Synthesis of hydrophilic hierarchical carbon via autonomous SiO₂ etching by fluorinated polymers for aqueous supercapacitor

Carbon electrodes for aqueous supercapacitors should have extensive surface area for higher energy and surface morphology enabling electrolyte ions to access the entire surface. The multiple micropores below 2 nm enhance the specific surface area, while mesopores of 2-50 nm allow easy ion transport through porous structure. Here, we synthesize a hierarchical carbon via both a polyvinylidene fluoride precursor directly converting to microporous carbon during pyrolysis and a sol-gel templating route producing the mesopore. Polytetrafluoroethylene is added to induce mesopore by thermal decomposition. Both the fluorine-containing polymers autonomously remove the silica template using evolving HF and C₂F₄ gas during pyrolysis. The dimethylformamide polar solvent helps dissolve both polymers and form alkaline condition beneficial for sol-gel process. The sol-gel–processed carbon exhibits wide pore ranges of over 50 nm, leading to surface area of 1230 m² g⁻¹ with capacitance of 105 F g⁻¹ in neutral Na₂SO₄. The sol-gel–route develops the hydrophilic surface, effectively reducing the electrode resistance in aqueous electrolyte and promoting porous surface utilization. The capacitance retention of 78% exhibits at 10-fold faster rate due to the hierarchically structured pore and hydrophilic surface. Both the energy and power densities are superior to commercial activated carbon with larger area.