Cork activated carbon as a new sustainable electrode for electrochemical desalination: Customized surface chemistry for improved performance

Capacitive deionization (CDI) desalination has proven to be a promising solution to combat water scarcity, standing out for its efficiency and low energy consumption. In this study we investigated the feasibility and sustainability of using recycled cork stoppers as carbon electrodes for CDI. The cork stoppers underwent carbonization at three different temperatures (500, 700 degrees C, and 900 degrees C) and then activation with Potassium hydroxide (KOH) at 850 degrees C. The as-obtained electrodes (ECAC) demonstrated salt adsorption capacities (SAC) comparable to other biowaste carbon electrodes. The potential of zero charge (E-PZC) values of the electrodes reflected the influence of synthesis conditions on their surface properties. Considering the E-PZC, symmetric configuration, in which both electrodes (cathode (-) || (+) anode) were made of the same material (ECAC(-)||(+)ECAC), and asymmetric electrodes, using different materials (ECAC(-)||(+)YP80-F) were investigated. The use of asymmetric electrodes proved to be mandatory to obtain high charging efficiency and desalination capacity. It was found that the E-PZC determines the correct electrode configuration to prevent the deleterious effect of co-ions repulsion. Herein, we used the carbonization temperature as a new strategy to tune the E-PZC in order to obtain electrodes with the desired surface properties for application in CDI, thus avoiding the usual laborious and costly chemical-based approaches. Regarding the desalination performance, asymmetry combined with the appropriate cell potential was optimized to obtain charging efficiencies close to 100 % and maximum SAC, thus resulting in minimized specific energy consumption. This study not only confirms the efficacy of cork stoppers as electrodes for CDI but also promotes the use of recycled materials, contributing to a circular economy and environmental impact mitigation.