Insights into the Origins of Solar-Assisted Electrochemical Water Oxidation in Allotropic Co5.47N/CoN Heterojunctions

Solar irradiations can efficiently promote the kinetics of oxygen evolution reaction (OER) during water splitting, where heterojunction catalysts exhibit excellent photo-responsive properties. However, insights into the origins of photo-assisted OER catalysis remain unclear, especially the interfaced promotion under convergent solar irradiation (CSI). Herein, novel allotropic Co5.47N/CoN heterojunctions were synthesized, and corresponding OER mechanisms under CSI were comprehensively uncovered from physical and chemical aspects using the in-situ Raman technique and electrochemical cyclic voltammetry method. Our results provide a unique mechanism where high-energy UV light promotes the Co3+/4+ conversion process in addition to the ordinary photoelectric effect excitation of Co2+ material. Importantly, visible light under CSI can produce a photothermal effect for Co2+ excitation and Co3+/4+ conversion, which promotes the OER significantly more than the usual photoelectric effect. As a result, Co5.47N/CoN (containing 28% CoN) obtained 317.9% OER enhancement, which provides a pathway for constructing excellent OER catalysts.