MXene-Based Single-Atom Catalysts for Electrochemical Reduction of CO2 to Hydrocarbon Fuels

The sustainable and cost-effective reduction of electrochemical CO2 to valuable chemicals or fuels is a promising solution to mitigate greenhouse gas emissions and energy demands. Herein, the potential of MXenes as an anchoring site for isolated transition metal (TM) atoms is explored to develop efficient single-atom catalysts (SACs) for the electrochemical CO2 reduction reaction (CO2RR). We design a series of SACs from 3d (Sc, Ti, V, Cr, Mn), 4d (Y, Zr, Nb, Mo), and 5d (Hf) transition metals, supported on an O-terminated MXene (TM@Ti2CO2) using well-defined first-principles calculations. Our results show that the TMs anchored on top of the carbon atom of Ti2CO2 (hollow-C site) exhibit the most stable configuration. The electronic calculations demonstrate a strong correlation between adsorption energy and various chemical properties such as average bond distances (d(TM-O)), Bader charge, work function, and d-electron center of the metal, suggesting that the complex interplay between the electronic and geometric properties of the adsorbing atom can serve as descriptors for determining the adsorption energy. The filling of d-orbitals influences the degree of charge transfer by creating an attractive interaction between the CO2RR intermediate species and single TM atoms with a positive charge, promoting efficient catalytic CO2 reduction through charge-induced dipole interactions. Particularly, the Ti atom anchored on Ti2CO2 exhibited the most favorable performance as a catalyst for the CO2RR, exhibiting the lowest limiting potential among the SACs examined. Moreover, most of the examined SACs showed selectivity toward the CO2RR over the hydrogen evolution reaction by comparing the changes in the Gibbs free energy of the first hydrogenation step. Our study offers valuable insights for developing MXene-based SACs for the CO2RR, paving the way for efficient electrocatalyst design in the future.