Breaking the linear scaling relations in MXene catalysts for efficient CO2 reduction

Electrocatalytic carbon dioxide reduction reaction (CO2RR) toward value-added fuels has attracted increasing attention in carbon-neutral and energy-production fields, but the catalytic efficiency is seriously hindered by the robust linear scaling relations between adsorption energies of intermediates. Herein, we have extensively investigated the effect of a series of group ⅣB, ⅤB, and ⅥB transition metal (TM) atoms substitution for middle Mo in Mo3C2 MXene on the catalytic performance of CO2RR. Our results suggest that the captured CO2 can be selectively reduced to methane (CH4) on both Mo3C2 and Mo2TMC2 bimetal MXenes. We highlight that TM substitution can significantly reduce the limiting potential (UL) of CO2RR from −0.651 V (Mo3C2) to −0.350 V (Mo2TiC2) by decreasing the Gibbs energy difference of rate-determining step (OCH2O* + H++e-= HOCH2O*). The modulation mechanism is illuminated that TM substitution in Mo3C2 MXene gives rise to the upshift of d-band center of Mo atoms, which selectively tunes the adsorption strength of OCH2O* and HOCH2O*, resulting in breaking their linear scaling relations. Further analyses on electron localization function (ELF) visualize the TM substitution induced stronger surface localization lone electrons, which endows the surface Mo with promoted chemical activity. The dynamical stability of Mo2TiC2 has been well verified by phonon dispersion curves and ab initio molecular dynamics (AIMD) simulations, suggesting the robust stability of Mo2TiC2 as an electrocatalyst for CO2RR. Our findings pave the way of MXenes for CO2 capture and pioneer the application of Mo2TiC2 as a novel and efficient catalyst for CO2 to CH4.