Graphene-sustained bipolar covalent organic framework for symmetric supercapacitors and capacitive deionization systems with superior performance†

Abstract

Bipolar covalent organic frameworks (COFs) with dual active center characteristics have attracted much attention owing to their higher capacity and power/energy output, and good cycling stability, which endow them with high promise for being applied in Faraday-based symmetric supercapacitors (SSCs) and capacitive deionization (CDI). Herein, we fabricated a bipolar covalent organic framework (DQHBA-COF) integrating pyrazine and 1,4-dihydropyrazine species and employed graphene as a conductive substrate to guide the uniform dispersion of the COF on its surface. The DQHBA-COF in the as-prepared nanocomposite (DQHBArGO) displays improved conductivity and excellent ion storage efficiency due to the acquisition of π-electrons delocalized from graphene. Consequently, the aqueous Na⁺ SSC based on DQHBArGO-75 achieves a high energy output of 59.2 W h kg⁻¹ and excellent cycling stability. Additionally, the DQHBArGO-75-based symmetric CDI system exhibits an astonishing salt removal capacity of 74.9 mg g⁻¹ along with outstanding recycling ability (no degradation after 100 cycles). This work highlights a new perspective for designing Faraday material-based SCs and CDI systems with symmetrical architectures.