Niobium Phosphate Glass Thin Film As an Intermediate-Temperature Proton Conductor

Fuel cells operating at intermediate temperatures between 200°C and 400°C have attracted much attention because of the advantages such as enhanced reaction kinetics, resistance to CO poisoning, potential use of renewable fuels, reducing or eventually eliminating the noble metal catalysts. At intermediate temperature, phosphate glasses are suited to new solid state electrolytes. Phosphate glasses containing alkali ion have a structure in which protons have higher mobility and have been shown to possess high ionic conductivities because the hydrogen bonding network maintains between the adjacent oxide ions in the structures allowing for proton mobility by the hopping mechanism. However, the materials based on phosphate glasses have some problems. Contents of phosphorus can change due to volatilization during heat treatment and the glass structure can even break down through hydrolysis. Therefore, one of the solutions for the problem is improving the chemical and mechanical stability of phosphate glasses. Niobium ions in phosphate glass network have been reported as to increase the proton conductivity of the phosphate glasses, effectively preserving P content from severe volatilization. In this study, we report the chemical stability and the electrical properties at intermediate temperature of niobium phosphate glass thin films fabricated through sol-gel processing.