Theoretical regulating the T-site composition of Janus MXenes achieving efficient bifunctional ORR/OER catalysts

The development of metal-air batteries relies heavily on efficient bifunctional catalysts for oxygen reduction/ evolution reactions (ORR/OER). Herein, we employ first-principles calculations to investigate the structureactivity relationship between the composition of terminal atoms and the catalytic activity of Pt-doped V_Cl-Ti₂CO_2-xCl_x single-atom catalysts (SACs). Firstly, the results demonstrate clear linear correlations between the composition and the work function, interlayer average transfer charges (Δq), and the integrated crystal orbital Hamilton population (ICOHP) of the Pt-O bond that adsorbs OH. Besides, the difference in the average transferred charge between the Ti and the C layers (Δq_5–3) and the ICOHP of Pt-O bond adsorbing OH can be used as effective descriptors of bifunctional performance of Pt-doped V_Cl-Ti₂CO_2-xCl_x. Furthermore, the bonding and charge transfer between the active site Pt and adsorbed intermediate OH are elucidated, revealing the bridging role of d_xz and d_z2 orbitals of Pt during the activation process. Based on the above understanding, we reported a catalyst of Pt-V_Cl-Ti₂CO_0.22Cl_1.78 with a low bifunctional overpotential (η^Bi = 1.00 V), effectively reducing the overpotential of Pt-doped Ti₂CO₂. This study extensively investigates the impact of terminal composition control on the ORR/OER activity, providing robust support for the design of highly active Janus MXene-based SACs. © 2024 Elsevier Ltd.