Niobium phosphate is an interesting proton conductor operational in the intermediate temperature range. In the present work two forms of phosphates were prepared: an amorphous one with high specific area and a crystalline one with low specific surface area. Both phosphates exhibited very low proton conductivities. An activation process was developed to convert the phosphates into crystal grains with a phosphorus rich amorphous phase along the grain boundaries. As a result, the obtained niobium phosphates showed considerably enhanced and stable proton conductivities. The activation effect was prominent when the high surface area amorphous phosphate was used as the precursor. At 250 °C thus obtained niobium phosphate showed a high and stable conductivity of 0.03 S cm−1 under dry atmosphere and of 0.06 S cm−1 at a water partial pressure of 0.12 atm.
Huang, Y., Yu, L., Li, H., Wang, C., Li, Q., & Shuai, Q. (2016). Enhanced proton conductivity of niobium phosphates by interfacing crystal grains with an amorphous functional phase. Solid State Ionics, 294, 54-58. https://doi.org/10.1016/j.ssi.2016.06.018