Charge transfer and orbital reconstruction of non-noble transition metal single-atoms anchored on Ti2CTx-MXenes for highly selective CO2 electrochemical reduction

Inspired by MXene nanosheets and their regulation of surface functional groups, a series of Ti2C-based single-atom electrocatalysts (TM@Ti2CTx, TM = V, Cr, Mn, Fe, Co, and Ni) with two different functional groups (T = -O and -S) was designed. The CO2RR catalytic performance was studied using well-defined ab initio calculations. Our results show that the CO2 molecule can be more readily activated on TM @Ti2CO2 than the TM@Ti2CS2 surface. Bader charge analysis reveals that the Ti2CO2 substrate is involved in the adsorption reaction, and enough electrons are injected into the 2 pi *u orbital of CO2, leading to a V-shaped CO2 molecular configuration and partial negative charge distribution. The V-shaped CO2 further reduces the difficulty of the first hydrogenation reaction step. The calculated Delta G of the first hydrogenation reaction on TM@Ti2CO2 was significantly lower than that of the TM@Ti2CS2 counterpart. However, the subsequent CO2 reduction pathways show that the UL of the potential determining step on TM@Ti2CS2 is smaller than that of TM@Ti2CO2. Combining the advantages of both TM@Ti2CS2 and TM@Ti2CO2, we designed a mixed functional group surface with -O and -S to anchor TM atoms. The results show that Cr atoms anchored on the surface of mixed functional groups exhibit high catalytic activity for the selective production of CH4. This study opens an exciting new avenue for the rational design of highly selective MXene-based single-atom CO2RR electrocatalysts. (C) 2022, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published Elsevier B.V. All reserved.