Urine electrooxidation for energy–saving hydrogen generation

Abstract

Urea electrooxidation offers a cost-effective alternative to water oxidation for energy-saving hydrogen production. However, its practical application is limited by expensive urea reactants and sluggish reaction kinetics. Here, we present an efficient urine electrolysis system for hydrogen production, using cost-free urine as feedstock. Our system leverages a discovered Cl-mediated urea oxidation mechanism on Pt catalysts, where adsorbed Cl directly couple with urea to form N-chlorourea intermediates, which are then converted into N2 via intermolecular N–N coupling. This rapid mediated-oxidation process notably improves the activity and stability of urine electrolysis while avoiding Cl-induced corrosion, enabling over 200 hours of operation at reduced voltages. Accordingly, a notable reduction in the electricity consumption is achieved during urine electrolysis (4.05 kWh Nm−3) at 300 mA cm−2 in practical electrolyser for hydrogen production, outperforming the traditional urea (5.62 kWh Nm−3) and water (4.70–5.00 kWh Nm−3) electrolysis. Urea electrooxidation offers an energy-saving route for hydrogen production but faces challenges from costly reactants and slow kinetics. Here, the authors introduce a chlorine-mediated electrolysis system using natural urine as feedstock, achieving enhanced and cost-effective hydrogen production.