(713d) Redox Flow Desalination Driven By Sunlight Using Dye-Sensitized Photoanode

Water desalination represents a promising technological solution to address water shortage problems in many parts of the world. To make desalination a sustainable solution in the long term, it is necessary to power the process using renewable energy sources. Water desalination driven by sunlight is a potential, energy-efficient alternative to fossil fuel-based thermal desalination, such as multi-stage flash or multiple-effect distillation. Thus, several solar technologies, such as solar thermal desalination (STD), photovoltaic reverse osmosis (PV-RO), and photovoltaic electrodialysis (PV-ED), are currently being investigated. STD consumes high volumetric energy due to the phase change accompanying water evaporation. Although PV-RO and PV-ED require low volumetric energy compared to STD, a high water production cost is a remaining challenge because of the high price of commonly used silicon PV-cells. The use of dye-sensitized solar cells (DSSCs) could be an affordable alternative to PV-powered desalination processes because the cell can be fabricated using relatively inexpensive materials. In DSSCs, a photoanode drives a redox reaction under light illumination, and this redox reaction can be used to process water in an integrated solar cell and desalination device. Here, we demonstrate the use of a redox couple that mediates the conversion of light energy into the electrical driving force for water desalination. We constructed a redox flow desalination cell with a dye-sensitized photoanode as one of the electrodes, in which a redox couple (I^−/I₃^−) enables energy conversion and sustains ion transport and ion separation in the cell. The cell consisted of electrode channels recirculating the redox couple, and feed channels fed with 50 mM NaCl as model saltwater, separated by an alternative array of anion and cation exchange membranes. The current-voltage characteristics of the photoanode were tested under dark and illumination conditions in the desalination cell. When controlled by an external power, the redox couple enabled the separation of the model saltwater and produced a diluted stream at a freshwater level. The separation was also achieved by only sunlight, indicating that integrating photon-to-electron conversion and water desalination processes within a single device is a viable approach for solar-powered water desalination.