Electrophoretically Deposited Graphene Oxide on Reusable Acid-Washed Nickel Foam Substrate for Sustainable Capacitive Ion Desalination

Graphene Oxide (GO) comprises unique features that make it a potential material for capacitive deionization (CDI) of brackish and saline water, such as Graphene Oxide's increased surface area providing more ion adsorption sites, the chemical stability of Graphene Oxide across a wide pH and ionic strength range contributing to the longer operational time of the CDI electrodes, the possibility of modification of the Graphene Oxide with various surface functional groups in order to alter the selectivity of the CDI electrode for ions, and the easy dispersibility of Graphene Oxide in various aqueous media and solvents. However, the method of loading Graphene Oxide as an active material on the current collector, as well as the preparation of the current collector before loading the active material, can significantly impact the desalination performance of the system. Hence, exploring an efficient loading method of Graphene Oxide on a high-charge transfer-capable current collector is required that would inherit a higher electrochemical performance along with a higher salt removal capacity. To mitigate the drawbacks of currently employed materials and methods, we present a facile, scalable, and efficient method of preparing CDI electrodes by electrophoretic coating of GO on acid-washed Nickel foam. The Nickel foam as a current collector was subjected to acid washing with various concentrations of acid, and simultaneous material and electrochemical characterization were conducted to optimize the acid concentration. Further, the deionized (DI) water and acid-washed Nickel foam current collectors were dip-coated and electrophoretically coated with graphene Oxide which, on performing the physiochemical and electrochemical characterization, displayed the specific capacitance and current density in the order electrophoretically coated GO on acid-washed Nickel foam > dip-coated GO on acid-washed Nickel foam > electrophoretically coated GO on DI-washed Nickel foam > dip-coated GO on DI-washed Nickel foam. In comparison to the dip-coated GO on DI-washed Nickel foam, electrophoretically coated GO on acid-washed Nickel foam demonstrates a multi-fold increase in the specific capacitance and current density. We attempted to reuse the current collectors to make the CDI sustainable and cost-effective, and upon experimentation, they demonstrated the same electrochemical properties as a new electrode. The use of three-dimensional electrophoretically coated GO on acid-washed Nickel foam electrodes in a CDI device contributed to the efficient charge transfer ability of the CDI and resulted in a substantial increase in salt adsorption capacity with excellent recyclability and efficient regeneration of the electrodes.