Application of protonic acid-doped silica gels to electric double-layer capacitors

Silica gels doped with several protonic acids such as HClO4, H2SO4 and H3PO 4 have been prepared by the sol-gel method and totally solid electric doubl e-layer capacitors have been successfully fabricated using the highly proto n-conductive silica gels as an electrolyte and activated carbon powder (ACP ) hybridized with the silica gels as a polarizable electrode. It was found that the addition of HClO4, which had the highest value of acid dissociatio n constant among these three acids, most effectively increased the proton c onductivity of the resultant acid-doped silica gels. Tablets of the HClO4-d oped silica gels exhibited conductivities as high as 10(-5)-10(-2) S cm(-1) at room temperature in dry N-2 atmosphere. One of the capacitors fabricate d using the protonic acid-doped silica gels had a capacitance of 44 F/(gram of total ACP in the capacitor), which was comparable to those of conventio nal capacitors using liquid electrolytes.