Tuning interfacial proton transfer for directing oxygen reduction reaction toward hydrogen peroxide

Proton transfer at the electrified interface plays a pivotal role in proton-coupled electron transfer (PCET) reactions. However, tuning the interfacial proton transfer through the electrolyte remains a largely unexplored yet effective approach for boosting the electrochemical performance. Here, we demonstrate that the chelation strength of chelating molecules can serve as a criterion for selecting alkaline electrolyte additives to direct the oxygen reduction reaction (ORR) toward hydrogen peroxide (H2O2) electrosynthesis. We reveal that chelating molecules enter the solvation shell of cations, disrupting the long-range connectivity of hydrogen-bond networks by forming rigid near-range hydrogen bonds. The hydrogen-bond networks serve as a channel for proton transfer through hopping. This reshaped hydrogen-bond networks slow down the proton transfer process. Subsequently, ethylenediaminetetraacetic acid (EDTA), with its high chelation strength, finely regulates proton availability at the electrified interface. This modulation effectively decelerates the 4e−-involved PCET kinetics, steering the ORR towards the 2e− pathway of a lower energy barrier. As a result, EDTA-containing electrolytes achieve significantly higher H2O2 selectivity and Faradaic efficiency than other systems. This work underscores the importance of the interfacial hydrogen-bond networks in electrochemical reaction kinetics and could guide the design of electrolytes for various electrochemical reactions.