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

Abstract

Based on the synergy between MoP and N-doped carbon, MoP nanoparticles encapsulated in N-doped carbon hollow spheres were synthesized using inorganic-organic hybrids as precursors, which shows an excellent stability and activity with an overpotential 96 mV at 10 mA cm −2 and a small Tafel slope of 53 mV dec −1 in alkaline solution. • A template-free approach was developed to fabricate MoP@NC hollow microsphere. • Inorganic-organic hybrids were used as precursors. • Remarkable electrocatalytic hydrogen evolution performance could be achieved. • The synergy between MoP and the pyridinic N could optimize the electronic structure. 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-H ads bond and thereby enhance HER performance. In addition, the pyridinic N atoms at the interactive sites play a key role in adsorbing H 2 O 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 MoP-based hollow sphere electrocatalysts for alkaline HER through designing inorganic-organic hybrid precursors.