(658g) Electrocatalytic Oxygen Evolution over Amorphous Ni-Fe Nanoparticles in Alkaline Electrolyte

Electrocatalytic oxygen evolution reaction (OER) plays the key role in efficient and stable platform for many promising renewable energy conversion and storage devices, such as water electrolyzers, solar water-splitting cells, and lithium-air batteries. The OER at the anode often couples with electrochemical or photoelectrochemical CO₂ reduction and H₂ evolution reactions at the cathode for the above devices, however, limits the performance of the entire system because of its sluggish kinetics, insufficient reaction sites or low stability catalysts (even noble metals). Different transition metal catalysts have been systematically investigated in order to increase the activity of OER catalysts and to improve the performance of energy conversion and storage systems. Ni-Fe system is found to be one of the most promising bimetallic catalytic systems with more robust stability, lower cost and higher activity than the IrO₂, the well-known best OER catalyst. Herein, we report 4 nm Ni−Fe nanoparticles (Ni_yFe_1−yO_x/C) featuring amorphous structures prepared via a solution-phase nanocapsule method as 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 also 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. These supported amorphous Ni−Fe nanoparticles may potentially be applicable in the (photo)electrochemical cells for water splitting to make H₂ fuel or CO₂ reduction to produce usable fuels and chemicals.