Charge-orbital synergistic engineering of TM@Ti 3 C 2 O 1- x B x for highly selective CO 2 electrochemical reduction.

Inspired by MXene nanosheets and their regulation of surface functional groups, a series of Ti 3 C 2 -MXene-based single TM atom electrocatalysts with a doped boron (B) atom (TM@Ti 3 C 2 O 2- x B x , TM is V, Cr, Mn, Fe, Co or Ni, x = 0.11) are proposed for achieving a high performance catalytic CO 2 reduction reaction (CO 2 RR). The results reveal that the doped B atom involves in the adsorption reaction of CO 2 molecules and CO intermediates in the CO 2 RR. The TM-to-C and B-to-C π-back bonding contribute to the activation of the CO 2 molecules and CO intermediates in the CO 2 RR. Enough electrons from the single TM atom and B atom occupied orbitals can be injected into the CO 2 molecules and *CO intermediates through direct bonding interactions, which effectively alleviates the difficulty of the first hydrogenation reaction step and further helps CO reduction towards CH 4 . The calculated values of Δ G for the first hydrogenation reaction and the formation of *CHO on Ti 3 C 2 O 2- x B x are significantly smaller than those of other single-atom catalysts (SACs). Fe@Ti 3 C 2 O 2- x B x is found to have the highest electrocatalytic activity with a limiting potential of ∼0.40 V and exhibits a high selectivity for obtaining CH 4 through the CO 2 RR compared with the hydrogen evolution reaction. This work is expected to open a research path for engineering the charge-orbital state of the innate atoms of a substrate based on mechanistic insights, which guides the rational design of highly selective MXene-based CO 2 RR electrocatalysts.