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

Zheng Cao, Shen Hu, Qi Yang, Jian Yu, Yanan Pan, Jiabao Zuo, Haiou Song*, Zhiwen Ye, Shupeng Zhang ^*

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 (127.93 F/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.

环境与能源密不可分，两者的协同统一，才能更有效地实现绿色环保。淡水的缺乏和能源的短缺正在影响世界各国的经济。电容去离子(CDI)因其环境兼容性强、效率高、低成本等优点在海水淡化领域备受关注。此外，基于氧化还原反应(ORR)的锌空气电池(ZABs)因其较高的理论比容量和良好的安全性，被认为是极具潜力的新一代能量转换器件。目前，ZABs的输出电压一般在1.4-1.5 V之间，而CDI的施加电压需要控制在1.8 V以内，这为两种技术的合作奠定了基础。

CDI器件的脱盐效果和ZABs的性能与它们的电极材料密切相关。石墨烯是一种sp²杂化的二维碳纳米片，具有较高的比表面积和优良的电化学性能，被广泛用于CDI和ORR领域。但因其结构稳定难以反应，需要进一步功能化修饰。例如氧化石墨烯(GO)表面含有足够的含氧官能团可以参与各类反应。ZIF-8是一种多孔材料，在许多领域也倍受关注。理想的方法是将GO与ZIF-8结合，获得能通过激活快速转移电子的高性能N掺杂材料。这为石墨烯基N掺杂多孔碳组装ZABs驱动CDI的应用提供了机会。

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