Framework-to-carbon conversion strategy for nitrogen–silicon co-doped microporous carbons with superior energy storage performance

Abstract

Developing heteroatom-doped porous carbons with tailored architectures is a promising strategy for enhancing the energy storage performance of next-generation supercapacitors. Herein, we report the design and synthesis of two nitrogen–silicon co-doped microporous carbons (NSi@C-1 and NSi@C-2) prepared from silicon-containing covalent triazine frameworks (Si-CTFs). These Si-CTFs were constructed by the condensation of 4,4′,4″,4‴-silanetetrayltetrabenzaldehyde (Si-4CHO) with two different carboximidamide linkers, namely, terephthalimidamide (TP-2NHNH₂) and [1′-biphenyl]-4,4′-dicarboximidamide (BP-2NHNH₂), resulting in tunable porosity and distinct structural architectures. The direct carbonization route enables the uniform incorporation of N and Si heteroatoms within a hierarchical porous network, simultaneously improving the electrical conductivity and redox activity. NSi@C-2, featuring an extended biphenyl linker, exhibited a higher surface area (732 m² g⁻¹), larger pore volume (0.59 cm³ g⁻¹), and higher electrical conductivity (4.23 S cm⁻¹) than NSi@C-1. Owing to these structural features, the material exhibits exceptional electrochemical properties, achieving a specific capacitance of 403 F g⁻¹ at 0.5 A g⁻¹ and retaining 95.25% of its initial capacitance after 10 000 charge–discharge cycles in a three-electrode system. A symmetric NSi@C-2-based supercapacitor device exhibited a high capacitance of 211 F g⁻¹, an impressive energy density of 152 W h kg⁻¹ at a power density of 1037 W kg⁻¹, and exceptional cycling stability (91.50% retention after 10 000 cycles). The synergistic effects of hierarchical porosity, extended π–π conjugation, and N–Si dual-doping collectively endow NSi@C-2 with superior ion diffusion, efficient electron transport, and abundant active sites. This study establishes a facile framework-to-carbon conversion strategy for constructing multifunctional heteroatom-doped carbons with tunable porosity and electronic properties for advanced energy-storage applications.