Stabilization of CO₂ adsorption on Bi(111) electrode in electrochemical environment using non-metallic cations: A first principles study.

Adsorption and stabilization of CO₂ on electrodes are the initial processes in electroreduction of CO₂. Metal cations are found to be critical for these processes. In the present work, we study the effect of non-metallic cations NH₄⁺ and NH₃CH₃⁺ on the adsorption and stabilization of CO₂ on Bi(111) electrode using density functional theory calculations in which the number of electrons in the system is adjustable for maintaining constant electrode potential, i.e., it’s work function. We find that in the absence of the cations, CO₂ physisorbs on the electrode with work function of 2.63 eV or higher, while it chemisorbs at a lower work function forming metastable conformations. In the presence of NH₄⁺ or NH₃CH₃⁺, chemisorption of CO₂ on Bi(111) is found to occur at a work function lower than 3.23 eV. However, it again forms a metastable configuration unless the work function is lower than 2.63 eV, at which point the actual binding energy of CO₂ on Bi(111) is negative indicating a stable adsorption configuration. Furthermore, we establish that CO₂ binds to Bi(111) only via the C atom. Ab initio molecular dynamics simulations confirm the stability of the adsorption of CO₂ on Bi(111) in the presence of the above non-metallic cations. These results suggest that besides metallic cations, non-metallic cation can be used for stabilizing the CO₂ adsorption on the electrode.