Effect of Explicit Water Molecules on the Electrochemical Hydrogenation of CO2 on Sn(112)

Abstract

Water is typically treated as an implicit solvent in modeling electrochemical reactions in an aqueous environment. Such treatment may not be adequate, as a series of concerted or sequential proton-electron transfer steps that explicitly involve water molecules are likely to play important roles in a reaction, such as the electrochemical hydrogenation of CO2. Herein, we use the electrochemical hydrogenation of CO2 on the Sn(112) surface as a model, and employ the density functional theory (DFT) method to examine the effect of up to 12 explicit water molecules on the stability of the hydrogenation intermediates. Our results show that six water molecules are needed to account for the local interaction between an intermediate and the water solvent. Furthermore, the hydrogen bonding interaction between the explicit water molecules and intermediates causes a significant stabilization to the O-containing intermediates, such as the HCOO* and CHO* + OH* species. The inclusion of explicit water molecules also altered the prediction of the potential-limiting step from the formation of H* atoms without the explicit water molecules to the formation of H2COO* in the presence of water molecules and increased selectivity towards methane. This work provides useful insights into the electrocatalytic hydrogenation of CO2, emphasizing the importance of including explicit water molecules to account for the hydrogen bonding interaction between solvent water molecules and the reaction intermediates.

Perspectives on Advancing Sustainable CO2 Conversion Processes: Trinomial Technology, Environment, and Economy

“…Although the continuum model provides a computationally cheap method to describe the systems, , it usually ignores directional interaction such as hydrogen bonding , and lateral interactions of adsorbate–slab , and electrolyte–adsorbate. , Microsolvation models for the case of CO 2 reduction with careful assessment of solvent–adsorbate interactions have showed higher accuracy compared to implicit solvation, while maintaining computationally cheap calculations . For the explicit solvent model, all the possible interactions are accurately described, yet large simulation cells and long-time simulation should be used to avoid sampling issues, making it computationally expensive; the pace at which computational resources are evolving allows the use of these methods as reliable tools to quantify the solvent effect. , …”

“…296 For the explicit solvent model, all the possible interactions are accurately described, yet large simulation cells and long-time simulation should be used to avoid sampling issues, making it computationally expensive; the pace at which computational resources are evolving allows the use of these methods as reliable tools to quantify the solvent effect. 297,298 Kinetic Mechanism. The information on the reaction kinetics is also crucial for the optimization of existing processes and the discovery of new catalytic materials.…”