Fundamental aspects in CO2 electroreduction reaction and solutions from in situ vibrational spectroscopies

Using renewable energy to drive carbon dioxide reduction reaction (CO2RR) electrochemically into chemicals with high energy density is an efficient way to achieve carbon neutrality, where the effective utilization of CO2 and the storage of renewable energy are realized. The reactivity and selectivity of CO2RR depend on the structure and composition of the catalyst, applied potential, electrolyte, and pH of the solution. Besides, multiple electron and proton transfer steps are involved in CO2RR, making the reaction pathways even more complicated. In pursuit of molecular-level insights into the CO2RR processes, in situ vibrational methods including infrared, Raman and sum frequency generation spectroscopies have been deployed to monitor the dynamic evolution of catalyst structure, to identify reactive intermediates as well as to investigate the effect of local reaction environment on CO2RR performance. This review summarizes key findings from recent electrochemical vibrational spectrosopic studies of CO2RR in addressing the following issues: the CO2RR mechanisms of different pathways, the role of surface-bound CO species, the compositional and structural effects of catalysts and electrolytes on CO2RR activity and selectivity. Our perspectives on developing high sensitivity wide-frequency infrared spectroscopy, coupling different spectroelectrochemical methods and implementing operando vibrational spectroscopies to tackle the CO2RR process in pilot reactors are offered at the end.