Understanding the Roles of Hydroxide in CO2 Electroreduction on a Cu Electrode for Achieving Variable Selectivity

Hydroxide-derived copper (OH/Cu) electrodes exhibit excellent performance for the electrocatalytic CO2 reduction reaction (CO2RR). However, the role of hydroxide (OH) in CO2RR remains controversial; therefore, the origin of the selectivity enhancement emerging on OH/Cu has not been fully understood. In the present work, we quantitatively evaluated surface OH by electroadsorption and established a direct correlation between the OH amount and selectivity for the production of CH4 and C2+ on OH/Cu with the help of computational investigations concerning work functions of the surface. Based on these findings, we demonstrated variable selectivity using OH/Cu electrodes having a controlled OH amount; three OH/Cu electrodes realized their distinct selectivity such as Faradic efficiency (FE) for the production of CH4 (CH4 FE) of 78%, C2+ FE of 71%, and the ratio of C2+-to-CH4 >355. The proposed simple strategy for selectivity control would contribute to further quantity synthesis of value-added chemicals using CO2RR.