Mechanistic insight into hydration-enhanced electrochemical CO2 reduction on Ru single-atom catalysts: A computational investigation

Using density functional theory (DFT) calculations, we investigated the electrocatalytic reduction of CO2 on Ru-doped graphene (Ru/G3C) and its nitrogen-coordinated counterpart (Ru/G3N). We found that nitrogen doping significantly enhances CO2 adsorption energy by 0.695 eV. To account for water production under experimental conditions, we analyzed both catalysts with saturated water coverage (3H(2)O@Ru/G3C and 3H(2)O@Ru/G3N) and examined CO2 reduction pathways involving COOH* and HCOO* intermediates to identify the potential determining step (PDS). Under pristine conditions, CO2 conversion to CH4 predominantly follows the HCOO* pathway, with a limiting potential (U-L) of -0.263 V for the PDS of HCOOH to H2COOH. When water is saturated (3H(2)O@Ru/G3C), formic acid formation becomes favorable at low potentials, with a U-L of -0.862 eV for the HCOOH to H2COOH step, ultimately leading to methanol or methane at higher reducing potentials. For Ru/G3N, CH4 formation via either the HCOO* or COOH* pathway requires a higher reducing potential (similar to 1 eV), making CO generation the dominant product at lower potentials. Water saturation (3H(2)O@Ru/ G3N) lowers the PDS for CH4 formation to 0.338 eV but still results in CO as the primary product at low potentials, with methanol and methane emerging as possible products at higher potentials. Overall, Ru/G3N is more suited for CO production, with potential for multi-product formation under water-rich conditions.