Coupling NiCoS and CoFeS Frame/Cagelike Hybrid as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Engineering earth-rich, high-efficiency, and nonprecious electrocatalysts is an essential demand for water electrolysis to obtain clean and sustainable fuels. In this research, novel hybrid electrocatalysts based on coupling a hierarchical porous NiCo-mixed metal sulfide with a nanosheet structure (denoted as NiCoS) and a novel three-dimensional (3D) mesoporous open-cage/framelike structure of CoFeS are designed for oxygen evolution reaction (OER). In this regard, the single-step synthesis of a cobalt iron Prussian blue analog (CoFe PBA) frame/cagelike structure was performed without any etching step. Following a comparative study, CoFe PBA precursors were converted and doped with S, Se, and P vapors (CoFeS, CoFeSe, and CoFeP) by annealing the precursors with sulfur, selenium, and sodium hypophosphite powders, respectively. The electrochemical measurements demonstrated that CoFe doped with S and Se almost have similar performances for OER and are better than the P-doped one. In the last step, NiCoS nanosheet arrays were electrodeposited as a shell layer on CoFe (S, Se, and P) to examine their effect on the catalytic activity toward OER, and CoFeS@NiCoS showed better catalytic activity than CoFeSe@NiCoS and CoFeP@NiCoS. It can show the lowest overpotential of 293 mV at a current density of 100 mA cm–2 with a Tafel slope of 40.6 mV dec–1 and has pre-eminent long-range catalytic durability in 1.0 M KOH. This performance was comparable to those of noble-metal-free and commercial RuO2 catalysts. Its excellent electrocatalytic activity benefits from the frame/cagelike and nanosheet structures and good synergistic effects between multiple hybrid components (Ni, Co, Fe, and S), which leads to producing highly exposed active sites and accelerating mass and electron transport. This study represents an efficient approach to rationally design and synthesize three-dimensional porous architecture catalysts based on transition metals as highly efficient nonprecious electrocatalysts for the energy-pertinent reaction.