Analyzing elementary electrode reactions for protonic ceramic fuel cells by proton/deuteron isotope effect

This study elucidates the elementary reactions occurring within the electrode impedance of proton-conducting ceramic fuel cells, using the distribution of relaxation times and the relaxation process involved in proton/deuteron substitution. We identified impedance components attributable to the steam production reaction of protons crossing the electrolyte on the triple phase boundary by observing the change in these components when the gas on the anode was switched from light hydrogen to heavy hydrogen during the power generation and shutdown phases of the fuel cell. It was noted that the steam formation reaction presents the highest resistance in proton-conducting ceramic fuel cells, implying the need for a catalyst to enhance this reaction within the electrode. [Display omitted] •Isolation and identification of the impedance of the steam production reaction.•Exploration of the proton/deuteron isotope effect on electrode impedance.•Revelation of the rate-limiting reaction of PCFC cathode.