Broadband electric spectroscopy of proton conducting SPEEK membranes

► For first time electric response of SPEEK membranes was investigated with BES. ► Two polarization phenomena correlated to σ are detected in SPEEK. ► Interfacial σ is due to charge migration between interfaces with different ɛ*. ► Bulk σ via Grotthus charge transfer and linked to electrode polarization phenomena. ► Thermal transitions were revealed with thorough DSC studies.