The regulation of biochar surface potential to achieve rapid capacitive deionization

Capacitive deionization (CDI) is a promising desalination technology. In the design and fabrication of high-performance CDI electrodes, the modification of activated carbon is widely adopted to improve the desalination capacity. In this work, aiming at the regulation of surface potential, activated carbon was doped with N and S, showing improved conductivity, wettability, and optimized pore structure. The difference in the potential of zero charge (Epzc) generated by the heteroatom doping was employed to enlarge the actual adsorption voltage window, and to improve the salt adsorption capacity (SAC) and total salt adsorption capacity at long periods. SAC of 14.4 mg g-1 was achieved with a high average salt absorption rate (ASAR) of 8.2 mg g-1 min-1 under 1.2 V in a 500 mg L-1 NaCl solution. Moreover, the total SAC of asymmetric configuration of N, S-doped biochar of 50 cycles achieved 545.8 mg g-1, 19.7% more than that of the symmetric configuration of unmodified biochar. The doping of N and S atoms on biochar brings excellent electrochemical performance and desalination capacity, and the rational utilization of Epzc after heteroatom doping provides a reasonable method for the design of CDI configuration.