The freshwater scarcity and increasing energy demand are two challenging global issues. Herein, we propose a new route for desalination, self-sustained visible-light-driven electrochemical redox desalination. We propose a novel device architecture involving internal integration of a quasi-solid-state dye-sensitized solar cell and continuous redox-flow desalination units with a bifunctional platinized-graphite-paper electrode. Both the solar cell and redox-flow desalination units are integrated using the bifunctional electrode with one side facing the solar cell operating as a positive electrode and the other side facing the redox-flow desalination unit operating as a negative electrode. The solar cell contains a gel-based tri-iodide/iodide redox couple sandwiched between an N719 dye-modified photoanode and cathode. In contrast, the redox-flow desalination consists of re-circulating ferro/ferricyanide redox couple sandwiched between the anode and cathode with two salt streams located between these electrodes. The performances of bifunctional electrodes in both redox couples were thoroughly investigated by electrochemical characterization. The brackish feed can be continuously desalted to the freshwater level by utilizing visible light illumination. As a device, this architecture combines energy conversion and water desalination. This concept bypasses the need for electrical energy consumption for desalination, which provides a novel structural design using photodesalination to facilitate the development of self-sustained solar desalination technologies.

Developing redox media as flow electrodes is a critical key in electrodialysis (ED) cells during the desalination process, enabling continuity, low cost and easy operation for freshwater production. Herein, we present viologen redox media as positive and negative flow electrodes in a continuous desalinated ED device. The viologen is reduced at the negative reservoir and oxidized at the positive side with blockage of ion exchange membranes, acting as a catalysis medium. The water product with 284 ppm can be extracted from the as-prepared 6000 ppm salt feed, and a salt removal efficiency of up to 95.3% is achieved. Cyclic voltammetry is performed to investigate the electrochemical behaviors of viologen. In addition, the desalination performance influence from the different current densities, cyclability, and various salt concentrations is further explored in detail. The current research will be significant to the further development of electrodialysis desalination technologies for freshwater production.

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