Interface Engineering of CoS₂/Co(OH)F Heterostructures for In Situ Co⁴⁺ Formation and Enhanced Oxygen Evolution...

The directional reconstruction into high-valent active species is critical for enhancing the oxygen evolution reaction (OER) kinetics and, consequently, the overall efficiency of water electrolysis for green hydrogen production. Here, we introduce the interfacial engineering of Co(OH)F nanosheets anchoring with CoS₂ particles (CoS₂/Co(OH)F) to promote the in situ formation of Co⁴⁺ species, achieving high OER performance. Remarkably, the optimized CoS₂/Co(OH)F-2.5 catalyst demonstrates a low overpotential of 318 mV at 100 mA cm^-2 with a small Tafel slope of 73.4 mV dec^-1 in 1.0 M KOH, outperforming commercial RuO₂ and most reported Co-based electrocatalysts. Combined experimental and theoretical analyses reveal that the heterointerface between lattice-distorted CoS₂ and Co(OH)F, along with their optimal synergistic effect, promotes dynamic reconstruction into high-valent Co⁴⁺ active species. These species favor the lattice oxygen oxidation mechanism, thereby significantly enhancing OER kinetics. Moreover, the optimized catalyst achieves low cell voltages of 1.77 and 1.93 V at industrial current densities of 500 and 1000 mA cm^-2 (80 °C) in an anion exchange membrane (AEM) water electrolyzer, with good stability exceeding 140 h. This work offers a viable strategy for developing noble-metal-free electrocatalysts for efficient water electrolysis.