Unraveling the rate-limiting step of two-electron transfer electrochemical reduction of carbon dioxide

Electroreduction of CO2 is heavily investigated but its reaction mechanism needs to be further explored. Here, the authors investigate pH dependency and kinetic isotope effect with respect to the rate expression of CO2 electroreduction to gain further insights into the rate-limiting step. Electrochemical reduction of CO2 (CO2ER) has received significant attention due to its potential to sustainably produce valuable fuels and chemicals. However, the reaction mechanism is still not well understood. One vital debate is whether the rate-limiting step (RLS) is dominated by the availability of protons, the conversion of water molecules, or the adsorption of CO2. This paper describes insights into the RLS by investigating pH dependency and kinetic isotope effect with respect to the rate expression of CO2ER. Focusing on electrocatalysts geared towards two-electron transfer reactions, we find the generation rates of CO and formate to be invariant with either pH or deuteration of the electrolyte over Au, Ag, Sn, and In. We elucidate the RLS of two-electron transfer CO2ER to be the adsorption of CO2 onto the surface of electrocatalysts. We expect this finding to provide guidance for improving CO2ER activity through the enhancement of the CO2 adsorption processes by strategies such as surface modification of catalysts as well as careful control of pressure and interfacial electric field within reactors.

Automated summary

By investigating the pH dependency and kinetic isotope effect of CO2 electroreduction, the authors reveal that the rate-limiting step of CO2ER is mainly the adsorption of CO2. This finding is expected to provide guidance for improving CO2ER activity through strategies such as surface modification of catalysts and precise control of pressure and interfacial electric field within reactors.