Optically transparent ultrathin NiCo alloy oxide film: Precise oxygen vacancy modulation and control for enhanced electrocatalysis of water oxidation

Oxygen evolution reaction (OER) impedes the electrochemical water splitting for H2 production primarily because of the sluggish kinetics. Cobalt oxides with abundant oxygen vacancies (Vos) have been proved to be the promising OER electrocatalysts showing high catalytic performance. However, precisely controlling the concentration of the Vos and large-scale synthesis of these electrocatalysts are still not resolved. Herein, we propose an e-beam evaporation alloy-UV/O3 oxidation method for fabricating optically transparent alloy oxide films (f-Ni0.1Co0.9Ox) only 10 nm thick. The concentration of the oxygen vacancies is positive correlated with the Ni content in the alloy oxides. The optimum binary Ni/Co (1/9) alloy oxide with the best defect O/lattice O ratio (0.952) exhibits ultrahigh OER mass activity of 3055 A g−1 at 250 mV overpotential in 1.0 M KOH, almost 7.5 times and 190 times as high as CoOx and the commercial benchmark RuO2 OER catalysts, respectively. Moreover, directly depositing f-Ni0.1Co0.9Ox film on the top of the tandem-junction a-Si PV cell realizes wireless unassisted solar-driven water splitting with high solar-to-hydrogen conversion efficiency. The key roles of modulating the electron structure, stably reversible spinel structure and the reaction barrier reduction were revealed in situ spectroscopy and density functional theory calculations. This study provides a new perspective of oxygen vacancy modulation for high electrocatalysis performance via large-scale synthesis of such bimetallic alloy oxides.