Effect of Ammonium-Based Cations on CO<sub>2</sub> Electroreduction
Kaige Shi, Duy Le, Theodoros Panagiotakopoulos, Talat S. Rahman, Xiaofeng Feng
Abstract
Electrolyte cations play a critical role in the electrochemical CO 2 reduction reaction (CO 2 RR), as indicated by recent studies using alkali metal cations. Here, we show that nonmetal cations such as ammonium-based cations can have a profound effect on the CO 2 adsorption characteristics and CO 2 RR activity that may supersede those of metal cations. Our ab initio calculations based on the grand canonical density functional theory find that both NH 4 + and CH 3 NH 3 + help bind CO 2 to a Bi electrode more strongly than Na + and track this difference to the electrostatic interaction between the cations and adsorbed *CO 2, which depends on the characteristics of the charge distribution and hydration shell of the cations. Our experimental studies confirm the strong promotional effect of the nonmetal cations, particularly CH 3 NH 3 +, on the CO 2 RR and further reveal a significant impact of the cation identity and concentration on CO production activity but a minor one on formate. The cation-stabilized CO 2 adsorption is essential for CO production but not necessary for formate production.