For the purpose of purifying H-2 from gaseous mixtures from thermochemical water decomposition processes, the characteristics of zirconia-silica composite membranes coated on porous ceramic tubing were investigated up to 773 K. The maximum content of the Zr(OC3H7)(4) in the metal-alkoxide solution used successfully in the coating process was 60 mol%. The separation experiments for the gaseous mixtures of H-2-H2O-HBr (for the UT-3 process) and of HI-H2O (for the IS process) were carried out at 423-773 K, and it was found that hydrogen can be purified as reject stream and that HBr and HI can be recovered from the permeation side of the membranes.