The energy conversion efficiency of hybrid organic-inorganic perovskite solar cells (PSCs) has reached a value comparable to commercially available silicon solar cells. The main challenges for their commercialization are instability and toxicity.

Catalytic materials are the greatest challenge for the commercial application of water electrolysis (WEs) and fuel cells (FCs) as clean energy technologies. There is a need to find an alternative to expensive and unavailable platinum group metal (PGM) catalysts. This study aimed to reduce the cost of PGM materials by replacing Ru with RuO2 and lowering the amount of RuO2 by adding abundant and multifunctional ZnO. A ZnO@RuO2 composite in a 10:1 molar ratio was synthesized by microwave processing of a precipitate as a green, low-cost, and fast method, and then annealed at 300°C and 600°C to improve the catalytic properties. The physicochemical properties of the ZnO@RuO2 composites were investigated by X-ray powder diffraction (XRD), Raman and Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), UV-Vis diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The electrochemical activity of the samples was investigated by linear sweep voltammetry in acidic and alkaline electrolytes. We observed good bifunctional catalytic activity of the ZnO@RuO2 composites toward HER and OER in both electrolytes. The improved bifunctional catalytic activity of the ZnO@RuO2 composite by annealing was discussed and attributed to the reduced number of bulk oxygen vacancies and the increased number of established heterojunctions.