Metallic Ni₃N nanosheets with exposed active surface sites for efficient hydrogen evolution

Atomically thin metallic Ni₃N nanosheets fabricated as the hydrogen evolution cathode exhibit remarkable HER activity close to that of a commercial Pt/C electrode. The Ni atoms accompanied by surrounding N atoms on the N–Ni surface demonstrate a small ΔGH* of 0.065 eV due to the Ni–N co-effect, and thus act as the most active HER sites.