Understanding the water molecule effect in metal-free B-based electrocatalysts for electrochemical CO2 reduction

Abstract

Electrocatalytic CO₂ reduction (CO₂RR) is a feasible and economical way to eliminate CO₂via converting it into useful products. However, this process is hampered by the lack of highly active and stable catalysts. Against this backdrop, single and double boron atom-doped bismuthene catalysts (B@Bi and B₂@Bi) for the CO₂RR were designed. The nature of the CO₂ activation and reduction mechanisms on B@Bi and B₂@Bi was explored using density functional theory (DFT) and ab initio molecular dynamics simulations (AIMD). The results indicate that the most feasible product is CH₄ on B@Bi, while the C₂H₄ product is both thermodynamically and kinetically favored on B₂@Bi. Moreover, water molecules were also introduced to explore their effects on the CO₂RR performance. In an environment with 30H₂O molecules, hydrogen bonding interactions between the water molecules and the intermediate reduce the η values of CH₄ (0.25 V) on B@Bi and C₂H₄ (0.90 V) on B₂@Bi compared to those in the gas phase. The thermodynamic potential-determining step (PDS) for CH₄ synthesis changes from *OCH in the gas phase to *OCH₂ formation on B@Bi due to the number of hydrogen bonds and intermediates with different polarity. C–C coupling is still the PDS for C₂H₄ generation on B₂@Bi. The calculation of the hydrogen evolution reaction (HER) as a reaction competitive with the CO₂RR shows that B@Bi and B@Bi offer excellent selectivity in the water environment. This work provides useful insights into the development of highly efficient metal-free CO₂RR electrocatalysts and highlights the critical role of hydrogen bonding with water molecules in CO₂RR.