Metal-organic framework-derived CoS2@FeS2 heterostructure with synergistic electronic modulation for oxygen evolution...

The rational design of earth-abundant, high-performance electrocatalysts for the oxygen evolution reaction (OER) is pivotal to advancing green hydrogen production. Herein, we report a CoS2@FeS2 heterostructure synthesized via a one-step sulfidation of a nitro-functionalized Co-based metal-organic framework (Co-MOF-NO2) precursor, which serves simultaneously as a structural template and a source of Co, N, and C. The resulting composite features intimately contacted CoS₂/FeS₂ heterointerfaces, a hierarchically porous architecture, and an in situ formed N,S co-doped carbon matrix. The optimized CoS2@FeS2 electrocatalyst delivers an exceptionally low overpotential of only 239 mV at 10 mA cm^-2, a small Tafel slope of 65.4 mV dec^-1, and a drastically reduced charge transfer resistance of 0.434 Ω in 1.0 M KOH, significantly outperforming single-component CoS₂ and the majority of previously reported Co/Fe-based sulfide catalysts. Long-term chronopotentiometry confirms negligible potential decay over 50 h of continuous operation. In situ Raman spectroscopy reveals that Co sites undergo selective surface reconstruction to form the true active CoOOH phase, while Fe acts as an electronic modulator that optimizes the adsorption energetics of oxygenated intermediates without self-reconstruction. Post-OER characterization further demonstrates a unique crystalline-FeS₂-core/amorphous-CoOOH-shell architecture that underpins the outstanding durability. This work not only establishes a straightforward MOF-derived strategy for fabricating bimetallic sulfide heterostructures, but also provides deep mechanistic insight into the distinct roles of Co and Fe, offering valuable guidance for the design of efficient and stable non-precious-metal OER catalysts.