 400 cycles (290 mAh g−1) and 89% capacity retention under 500 mA g−1 after 1000 cycles (212 mAh g−1). Considering material sustainability and batteries’ high performances, the colloidal electrolyte may provide a feasible substitute beyond the liquid and all-solid-state electrolyte of ZIBs. Supplementary Information The online version contains supplementary material available at (10.1007/s40820-021-00595-6).

In this work, the hierarchical porous Ni1.5Co1.5S4/g-C3N4 composite was prepared by growing Ni1.5Co1.5S4 nanoparticles on graphitic carbon nitride (g-C3N4) nanosheets via a hydrothermal route. Due to the self-assembly of larger size g-C3N4 nanosheets as a skeleton, the prepared nanocomposite possesses a unique hierarchical porous structure that can provide short ions diffusion and fast electron transport. As a result, the Ni1.5Co1.5S4/g-C3N4 composite exhibits a high specific capacitance of 1827 F g−1 at a current density of 1 A g−1, which is 1.53 times that of pure Ni1.5Co1.5S4 (1191 F g−1). In particular, the Ni1.5Co1.5S4/g-C3N4//activated carbon (AC) asymmetric supercapacitor delivers a high energy density of 49.0 Wh kg−1 at a power density of 799.0 W kg−1. Moreover, the assembled device shows outstanding cycle stability with 95.5% capacitance retention after 8000 cycles at a high current density of 10 A g−1. The attractive performance indicates that the easily synthesized and low-cost Ni1.5Co1.5S4/g-C3N4 composite would be a promising electrode material for supercapacitor application.

Silicon anode is considered as one of the candidates for graphite replacement due to its highest known theoretical capacity and abundant reserve on earth. However, poor cycling stability resulted from the “volume effect” in the continuous charge-discharge processes become the biggest barrier limiting silicon anodes development. To avoid the resultant damage to the silicon structure, some achievements have been made through constructing the structured space and pore design, and the cycling stability of the silicon anode has been improved. Here, progresses on designing nanostructured materials, constructing buffered spaces, and modifying surfaces/interfaces are mainly discussed and commented from spatial structure and pore generation for volumetric stress alleviation, ions transport, and electrons transfer improvement to screen out the most effective optimization strategies for development of silicon based anode materials with good property.

In this dissertation, partial element substitution was used to improve the hydrogen storage properties and electrochemical cycle stability of AB3 type alloys. In addition composite method was proposed to enhance the cycle durability of AB3 type alloys. Meanwhile a critical review on the working principles, advantages and drawbacks, limitations of six categories of techniques commonly applied on the characterization of hydrogen storage materials was presented. These techniques include the Sieverts technique, gravimetry, secondary ion mass spectrometry, thermal desorption spectroscopy, neutron scattering and electrochemical technique. The microstructure and hydrogen storage properties of cost-competitive La0.51-xY0.05+xCa1.03Mg1.32Ni9 (x=0, 0.15, 0.35) alloys were investigated. The change of Y content would alter the microstructure of La-Y-Ca-Mg-Ni alloy such as phase abundance, lattice parameters and cell volume. The Y abundant sample exhibited a higher absorption plateau pressure, lower hydrogen capacity and relatively inferior hydrogen absorption kinetics. In addition the hydride stability was reduced with the increase of Y content. The electrochemical properties of La0.51-xY0.05+xCa1.03Mg1.32Ni9 (x=0, 0.15, 0.35) alloy powder were systematically investigated. The increase of Y content in sample alloy would result in an improvement of cycle stability, suppression of particle pulverization, reduction of formation of corrosion products and elevation of rate capability at higher discharge rate. However excessive Y in the alloy would lead to a decrease in maximum capacity. Overall the electrodes made by La0.42Y0.22Ca0.78Mg1.01Ni9 alloy exhibited the best performance; the cycle stability was improved without significant loss in maximum capacity. The electrochemical performances of composite electrode composed of La0.51Y0.05Ca1.03Mg1.32Ni9 and x wt% La0.63Nd0.08Pr0.02Ce0.27(Al0.02Co0.14Mn0.06Ni0.78)5 (x =10, 30, 50) have also been studied. The electrode with 30 wt% AB5 electrode exhibited the best overall performance; both cycle durability and maximum discharge capacity were enhanced, although the rate capability was deteriorated. The linear polarization and potentiostatic discharge test indicated that rate capability of both La-Y-Ca-Mg-Ni and composite electrodes was dominant by charge transfer reaction at electrode surface at lower discharge rate, and the discharge performance became hydrogen diffusion dependent when the discharge current density rose.

In this paper, a novel additive, calcium metaborate (CMB), is proposed to improve the high-temperature characteristics of the nickel electrodes for nickel–metal hydride batteries. As a soluble calcium salt, CMB can easily and uniformly be dispersed in the nickel electrodes. The effects of CMB on the nickel electrode are investigated via a combination of cyclability, capacity retention, electrochemical impedance spectroscopy, scanning electron microscope and X-ray diffraction. Compared with conventional nickel electrodes, the electrode containing 0.5 wt.% CMB exhibits superior electrode properties including enhanced discharge capacity, improved high-rate discharge ability and excellent cycle stability at an elevated temperature (70 °C). The improved cell performance of the nickel electrode containing CMB additives can be attributable to the increased oxygen evolution overvoltage and slower oxygen evolution rate. Compared with insoluble calcium salts, such as Ca(OH) 2 , CaCO 3 , and CaF 2 , CMB is more effective as a cathode additive to improve the high-temperature performance of Ni–MH batteries.

In this paper, an alternative approach to improve the high-temperature performance of nickel–metal hydride (Ni–MH) batteries is proposed by introducing NaOH electrolyte with sodium metaborate (NaBO2) additives. Compared with conventional batteries using KOH electrolyte, the in-house prepared batteries with proposed electrolytes exhibit an enhanced discharge capacity, improved high-rate discharge ability, increased cycle stability and reduced self-discharge rate at an elevated temperature (70 °C). The charge acceptance of these Ni–MH batteries at 70 °C is over 96% at a charge/discharge rate of 1 C. These performance improvements are ascribed to the increased oxygen evolution overpotential, slower oxygen evolution rate and lower electrochemical impedance, as indicated by CV, steady-state polarization measurements and EIS. The results suggest that the proposed approach be an effective way to improve the high-temperature performance of Ni–MH batteries.

Sodium tungstate (Na2WO4) used as new electrolyte additive to enhance the high-temperature performance of Nickel–metal hydride (Ni–MH) battery is investigated in this paper. The effects of Na2WO4 on nickel hydroxide electrodes are investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and a charge/discharge test. It is found that the Ni–MH cell with the conventional KOH electrolyte containing 1 wt.% Na2WO4 additive exhibits higher discharge retention and better cycling performance than the cell without Na2WO4 additive at both 25 °C and 70 °C. These performance improvements are ascribed to the enhancement of oxygen evolution overvoltage and lower electrochemical impedance, as indicated by CV and EIS. The results suggest that the proposed approach be an effective way to improve the high temperature performance of Ni–MH batteries.

TiO2 is well‐known nanomaterials and mostly used as solid nanoparticles, and normal hollow spheres for photocatalysts or electrode materials. In this study, a novel self‐templated method is presented to successfully fabricate high‐surface‐area ultrathin nanosheets constructed TiO2 hollow spheres through the solvothermal treatment of the titanate–silicone composite particles combined with calcination. The uniquely structured hollow spheres exhibit excellent rate capability and good cycle stability even at a high current density of ≈10 C for the anode material of Li‐ion battery.