Electrodeposited Porous Nickel-Copper as a Non-Noble Metal Catalyst for Urea-Assisted Anion Exchange Membrane Electrolysis for Hydrogen Production

Replacing the oxygen evolution reaction with other less energy-intense oxidizing reactions is an attractive option to reduce the energy demand for hydrogen production in an anion exchange membrane (AEM) water electrolyzer using transition metals and their alloys. Since urea is commonly available as a waste product, pairing the urea oxidation at the anode with hydrogen evolution at the cathode in alkaline electrolysis can alleviate environmental issues while simultaneously producing hydrogen. In this respect, we prepared nickel-copper films on nickel felt substrate as a urea oxidation catalyst, which exhibited a lower Tafel slope compared to oxygen evolution, indicating a more favorable reaction pathway. Confirming the improvement, in an AEM electrolyzer, a current density of 50 mA cm(-2) required a cell voltage of 1.60 V for urea coupled hydrogen production compared to 1.83 V for water oxidation. Nitrogen and carbon dioxide were identified using mass spectrometry (MS) as the main gaseous products during urea electrolysis. A relatively stable zero-gap AEM urea electrolyzer operation at room temperature for over 120 h and at 323.15 K under intermittent power conditions, using nickel-copper catalyst as anode and nickel-molybdenum catalyst as cathode, was demonstrated. Finally, an efficient hydrogen production in the zero-gap alkaline urea electrolyzer at a lower voltage than for water electrolysis was proven using online MS analysis. These results validate the feasibility of reducing the specific energy consumption of electrolyzers used for low-carbon hydrogen production with renewable energy sources.