Solar driven hydrogen releasing from urea and human urine

Abstract

Urea has been considered as a potential hydrogen source, while the conventional methods to extract hydrogen from urea are typically energy intensive processes. Here we report the first demonstration of solar driven hydrogen releasing from urea and human urine in a photoelectrochemical cell, with the assistance of Ni(OH)₂ modified metal oxide photoelectrodes (e.g., TiO₂ and α-Fe₂O₃). Ni(OH)₂ serves as a urea oxidation catalyst. Under light illumination, photoexcited holes generated at the metal oxide electrode oxidize urea, while photoexcited electrons reduce water to produce hydrogen gas at the Pt counter electrode. Urea oxidation was achieved under a small external bias or even at zero bias. Significantly, we observed continuous and stable hydrogen evolution at the Pt electrode in both urea and human urine electrolyte solutions under AM 1.5G (100 mW cm⁻²) light illumination. This work presents a safe, low energy cost, environmentally friendly and sustainable method to produce hydrogen, and simultaneously treat urine.