Sphere-like Naphthalene-Based Microporous Nickel Phosphonate Facile for Asymmetric Supercapacitor Devices and Bifunctional Oxygen Electrocatalysts

To produce clean energy due to the lack of fossil fuels, the development of cost-effective and highly efficient energy storage devices and multifunctional electrocatalysts is essential to substitute noble metal-based electrocatalysts. In this context, transition metal-based nickel phosphonate material (NiNAP) has been synthesized using 1,1′-binaphthyl-2,2′-diyl hydrogenphosphate and nickel nitrate hexahydrate in a hydrothermal reaction pathway in the absence of a templating pathway. The organic-inorganic hybrid structure with microporous arrays as a potential electrode material facilitates energy storage and conversion reactions. For the first time, a sphere-like NiNAP material has been developed, which is a potential electrode material for asymmetric supercapacitor applications with high specific capacitance and both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) with a low overpotential and higher current density. Moreover, the NiNAP material exhibits a specific capacitance of 4456 F g^-1 in three-electrode assembly and 455 F g^-1 in asymmetric supercapacitor at a scan rate of 1 mV s^-1, where the energy and power density are estimated to be 204 W h kg^-1 and 409 W kg^-1, respectively. Interestingly, the NiNAP material displays outstanding catalytic activity toward OER with a low overpotential of 242 mV at the current density of 10 mA cm^-2 and excellent ORR activity with an onset potential of 0.74 V vs RHE. Also, it shows long-term stability without significant changes in the current density for OER and ORR.