Enhancing hydrogen production capability from urine-containing sewage through optimization of urea oxidation pathways

Abstract

The electrochemical urea oxidation reaction (UOR) represents a promising route to sustainable hydrogen production and reuse of urea-containing sewage. However, the efficiency of UOR is hindered by the dehydrogenation of intermediate *CONH2NH and the conversion of toxic intermediate the *CO. Herein, we report a robust strategy to elevate UOR performance by introducing iron (Fe) atoms into the Ni3S2@NiSe2 heterojunctions (denoted Fe-Ni3S2@NiSe2). The Fe-Ni3S2@NiSe2 exhibits remarkable selectivity and electrocatalytic activity towards UOR, attributed to its reconstruction into Fe-NiOOH species during UOR process, as confirmed by in-situ Raman technology. Utilizing Fe-Ni3S2@NiSe2 as both the cathode and anode in a single-chamber electrolytic cell, the hydrogen production rate reaches 588.4 μmol h−1 in simulated urea-containing sewage and 432.1 μmol h−1 in actual human urine, respectively. Notably, in both scenarios, no oxygen product is detected, and the hydrogen production efficiency surpasses that of traditional water splitting by 5.8-fold and 4.3-fold, respectively. In-situ infrared spectroscopy study reveals that the UOR process involves the cleavage of C-N bond and the generation of CO2. Density functional theory calculations further signifies that the incorporation of Fe facilitates the dehydrogenation of *CONH2NH intermediates, strengthens the d-p hybridization, and weakens O-H bonds, thereby resulting in reduced energy barriers for UOR. Our strategy holds promise for efficient hydrogen production from sewage via UOR, offering potential implications for wastewater treatment and clean energy generation.