Free-standing phosphorous-doped molybdenum nitride in 3D carbon nanosheet towards hydrogen evolution at all pH values

Highly efficient electrocatalysts towards hydrogen evolution reaction (HER) with large current density at all-pH values are critical for the sustainable hydrogen production. Herein, we report a free-standing HER electrode, phosphorous-doped molybdenum nitride nanoparticles embedded in 3-dimentional carbon nanosheet matrix (P-Mo₂N-CNS) fabricated via one-step carbonization and in-situ formation. The as-prepared catalyst shows free-standing architecture with interconnected porous microstructure. P-doped Mo₂N nanoparticles with an average diameter of 4.4 nm are well embedded in the 3-dimentional vertical carbon nanosheets matrix. Remarkable electrocatalytic HER performance is observed in alkaline, neutral and acidic media at large current densities. The overpotential of P-Mo₂N-CNS to drive a current density of 100 mA cm⁻² in 0.5 M H₂SO₄ and 1.0 M PBS is only 181 and 221 mV, respectively. In particular, the current density reaches up to 1000 mA cm⁻² at a low overpotential of 256 mV in 1.0 M KOH, much better than that of the commercial Pt/C catalyst. Density functional theory calculations suggest the optimized H sorption kinetics on Mo₂N after P doping, elucidating the superior activity.