Iron-Tuned 3D Cobalt–Phosphate Catalysts for Efficient Hydrogen and Oxygen Evolution Reactions Over a Wide pH Range

The design and synthesis of highly efficient and low-cost bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are crucial for electrochemical water splitting associated with clean and renewable energy technologies. In this study, a novel Fe-doped cobalt–phosphate nanosheet-packed 3D microsphere developed on a planar Cu substrate (FexCo3–x(PO4)2/Cu) with a tunable stoichiometry (x = 0–0.64) is fabricated using a facile one-step electrodeposition approach from a Reline-based deep eutectic solvent. The Fe-tuned integrated electrode exhibits superior HER electrocatalytic performance over a wide pH range and robust bifunctional catalytic activity for overall water splitting in alkaline media. The optimized Fe0.43Co2.57(PO4)2/Cu needs overpotentials of only 108.1, 128.8, and 291.5 mV to drive a promising current density of 100 mA cm–2 in 1.0 M KOH, 0.5 M H2SO4, and 1.0 M phosphate-buffered saline, respectively, along with outstanding durability. Moreover, the developed Fe0.43Co2.57(PO4)2/Cu can catalyze both HER and OER in 1.0 M KOH with high efficiency and robust stability over 100 h. The remarkably enhanced performance of the integrated FexCo3–x(PO4)2/Cu can be ascribed to the modification of the O active electronic property in phosphate with Fe doping, which results in optimal hydrogen adsorption on the active sites. Further, the unique 3D microsphere structure coupled with a 2D nanosheet internal architecture offers abundant catalytic interfaces with more active sites and favorable transfer kinetics. All these synergistically contribute to its superior electrochemical performance.

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