Effect of C[sbnd]F bonds introduced by fluorination on the desalination properties of activated carbon as the cathode for capacitive deionization

Abstract

CF bonds are introduced on activated carbon (AC) by fluorination, and the resulting fluorinated AC (FAC) is fabricated into electrodes to investigate the effect of CF bonds on the capacitive deionization (CDI) performance. The concentration of CF bonds on the AC surface is a high as 19.5%, but the specific surface area of FAC is reduced by etching of the pore walls. Nevertheless, the specific capacitance of FAC is up to 30% higher than that of raw AC (RAC). The negative surface charge formed by the electronegativity difference between carbon and fluorine causes an increase in the open circuit potential (OCP) of the CDI cell, which results in a higher charge efficiency. Therefore, the specific electrosorption capacity of FAC is 16.5 mg g−1, which increased by 59% compare to that of RAC. These results are attributed to multiple factors of the negative surface charge and the OCP formed by CF bonds, which diminish the co-ion expulsion effect, thereby enhancing the CDI performance.