Single-Source Assisted Synthesis of Spin-Regulated Cobalt/Nickel Co-Doped Pyrite FeS₂: Enhanced Spin Channels in Co-Ni-Fe Oxyhydroxides for Efficient Alkaline Oxygen Evolution Reaction

Controlling spin states in earth-abundant electrocatalysts is substantial for enhancing the oxygen evolution reaction (OER). However, managing spin in pyrite-type disulfides remains challenging. In this study, a spin-tuned Co/Ni-FeS₂ is synthesized via pyrolysis of molecular metal-thiolate complexes in a sulfur-rich, inert environment. This approach enables precise dopant control, atomic-scale uniformity, and scalable production that surpasses those of traditional hydrothermal or sulfidation methods, offering a versatile platform for designing multi-metal pyrites. Structural and spectroscopic analyses confirm the successful substitution of iron by cobalt and nickel, demonstrating that co-doping modifies spin and electronic states. This results in increased spin polarization, improved electron transport, and lower energy barriers for oxygen-oxygen bond formation. In situ X-ray absorption spectroscopy and post-catalytic examinations reveal controlled reconstruction into mixed-metal oxyhydroxides containing high-valence iron, cobalt, and nickel as active centers. The optimized 6% Co, 2% Ni-FeS₂ shows excellent OER performance, with an overpotential of 193 mV at 10 mA cm⁻², a Tafel slope of 55 mV dec⁻¹, and high durability. Density functional theory suggests that co-doping enhances spin-selective pathways and adsorption energetics, providing a solid foundation for spin-regulated pyrite electrocatalysts in water splitting and other clean energy applications.