Mn-Incorporated High-Entropy Quaternary Sulfide CoNiFeMnS for Efficient Electrocatalytic Oxygen Evolution Reaction

Abstract

Electrochemical water splitting is promising for sustainable hydrogen production but limited by sluggish oxygen evolution reaction (OER) kinetics. Noble-metal catalysts (e.g., RuO₂, IrO₂) are benchmarks but suffer from high cost and poor durability, prompting the search for noble-metal-free alternatives. Quaternary high-entropy sulfides (HESs) are attractive due to their structural stability, tunable electronics, and abundant active sites. The Mn-doped CoNiFeMnS HES is fabricated via a facile two-step coprecipitation-solvothermal strategy using a CoNiFeMn high-entropy metal–organic framework (HEMOF) precursor. Characterizations confirm uniform Mn doping into the face-centered cubic (fcc) structure, forming a micropolygonal morphology that enhances active site exposure. Mn doping modulates electronic structure via electron redistribution among Co, Fe, and Ni, generating high-activity Ni centers. Electrochemical tests show CoNiFeMnS outperforms Mn-free CoNiFeS, with OER overpotential reduced from 301 mV to 208 mV at 10 mA cm⁻², accompanied by a low Tafel slope (65.19 mV dec⁻¹), enhanced double-layer capacitance (12.15 mF cm⁻²), reduced charge-transfer resistance (141.1 Ω), and excellent 80 h stability. This work provides a scalable route for Mn-doped HESs and clarifies Mn’s regulatory role in OER optimization, guiding the design of high-performance noble-metal-free OER catalysts.