a multi - phase proton conducting material comprising a proton - conducting ceramic phase and a stabilizing ceramic phase . under the presence of a partial pressure gradient of hydrogen across the membrane or under the influence of an electrical potential , a membrane fabricated with this material selectively transports hydrogen ions through the proton conducting phase , which results in ultrahigh purity hydrogen permeation through the membrane . the stabilizing ceramic phase may be substantially structurally and chemically identical to at least one product of a reaction between the proton conducting phase and at least one expected gas under operating conditions of a membrane fabricated using the material . in a barium cerate - based proton conducting membrane , one stabilizing phase is ceria .