Mechanistic insight into electrochemical CO 2 reduction on Mo single-atom catalyst and its hydrate: A computational study

By using density functional theory calculation, we investigated the CO 2 reduction to CH 4 on molybdenum -doped graphene (Mo@Gra) and identified two major paths from the HCOO* and COOH* intermediates with different onset potential. Both HCOO* and COOH* would continent hydrogenating to CH 4 by an eight proton -electron coupling transfer process via HCOO path and COOH path. By the HCOO path, the formation of HCOO* is exergonic and the potential determining step (PDS) is OH* to H 2 O* by an endergonic process of 0.70 eV. On the other hand, the formation of COOH* from CO 2 * is endergonic with the same PDS and a limiting potential (U L ) of -0.70 V. In addition, nitrogen coordinated Mo-graphene (Mo@3N-Gra) also illustrated for CO 2 reduction and the corresponding U L is found to be -1.88 V. In addition, we also explore the mechanisms of CO 2 reduction on the water pre -adsorption surface for realistic experiments. The U L required to overcome was reduced to -0.25 V for 3H 2 O*Mo@Gra with three H 2 O co -adsorption environment, suggesting the catalytic performance can be enhanced by water promotion effect. Two structures of hydrated structures, 2H 2 O*OH*Mo@3N-Gra and 3H 2 O*Mo@3N-Gra, were selected for stimulate realistic experiments. Compared to the Mo@3N-Gra catalyst, the U L reduces to -0.48 and -0.70 V for 2H 2 O*OH*Mo@3N-Gra and 3H 2 O*Mo@3N-Gra, respectively. Although, MoN doped graphene has better CO 2 capture ability and selectivity, it needs more onset potential to produce CH 4 . Our calculations demonstrated that the electrocatalytic performance can be enhanced by the hydration effect.