Proton-Conducting Non-Aqueous Gel Electrolyte for a Redox Capacitor System

Abstract

Novel non-aqueous proton (H⁺)-conducting polymeric gel systems have bee proposed for utilization as quasi-solid electrolytes in electrochemical capacitors. The gel systems consist of poly(vinylidenedifluoride) (PVdF) or poly(vinylidenedifluoride-co-hexafluoropropylene) (PVdF-HFP) matrix polymer swollen with dimethylformamide (DMF) solutions containing phosphoric acid (H₃PO₄) or trifluoromethanesulfonic acid (CF₃SO₃H). High ionic conductivity of 4.5 mS cm⁻¹ was obtained at 60°C for a PVdF-HFP-based polymeric gel containing 85 mass% of 0.5 M CF₃SO₃H/DMF with sufficient mechanical stability over the temperature range of 20–60°C. Redox process of hydrous ruthenium oxide, RuO₂·xH₂O, gave high pseudo-capacitance in the PVdF-HFP-based polymeric gel. The pseudo capacitance behavior was somewhat influenced by the composition of electrode/electrolyte interface. The discharge capacitance of ca. 350 F g⁻¹ (with respect to the mass of the oxide) was obtained for PVdF-HFP-based gel using RuO₂·xH₂O electrode prepared by a “wet process”.