Improving the onset of oxygen redox reactions by activating surface defects with visible light on a ZnO-based electrode

Abstract

This study investigates the influence of photoactivated oxygen vacancies (VO) on the activation of oxygen redox reactions, such as evolution (OER) and reduction (ORR) reactions. The reactions were carried out on the surface of an electrode prepared with ZnO prepared by green synthesis and supported on sterling silver. Structural and surface analyses using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) confirmed the presence of oxygen vacancies. Electrochemical analysis performed in an alkaline medium showed that Vo exhibited photoactivation under visible light illumination. This photoactivation process facilitated electron transfer, resulting in the formation of superoxide intermediates ${(O}_2^{-})$. These intermediates contribute to the generation of singlet oxygen (¹O₂), which enhances OER activity and enables the photoexcitation of adsorbed peroxides and singlet oxygen. This process promotes the formation of triplet oxygen (³O₂), which improves the ORR kinetics. The incorporation of Mg into the Zn-O matrix may play an essential role in these processes. These results provide new insights into the design of electrocatalysts using visible-light-activated redox processes for rechargeable batteries and fuel cell applications.