Titanium phosphorus oxide membranes for proton conduction at intermediate temperatures

Titanium phosphorus oxide membranes (TiP) were prepared by the sol–gel method and evaluated for use as proton conductive materials at intermediate temperatures. Titanium phosphorus oxide sol solutions were prepared by the hydrolysis of titanium isopropoxide (TTIP) using hydrochloric acid as a catalyst in isopropanol solutions, and the addition of an appropriate amount of phosphoric acid (H3PO4). A new concept for structurally composite membranes is proposed for proton conductive membranes. A composite structure of type CM-B, where the pores of a porous titanium oxide layer are filled with titanium phosphorus oxide, was found to be effective for high electrical conductivity as well as mechanical strength. Electrical conductivities as high as 0.1 and 0.06 S cm−1 at 100 and 300 °C, respectively, under a partial pressure of water of 50 kPa, was achieved for the CM-B type membranes. Moreover, structurally composite TiP membranes, prepared on porous alumina substrates, showed gaseous permeances of less than 4.5×10−10 mol s−1 m−2 Pa−1 for hydrogen and nitrogen at 130 °C, indicating that structurally composite TiP membranes have gas-tight properties.