Double Transition Metal Carbides MXenes (D-MXenes) as Promising Electrocatalysts for Hydrogen Reduction Reaction: Ab Initio Calculations

[Image: see text] Double-transition-metal MXenes (D-MXenes) have been widely pursued in the advancement of the renewable energy storage technology in recent years. In this work, the hydrogen evolution reaction (HER) catalytic mechanism of several oxygen-terminated D-MXenes with the chemical formula of M′(2)M″C(2)O(2) (M′ = Mo, Cr; M″ = Ti, V, Nb, Ta) is theoretically studied. For comparison, the corresponding monometallic MXenes (M-MXenes, M′(3)C(2)O(2)) are fairly compared by means of the density functional theory calculations. Based on our theoretical results, the HER performance of M-MXenes can be improved by constructing a “sandwich-like” ordered D-MXene configuration. Moreover, the HER performance of Mo-based D-MXenes (Mo(2)M″C(2)O(2)) is superior to that of Cr-based D-MXenes (Cr(2)M″C(2)O(2)), which highlights that the HER activity of Mo(2)VC(2)O(2) and Mo(2)NbC(2)O(2) is better than that of Pt(111). This work not only unravels the HER mechanism of D-MXenes (M′(2)M″C(2)O(2)) but also paves the way in designing emergent MXene-based HER electrocatalysts with high efficiency.