Electrocatalytic Oxygen Evolution over Nano Scaled Amorphous Ni−Fe Particles in Alkaline Electrolyte

Electrocatalytic water oxidation plays the key role as efficient and stable platform in some of the promising renewable energy conversion and storage devices, such as water electrolyzers, solar water-splitting cells, and lithium-air batteries. The electrocatalytic oxygen evolution reaction (OER) at the anode often couples with electron or photoelectron CO₂ reductionand, H₂ evolution reactions at the cathode for the above devices but limits the performance of the entire system because of the sluggish OER kinetics, insufficient reaction sites, or low stability of precious metal catalysts. Series of different transition metallic catalysts were investigated in order to significantly increase the activity of OER catalysts and efficiently improve the performance of energy conversion and storage systems. Ni-Fe system is found to be the most promising bimetallic catalytic system with robust stability, much lower cost, and considerably higher activity than the IrO₂, the well-known best OER catalyst. Nano scaled catalysts with high electrochemical surface area (ECSA) not only exhibits a promising feasibility to effectively increase the performance of OER catalysts, but also to be simply utilized in renewable energy conversion and storage devices Herein, we reported 4 nm Ni−Fe nanoparticles (Ni_yFe_1−yO_x/C) featuring amorphous structures prepared via a solution-phase nanocapsule method for active and durable OER electrocatalysts in alkaline electrolyte. The Ni−Fe nanoparticle catalyst containing 31% Fe (Ni_0.69Fe_0.31O_x/C) shows the highest activity, exhibiting a 280 mV overpotential at 10 mA cm⁻² (equivalent to 10% efficiency of solar-to-fuel conversion) and a Tafel slope of 30 mV dec⁻¹ in 1.0 M KOH solution. The achieved OER activity outperforms NiO_x/C and commercial Ir/ C catalysts and is close to the highest performance of crystalline Ni−Fe thin films reported in the literature. In addition, a Faradaic efficiency of 97% measured on Ni_0.69Fe_0.31Ox/C suggests that carbon support corrosion and further oxidation of nanoparticle catalysts are negligible during the electrocatalytic OER tests. Ni_0.69Fe_0.31O_x/C further demonstrates high stability as there is no apparent OER activity loss (based on a chronoamperometry test) or particle aggregation (based on TEM image observation) after a 6 h anodization test. The high efficiency and durability make these supported amorphous Ni−Fe nanoparticles potentially applicable in the (photo)electrochemical cells for water splitting to make H₂ fuel or CO₂ reduction to produce usable fuels and chemicals.