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 CO 2 on Ru-doped graphene (Ru/G3C) and its nitrogen-coordinated counterpart (Ru/G3N). We found that nitrogen doping significantly enhances CO 2 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 CO 2 reduction pathways involving COOH* and HCOO* intermediates to identify the potential determining step (PDS). Under pristine conditions, CO 2 conversion to CH 4 predominantly follows the HCOO* pathway, with a limiting potential (U L ) of –0.263 V for the PDS of HCOOH to H 2 COOH. 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 H 2 COOH step, ultimately leading to methanol or methane at higher reducing potentials. For Ru/G3N, CH 4 formation via either the HCOO* or COOH* pathway requires a higher reducing potential (∼1 eV), making CO generation the dominant product at lower potentials. Water saturation (3H 2 O@Ru/ G3N) lowers the PDS for CH 4 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.