NiCu mixed metal oxide catalyst for alkaline hydrogen evolution in anion exchange membrane water electrolysis

Highlights: • Tailored NiCu oxidation state leads to an exceptional hydrogen evolution reaction (HER) performance. • HER depends on KOH concentration with higher HER activity at higher concentrations. • NiCu MMO HER depends on the type of ionomer and ionomer to catalyst ratio. • Using Ir black as an anode, NiCu MMO cathode achieves AEM electrolyzer performance of 1.85 A/cm² at 2 V in 1 M at 50 °C. -- Abstract: We report on the optimization of nickel-copper catalysts for superior performance as a cathode catalyst in anion exchange membrane (AEM) water electrolysis. The bifunctional system of NiCu mixed metal oxide (MMO) nanosheets includes Ni metallic, NiO, and CuO oxides provide rapid kinetics for the hydrogen-evolution reaction (HER) of the Volmer step. In-situ Raman spectroscopy for NiCu MMO proved that nickel hydroxide was sustained under HER conditions for at least 30,000 s, which may explain why the exceptional activity of NiCu MMO as compared to other nickel-copper catalysts is maintained over time. The activity of the NiCu MMO for the HER activity in alkaline electrolytes increased as KOH concentration raised from 0.1 M to 1 M. The NiCu MMO nanosheets showed superior stability under alkaline HER conditions for 30 h. The use of Nafion ionomer in the ink resulted in a higher HER current density as compared to inks with a Fumion anion ionomer. The maximum HER performance was achieved at a Nafion ionomer to catalyst weight ratio of 0.5. Using Ir black as the anode, the NiCu MMO cathode gave an AEM electrolyzer performance of 1.85 A/cm² at 2 V in 1 M KOH at 50 °C. The NiCu MMO catalyst developed here delivers AEM performance comparable to PEM water electrolysis.