Mechanistic insights into CO₂ reduction on pristine and functionalized VNbC MXenes

The advancements of CO2 reduction technologies rely critically on the design of highly efficient catalysts, with CO2 activation serving as the primary step in electrochemical reduction. The newly emerging class of two-dimensional materials, double transition metals (DTMs) MXenes, has attracted significant interest in the CO2 reduction reaction due to its unique structural and electronic properties. In this study, CO2 adsorption on pristine VNbC and functionalized VNbCTx (T = -F, -O, -OH; x = 2) (DTMs) MXenes has been investigated through density functional theory (DFT) calculations. Electronic analysis revealed that pristine as well as functionalized MXenes exhibit metallic behavior. The functionalization is found to alter the CO2 adsorption performance, with OH-functionalized MXene, VNbCTx (T = -OH; x = 2), showing the efficient performance with an adsorption energy of -3.27 eV, which results in spontaneous conversion of the CO2 molecule into a formate (HCOO−) ion. In this study, the alternative surface hydroxylation mechanism overcomes the thermodynamic barrier related to multi-step CO2 hydrogenation, by capturing hydrogen from the MXenes surface, and thereby enabling stable formation of HCOO− ion. Further, formic acid formation is observed after the co-adsorption of HCOO− and H atom on VNbC(OH)2 MXene. The CO2 activation and reduction pathways were analyzed with a detailed structural, electronic, and vibrational analysis. Therefore, our results highlighted VNbC(OH)2 MXene as a promising material and also uncovered mechanistic insights into termination-driven electronic effects, thereby providing valuable insights for advancing the rational design of advanced MXenes for CO2 transformation.