Development of high protonic conductors based on amorphous mesoporous alumina

The proton conductivity of amorphous mesoporous alumina synthesized with various pore sizes was examined. A systematic dependence of conductivity upon pore size was observed, with increased conductivity as the pore size increased. The highest conductivity, 0.004 S·cm− 1, was obtained at 303 K and 90% relative humidity (RH). The RH dependence of the water content was determined. Proton mobility was investigated by 1H-NMR. At 30% RH, the width of the 1H-NMR line decreased with increasing pore size, suggesting an increase in proton mobility. At 90% RH, the increase of the 1H-NMR sharp peak is accordant with the increase in conductivity as the pore size increased.