Lifespan Characterization of Oxidized Nife Catalysts for Alkaline Oxygen Evolution Reaction

Alkaline anion exchange membrane (AAEM) electrolyzers have high potential to support renewable energy systems by storing energy in the form of hydrogen. However, the sluggish kinetics of the anodic half reaction, the oxygen evolution reaction (OER), significantly hinders the efficiency of these devices. Large overpotentials of 300 mV or more are needed to overcome the slow kinetics of the OER, which diminishes the feasible efficiency of this process by tens of percent. Ultimately, these higher energy barriers translate to financial costs and limit the practicality of AEM water electrolysis.

Effective electrocatalysts can lower the overpotential for OER, but these catalysts need to be highly active, stable for thousands of hours, and inexpensive. The state-of-the-art catalysts for the OER in the current generation of electrolyzers are IrO_x and RuO_x; however, these catalysts contain precious transition metals that are prohibitively costly to deploy on a large scale. Oxidized nickel-iron based catalysts (NiFeO­_x) are promising non-precious alternatives, which have shown activity that is even higher than IrO_x in alkaline conditions. However, the long-term stability of these materials has not been adequately demonstrated to date.

We have synthesized carbon-supported NiFealloy using a facile wet-impregnation method. The alloy catalyst can then be pretreated to generate a catalytically active NiFeO_x phase. We have shown that these alloy-based NiFeO_x catalysts achieve a current density of 10 mA/cm² at approximately 280 mV of overpotential at room temperature and at 240 mV of overpotential at 70°C in alkaline aqueous solution. However, the stability of this catalyst in concentrated alkaline electrolytes is ambiguous. Moreover, we have found evidence that the catalyst displays unpredictable stability after spending up to several hundred hours in a colloidal suspension comprising carbon supported NiFeO_x, Nafion ionomer, and isopropyl alcohol. Ongoing work is focused on utilizing identical location transition electron microscopy techniques in tandem with electrochemical degradation treatments to investigate the structure and composition of the catalyst throughout its lifetime.