The composition, structure, and dynamics of electrode-electrolyte interface have a substantial impact on the rate and energy efficiency of electrochemical reactions . A growing body of literature demonstrate the importance of multiple factors at electrochemical interfaces, such as pH , ions 2 and solvents , in the kinetics of interfacial proton-coupled electron transfer (PCET). However, the understanding of the mechanisms through which the microenvironment affects PCET remains tenuous. Although the widely used Butler-Volmer (BV) equation is instrumental in deducing reaction mechanisms and identifying rate-determining steps (RDS) , its empirical nature makes it challenging to deduce the molecular level picture of interfacial PCET processes . The Marcus-Hush-Chidsey (MHC) theory for PCET can provide molecular level insights into the electrode kinetics . However, the connections of key parameters in this theoretical framework to experimentally accessible variables are elusive, thus hampering its applications to unravel the convoluted effects of microenvironment on PCET processes.