Enhanced hybrid capacitive deionization performance by the mass balance of electrodes

The ion removal capacity of carbon based capacitive deionization (CDI) is limited by the double-layer mechanism. Replacing one electrode of the conventional carbon-based symmetric CDI with a battery-like ion insertion material to obtain hybrid capacitive deionization (HCDI) can significantly improve the adsorption capacity. Various ion insertion materials have been adopted for HCDI, however, how to optimize the performance of the HCDI system by matching the two electrodes with different ions removal mechanism remains challenging. In this work, a HCDI desalination cell was demonstrated by using NaTi2 (PO4)3/reduced graphene oxide composites (NTP-rGO-700) as the cathode and activated carbon (AC) as the anode. Based on the mass balance strategy of electrodes and the electrochemical behavior of hybrid capacitors with different AC:NTP-rGO-700 mass ratios, the HCDI desalination cell was assembled with the optimal AC:NTP-rGO-700 mass ratio of 2:1. At an operating voltage of 1.6 V and a current density of 125 mA·g−1, the specific adsorption capacity (SAC) of the HCDI cell can reach 51 mg·g−1 with an average salt adsorption rate (ASAR) of 2 mg·g−1·min−1, and the energy consumption (Em) is 136.53 kJ·mol−1. This work provides an efficient approach for developing high performance HCDI cell. •Desalination of high concentration water calls for high performance hybrid capacitive deionization (HCDI).•Electrodes mismatch limits further improvement of HCDI performance.•The optimal mass ratio of electrodes was determined by their electrochemical behavior.•The HCDI cell assembled with AC:NTP-rGO-700 mass ratio of 2:1 exhibits good cycling stability.•The mass balance strategy provides new opportunities for developing high performance HCDI.