Room-temperature sulfur doped NiMoO₄ with enhanced conductivity and catalytic activity for efficient hydrogen...

Transition metal oxides have been acknowledged for their exceptional water splitting capabilities in alkaline electrolytes, however, their catalytic activity is limited by low conductivity. The introduction of sulfur (S) into nickel molybdate (NiMoO₄) at room temperature leads to the formation of sulfur-doped NiMoO₄ (S-NiMoO₄), thereby significantly enhancing the conductivity and facilitating electron transfer in NiMoO₄. Furthermore, the introduction of S effectively modulates the electron density state of NiMoO₄ and facilitates the formation of highly active catalytic sites characterized by a significantly reduced hydrogen absorption Gibbs free energy (ΔG_H*) value of -0.09 eV. The electrocatalyst S-NiMoO₄ exhibits remarkable catalytic performance in promoting the hydrogen evolution reaction (HER), displaying a significantly reduced overpotential of 84 mV at a current density of 10 mA cm^-2 and maintaining excellent durability at 68 mA cm^-2 for 10 h (h). Furthermore, by utilizing the anodic sulfide oxidation reaction (SOR) instead of the sluggish oxygen evolution reaction (OER), the assembled electrolyzer employing S-NiMoO₄ as both the cathode and anode need merely 0.8 V to achieve 105 mA cm^-2, while simultaneously producing hydrogen gas (H₂) and S monomer. This work paves the way for improving electron transfer and activating active sites of metal oxides, thereby enhancing their HER activity.