Synthesis and Proton Conductivity of the Mixed Cation Phosphate, KCo_1−xH_2x(PO₃)₃ • yH₂O with a with a One-dimensional Tunnel Structure

Abstract

A mixed cation phosphate, KCo_1−xH_2x(PO₃)₃ • yH₂O, with a tunnel structure was synthesized by a coprecipitation method and investigated as a proton conductor. KCo_1−xH_2x(PO₃)₃ • yH₂O formed a solid solution in the range of x = 0–0.18, and the enhancement of the absorption peaks corresponding to the vibration and stretching modes of OH and POH were observed for increasing x. The sample with x = 0.18 exhibited a high proton conductivity in the temperature range of 25–250°C, and the value of 2.6 x 10⁻³ Scm⁻¹ was obtained at 250°C. This sample maintained a high proton conductivity of over 10⁻³ Scm⁻¹ at 150°C for 9 h, and no electron conductivity was confirmed in a hydrogen or oxygen gas atmosphere.