Electrochemical conversion of CO2 to formic acid on TiVC MXenes: A computational prediction

MXenes are a rapidly growing family of two-dimensional (2D) nanomaterials distinguished by their remarkable catalytic activity and large surface area. TiVC is a recently synthesized M2C-type MXene composed of titanium, vanadium, and carbon atoms. In this study, we have investigated CO2 adsorption and activation on pristine and surface-functionalized (O, Cl, F, S, and OH) configurations of ordered TiVC (O-TiVC) and solid solutions (S-TiVC). Our study reveals that both O-TiVC and S-TiVC MXenes effectively activate CO2 for its catalytic conversion, with maximum adsorption energies of -363.3 kJ/mol and -296.5 kJ/mol, respectively. Additionally, both configurations are found to dissociate the CO2 molecule spontaneously upon contact. After functionalization of TiVC (by -O, -Cl, -F, and -S), the strong chemisorption of CO2 turns into weak physisorption, whereas -OH functionalization of both O-TiVC and S-TiVC MXenes results in the conversion of the CO2 molecule into a formate (HCOO-) ion intermediate. Furthermore, the co-adsorption of this formed HCOO- and an H atom led to formic acid (HCOOH) formation on both -OH functionalized O-TiVC and S-TiVC surfaces. Thus, in our study, we found that the formation of HCOOH at the surface of -OH functionalized TiVC MXene efficiently bypasses the major thermodynamic barrier associated with multi-step CO2 hydrogenation steps.