The aim of this work is to study the effect of CO2 under pressure on hybrid inorganic-organic polymer electrolytes, by using broad band dielectric spectroscopy (BDS) in the frequency interval 40 Hz-10 MHz and in the temperature range of -80 to 120 degrees C. Eleven inorganic-organic hybrid materials of the ORMOCERs type, with general formula {Al[O(CH2CH2O)(8.7)](p)/(LiClO4)(z)}(n) were treated by applying CO2 at 293 K and 5 MPa. The results demonstrated that the CO, treatment generally depressed the conductivity of about one order of magnitude. The decreased conductivity in treated complexes is explained in terms of a smaller anion-trapping ability of the Al centers. Residual CO2 molecules are likely to inhibit the interaction of the perchlorate anions with Al centers within the structure. Segmental motion of the polymer chains plays a crucial role in the conductivity of investigated samples, while the ion-hopping phenomenon is the most important charge transfer mechanism both in the pristine and CO2 treated materials. Equivalent conductivity studies have elucidated the different ionic species present at various salt concentrations and gave insight about the role of CO, in modifying the transport properties of the samples. (c) 2005 Elsevier Ltd. All rights reserved.