Insights into the Origins of Solar-Assisted Electrochemical Water Oxidation in Allotropic Co_5.47N/CoN Heterojunctions

Solar irradiation can efficiently promote the kinetics of the oxygen evolution reaction (OER) during water splitting, where heterojunction catalysts exhibit excellent photoresponsive properties. However, insights into the origins of photoassisted OER catalysis remain unclear, especially the interfaced promotion under convergent solar irradiation (CSI). Herein, novel allotropic Co_5.47N/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 Co^3+/4+ conversion process in addition to the ordinary photoelectric effect excitation of the Co²⁺ material. Importantly, visible light under CSI can produce a photothermal effect for Co²⁺ excitation and Co^3+/4+ conversion, which promotes the OER significantly more than the usual photoelectric effect. As a result, Co_5.47N/CoN (containing 28% CoN) obtained 317.9% OER enhancement, which provides a pathway for constructing excellent OER catalysts.