Abstract Non-blocking electrode processes in a protonic conductor, bonded hydronium-NASICON, have been investigated at room temperature by Impedance Spectroscopy. A comparison of the platinum-paste electrode morphology and reactions with those of ZrO 2-based cells is given. The electrode impedance shows a dramatic change when varying the hydrogen partial pressure P H 2. The frequency dispersion (impedance) data have been successfully analyzed using the Boukamp EQIVCT fitting program, and an equivalent circuit has been accordingly presented. The rise of diffusion-controlled effects at low P H 2 is also manifested.