Probing Sulfur-Mediated Surface Dynamics in Oxomolybdate Nano-Rods toward Efficient Oxygen Evolution

This study offers strategic approach to enhance oxygen evolution reaction (OER) by synthesis of sulfur-doped nickel molybdate (S-NiMoO₄) using a one-pot hydrothermal approach. The optimized catalysts, featuring 10% S doping, reveals a remarkable activity with an overpotential of 289 mV at a current density of 10 mA cm^-2, with a high turnover frequency (TOF) of 0.465 s^-1 and a low charge transfer resistance (6.6 Ω). Structural and surface analysis confirm successful sulfur incorporation and subsequent surface reconstruction during OER, leading to the formation of catalytically active SO₄ ^{2 -} species. DFT calculations reveal that S doping and subsequent SO₄ ^{2 -} adsorption, shift the d-band center closer to the Fermi level, facilitating enhanced OH^- adsorption and improve M─O binding interactions critical for OER. Further, the S-NiMoO₄ improves the OER activity by modifying the electrode-electrolyte interface and promoting Ni³⁺/Ni⁴⁺ redox transitions. A volcano-type relationship between surface charge accumulation and current density establishes 10% S doping as the ideal condition for balanced electronic and catalytic properties. Excellent durability over 30 h and faradic efficiency of 92% obtained. This study demonstrates the dual function of sulfur in surface reconstruction and lattice doping, providing a viable approach for creating long-lasting and effective anion-modified electrocatalysts.