Desalination Fuel Cell Stacks: Scaling up the Co-Production of Electricity and Clean Water

Abstract

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 three different anolyte and catholyte solutions, with highest open circuit voltage (OCV) and improved polarization performance for 0.5M HClO4 and 0.5M NaOH in the catholyte and the anolyte, respectively. We also investigated the feed flow rate impact on DFC polarization performance and salt removal. Overall, we show successful implementation of a scaled-up DFC.