Ternary NiCoFe nanosheets for oxygen evolution in anion exchange membrane water electrolysis

Tuning nickel-based catalyst activity and understanding electrolyte and ionomer interaction for oxygen evolution reaction (OER) is crucial to improve anion exchange membrane (AEM) water electrolyzers. Herein, an investigation of multimetallic Ni_0.6Co_0.2Fe_0.2 OER activity, coupled with in-situ Raman spectroscopy to track dynamic structure changes, was carried out and compared to other Ni catalysts. The effect of KOH concentration, KOH purity, ionomer type, and electrolyte with organic cations was evaluated. The Ni_0.6Co_0.2Fe_0.2 catalyst achieved 10 mA/cm² at 260 mV overpotential with stability over 50 h and 5000 cycles in 1 M KOH. In-situ Raman spectroscopy showed that Ni_0.6Co_0.2Fe_0.2 activity originates from promoting Ni(OH)₂/NiOOH transformation at low potentials compared to bi- and mono-metallic nickel-based catalysts. Fumion anion ionomer in the catalyst inks led to a lower OER activity than catalysts with inks containing Nafion ionomer. The OER activity of Ni_0.6Co_0.2Fe_0.2 is adversely influenced in the presence of fumion anion ionomer and benzyltrimethylammonium hydroxide (BTMAOH) with possible phenyl oxidation under applied high anodic potentials. The alkaline AEM water electrolyzer circulating 1 M KOH electrolyte, with a Pt/C cathode and a Ni_0.6Co_0.2Fe_0.2 anode, achieved 1.5 A/cm² at 2 V.