A new type of CsHSO4-HZSM-5 inorganic composite electrolyte membrane is prepared by mechanically mixing CsHSO4 (CHS) and nanometer-scale HZSM-5 zeolite powders. The effects of HZSM-5 on the crystallite structure, proton conductivity, and thermal stability of the CsHSO4 electrolyte are investigated. Incorporation of HZSM-5 is found to significantly increase the low-temperature proton conductivity of the CsHSO4 electrolyte, extending its operating temperature down to 100 degrees C. The composite electrolyte with 40 mol% HZSM-5 shows the highest proton conductivity in the measured temperature range. The low-temperature activation energy of the composite with 40 mol% HZSM-5 is lower than that of the CHS-SiO2 composite. The improvement of the proton conductivity can be attributed to the enhanced interfacial interaction between the two phases. And the small HZSM-5 particles lead to a change in the bulk properties of the ionic salts. The melting point of the CHS-HZSM-5 composite electrolyte is lower than that of the pure CHS electrolyte. The CHS-HZSM-5 composite electrolyte is suitable for polymer electrolyte membrane fuel cells operated at 100-200 degrees C. (c) 2009 Elsevier B.V. All rights reserved.