Title : Visible-light-driven CO2 conversion on group-10 metal–supported janus MXene with enhanced solar-to-hydrogen efficiency
Abstract:
Water splitting and CO2 conversion through photocatalysis offer sustainable routes to generate green energy and valuable hydrocarbons. Our previous DFT studies [1,2] identified Janus-functionalized MXenes M2COT (M = Sc, Zr, Hf; T = S/Se) as promising photocatalysts, with Sc2COS showing visible-light activity. Its asymmetric charge distribution creates an intrinsic electric field that optimizes band alignment for water splitting, achieving up to 4% solar-to-hydrogen efficiency under strain. Sc2COS can drive both hydrogen evolution and CO2 reduction to CH4, with analyses of its electronic and catalytic properties confirming spontaneous CO2 reduction under photoexcitation [3]. Despite its promising photocatalytic behavior, Sc2COS faces challenges such as a large band gap, low STH efficiency, and poor CO2 activation, leading only to weak physisorption and requiring impractically high pressures for full conversion. To address this, we introduced group-10 transition metal adatoms (Ni, Pd, Pt) on the Sc2COS surface, creating active sites to enhance its catalytic reactivity. These group-10 transition metals act as single-atom catalysts (SACs) when anchored on the Sc2COS surface, serving as electron-trapping centers that promote charge transfer from photogenerated carriers. The presence of Ni, Pd, or Pt enables strong CO2 adsorption and activation by inducing bending in the otherwise linear CO2 molecule. The incorporation of these atoms also introduces defect states above the Fermi level, effectively forming a new conduction band while maintaining the semiconducting nature of the system. As a result, the band gap of pristine Sc2COS (2.57 eV) is significantly reduced to 1.89 eV for Ni@Sc2COS, 1.77 eV for Pd@Sc2COS, and 1.25 eV for Pt@Sc2COS, thereby enhancing visible-light absorption and photocatalytic performance. Importantly, the intrinsic internal electric field between the two asymmetrical surfaces of Sc2COS remains unaffected by the metal decoration. This field continues to facilitate favorable band-edge alignment with respect to the oxidation potential (1.23 eV vs. NHE), hydrogen reduction potential (0 eV vs. NHE), and CO2 reduction potentials at pH = 5. The reduced band gaps contribute to a marked increase in STH efficiency across all systems. Moreover, the introduction of transition metal adatoms renders the CO2 reduction reaction (CO2 RR) more exothermic along all feasible reaction pathways, significantly lowering the limiting potential. Under moderate conditions (1 atm and elevated temperature), CO2 adsorption and CH4 desorption occur readily. All three systems exhibit strong CO2 RR selectivity over the competing hydrogen evolution reaction (HER). The low limiting potentials and overpotentials observed indicate that Ni-, Pd-, and Pt-decorated Sc2COS surfaces possess high catalytic efficiency and hold great promise for enhanced CO2 conversion and renewable fuel generation.
