In past decades, the intensification of human activities has led to an increase in pollution and energy demand. Photoelectrochemical systems have emerged as an alternative for the decentralized management of domestic wastewater with the potential of recovering energy while degrading pollutants such as urea. Tungsten oxide (WO3) has been traditionally used for water splitting, but the use of this material for the removal of waste from water coupled to hydrogen production is not deeply known until now. This contribution shows an exhaustive and systematic investigation on WO3 photoanodes for the photoelectrochemical oxidation of urea and the generation of hydrogen, with insights on the reaction mechanism, detailed nitrogen balance investigation of the process, and analysis of the performance compared to well-accepted materials. The WO3 platelets were successfully synthesized in situ on fluorine doped tin oxide glass by a hydrothermal method. The performance of WO3 was compared to titanium dioxide (TiO2) as a benchmark. The photocurrent was enhanced for both electrodes when urea was added to the electrolyte, with WO3 showing one order of magnitude higher photocurrent than TiO2. The WO3 electrode showed a peak incident photon-to-current efficiency of 43% at 360 nm and a much greater rate constant for urea oxidation (1.47 × 10−2 min−1), compared to the TiO2 photoanode (16% at 340 nm and 1.1 × 10−3 min−1). The influence of different reactor configurations was also evaluated testing one- and two-compartment back-face irradiated photoelectrochemical cells. Hydrogen was generated with a Faradaic efficiency of 87.3% and a solar-to-hydrogen conversion efficiency of 1.1%. These findings aim to contribute to the development of technologies based on the photoelectrochemical production of hydrogen coupled with the oxidation of pollutants in wastewater. © 2023 The Authors

This work was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie-Curie grant agreement No 812574 (REWATERGY) and under grant agreement No 820718 (PANIWATER). Alvaro ´ Tolosana Moranchel also thanks the Consejería de Educacion, ´ Juventud y Deporte of the Comunidad de Madrid for the Ayuda Destinada a la Atraccion ´ de Talento Investigador (2020-T2/AMB-19927) granted to him. The authors also thank Delft IMP for supporting this research.

Supplementary data to this article can be found online at https://doi.org/10.1016/j.jclepro.2023.138200.

Peer reviewed