Ammonium Polyphosphate Induced Bimetallic Phosphides Nanoparticles Coated with Porous N-doped Carbon for Efficiently Electrochemical Hydrogen Evolution

Abstract Transition metal phosphides (TMPs) have increasingly become the research focus of hydrogen evolution catalysts. In this paper, bimetallic phosphide electrocatalyst (MoP/MoNiP@NC) is prepared by predesigned supramolecular gels as precursors via a simple carbonization and phosphorating process, which experience a self-assembly process of ammonium polyphosphate (APP), phosphomolybdic acid hydrate (PMo12), polyaniline (PANI) and Ni2+ ions via electrostatic and coordination interaction during heating in aqueous solutions. Ammonium polyphosphate as a new phosphorus source with non-toxicity and non-corrosive gas is reported for the first time and exhibits strong coordination ability with metal ions and polyoxometalate. MoP/MoNiP@NC displays satisfactory hydrogen evolution activity with low overpotentials of 94 and 137 mV at 10 mA cm-2 as well as excellent durability for 24 h in 1.0 M KOH and 0.5 M H2SO4, respectively. It is worth noted that the hydrogen evolution performance of the electrocatalyst is superior to the commercial Pt/C at a current density > 80 mA cm-2 under alkaline solution. The remarkable HER activity can be attributed to the synergistic effect of MoNiP and MoP nanoparticles, N-doped porous carbon layers protecting the nanoparticles from corrosion, exposing large amount of active sites and enhancing the mass transfer process. Density functional theory (DFT) calculations illustrate that the best active sites come from the negative P sites of MoNiP nanoparticles. This work provides an environment friendly and reproducible strategy for using APP as a green phosphorus source to synthesize transition metal phosphides as efficient electrocatalysts for energy conversion.