Conductivity of CsH2PO4 and SiO2 composites under ambient and humid conditions over time

Cesium Dihydrogen Phosphate (CDP) is a well-studied solid state protonic conductor for hydrogen fuel cell electrolyte applications at intermediate temperatures (235C). However, at the temperature that CDP begins to exhibit high protonic conductivity, it begins to chemically decompose in the absence of humidity. Silicon dioxide (SiO$_{\mathrm{2}})$ is known for its hygroscopic properties and has been used in several applications where adsorption of water is desired. CDP was prepared and characterized with powder x-ray diffraction. Composites of 0.8CsH$_{\mathrm{2}}$PO$_{\mathrm{4}}$/0.2SiO$_{\mathrm{2}}$ were synthesized by mechanically dry mixing CDP with silica nano-powder. Electrochemical impedance spectroscopy was carried out over the span of 10 hours at isotherm (260C) under both dry and humid conditions for all pellet samples. After 10 hours, conductivity values of pure CDP measured at 6.18x10$^{\mathrm{-5\thinspace }}$S cm$^{\mathrm{-1}}$ in dry conditions and 8.37x10$^{\mathrm{-4}}$ S cm$^{\mathrm{-1}}$ in humidity. The composite demonstrated conductivity at 1.768x10$^{\mathrm{-3}}$ S cm$^{\mathrm{-1}}$ and 2.69x10$^{\mathrm{-3\thinspace }}$S cm$^{\mathrm{-1}}$ in dry and humidity conditions, respectively.