In Situ Transformed CoOOH@Co₃S₄ Heterostructured Catalyst for Highly Efficient Catalytic OER Application

The deprived electrochemical kinetics of the oxygen evolution reaction (OER) catalyst is the prime bottleneck and remains the major obstacle in the water electrolysis processes. Herein, a facile hydrothermal technique was implemented to form a freestanding polyhedron-like Co₃O₄ on the microporous architecture of Ni foam, its reaction kinetics enhanced through sulfide counterpart transformation in the presence of Na₂S, and their catalytic OER performances comparatively investigated in 1 M KOH medium. The formed Co₃S₄ catalyst shows outstanding catalytic OER activity at a current density of 100 mA cm^-2 by achieving a relatively low overpotential of 292 mV compared to the pure Co₃O₄ catalyst and the commercial IrO₂ catalyst. This enhancement results from the improved active centers and conductivity, which boost the intrinsic reaction kinetics. Further, the optimized Co₃S₄ catalyst exhibits admirable prolonged durability up to 72 h at varied current rates with insignificant selectivity decay. The energy dispersive X-ray spectroscopy (EDX) and Raman spectra measured after the prolonged OER stability test reveal a partial transformation of the active catalyst into an oxyhydroxide phase (i.e., CoOOH@Co₃S₄), which acts as an active catalyst phase during the electrolysis process.