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

Abstract

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.

Nickel-Iron Alloy Nanoparticle Characteristics Pre- and Post-Reaction With Orange G

“…This peak position indicates either an alpha or gamma hydroxide species [44]- [47]. The Fe2p 1/2 peak at 724 eV is present for Ni4Fe10 and Ni5Fe10 as-synthesized samples, indicating the presence of iron oxide and iron hydroxide species [44], [48]. The Fe2p 3/2 and Fe2p 1/2 peaks are similar for NiFe alloy nanoparticles found in literature for the treatment of azo dyes [8], [41].…”

“…4 shows detailed scans of the Ni 2p binding energy region of each of the ratios before and after reaction with Orange G. Each ratio has four distinct peaks at 855.4 eV, 861.3 eV, 873.1 eV, and 879.6 eV for the as-synthesized samples. The Ni2p 3/2 peak at 855.4 eV indicates the presence of nickel hydroxide, and the Ni2p 1/2 peak at 873.1 eV indicates the presence of nickel oxide [44], [51]. The Ni2p 3/2 and Ni2p 1/2 peaks are similar for NiFe alloy nanoparticles found in literature for the treatment of azo dyes [8].…”

“…Fig. 3g and 3h show a small shoulder at 707 eV, which is indicative of Fe metal [44], [49]. As Ni content decreases from Ni3.5 to Ni1, the Fe metal shoulder is no longer present.…”

“…The Fe2p 3/2 peak is observed in each of the as- synthesized samples (black line) and occurs at the peak position of 711.3 to 711.8 eV range. This peak position indicates either an alpha or gamma hydroxide species [44]- [47]. The Fe2p 1/2 peak at 724 eV is present for Ni4Fe10 and Ni5Fe10 as-synthesized samples, indicating the presence of iron oxide and iron hydroxide species [44], [48].…”

Cosynergistic Molybdate Oxo‐Anionic Modification of FeNi‐Based Electrocatalysts for Efficient Oxygen Evolution Reaction

“…Iron is known to modulate NiOOH phase under alkaline OER. [25,36] However, the dynamic stabilization of Ni in FeNi(MoO 4 ) x @NF is due to the cosynergy of molybdate oxoanions that provide instantly active and highly stable active sites (Figure S31, Supporting Information). The stabilization of Ni redox in Fe(MoO 4 ) x @NF (arisen from NF) renders a moderate potential window after 250 continuous CV cycles, between those of FeNi(MoO 4 ) x @NF (with no shift) and FeNi@NF (with the most shift) (Figure S32, Supporting Information).…”