Operando electrochemiluminescence imaging of intermediate evolution and kinetics in electrocatalytic nitrate reduction

Electrocatalytic nitrate reduction (NO3RR) provides a sustainable approach for removing nitrate pollutants and producing valuable nitrogen chemicals. However, understanding catalytic behavior under realistic dilute conditions remains challenging, as conventional electrochemical measurements rely on ensemble-averaged signals that obscure dynamic interfacial processes at individual particles. Here we show an operando electrochemiluminescence (ECL) microscopy strategy that visualizes and evaluates apparent NO3RR kinetics at the single-particle level. Using Cu(111) nanosheets as a model catalyst, we convert reaction-induced optical responses into spatially resolved descriptors of nitrate adsorption and intermediate evolution. The time-dependent ECL response reveals the generation and diffusion of nitrite, a key intermediate in nitrate reduction. These descriptors provide apparent kinetic mapping, uncovering substantial kinetic heterogeneity of individual particles. Correlative imaging of intermediate diffusion demonstrates that interparticle coupling influences apparent catalytic performance by modulating intermediate accumulation and interfacial mass transport under dilute nitrate conditions. This approach provides an operando optical microscopy platform for visualizing dynamic catalytic interfaces and linking interfacial processes with apparent catalytic performance. Understanding catalytic dynamics at electrochemical interfaces is important, while reactions at individual particles remain difficult to observe. Here, the authors report an operando electrochemiluminescence microscopy approach to visualize nitrate reduction processes and monitor apparent kinetics.