Chemical Structure of Fe-Ni Nanoparticles for Efficient Oxygen Evolution Reaction Electrocatalysis

Bimetallic iron-nickel-based nanocatalysts are perhaps the most active for the oxygen evolution reaction (OER) in alkaline electrolytes. Recent developments in literature have suggested that the ratio of iron and nickel in Fe-Ni thin films plays an essential role in the performance and stability of the catalysts. In this work, the metallic ratio of iron to nickel was tested in alloy bimetallic nanoparticles. Similar to thin films, nanoparticles with iron-nickel atomic compositions where the atomic iron percentage is ≤50% outperformed nanoparticles with iron-nickel ratios of >50%. Nanoparticles of Fe₂₀Ni₈₀, Fe₅₀Ni₅₀, and Fe₈₀Ni₂₀ compositions were evaluated and demonstrated to have overpotentials of 313, 327, and 364 mV, respectively, at a current density of 10 mA/cm². While the Fe₂₀Ni₈₀ composition might be considered to have the best OER performance at low current densities, Fe₅₀Ni₅₀ was found to have the best current density performance at higher current densities, making this composition particularly relevant for electrolysis conditions. However, when stability was evaluated through chronoamperometry and chronopotentiometry, the Fe₈₀Ni₂₀ composition resulted in the lowest degradation rates of 2.9 μA/h and 17.2 μV/h, respectively. These results suggest that nanoparticles with higher iron and lower nickel content, such as the Fe₈₀Ni₂₀ composition, should be still taken into consideration while optimizing these bimetallic OER catalysts for overall electrocatalytic performance. Characterization by electron microscopy, diffraction, and X-ray spectroscopy provides detailed chemical and structural information on as-synthesized nanoparticle materials.