Ni/Fe Fluorides (Hydroxide) Nanocomposite as Efficient OER Catalyst

The synthesis of efficient oxygen evolution reaction (OER) catalysts that markedly reduce the overpotential over an extended period is crucial for electrolytic water splitting toward hydrogen production. A kind of Ni/Fe fluoride (hydroxide) nanocomposite OER catalyst is designed and prepared by a two-step method for the first time. The nanocomposite with the optimal OER performance (Ni : Fe precursor ratio of 9 : 1) is observed to possess a nanoparticle morphology with size of about 100 nm. Each nanoparticle hosts extensive nanoregions of Ni₄OHF₇, NiFeF₅ ⋅ 2H₂O and Fe_1.9F_4.75 ⋅ 0.95H₂O phases. The optimal nanocomposite (Ni : Fe precursor ratio of 9 : 1) exhibits OER overpotential of merely 208 mV and 349 mV at 10 mA cm^-2 and 100 mA cm^-2 respectively, tafel slope of 53.1, and outstanding stability for 10 h duration at 100 mA cm^-2. The superior OER catalytic performance of the optimal nanocomposite after CV activation is mainly ascribed to the comprehensive catalytic effect of multiple Ni, Fe active sites from three phases, the smaller charge transfer resistance achieved at this particular Ni : Fe precursor ratio. The abundant resources of Ni, Fe, F elements and the superior OER properties of the Ni/Fe fluorides (hydroxide) nanocomposite, make it a good OER catalyst candidate for electrolytic water splitting toward hydrogen production.