Hierarchical ultrafine nanosheet-based O-doped FeCoS2 microsphere catalyst for highly efficient oxygen evolution reaction

Developing highly efficient, stable and non-noble metal-based electrocatalysts for the oxygen evolution reaction (OER) remains a great challenge so far. Here, we report a hierarchical ultrafine nanosheet-based O-doped FeCoS₂ microsphere catalyst (O–FeCoS₂), which exhibits a high OER performance with a low overpotential of 277 mV at 10 mA cm⁻², and a small Tafel slope of 35.7 mV dec⁻¹ in alkaline media. OER catalytic mechanism demonstrates that the introduction of O in FeCoS₂ can promote the oxidize and dissolve of S atom to form SO₃²⁻ and SO₄²⁻ species, accelerating the generation of layered FeCo (oxy)hydroxide (FeCoOOH) true active species on the surface of FeCoS₂; The formed SO₃²⁻ and SO₄²⁻ can adsorb on the FeCoOOH surface, modifying the electronic structure of FeCoOOH to promote the conversion process of the RDS step (∗OH to ∗O), improving the OER process. Together with the well central void space of the hierarchical ultrafine nanosheet-based microsphere structure, the reaction kinetics and charge exchange capacity at the catalyst-electrolyte interface were also improved, and thus the O–FeCoS₂ catalyst finally displays an outstanding OER performance. This work provides a promising insight into understanding the OER enhancement mechanism of FeCo-based sulfide electrocatalyst systems and supports an attractive strategy to explore other low-cost but efficient OER catalysts.