Template-free fabrication of MoP nanoparticles encapsulated in N-doped hollow carbon spheres for efficient alkaline hydrogen evolution

Encapsulating transition metal phosphides into nitrogen-doped carbon (NC) materials is an effective strategy to enhance the electrocatalytic performance. Herein, we develop a novel template-free approach to rationally fabricate molybdenum phosphide (MoP) nanoparticles encapsulated in N-doped carbon (MoP@NC) hollow microspheres for alkaline hydrogen evolution reaction (HER) by employing inorganic-organic hybrids as precursors, in which phosphorus source of the MoP@NC derives from tetra (hydroxymethyl) phosphorus chloride for the first time. The optimized MoP@NC sample shows a low overpotential of 96 mV at 10 mA cm-2, a small Tafel slope of 53 mV dec? 1, and excellent stability. The enhanced HER performance is mainly attributed to the integrated effects of a distinctive hollow structure, high pyridinic N-doping level, and the extremely intimate synergy between MoP and NC. Theoretical calculations indicate that the active sites of the catalyst are mainly located at Mo atoms adjacent to the pyridinic N-doped carbon layer (pyridinic-N-MoP); the synergistic interaction between MoP and pyridinic N (rather than pyrrolic or graphitic N) atoms can lower the d band center of Mo, weaken the Mo-Hads bond and thereby enhance HER performance. In addition, the pyridinic N atoms at the interactive sites play a key role in adsorbing H2O and preventing the adsorption of OH*, resulting in accelerating the water splitting. This work provides a new method to rationally synthesize high-efficient and stable MoPbased hollow sphere electrocatalysts for alkaline HER through designing inorganic-organic hybrid precursors.

Automated summary

Encapsulating transition metal phosphides into nitrogen-doped carbon materials is an effective strategy to enhance electrocatalytic performance. The synthesized MoP@NC hollow microspheres show excellent performance in alkaline hydrogen evolution reaction, attributed to their distinctive structure, high nitrogen-doping level, and synergistic effect between MoP and NC. Theoretical calculations suggest that the active sites of the catalyst mainly lie at Mo atoms adjacent to pyridinic N-doped carbon layer, and the interaction between MoP and pyridinic N atoms contributes to the enhanced HER performance.