The world faces a rising demand for potable water and electricity, while a lack of clean water and use of polluting electricity sources are major hazards¹. Nowadays reverse osmosis (RO) is widely used for sea and brackish water desalination², where RO consumes ~3-4 kWh/m³ for seawater desalination³. A new class of water treatment technologies is emerging that is distinguished from the classical methods by utilizing chemical energy to power both water treatment and electricity generation simultaneously from a single electrochemical cell. When using the hydrogen/oxygen redox couple, such a cell is termed a desalination fuel cell (DFC) which was introduced by our group in 2020⁴.

A DFC utilizes a fuel cell anode and cathode to catalyze the chemical-to-electrical energy conversion, as well as a cation and anion exchange membrane to desalinate the feedwater flowing through the cell. A device with a single feed channel (figure a) was able to produce up to 10 kWh/m³ while desalinating water with sea-water level salinity⁴. In order to for this nascent technology to become practical, scale-up strategies need to be proposed and demonstrated.

In this work we show results from the first scaled DFC, where we utilize scaling rules associated with electrodialysis by increasing the number of membrane pairs to allow either two or three feed channels (Figure b). We find the three feed channel device was associated with high voltage loss in the ohmic region and lower limiting current (figure c), but the salt concentration behaved linearly as a function of the current density as expected (figure d). The main voltage losses are clearly emanated from the cathode and the anode sides as the membranes potential loss was proven to be insignificant⁵. We showed that implementing higher acid concentration in the catholyte and higher base concentration in the anolyte channels can significantly improve performance of the stack. Figure (e) shows results using five different anolyte and catholyte solutions, with highest OCV and improved polarization performance for 0.5M HClO₄ and 0.5M NaOH in the catholyte and the anolyte, respectively. Figures (f and g) compares the polarization performances and the salt removal for different feed flow rates in three feed channel DFC. Overall, we show successful implementation of a scaled-up DFC.

References:

1. Mekonnen, M. M. & Hoekstra, A. Y. Sustainability: Four billion people facing severe water scarcity. Sci. Adv. 2, 1–7 (2016).
2. Greenlee, L. F., Lawler, D. F., Freeman, B. D., Marrot, B. & Moulin, P. Reverse osmosis desalination: Water sources, technology, and today’s challenges. Water Research vol. 43 2317–2348 (2009).
3. Al-Karaghouli, A. & Kazmerski, L. L. Energy consumption and water production cost of conventional and renewable-energy-powered desalination processes. Renewable and Sustainable Energy Reviews vol. 24 343–356 (2013).
4. Atlas, I., Abu Khalla, S. & Suss, M. E. Thermodynamic Energy Efficiency of Electrochemical Systems Performing Simultaneous Water Desalination and Electricity Generation. J. Electrochem. Soc. 167, 134517 (2020).
5. Abdalla, S., Khalla, S. A. & Suss, M. E. Voltage loss breakdown in desalination fuel cells. Electrochem. commun. 132, 107136 (2021).