Valency effects of cation dopant on ultraphosphate glass electrolytes for intermediate temperature fuel cells

抄録

Some solid phosphates show high protonic conductivity in the intermediate temperature range at 150–250°C. Although the conductivity of crystalline phosphate materials, such as CsH₂PO₄ and CsHSO₃, is high at intermediate temperature, it decreases significantly below phase transition temperature. In order to quench the structure of the high temperature phase with high conductivity, non-crystalline ultraphosphate glasses without phase transition in the wide temperature range at 25–250°C were evaluated. In the present work, the valency effects of cation dopant on protonic conductivity and glass structure were investigated. The P–O bonding was strengthened by doping trivalent La, which decreased proton conductivity. On the other hand, orthophosphate and end phosphate structures were formed by doping univalent Cs. The conductivity of 30Cs₂O–70P₂O₅ glass was 1.7 × 10⁻³ S/cm at 200°C. However, the production of free orthophosphoric acid deteriorated the chemical stability for Cs-doped phosphate glasses. The 30ZnO–70P₂O₅ glass has a potential as an electrolyte of intermediate temperature fuel cells, since a maximum power density of 1.2 mW/cm² was obtained at 200°C.