Electronic Structure Engineering in NiFe Sulfide via A Third Metal Doping as Efficient Bifunctional OER/ORR Electrocatalyst for Rechargeable Zinc-Air Battery

Ti, V, Cr, Mn, Co, and Cu, have been investigated as a third dopant in NiFe sulfide for enhanced oxygen evolution reaction (OER)/oxygen reduction reaction (ORR). The effects of dopant on surface electronic structure, conductivity, and thermodynamic barrier of reaction are addressed and discussed. For the OER, X-ray photoelectron spectroscopy analysis shows that electron transferring from the Ni to the dopants enhances the catalytic performance of the sulfide. Cu doped NiFe sulfide exhibits the best OER performance. For the ORR, density functional theory calculation indicates that Ti, V, Mn, Co, and Cu upshift the d-band center (ɛ_d), while Cr downshifts the ɛ_d. Among the dopants, V leads to optimized electronic structure modification, giving optimized adsorption energy of *O on the Ni, the lowest rate determining step ΔG₁, and the best ORR activity. By considering E₁₀-E_1/2 together with the maximum current density of the OER and limited diffusion current density of the ORR, NiFeVS exhibits the best OER/ORR bifunctionality. The performance of NiFeVS as a cathodic catalyst has also been evaluated in a zinc air battery, demonstrating a specific capacity of 698 mAh g⁻¹, maximum power density of 190 mW cm⁻², and a superior cycle stability of 2400 cycles (400 h).