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CoP 3 is a promising electrocatalyst for the hydrogen evolution reaction, however it is still challenging for CoP 3 -based catalyst to deliver excellent activities in a wide pH range. In this work, the self-standing Ni-doped CoP 3 nanowire arrays (Ni-CoP 3 NWs) on carbon fiber paper were synthesized by hydrothermal method followed with an in situ phosphating process. The results show that the Ni doping effectively boosts the electrocatalytic hydrogen evolution for CoP 3 NWs over the wide pH range with good stability. The Ni doped CoP 3 NWs sample with the Ni: Co mole ratio of 10% (Ni-CoP 3 -10%) shows a low overpotential of 66 mV to afford the current density of 10 mA cm−2 in 0.5 M H 2 SO 4 , which is the optimal catalytic performance in this work. Furthermore, Ni-CoP 3 -10% sample also shows excellent electrocatalytic performance in alkaline and neutral conditions, which needs the overpotential of 114 and 131 mV to afford the current density of 10 mA cm−2 in 1 M KOH and 1 M PBS, respectively. The enhanced electrocatalytic activity can be ascribed to that the Ni doping improves the electron transport, increases the electrochemical active surface area and optimizes the Gibbs free energy of hydrogen adsorption for the CoP 3 NWs, which develops it as a promising electrochemical catalyst for hydrogen evolution. • Ni doped CoP 3 nanowire arrays are prepared by vacuum encapsulation technique. • Ni doping boosts the HER activity for CoP 3 in wide pH media. • The reasons of the enhanced HER performance for Ni doped CoP 3 is revealed. [ABSTRACT FROM AUTHOR]

• Ammonium polyphosphate as a green phosphorus source is reported for the first time; • The supramolecular precursor is self-assembly by coordination and electrostatic interactions; • MoP/MoNiP@NC exhibits remarkable and stable HER performance; • Density functional theory (DFT) calculation assigns negative P sites as best active sites. 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 (PMo 12), 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 H 2 SO 4 , respectively. It is worth noted that the hydrogen evolution performance of the electrocatalyst is superior to the commercial Pt/C at a current density greater than 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. [ABSTRACT FROM AUTHOR]