Sulfur-Doped\nNickel Phosphide Nanoplates Arrays: A\nMonolithic Electrocatalyst for Efficient Hydrogen Evolution Reactions

Abstract

Searching\nfor cost-efficient electrocatalysts with high catalytic\nactivity and stability for hydrogen generation by means of water electrolysis\nwould make a great improvement on energy technologies field. Herein,\nwe report high-performance hydrogen evolution reaction (HER) electrocatalysts\nbased on sulfur-doped Ni₅P₄ nanoplate arrays\ngrown on carbon paper (S–Ni₅P₄ NPA/CP).\nThis ternary, robust, monolithic S–Ni₅P₄ NPA/CP exhibits remarkable performance for the HER compared to nickel\nphosphide and nickel sulfide catalysts. The S–Ni₅P₄ NPA/CP with ∼6% S presents the most promising\nbehavior for water electrolysis applications. Specifically, it shows\nan onset potential of 6 mV, needing overpotentials (η) of 56\nand 104 mV to attain current densities of 10 and 100 mA cm^–2 with a Tafel slope of 43.6 mV dec^–1. The turnover\nfrequency of 6% S–Ni₅P₄ NPA/CP is about\n0.11 s^–1 at overpotential of 100 mV, which is ca.\n10 and 40 times that of Ni₅P₄ NPA/CP and NiS₂ NPA/CP, respectively. It also shows remarkable stability\nand durability in 0.5 M H₂SO₄ solution. The\nresults indicate that S and P tune the electronic properties mutually\nand produce an active catalyst phase for the HER. Furthermore, the\ndensity functional theory calculations show that S–Ni₅P₄ NPA/CP exhibits only 0.04 eV of hydrogen adsorption\nfree energy­(Δ<i>G</i>_H^*), which is more suitable than Pt (∼−0.09\neV). We propose that the S-doping not only restrains the surface oxidation\nand dissolution of S–Ni₅P₄ NPA/CP in\nacid solution but also reduces the Δ<i>G</i>_H^*. We believe that\nour work will provide a new strategy to design transition metal phosphide\ncomposite materials for practical applications in catalysis and energy\nfields.