Na2O-B2O3-SiO2 and Na2O-P2O5-SiO2 glasses show a spinodal phase separation to SiO2 rich and Na2O center dot B2O3 or Na2O center dot P2O5 rich phases by heating. Herein we report for the first time the application of phosphosilicate glasses to fuel cells operated at moderate temperature. The glass was prepared by conventional melting method. The mixed-alkali glass showed 100% proton transport at 400-500 degrees C. Two crucial aspects, the first is the enhancement of proton transport number by mixing two types of alkali metal oxides, and the second is proton infiltration into the glass under hydrogen (fuel cell) atmosphere, are reported. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3574527] All rights reserved.