Controlled synthesis of Mo-doped Ni3S2 nano-rods: an efficient and stable electro-catalyst for water splitting

Abstract

Fabrication of stable, efficient, and inexpensive bifunctional electro-catalysts for water splitting has become increasingly attractive. Herein, for the first time, the direct growth of Mo-doped Ni₃S₂ on Ni foams using sodium molybdate as the Mo source at different temperatures is demonstrated. Effects of temperature on the morphology and water splitting performance of Mo-doped Ni₃S₂ were discussed in detail. It is found that the atomic stoichiometric ratios of Mo and Ni can be controlled by the adjusting of reaction temperature, while the obtained electro-catalysts demonstrate various morphologies, capacitances and chemisorption free energies of hydrogen, which lead to different current densities and hydrogen evolution efficiencies. The electro-catalyst synthesized at 200 °C (200-SMN/NF) demonstrates the best regular morphology and electrochemical properties. When employed in oxygen evolution reactions, 200-SMN/NF demonstrates a low over-potential of 180 mV at 100 mA cm⁻². Adapting it as a bifunctional electro-catalyst, a current density of 10 mA cm⁻² at a very low cell voltage of 1.53 V and cycling lifespan of more than 15 h was delivered. Further results indicated elevated hydrogen evolution reaction activity, consisting of a moderate 278 mV over-potential at a 100 mA cm⁻² hydrogen production current density, a small 72.9 mV dec⁻¹ Tafel slope, and a superior current density compared to that of precious catalyst Pt/C (40%) after −0.53 V. These results underscore the fact that 200-SMN/NF is a high-performance, precious-metal-free electro-catalyst, and provide the foundation for exciting opportunities in water splitting applications.