Ammonium Cation-Promoted CO<sub>2</sub> Electroreduction on Au in Acidic Media
Kaige Shi, John Janisch, Zhuanghe Ren, Zhen Meng, Deborah Israel, Duy Le, William E. Kaden, Talat S. Rahman, Xiaofeng Feng
Abstract
The electrochemical reduction of CO 2 in acidic media has received considerable attention, as it can mitigate the carbonate formation issue. However, the available protons in acidic media can boost the hydrogen evolution reaction (HER), so alkali metal cations are generally employed to promote the CO 2 reduction reaction (CO 2 RR) while suppressing the HER. Here we report that NH 4 + cations are more effective promoters of CO 2 electrolysis on Au in acidic media than Na + and K +, achieving a 3-fold improvement in the CO 2 RR activity. The promotional effect of NH 4 + cations is mainly attributed to their enhanced electrostatic stabilization of the CO 2 adsorption, which is the rate-limiting step for the CO 2 RR on Au. An estimation of the local pH under relevant conditions indicates that NH 4 + can mitigate the interfacial pH swing during the CO 2 RR compared to Na + and K + . Further studies on Au nanocatalysts of varying sizes indicate that the cation effect is independent of the catalytic sites. Our work advances the understanding of the cation effect on CO 2 RR using nonmetal cations and demonstrates a viable cation strategy to enhance CO 2 electrolysis.