Confinement of nitrogen-doped porous carbon between graphene layers as a bifunctional electrode for zinc-air battery-driven capacitive deionization

Abstract

Capacitive deionization (CDI) has attracted considerable attention because of its advantages, which include environmental compatibility, high efficiency and cost effectiveness, while zinc-air batteries (ZABs) are considered to be highly promising next-generation energy conversion devices. The synergy and unity of these two technologies will enable more effective green environmental protection. The desalination effect of CDI devices and the performance of ZABs are closely related to their electrode materials. Here, we used ZIF-8 and graphene oxide as precursors to prepare N-doped porous carbon after high temperature reduction and strong alkali activation. The overall three-dimensional porous carbon-based nanostructure (NJUST) exhibits its potential as a CDI electrode and ZAB cathode to enhance the efficient transport of ions and electrons. The material had a high specific surface area (1426.32 m2/g) and high specific capacitance (127.93F/g). The N-doped porous carbon between porous reduced graphene oxide layers could not only perform the oxygen reduction reaction, but can also provide storage sites for attracting and storing Na ions due to the N atoms it contains. These structural advantages greatly improved the CDI and ZAB performance. The maximum removal capacity in the CDI process was 15.59 mg/g for a 250 mg/L NaCl solution at 1.4 V. Such a configured CDI device was also powered by a Zn-air battery made from the NJUST with an open-circuit voltage of ∼ 1.4 V and had good oxygen reduction reaction activity.