Ni0.5Co0.5S nano-chains: a high-performing intercalating pseudocapacitive electrode in asymmetric supercapacitor (ASC) mode for the development of large-scale energy storage devices.

Grid-scale energy storage solutions are necessary for using renewable energy sources efficiently. A supercapattery (supercapacitor + battery) has recently been introduced as a new variety of hybrid devices that engage both capacitive and faradaic charge storage processes. Nano-chain architectures of Ni0.5Co0.5S electrode materials consisting of interconnected nano-spheres are rationally constructed by tailoring the surface structure. Nano-chains of the bimetallic sulfide Ni0.5Co0.5S are presented to have a superior charge storage capacity. The Ni0.5Co0.5S nano-chain electrode presents a capacitance of 2001.6 F g-1 at 1 mV s-1, with a specific capacity of 267 mA h g-1 (1920 F g-1) at 1 A g-1 in 4 M KOH aqueous electrolyte through the galvanostatic charge-discharge (GCD) method. The reason behind the high charge storage capacity of the materials is the predominant redox-mediated diffusion-controlled pseudocapacitive mechanism coupled with surface capacitance (electrosorption), as the surface (outer) and intercalative (inner) charges stored by the Ni0.5Co0.5S electrodes are close to 46.0% and 54.0%, respectively. Additionally, a Ni0.5Co0.5S//AC two electrode full cell operating in asymmetric supercapacitor cell (ASCs) mode in 4 M KOH electrolyte exhibits an impressive energy density equivalent to 257 W h kg-1 and a power density of 0.73 kW kg-1 at a current rate of 1 A g-1.

Nanocrystalline ß-NiS: a redox-mediated electrode in aqueous electrolyte for pseudocapacitor/supercapacitor applications.

Currently, enhancing the performance of electrochemical supercapacitors is the subject of intense research to fulfill the ever-increasing demand for grid-scale energy storage and delivery solution, thereby utilizing the full potential of renewable energy resources and decreasing our dependence on fossil fuels. Metal sulfides, such as cobalt sulfide (CoS), nickel sulfide (NiS), molybdenum sulfide (MoS), copper sulfide (CuS), and others, have recently emerged as a promising class of active electrode materials, alongside other supercapacitor electrode materials, due to their relatively high specific capacitance values and exceptional reversible redox reaction activities. The synthesis, characterizations, and electrochemical performances of single-phase nanocrystalline ß-NiS are presented here and the electrode based on this material shows a specific capacitance of 1578 F g-1 at 1 A g-1 from the galvanostatic discharge profile, whereas a capacitance of 1611 F g-1 at 1 mV s-1 was obtained through the CV curve in 2 M KOH aqueous electrolyte. Additionally, the electrode also performs well in neutral 0.5 M Na2SO4 electrolytes resulting in specific capacitance equivalent to 403 F g-1 at 1 mV s-1 scan rate. The high charge storage capacity of the material is due to the superior intercalative (inner) charge storage coupled with the surface (outer) charges stored by the ß-NiS electrode and was found to be 72% and 28%, respectively, in aqueous 2 M KOH electrolyte. This intercalative charge storage mechanism is also responsible for its excellent cycling stability. Additionally, we assembled aqueous asymmetric supercapacitors (ASCs) with activated carbon (AC) as the negative electrode and the ß-NiS electrode as the positive electrode. The combination of the ß-NiS electrode and AC with excellent cycling stability resulted in the highest specific energy equivalent to ∼163 W h kg-1 and a specific power of ∼507 W kg-1 at 1 A g-1 current rate.

Reinforcement of nanoporous lanthanum-doped zinc borate by vanadium selenide nanosheets for improved tribological activity.

Nanoporous zinc borate (ZB) and 10% lanthanum-doped porous zinc borate (LZB) were synthesized to explore the role of porosity and doping in zinc borate during lubrication. HR-SEM, TEM, and HR-TEM authenticated nanoporous structures. The tribological properties of their blends with paraffin oil (PO) were compared by employing ASTM D4172 and ASTM D5183 norms on a four-ball tester. Vanadium selenide nanosheets (VSe2) were used to reinforce the structure of LZB for further advancement of the tribological properties. The superiority of the LZB/VSe2 over LZB and VSe2 nanosheets could be adjudged by tribological data. The porosity and lanthanum doping have yielded commendable tribological activity. The VSe2 nanosheets have strengthened the LZB matrix. The other constituent oxides of tribofilm from the LZB matrix, based on EDX analysis and XPS studies of the worn surface, ZnO, B2O3, La2O3, and V2O5, have abetted lubrication. The AFM and SEM investigations of wear track corroborated the tribological results.

SrFeO3-δ: a novel Fe4+ ↔ Fe2+ redox mediated pseudocapacitive electrode in aqueous electrolyte.

Pseudocapacitors offer both high energy and high power, making them suitable for grid-scale electrochemical energy storage to harness renewable energy produced from sun, wind, and tides. To overcome performance degradation in terms of cycling fading and lower specific capacitance values at high charge/discharge rates of electrochemical pseudocapacitors based on transition-metal oxides, perovskite-structured SrFeO3-δ was envisaged as a negative electrode that harnesses the Fe4+/3+ and Fe3+/2+ redox couple to deliver superior performance. SrFeO3-δ offers high specific capacitances of ca. 733 F g-1 at a scan rate of 1 mV s-1 and ca. 743 F g-1 at a current density of 1 A g-1 and demonstrates excellent cyclic stability over 2500 repeated cycles with capacitance retention of >92%, achieving 94% coulombic efficiency. The good cycling stability is attributed to the inherent metallic electrical conductivity of SrFeO3-δ and the fortuitous tendency of the robust cation framework structure to accommodate flexible oxygen content. The surface capacitive and diffusion-controlled contributions for capacitance are about ∼30% and ∼70%, respectively, at peak current and a scan rate equivalent to 1 mV s-1. The higher capacitance and stable performance make SrFeO3-δ an economical and abundant pseudocapacitive electrode.