Mechanochemical synthesis of proton conductive composites derived from cesium dihydrogen phosphate and guanine

Solid inorganic–organic composites were synthesized from cesium dihydrogen phosphate (CsH2PO4, CDP) and guanine (C5H5N5O, Gn) to use the solid proton conductive electrolytes. CDP and Gn were mechanochemically milled in dry nitrogen atmosphere to obtain composites with xCDP·(100 − x)Gn (x = 90–50 mol%). The changes in chemical structure, such as tautomerism of Gn and formation of hydrogen bond between CDP and Gn, after solid-state mechanochemical treatment, were confirmed from FT-IR study. The CDP-Gn composite electrolytes showed significantly higher proton conductivity than those of raw substances, particularly in the lower temperature region than the superprotic phase-transition temperature of CDP. The 80CDP·20Gn composite, for example, showed in anhydrous and hydrous proton conductivities from 2.4 × 10−5 to 8.1 × 10−4 S cm−1, in dry nitrogen atmosphere, and from 1.3 × 10−4 to 1.3 × 10−3 S cm−1, in humidified nitrogen atmosphere (pH2O = 0.6 atm) on heating in the temperature range between 80 and 180 °C. From the FT-IR and impedance studies, tautomerism of Gn and newly developed hydrogen bonds between CDP and Gn are highly expected in the composites. These structural changes imply that a development of new chemical interactions to form the acid–base composite cluster is essential to improve the proton conductivity.