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