Charge-orbital synergistic engineering of TM@Ti₃C₂O_1-B for highly selective CO₂ electrochemical reduction

Inspired by MXene nanosheets and their regulation of surface functional groups, a series of Ti₃C₂-MXene-based single TM atom electrocatalysts with a doped boron (B) atom (TM@Ti₃C₂O_2-B, TM is V, Cr, Mn, Fe, Co or Ni, x = 0.11) are proposed for achieving a high performance catalytic CO₂ reduction reaction (CO₂RR). The results reveal that the doped B atom involves in the adsorption reaction of CO₂ molecules and CO intermediates in the CO₂RR. The TM-to-C and B-to-C π-back bonding contribute to the activation of the CO₂ molecules and CO intermediates in the CO₂RR. Enough electrons from the single TM atom and B atom occupied orbitals can be injected into the CO₂ 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 CH₄. The calculated values of ΔG for the first hydrogenation reaction and the formation of *CHO on Ti₃C₂O_2-B are significantly smaller than those of other single-atom catalysts (SACs). Fe@Ti₃C₂O_2-B is found to have the highest electrocatalytic activity with a limiting potential of ∼0.40 V and exhibits a high selectivity for obtaining CH₄ through the CO₂RR 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 CO₂RR electrocatalysts.