Improved photoelectrochemical activity of NiFe2O4/Bi2WO6 photoanode by ZnO nanorod array layer for bifunctional photocatalytic fuel cell

Abstract

Devising an effective and well-contacted multi-component electrode in the photocatalytic fuel cell (PFC) system remained a towering challenge. Herein, ZnO nanorod array (NR) layer on the fluorine-doped tin oxide (FTO) was utilized as a substrate for the fabrication of NiFe₂O₄/Bi₂WO₆/ZnO NR photoanode, which was then assembled into a sunlight responsive PFC for electricity generation during the sewage effluent treatment. Material tests disclosed that NiFe₂O₄ and Bi₂WO₆ were evenly dispersed on the highly ordered one-dimensional ZnO nanorods, providing excellent optical and electrochemical traits for photoelectrochemical activity. This composite photoanode formed dual-S scheme heterointerfaces between NiFe₂O₄-Bi₂WO₆ and Bi₂WO₆-ZnO NR, creating directed internal electric fields (IEFs). These IEFs promoted the migration of photoexcited electrons to the surface of composite, boosting charge carrier segregation efficiency of the carriers and facilitating the participation of plentiful active species in the mineralization of sewage effluent. As a result, the NiFe₂O₄/Bi₂WO₆/ZnO NR PFC achieved a maximum power density of 7.364 µW cm⁻² under sunlight with a chemical oxygen demand (COD) removal efficiency of 100 %, representing increase of 4.9 times and 2.7 times over the pristine ZnO NR, respectively. Additionally, the toxicological investigations testified that the detoxified sewage effluent unveiled had no hazardous effects on zebrafish species following treatment with the NiFe₂O₄/Bi₂WO₆/ZnO NR PFC.