Impact of Crystallinity and Ni–Fe Composition on the Oxygen Evolution Performance of NixFe1-xO Electrocatalysts in Anion Exchange Membrane Water Electrolysis

Expensive platinum group metals (PGMs) are used to enhance the anodic oxygen evolution reaction (OER) kinetics, and they represent a real bottleneck in the commercialization of anion exchange membrane water electrolyzers (AEMWEs). Therefore, we present a scalable and economical homogeneous precipitation method to synthesize NixFe1-xO nanoparticles with different Ni/Fe ratios, while reducing the dependence on expensive PGM-based electrocatalysts. The effects of Ni/Fe ratios in the synthesized NixFe1-xO, along with morphological and surface chemical characteristics, on electrocatalytic performance were thoroughly investigated with half-cell measurements. Furthermore, critical electrode design factors, that is, ink composition and electrocatalyst loading, were scientifically investigated and optimized. Among the explored compositions, amorphous Ni0.28Fe0.72O and crystalline Ni0.66Fe0.34O exhibited superior OER activity, achieving mean overpotentials of 359 mV and 359.1 mV at 10 mA cm−2, respectively. This superior activity was attributed to a higher concentration of Ni3+ (NiOOH), a highly active compound for OER. These high-performing samples were integrated as anodes in a lab-scale AEMWE for device-level evaluation. Ni0.28Fe0.72O achieved the highest performance at 80 °C, by delivering the current density of 7.81 A cm−2 against a cell voltage of 2.2 V. Whereas, Ni0.66Fe0.34O achieved a current density of 6.49 A cm−2 at 2.2 V. Both samples exhibited excellent stability during short-term durability tests (ca. 90 h) at 1 A cm−2 and 80°C.