A unique and cost effective hydrothermal procedure has been carried out for the synthesis of hexahedron shaped α MnMoO4 and its hybrid composite with graphene using three different weight percentages of graphene. Characterization techniques, such as XRD, Raman and FTIR analysis, established the phase and formation of the composite. The electrochemical characterization of the pseudocapacitive MnMoO4 and the MnMoO4/graphene composites in 1 M Na2SO4 displayed highest specific capacitances of 234 F g(-1) and 364 F g(-1), respectively at a current density of 2 A g(-1). Unlike many other pseudocapacitive electrode materials our prepared materials responded in a wide range of working potentials of (-)1 V to (+)1 V, which indeed resulted in a high energy density without substantial loss of power density. The highest energy densities of 130 Wh kg(-1) and 202.2 Wh kg(-1) were achieved, respectively for the MnMoO4 and the MnMoO4/graphene composite at a constant power delivery rate of 2000 W kg(-1). The synergistic effect of the graphene with the pseudocapacitive MnMoO4 caused an increased cycle stability of 88% specific capacitance retention after 1000 consecutive charge discharge cycles at 8 A g(-1) constant current density, which was higher than the virgin MnMoO4 with 84% specific capacitance retention.

Reducing anode catalyst layer proton-and electrontransport resistances in polymer electrolyte membrane water electrolyzers is critical to improving its performance and maximizing catalyst utilization at high current density. A hydrogen pump technique is adapted to measure the protonic conductivity of IrO x -based catalyst layers. The protonic resistance of the catalyst layer is obtained by subtracting the protonic resistance of an assembly of two NRE211 membranes hot-pressed together from an assembly of two NRE211 membranes with an IrO x intermediate layer. The through-plane and in-plane electronic conductivities were also measured using two-and four-probe methods, respectively. Using these techniques, the protonic and electronic conductivities of the IrO x catalyst layers with varying Nafion loading were measured. The results show that the limiting charge-transport phenomena in the IrO x catalyst layer can be either proton or electron transport, depending on the ionomer loading in the catalyst layer. These results are validated by numerical simulation, as well as by comparison to the high-frequency resistance of an electrolyzer with the same layer.

Conducting flexible carbon fiber (CF) cloth was used as a substrate for the hydrothermal growth of nickel hydroxide (Ni(OH)2) and cobalt hydroxy carbonate [Co(OH)xCO3] with unique hierarchical flowery architecture and then was used as a flexible supercapacitor electrode. In a three-electrode configuration in 6 M KOH aqueous electrolyte, the CF-Ni(OH)2 and CF-Co(OH)xCO3 electrode showed the maximum specific capacitance of 789 F/g and 550 F/g, respectively, at 2A/g current accompanied by outstanding cycle stability by retaining 99.9% and 99.5% specific capacitance over 1500 consecutive charge-discharge cycles at 5 A/g. However, the low cell voltage (0.4 V) restricted the respective specific energy to 4.38 and 3.05 Wh/kg at a specific power of 100 W/kg. To overcome the issue, two solid state flexible asymmetric supercapacitors were fabricated using the CF-Ni(OH)2 and CF-Co(OH)xCO3 as the anode and sonochemically deposited CNT over carbon fiber as the cathode material in PVA-KOH gel electrolyte. The as-fabricated flexible supercapacitors CF-Ni(OH)2//CF-CNT and CF-Co(OH)xCO3//CF-CNT were able to deliver high specific energy of 41.1 and 33.48 Wh/kg, respectively, at high specific power of 1.4 kW/kg accompanied by excellent cycle stability (retaining 98% and 97.6% specific capacitance, respectively, over 3000 charge-discharge cycle at 5 A/g).

Vanadium pentoxide (V 2 O 5 ) is renowned among the highly efficient supercapacitor electrode-materials for high power and energy densities, excellent specific capacitance, prolonged cycle lives, variable oxidation states of V, reversible nature of interconversions, theoretical importance, etc. Various synthetic methodologies and morphologies, formation of composites, and doping for tuning properties are the additional causes of interest. Different synthetic techniques like sol-gel, solvothermal, electro-deposition, electro-spinning, atomic layer deposition, etc. are employed to prepare V 2 O 5 -based electrode materials with merits and demerits. High rate of material agglomeration and poor conductivity limit its usage in pristine morphology. Accordingly, the impact on charge storage behavior of V 2 O 5 on blending with various carbon-based systems has been explored for materials like activated carbons, conducting polymers, carbon nanotubes and functionalized graphene systems as binary/ternary composites. The aim has been to optimize the key factors such as reduced nanostructure lumping, minimal interfacial resistance and ultrafast charge diffusion across hollow porous structures which may eventually lead to the theoretically expected high specific capacitance (> 1000 F g À 1 ). In this review, we have discussed on the recent progress in the research of V 2 O 5 -based materials and highlighted on the correlation between morphology and electrochemical performances. In the course, we have attempted to delineate the advantage-disadvantages of different composite morphologies that may help to outline the present status and future aspects of these materials that the authors believe will be of first-hand assistance especially to the beginners in the field of research.