Enhanced photoelectric desalination of Co3O4@NC/BiVO4 photoanode via in-situ construction of hole transport layer

The solar-driven photoelectrochemical desalination (SD-PED) technology, as a new emerging desalination technique, has been developed and attracted the increasing attention. However, practical application remains hampered by several constraints, including the rapid deterioration of photocurrent, and the long-term stability of system. In this research, MOF-derived nitrogen-doped carbon@Co₃O₄/BVO (Co₃O₄@NC/BVO) heterostructured photoanode was design for efficient and durable solar driven redox desalination. It exhibits an initial photocurrent of 2.40 mA/cm² and a desalination rate of 69.01 μg/(cm²·min) in the zero-bias state using the light as the driving force, without consuming electrical energy. Furthermore, the solar energy consumption of the photoanode is 0.187 μmol/J. The salt removal rate fluctuates within 1.36 μg/(cm²·min) throughout five cycles without any substantial decrease. Photo-luminescence, EIS and Mott-Schottky analysis are also performed to investigate interface reaction, charge separation and transfer mechanism between photoanode and electrolyte. The analysis of the charge-transfer paths on the heterojunction interface is conducted through in situ irradiation XPS. Further analysis of the generation and separation of •OH and h⁺ in the Co₃O₄@NC/BVO photoanode using electron paramagnetic resonance (EPR) showed that Co₃O₄@NC as an efficient hole transfer layer can effectively promote the separation and transfer of photo-generated electrons and holes. The excellent desalination performance is attributed to the synergistic effect of electron transfer in the Co₃O₄@NC/BVO heterojunction and hole transport in the Co₃O₄@NC efficient hole transport layer. This work is significant for the development of solar redox flow desalination.