Here we investigate the competitive electrosorption of mono- and divalent phosphate anions through electrochemical desalination and dilatometry based experiments. Through in situ dilatometry, we monitor the strain at the electrode surface as anions and cations are electrosorbed. Strain measurements show that the presence of divalent ions in the electrolyte promote a greater than anticipated electrode expansion process, as the cation (Na+) replaces the divalent anion (HPO42-). Furthermore, the expansion observed with Na+ was equal to the expansion observed with the HPO42-. Since the ionic radius of Na+ is smaller than HPO42-, the symmetric expansion suggests that divalent anions do not completely desorb during electrode regeneration, causing the adverse interactions with the cation during co-ion expulsion. This results in a decrease in desalination performance, indicated by decreased salt adsorption capacity. Conversely, an expected asymmetric expansion during anion and cation electrosorption occurs with monovalent phosphate anions (H2PO4-) indicating that monovalent ions are capable of being effectively replaced by the cation at the electrode surface.

In situ dilatometry of phosphate anion electroadsorption mechanisms

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.