A titanium carbide (Ti3 C2 Tx ) MXene is employed as an efficient solid support to host a nitrogen (N) and sulfur (S) coordinated ruthenium single atom (RuSA ) catalyst, which displays superior activity toward the hydrogen evolution reaction (HER). X-ray absorption fine structure spectroscopy and aberration corrected scanning transmission electron microscopy reveal the atomic dispersion of Ru on the Ti3 C2 Tx MXene support and the successful coordination of RuSA with the N and S species on the Ti3 C2 Tx MXene. The resultant RuSA -N-S-Ti3 C2 Tx catalyst exhibits a low overpotential of 76 mV to achieve the current density of 10 mA cm-2 . Furthermore, it is shown that integrating the RuSA -N-S-Ti3 C2 Tx catalyst on n+ np+ -Si photocathode enables photoelectrochemical hydrogen production with exceptionally high photocurrent density of 37.6 mA cm-2 that is higher than the reported precious Pt and other noble metals catalysts coupled to Si photocathodes. Density functional theory calculations suggest that RuSA coordinated with N and S sites on the Ti3 C2 Tx MXene support is the origin of this enhanced HER activity. This work would extend the possibility of using the MXene family as a solid support for the rational design of various single atom catalysts.

Heteroatom‐Mediated Interactions between Ruthenium Single Atoms and an MXene Support for Efficient Hydrogen Evolution