Improved performance in capacitive deionization of activated carbon electrodes with a tunable mesopore and micropore ratio

• A tunable ratio of mesopore to micropore can be achieved by combined chemical/physical activation process.
• A coconut shell-based activated carbon electrode was prepared for capacitive deionization.
• Enhanced desalination performance is ascribed to high specific surface area and high mesoporosity.

To improve the desalination performance, the coconut shell-based activated carbon electrodes were prepared by using a two-stage activation method. Both the specific surface area and the ratio of mesopore to micropore can be successfully manipulated by the activation process of KOH etching plus CO2 gasification. The results showed that the activated carbon electrodes with controlled mesoporosity exhibited higher specific capacitance and better rate capability as compared to the commercial one. The coexistence of mesopores and micropores can provide large surface area for ions to form an electrical double layer, while the enlarged mesoporosity can not only facilitate the ion transport but also improve the accessible surface area, suggesting the improved capacity of capacitive ion storage. From the desalination experiments at 1.0 V, the activated carbon electrode, associated with a specific surface area of 2105 m2 g− 1 and a 70.7% ratio of mesopore to total pore volume, presented an electrosorption capacity of 9.72 mg g− 1 and electrosorption rate constant of 0.060 min− 1, which were considerably higher than the micropore-dominant carbon electrodes. Therefore, the significantly improved desalination performance can be ascribed to the high surface area and the high ratio of mesoporosity in the activated carbon-based capacitive deionization.