A process for making an ion-conducting polymer comprises cross-linking polymers having functional groups such as alkyne groups and azide groups. An example ion-conducting polymer has cross-links including nitrogen-containing heterocycles formed by the reaction between the functional groups, such as 1,2,3-triazole groups formed by a cycloaddition reaction between alkyne and azide groups. The ion-conducting polymer may be used in an ion-electrolyte membrane. Examples include a proton-electrolyte membrane useful for fuel cells.