Cross-linked poly(ionic liquid) as precursors for nitrogen-doped porous carbons

Abstract

A soluble and easily dispersive cross-linked poly(ionic liquid), copolymer of 1-vinyl-3-butylimidazolium bromide ([VBIM][Br]) and divinylbenzene (DVB), was used as a precursor for nitrogen doped porous carbons (NPCs) with SiO₂ (from tetraethyl orthosilicate) as a template. The NPCs were characterized by infrared (IR) spectroscopy, nitrogen adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, thermo gravimetric analysis (TGA), elemental analysis and X-ray photoelectron spectroscopy (XPS). The specific surface area and porosity of NPCs depended on the carbonization temperature, the SiO₂/[VBIM][Br] ratio and the precursors. Under the optimized conditions, the NPC prepared from cross-linked poly(ionic liquid), P([VBIM][Br]–0.1DVB), gave a high specific surface area up to 1324 m² g⁻¹. XRD indicated that amorphous and disordered graphitic layers were dominant in NPCs. The nitrogen content was about 4–5 wt% in NPCs, and the nitrogen bonding state observed using XPS analysis was mainly pyridinic- and pyrrolic-N. Meanwhile, the cyclic voltammetry, gravimetric charge–discharge curves and electrochemical impedance spectroscopy of the NPCs were also investigated, the specific capacitance was up to 243 F g⁻¹ at 0.1 A g⁻¹, and the retention ratio was nearly 100% after charge–discharge cycling 2400 times at 2 A g⁻¹ in 6 M KOH electrolyte.