Mechanistic Insights into CO ₂ Reduction on Half-Metallic Oxygen-Vacant 2D-Janus TiCrCO ₂ MXene Surface

Artificial photosynthesis is a promising strategy to address environmental and energy challenges. However, its practical realization remains limited due to complex reaction pathways and insufficient molecular-level understanding. Recently developed 2D MXenes have emerged as attractive materials owing to their exceptional properties and have shown significant potential as catalysts and co-catalysts for CO 2 reduction. In this work, we systematically investigate the photocatalytic efficiency of oxygen-vacancy-engineered two-dimensional (2D) TiCrCO 2 Janus MXene (TiCrCO 2 (O v )) for CO 2 reduction employing spin-polarized density functional theory calculations. The TiCrCO 2 (O v ) system exhibits intrinsic half-metallicity, enabling spin-selective charge transport and efficient carrier separation. Hybrid HSE06 calculations reveal a suitable band gap (1.52 eV) and favorable band-edge alignment (CBM: −3.74 eV; VBM: −5.26 eV vs vacuum), providing sufficient driving force for both CO 2 reduction and water oxidation. Strong optical absorption spanning the UV−visible region further supports its photocatalytic potential. Electronic structure analyses reveal strong Ti- d −CO 2 - p hybridization and stabilization of key intermediates through significant charge transfer. To understand the catalytic selectivity, both hydrogenation and de-oxygenation pathways were explored. Reaction pathway analysis demonstrates a favorable hydrogenation route toward HCOOH formation with a low energy barrier of 0.96 eV, identifying it as the dominant product. The high energy barrier for other reduction products like CO, HCHO, CH 3 OH, and CH 4 indicates the selectivity of the selected catalysts towards HCOOH production. This study provides a mechanistic insight into the design of a catalyst for efficient and selective CO 2 reduction, and the potential application of 2D Janus MXene materials further.