Enhancing surface charge density of Graphene Oxide membranes through Al(OH)4− anion incorporation for osmotic energy conversion

Graphene oxide (GO) has been extensively studied for fabricating ion exchange membranes. This material is of interest due to its surface-governed charge which, combined with the interlayer distance between the GO flakes stack, offers ion selectivity. However, obtaining high-performing membranes with high ion selectivity and low ionic resistance remains challenging. To address this issue, Al(OH)4− anions are incorporated into graphene oxide membranes to increase their spontaneous negative surface charge. The anions are successfully formed and encapsulated through a reaction with the alumina support under alkaline conditions during the membrane fabrication. A modeling of the system proves the anchoring of the Al(OH)4− anions within the GO matrix. The incorporation of these anions significantly improves the permselectivity and reduces the ionic resistance, reaching approximately 95% and 2 Ω cm2, respectively. The GO-modified membranes also present mono-valent selectivity, which can boost reverse electrodialysis power densities.