Activation of defective nickel molybdate nanowires for enhanced alkaline electrochemical hydrogen evolution

Abstract

Designing highly-efficient and cost-effective electrocatalysts for the hydrogen evolution reaction (HER) in an alkaline solution is more complex and sluggish than for an acidic one. Herein, we report a controllable N-doping strategy to synthesize a series of N-doped porous metallic NiMoO₄ nanowires with concomitant oxygen vacancy defects (N-V_o-NiMoO₄ NWs) for promoting the alkaline HER ability and durability. Both experimental and theoretical results demonstrate that the doped-N at NiO₆ octahedral sites and the abundant oxygen vacancy defects confined in N-V_o-NiMoO₄ NWs with modified electronic arrangement could enhance the metallic conductivity, affect the surface areas, and lower the adsorption energy of hydrogen, resulting in an increased HER property. However, the excess doped-N leads to an opposite effect due to the reduced valence state of Ni centres. Therefore, alkaline HER ability of N-V_o-NiMoO₄ NWs exhibits a volcano-like trend vs. the nitrogen content, with N3-V_o-NiMoO₄ NWs being the best one. As a result, the N3-V_o-NiMoO₄ NWs show nearly zero onset overpotential, an overpotential of 55 mV at 10 mA cm⁻², and a Tafel slope of only 38 mV dec⁻¹ in 1.0 M KOH, which are superior to those of state-of-the-art platinum-free electrocatalysts.