Nafion-in situ sol-gel reactions were affected for Zr(OBu)(4) that permeated low water content membranes unidirectionally. IR peaks reflecting ZrO2 and incomplete hydrolysis of ZrOBu groups near both surfaces were detected. Vibrations of Zr(OEt)(4) detected near both sides arise from alkoxy exchange in the presence of the solvent EtOH. Unreacted alkoxy group bands are more distinct near the nonpermeated surface. An IR band for the ZnOBu group diminishes, whereas that for ZnOEt increases with increasing time near the permeated surface due to progressive alkoxy exchange. The ZrO2 band becomes more intense with time near the permeated surface. X-ray spectroscopy/scanning elect ron microscopy studies of Zr concentration across the membrane thickness verified compositional asymmetry. CO2 gas permeability versus upstream pressure plots are monotonically increasing, suggesting diffusion accompanied by complex plasticization.