Investigation of the Role of 3d-4d Elements in a Disordered Double Perovskite toward Efficient Photocatalytic Energy Conversion and Electrochemical Energy-Storage Behaviors

Toward the goal of achieving green and sustainable energy conversion and storage behaviors, double perovskite oxide materials are always pronounced not only due to their exciting properties but also for their advanced catalytic and electroactive nature. In order to understand the factual role of either 3d or 4d metal ions in double perovskites toward energy conversion and storage applications, herein we have demonstrated three ruthenium-based disordered double perovskites, namely, Ca2MnRuO6 (CMRO), Ca2Mn1.25Ru0.75O6 (CMRO-1), and Ca2Mn0.75Ru1.25O6 (CMRO-2), by varying the Mn/Ru stoichiometry. The well-characterized phase-pure polycrystalline oxides are employed as efficient photocatalysts for visible light-driven water oxidation in a neutral pH medium. Even a small quantity of the present catalyst can evolve larger amounts of oxygen compared to reported photocatalysts. Furthermore, electrochemical supercapacitor performance has been accomplished by the CMRO compounds and reduced graphene oxide (rGO) composite electrodes. The electrochemical measurement reveals that the as-fabricated CMRO-2 oxide-rGO composite electrode possesses much higher capacitance of 598.8 F/g at a scan rate of 2 mV/s in 0.5 M H3PO4 electrolyte solution compared to 0.5 M H2SO4 common electrolyte medium. Remarkably, the CMRO-2 and rGO composite electrode exhibited a maximum energy density of 431.1 Wh/kg at a power density of 14.4 W/kg in 0.5 M H3PO4 electrolyte. Notably, the slight variation of Mn/Ru concentration in title perovskite structures commendably affects the photocatalytic water oxidation and electrochemical supercapacitor performances. Such exciting structure–activity phenomena of 3d-4d transition metal-based oxide materials are also validated through density functional theory calculations.