a b s t r a c tWe 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 1WO 3 -35NaO 1/2 -8NbO 5/2 -5LaO 3/2 -51PO 5/2 glass that previously deformed at N 250°C improved to 350°C after alkali-proton substitution technique by the introduction of AlO 3/2 and/or YO 3/2 . However, the mobility of the proton carriers decreased by 1/20-1/50 by the introduction of AlO 3/2 and/or YO 3/2 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.
Using Raman and 31 P magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopies, we studied the structural changes in 35NaO 1/2 -1WO 3 -8NbO 5/2 -5LaO 3/2 -51PO 5/2 glass upon introducing Al 2 O 3 and/or Y 2 O 3 in order to understand the reduced mobility of proton carriers in glasses with Al 2 O 3 and/or Y 2 O 3 in which proton carriers were injected by alkali-proton substitution (APS). The Raman and 31 P MAS-NMR spectra showed that phosphate chains were shortened by the Al 2 O 3 and/or Y 2 O 3 introduced into 1W glass. This structural change increased the fraction of protons bound to oxygen atoms in the terminal PO 4 (i.e., the Q 1 unit) of the phosphate chains. Because the protons bound to terminal Q 1 units in phosphate chains tightly bind to oxygen atoms, as opposed to the protons bound to inner Q 2 units in phosphate chains, we attributed the reduced mobility of proton carriers upon introducing AlO 3/2 and/or YO 3/2 into 1W glass to the shortening of phosphate chains. From these results we propose that to obtain a highly proton-conducting glass after APS, the glass must have a composition of O/P<3.5 and thus a sufficiently high fraction of Q 2 units.
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