Covalent Triazine Frameworks Derived N/P/S-Rich Carbon Nanosheets Enable Ultra-high Capacity for Aqueous Redox-Enhanced Supercapacitors

Abstract

Controllable fabrication of multi-electroactive sites and morphology-ordered carbon electrodes with excellent capacity and alleviating self-discharge behavior for aqueous redox-enhanced supercapacitors (SC_RE) is highly desirable but still challenging. Herein, the N/P/S-rich carbon nanosheets with ultrathin thickness (2–3 nm) and hierarchical porous structure are successfully prepared via phytic acid-driven interfacial phosphorization strategy using S-bridged covalent triazine framework nanosheets (CTFS) as precursor, which are synthesized through a eutectic molten salt-induced ionothermal polymerization. The carbon electrode with adequate N/P/S active sites is pioneeringly introduced in SC_RE, clarifying that the coupling hierarchical porous structure and multi-electroactive sites can effectively enhance the interface interaction between carbon electrodes and redox electrolytes via the ex-situ characterizations and theoretical calculations. Consequently, the resultant N/P/S-rich carbon nanosheet (PCTFSC) enables SC_RE in KI-doped H₂SO₄ electrolyte to achieve state-of-the-art specific capacity (1586 mA·h·g^–1 at 1 A·g^–1) with 60% of capacity retention at 16 A·g^–1 and ultra-high energy density of 816 Wh·kg^–1, exceeding the reported aqueous supercapacitors thus far. Moreover, the PCTFS based SC_RE also exhibits a low self-discharge rate (holding 50% of open circuit potential after 15 h). This study provides new insights to design and regulate advanced carbon materials from the atom level and nano-morphology toward high performance SC_RE.

Keywords

Covalent triazine frameworks / N/P/S co-doping / Nanosheets / Supercapacitors / Energy storage

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