@article{algurainy_call_2022, title={Improving Long-Term Anode Stability in Capacitive Deionization Using Asymmetric Electrode Mass Ratios}, volume={2}, ISSN={["2690-0645"]}, DOI={10.1021/acsestengg.1c00348}, abstractNote={Activated carbon (AC) electrodes are used for desalination in capacitive deionization (CDI) because they provide a large, porous surface area at a low cost. In short-term tests, AC electrodes can achieve relatively high salt adsorption capacities. In long-term tests, desalination performance degrades significantly. The poor performance has been attributed to the corrosion of carbon in the anode electrode. Here, we show a simple strategy to improve anode stability by changing the mass ratio of AC electrodes (asymmetric configuration) in flow-through CDI (FT-CDI). Increasing the anode mass by double and triple decreased the anode half-cell potential by up to 21 and 64%, respectively, relative to cells with single anodes. Less positive anode potentials were associated with smaller shifts in the anode potential of zero charge and lower acidity in the effluent. Additional evidence for improved anode stability in the asymmetric configurations was the significantly lower charge transfer resistance and oxygen to carbon ratio content of the anodes at the end of the tests. After 48 h of operation, the salt adsorption capacity decreased by 68% in symmetric cells, but, in asymmetric cells, it was more stable and decreased by only 47% (double anode) and 17% (triple anode). These trends were consistent when the anode was located upstream or downstream of the cathode. We attribute the improved anode stability to reduced oxidation in the asymmetric cells, which was driven by lower oxidative half-cell potentials. This, in turn, maintained a stable desalination performance over long-term operation. Our results demonstrate that increasing the anode mass is an effective strategy to extend anode stability and improve long-term salt removal in FT-CDI.}, number={1}, journal={ACS ES&T ENGINEERING}, author={Algurainy, Yazeed and Call, Douglas F.}, year={2022}, month={Jan}, pages={129–139} }
 @article{algurainy_call_2020, title={Asymmetrical removal of sodium and chloride in flow-through capacitive deionization}, volume={183}, ISSN={["1879-2448"]}, DOI={10.1016/j.watres.2020.116044}, abstractNote={Capacitive deionization (CDI) is an electrochemical method of removing salt ions from brackish water. A common assumption in CDI is that monovalent ions (e.g., Na+, Cl−) are removed in a 1:1 symmetry on the electrodes. Validation of this assumption with techniques such as ion chromatography is not commonly performed, but is important to better understand how parasitic process, such as faradaic reactions, affect ion removals. In this study, we quantified the removals of Na+ and Cl− as a function of electrode orientation in flow-through CDI. When the cathode was positioned upstream, Na+ and Cl− removals approached a 1:1 symmetry, but when the anode was located upstream, we observed a significant drop in Na+, but not Cl−, removals. We attributed this drop to oxygen reduction reactions at the cathode that competed with Na+ adsorption. Oxidation of carbon in the upstream anode yielded H+ that enhanced the reduction of oxygen to H2O2 at the downstream cathode, which in turn diverted electrons from Na+ adsorption. In the absence of oxygen, Na+ removals increased in the upstream anode orientation and were comparable to Cl− removals, confirming that competition with oxygen reduction reactions was the primary reason for decreased Na+ removal. In the upstream cathode orientation, we show that H2O2 generated at the cathode can be oxidized at the downstream anode, possibly enhancing Na+ removals via internal electron recycling. Salt adsorption capacities calculated using actual ion removals did not always agree with those estimated using changes in solution conductivity, with the largest disagreement observed when conductivity data were corrected for pH changes. Our results highlight that faradaic reactions, particularly oxygen reduction reactions, can contribute to asymmetrical removals of monovalent ions in flow-through CDI.}, journal={WATER RESEARCH}, author={Algurainy, Yazeed and Call, Douglas F.}, year={2020}, month={Sep} }