Advanced proton conducting membrane for ultra-high rate solid flexible electrochemical capacitors

Abstract

Polymer electrolytes comprised of silicotungstic acid (SiWA) in cross-linked polyvinyl alcohol have been developed and characterized for ultra-high rate electrochemical capacitors (ECs). The solid polymer electrolytes outperformed liquid H₂SO₄ electrolytes in a similar cell setup. The polymer electrolyte enabled thin flexible solid double layer ECs demonstrated an exceptionally high rate capability of 50 V s⁻¹ in cyclic voltammograms and a 10 ms time constant in impedance analyses. Enhanced stability and water uptake were observed for the cross-linked polymer electrolytes compared to their non-cross-linked counterparts. Thermal analysis revealed an increase of water content with the percentage of cross-linking. Structural analyses suggested that SiWA in the cross-linked polymer electrolyte was more hydrated than SiWA in the non-cross-linked polymer electrolyte. In addition, a stronger hydrogen bonding interaction was observed due to an increase in the crystallized water content in hydrated SiWA suggesting a more stable proton-hopping network that can be leveraged for high conductivity.