Potential-Resolved Ratiometric Electrochemiluminescence for Identifying Site Distribution of Nickel Dopant in Cobalt Spinel Oxides

Metal doping is a well-established strategy for enhancing the catalytic performance of cobalt spinel oxides, where the site occupancy of dopants at octahedral versus tetrahedral positions critically governs electrochemical behavior. However, accurately identifying dopant site distribution remains challenging, hindering the mechanistic understanding and precise control of doping effects. Here, we introduce a highly sensitive potential-resolved ratiometric electrochemiluminescence (ECL) method to probe nickel site occupancy in Co₃O₄. A quantitative correlation was established between the logarithmic ratio of cathodic to anodic ECL intensities (lg(Ic/Ia)) and the ratio of octahedral-to-tetrahedral Ni sites (NiOh/NiTd), enabling semiquantitative analysis of site distribution with high sensitivity. The results reveal that increasing the NiOh/NiTd ratio shifts the ECL emission from anodic to cathodic, accompanied by a monotonic rise in lg(Ic/Ia). This trend is attributed to preferential Ni occupation of octahedral sites, which modulates the electronic structure of Co³⁺ centers, enhances electron transfer capability, and optimizes oxygen intermediate adsorption energy-collectively boosting oxygen reduction reaction (ORR) activity and inducing distinct ECL signatures. This study not only establishes a novel method for high-throughput screening of dopant site distributions in spinel oxides but also offers a framework for the rational design, quantitative regulation, and mechanistic elucidation of doping effects in functional materials.