Direct solar thermal splitting of water and on-site separation of the products — IV. Development of porous ceramic membranes for a solar thermal water-splitting reactor

A crucial element in the solar thermal water-splitting (STWS) reactor is the porous ceramic membrane that enables separation of hydrogen from the hot water-splitting reaction products. Zirconia porous membranes are manufactured by powder sintering at about 1800°C. When such a membrane is exposed in the solar reactor to a higher temperature, it loses its gas permeability due to pore closure by continued sintering. Efforts were made to inhibit the membrane sintering process and to postpone its fast occurrence to higher temperatures, by the use of special stabilized zirconia powders consisting of particles with a rounded shape. The fast sintering of membrane samples made of a homogeneous powder of relatively large spherical particles, prepared by the Sol–Gel method, occurred at some 200°C above the normal zirconia sintering temperature. The overall picture gathered from our experiments suggests, however, that it will be hardly possible to bridge the temperature gap between the normal sintering temperature of stabilized zirconia and the STWS reactor temperature, by the use of stabilized zirconia powders of a particular morphology.