Efficient H2O2 production from urine treatment based on a self-biased WO3/TiO2-Si PVC photoanode and a WO3/CMK-3 cathode

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Urine accounts for only 1% of municipal wastewater volume but contributes 80% of nitrogen, which has become one of the challenges for existing wastewater treatment plants. Herein, we proposed a novel approach based on a self-biased WO3/TiO2-Si PVC photoanode and a WO3-modified mesoporous carbon (CMK-3) cathode (WO3/CMK-3) to produce significantly high-value chemical H2O2 from urine treatment with effective total nitrogen removal. The central idea of the design is to achieve a feasible reversal of the thermodynamic trend of O2 reduction to H2O2 from a non-spontaneous to a strongly spontaneous process by combining it with a urine treatment reaction that releases large amounts of chemical energy in the photoelectrocatalytic (PEC) system. The results indicated that the H2O2 production was boosted remarkably by urine disposal reaction (5.13 mg cm−2 h−1) with a faradaic efficiency of 72%, and the WO3/CMK-3 cathode showed 6.1 and 2.5 times higher H2O2 production activity than the common gas diffusion electrode and carbon felt electrode, respectively. Moreover, urine was degraded effectively into N2 with a total nitrogen removal of 91.4% within 120 min, and the kinetic constant of urine degradation was 0.0397 min−1, which was 15.4 times that of the blank. The results of ESR and quenching experiments demonstrated that the amine group of urine selectively and rapidly converted into N2 by Cl•. This study provides new insights into efficient urine disposal and synchronous H2O2 production.