Single-Crystal Nitrogen-Rich Two-Dimensional Mo5N6 Nanosheets for Efficient and Stable Seawater Splitting.

Transition metal nitrides (TMNs) have great potential for energy-related electrocatalysis because of their inherent electronic properties. However, incorporating nitrogen into a transition metal lattice is thermodynamically unfavorable, and therefore most of the developed TMNs are deficient in nitrogen. Consequently, these TMNs exhibit poor structural stability and unsatisfactory performance for electrocatalytic applications. In this work, we design and synthesize an atomically thin nitrogen-rich nanosheets, Mo5N6, with the help of a Ni-inducing growth method. The as-prepared single-crystal electrocatalyst with abundant metal-nitrogen electroactive sites displays outstanding activity for the hydrogen evolution reaction (HER) in a wide range of electrolytes (pH 0-14). Further, the two-dimensional Mo5N6 nanosheets exhibit high HER activity and stability in natural seawater that are superior to other TMNs and even the Pt benchmark. By combining synchrotron-based spectroscopy and the calculations of electron density of state, we find that the enhanced properties of these nitrogen-rich Mo5N6 nanosheets originates from its Pt-like electronic structure and the high valence state of its Mo atoms.