Intrinsic dipole engineering for enhanced hydrogen evolution of 2D Janus MXenes

Harnessing intrinsic properties to modulate the electronic structure of two-dimensional (2D) materials is essential for clean energy conversion, but challenging. Herein, we demonstrate that tuning intrinsic dipole is an effective strategy to enhance hydrogen evolution reaction (HER) activity of 2D Janus MXenes, which is exemplified by Mo2C_XY (X/Y = O, F, S, H, OH), using density functional theory calculations. Particularly, Mo2C_OF exhibits four intrinsic dipoles (μS↑, μM↑, μL↑, and μ↓), each characterized by distinct magnitudes and/or directions originated from the Mo3+ displacement and its phase change. We propose a single-atom dipole moment to elucidate the underlying mechanism controlling the variation of intrinsic dipole moments in Janus monolayer MXenes. It is found that intrinsic dipole significantly influences the HER activity. Specifically, the adsorption energy of H is reduced when the dipole direction points toward the adsorbed intermediate. Among them, Mo2C_OOH has the Gibbs free energy of −0.04 eV, surpassing the catalytic performance of commercial Pt. Furthermore, we demonstrate that intrinsic dipoles can be tuned via external strain or electronic doping, providing a pathway for optimizing catalytic performance.