Stine Roen

• Roen, Stine; Strandbakke, Ragnar; Norby, Truls & Polfus, Jonathan (2026). Deconvoluting electrode polarization resistances underestimated due to electronic leakage in proton ceramic cells. Electrochimica Acta. ISSN 0013-4686. 575, p. 1–9. doi: 10.1016/j.electacta.2026.149534. Full text in Research Archive Show summary

  Proton ceramic cells lose faradaic efficiency through electronic leakage in the electrolyte that electrochemical impedance spectroscopy cannot resolve directly. Proton conducting electrolytes such as BaZr0.7Ce0.2Y0.1O3 δ (BZCY721) exhibit non-negligible p-type electronic conductivity that short-circuits the electrode polarization processes, causing systematic underestimation of their impedances. Here, we apply a correction procedure in which the electronic resistance is placed in parallel with the faradaic resistances in equivalent-circuit analysis, thus yielding true electrode polarization resistances. The procedure is applied to a symmetric cell comprising porous Ba0.95La0.05Fe0.7Ni0.2Zn0.1O3 δ (BLFNZ) electrodes on BZCY721 and the ionic and electronic transport numbers are obtained by fitting the measured total electrolyte conductivity based on defect chemistry and transport equations. Accounting for the electronic short-circuit markedly alters the deconvoluted electrode polarization resistances, activation energies, pre-exponential factors, and reaction orders. The apparent electrode polarization resistance is underestimated by approximately one order of magnitude at 600◦C, and the activation energy is reduced from the apparent 1.3 eV to 0.8 eV. The corrected charge-transfer and mass-transfer conductances are consistent with proton transfer (p0O2 and p1/2H2O dependences) and combined oxygen exchange and oxide ion diffusion in the electrode (p1/4O2 and p0H2O dependences), respectively. The impact of the electronic leakage is quantified by equivalent circuit analysis of the electronic and faradaic conductances.

• Roen, Stine; Strandbakke, Ragnar & Norby, Truls (2025). Current-overpotential relationships from electrochemical impedance spectroscopy (EIS) under DC bias – A tutorial exercise applied to a Pt||YSZ electrode. Solid State Ionics. ISSN 0167-2738. 428. doi: 10.1016/j.ssi.2025.116939. Full text in Research Archive Show summary

  Electrochemical impedance spectroscopy (EIS) of electrode polarisation offers the possibility to delineate overpotentials into ohmic, charge transfer kinetic, and transport and other mass transfer contributions, commonly applied and interpreted under open circuit conditions. It is sometimes also applied under DC bias, as it in principle then can provide information about net anodic or cathodic processes. However, the impedances so obtained are seldomly converted to overpotentials and therefore remain as qualitative indicators only. Here, we tutorially derive formalism of converting resistances from EIS under DC bias properly into overpotential contributions to the total overpotential, allowing identification of their origins from their dependencies on the current. We illustrate the methodology by generated model current-voltage curves and then apply it to an experimental data set for a Pt electrode on an yttria-stabilised zirconia (YSZ) oxide ion conducting electrolyte. The result reveals that a dominating electrode polarisation easily taken to reflect mass transfer in fact behaves like a second charge transfer step following Butler-Volmer kinetics, allowing us to hypothesise a new model for the O2,Pt||YSZ electrode. Our tutorial exercise is applicable to both liquid- and solid-state electrochemistry and should apply equally also to EIS under DC bias of any types of junctions.

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• Roen, Stine; Strandbakke, Ragnar & Polfus, Jonathan M. (2024). Electrochemical Characterization of Ba0.95La0.05(Fe1−x−yMxZny)O3−δ (M = Ni, Cu) as Air/Steam Electrode in Proton Ceramic Electrochemical Cells. Full text in Research Archive
• Roen, Stine; Norby, Truls; Strandbakke, Ragnar & Polfus, Jonathan M. (2023). Electrochemical characterization of Ba0.95La0.05(Fe0.7Ni0.2Zn0.1)O3-δ for proton ceramic electrochemical cells. Full text in Research Archive

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