Mechanistic Insights into the Abrupt Change of Electrolyte in CO2 Electroreduction

The electrolyte plays a crucial role in the performance of the electrocatalytic reduction of CO2. However, significant changes in ionic species and concentration of electrolyte may take place over CO2 electrolysis, and these changes are usually disregarded in the evaluation of the catalytic performance. In this work, we rigorously analyzed the changes of the commonly used electrolytes over CO2 electrolysis with different ion-selective membranes and elucidated the detailed mechanism of the changes in electrolytes. For most conditions in both H-type cell and gas diffusion electrode-type flow cell, the composition and concentration as well as pH of electrolyte could experience a rapid variation over electrolysis. The changes of electrolytes are linked to several reasons: (i) the OH– generation by cathodic reaction and H+ generation by water oxidation, (ii) neutralization reaction for different ionic species, as well as (iii) the ionic species transfer via membranes. In addition, we demonstrated that the cathodic potential applied on electrocatalysts as well as the catalytic selectivity could be misestimated without considering the electrolyte changes during the CO2 reduction.