Improving thermal stability and its effects on proton mobility in proton-conducting phosphate glasses prepared by the electrochemical substitution of sodium ions with protons

We investigated electrochemical substitution involving the electrochemical oxidation of hydrogen with proton injection into an oxide glass. This was accompanied by the electrochemical reduction of sodium ions and the discharge of metallic sodium out of the glass. This is referred to as the alkali-proton substitution technique and we applied it to a sodium-containing phosphate glass. The thermal stability of the 1WO3-35NaO1/2-8NbO5/2-5LaO3/2-51PO5/2 glass that previously deformed at > 250 °C improved to 350 °C after alkali-proton substitution technique by the introduction of AlO3/2 and/or YO3/2. However, the mobility of the proton carriers decreased by 1/20-1/50 by the introduction of AlO3/2 and/or YO3/2 while the thermal stability improved. Based on infrared absorption spectra the reduced mobility can be attributed to the increase in protons that are tightly bound to oxygen by weak hydrogen bondings.