Ionogel electrolytes at medium temperatures were prepared by composite of ionic liquid [1-butyl-3-methylimidazole][bis-(fluoromethane-sulfonyl) amide] ([BMIM][TFSI]) with the proton-conducting inorganic solid acid CsHSO4. The incorporation of only 10 wt.% of the ionic liquid into the solid acids drastically increased the conductivity of solid acids over a wide temperature range. The ionogel electrolytes contained up to 40 wt.% of the ionic liquid within their inorganic CsHSO4 networks and had an ion conductivity of 2 x 10(-2) S/cm. (c) 2008 Elsevier B.V. All rights reserved.