Trends in competing oxygen and chlorine evolution reactions over MXenes

This study employs density functional theory (DFT) calculations combined with descriptor-based analysis to evaluate the catalytic activity and selectivity of MXenes for the chlorine evolution reaction (CER) and the oxygen evolution reaction (OER). Simulations are conducted using the Perdew–Burke–Ernzerhof (PBE) functional with D3 dispersion corrections, as implemented in the Vienna Ab initio Simulation Package (VASP). Structural relaxations and vibrational frequency analyses are performed to compute adsorption free energies. Electrochemical conditions are modeled using the computational hydrogen electrode (CHE) approach, enabling accurate assessment of reaction energetics and selectivity trends under anodic polarization. The results reveal that pristine MXenes exhibit low catalytic activity toward CER. However, under anodic conditions, electrochemical oxidation of MXenes leads to the formation of single-atom catalysts (SACs) featuring isolated metal atoms with one- or two-branched active site geometries. These SAC configurations significantly enhance the selectivity and efficiency of MXenes for CER. Among the materials screened, group V-based MXenes—namely V2X, Nb2X, and Ta2X—emerge as especially promising candidates, offering cost-effective, platinum-group-metal-free (PGM-free) alternatives for industrial-scale applications. This work advances the field of sustainable catalysis by demonstrating the potential of MXenes as electrochemically tunable SACs. The findings provide a framework for designing low-cost, selective electrocatalysts for CER, with implications for industrial electrolysis, water treatment, and green chemical production.