Advancing sustainable hydrogen production: Urea-assisted alkaline water electrolyzer with circular nickel catalysts

In this work, we report a circular-economy approach to hydrogen production through the integration in an anion exchange membrane water electrolyzer (AEMWE) a nickel-based electrocatalyst prepared through circular recovery methods and hybridizing the electrolysis using urea oxidation. Ni(OH)2 and NiO electrocatalysts are recovered from nickel-plating wastewater via a scalable hydrothermal synthesis. Urea, a common environmental pollutant, replaces the oxygen evolution reaction (OER) with urea oxidation, thereby reducing the overall energy demand. Hydrogen production using these circular catalysts and urea achieves performance comparable to benchmark nickel anodes at industrially relevant current densities, with a cell potential reduction of up to 0.25 V relative to OER. Gas chromatography, ion chromatography, and differential electrochemical mass spectrometry (DEMS) analyses identify N2 and NO2− as the main nitrogen-containing products. Carbon adsorption species leads to partial deactivation during prolonged operation; however, the activity can be readily restored by polarity reversal or electrolyte switching. Finally, life cycle assessment (LCA) confirms that coupling urea oxidation with recycled nickel catalysts significantly lowers the CO2-equivalent footprint of hydrogen production, demonstrating the effectiveness of this circular and energy-efficient approach.