Understanding of strain effect on Mo-based MXenes for electrocatalytic CO2 reduction

Strain engineering is a powerful approach to tuning the electrocatalytic properties, but the systematic understanding of the strain effect in electrochemical reduction of carbon dioxide (CO2RR) is still lacking. Here, we have extensively investigated the impact of strain on the catalytic selectivity and activity of Mo-based MXenes towards CO2RR. Our calculations suggest that strain can effectively tune the CO2 activation and reduction processes on MXenes, endowing great potential to obtain enhanced electrocatalytic performance. Notably, the activated CO2 can be selectively reduced to methane (CH4) on all electrocatalysts, which is conducive to restricting the production of HCOOH, H2CO, CH3OH and H2 (HER). Then, we highlight that compressive strains can reduce the limiting potential (UL) of CO2RR on Mo2C and Mo3C2 from -0.68 and -0.66 V to -0.49 and -0.38 V at the strain of -4%@Mo2C and -6%@Mo3C2, respectively, which are superior to benchmark Cu (211) (-0.67 V). Further mechanism analysis illuminates that the strain can significantly modify the d-band center of MXene, which endows the selective modulation of the adsorption strength of OCH2O* and HOCH2O* to achieve promoted catalytic activity. Our results provide an in-depth understanding of the strain effect and rational design principles for enhanced electrocatalytic CO2RR.