From Empiricism via Fundamentals to Improved Performance of Proton Ceramic Electrochemical Cells (BRIDGE) (completed)

• Navarrete, Laura; Almar, Laura; Tarach, Mateusz; Vøllestad, Einar; Mahmood, Asif & Catalán-Martinez, David [Show all 10 contributors for this article] (2025). Tailoring sintering properties of BaGd0.3La0.7Co2O6-δ steam electrodes for pressurized tubular proton-ceramic electrolysis cells. Journal of the European Ceramic Society. ISSN 0955-2219. 45(5), p. 1–8. doi: 10.1016/j.jeurceramsoc.2024.117162. Full text in Research Archive Show summary

  We herein address manufacturing constraints related to the high-temperature sintering step required for reaching adequate adhesion of oxygen/steam electrodes on proton ceramic electrolytes, particularly in tubular geometry. Incorporating various sintering aids such as Cu, Co, and Ni oxides improves the sinterability of the electrodes and reduces the sintering temperature to 950 °C. The ceramic-ceramic composite electrodes based on BaGd0.3La0.7Co2O6-δ (BGLC37) and BaZr0.7Ce0.2Y0.1O6-δ (BZCY) show good and robust electrode-electrolyte adhesion. Composite electrodes were tested under different operation conditions, i.e., temperatures and oxygen partial pressures in symmetrical cell configuration, achieving apparent polarisation resistances below 0.6 Ω·cm2 at 600 °C in wet air for all the electrodes with sintering aids. Finally, BGLC37/BZCY with 2 wt% of CuO electrodes were successfully applied on pre-reduced and sealed BZCY/Ni-supported tubular half-cells with 16 cm2 active area and measured in electrolysis mode at 600 °C and high steam pressure. The results open a route to manufacturing steam electrodes for large-scale electrolysis cells.

• Gudmundsdottir, Jonina Björg; Thoreton, Vincent; Jiang, Bo; Pokle, Anuj; Vøllestad, Einar & Haugsrud, Reidar [Show all 7 contributors for this article] (2025). Oxygen exchange kinetics of BaGd0.3La0.7Co2O6−δ with exsolved Co3O4 nanoparticles in dry and humid atmospheres. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 27(16), p. 8467–8477. doi: 10.1039/d4cp04791e. Full text in Research Archive Show summary

  The oxygen exchange kinetics of BaGd0.3La0.7Co2O6−δ were investigated with pulsed isotope exchange (PIE) measurements in dry and humid atmospheres in the temperature range 400–600 °C in 0.005–0.21 bar O2. Synchrotron X-ray diffraction and scanning transmission electron microscopy (STEM) revealed exsolved Co3O4 nanoparticles dispersed on the surfaces that may contribute to the catalytic activity of the material towards the oxygen exchange reactions. The obtained oxygen exchange rate was 4.45 × 10−3 mol m−2 s−1 at 600 °C in 0.21 bar O2 with an activation energy of 0.76 eV. The rate determining step of the exchange reaction was determined to be dissociative adsorption of oxygen in both dry and humid atmospheres based on the individual rates of dissociative adsorption and incorporation, as well as pO2 dependencies of the oxygen exchange rate of around 1. The effect of water on the oxygen exchange rate was found to be dependent on the oxygen partial pressure, decreasing the rate at 0.21 bar O2 and 600 °C by a factor of approx. 2, while increasing the rate at 0.02 bar and 0.005 bar O2 by a similar amount. In situ thermogravimetric analysis was used to characterise the oxygen non-stoichiometry of the material throughout the oxygen exchange measurements.

• Wachowski, Sebastian Lech; Szpunar, Iga; Pospiech, Joanna; Balcerzak, Daria; Mielewczyk-Gryn, Aleksandra & Nadolska, Malgorzata [Show all 12 contributors for this article] (2024). Physicochemical properties of La0.5Ba0.5Co1-xFexO3-δ (0 ≤ x ≤ 1) as positrode for proton ceramic electrochemical cells. Acta Materialia. ISSN 1359-6454. 284. doi: 10.1016/j.actamat.2024.120585. Full text in Research Archive Show summary

  We report on essential properties of materials in the series La0.5Ba0.5Co1-xFexO3-δ as positrodes for proton ceramic electrochemical cells (PCECs). The unit cell and thermochemical expansion coefficient (TCEC) of these cubic perovskites decrease with iron content x, the TCEC of La0.5Ba0.5FeO3-δ going as low as 11⋅10-6 1/K. The materials behave as LaMO3 perovskites with small band gaps and Ba acting as acceptors compensated by electron holes and oxygen vacancies. The electrical properties are dominated by p-type conduction with high large polaron mo- bilities for the Co-rich compositions at low temperatures, shifting towards small polaron mobilities with increasing Fe content. X-ray absorption spectroscopy (XAS) shows that Co is in a high spin state and takes on the main part of the cation oxidation state changes, and that hole states are in orbitals overlapping with the O 2p states, confirming the large polaronic behaviour, while holes on Fe are more localised at the cation. Hydration is more pronounced in inert atmospheres, as hydration of oxygen vacancies is easier than hydrogenation and in- creases with Fe content, in line with the commonly accepted finding that delocalization of holes disfavours protonation. Fe-rich compositions benefit from lower TCEC and higher hydration and hence expected proton permeability, at the cost of lower electronic conductivity. The surfaces are hydrophobic irrespective of Fe content, suggesting weak chemisorption of the underlaying water layer, possibly giving relatively many available surface sites for oxygen adsorption, but limited surface proton conductance – both of importance to positrodes for operando PCECs

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• Vøllestad, Einar; Strandbakke, Ragnar; Gudmundsdottir, Jonina Björg & Singh, Kalpana (2024). Bulk or Surface? Reaction pathways in PCEC positrodes – learnings and questions from model electrode studies. Full text in Research Archive
• Gudmundsdottir, Jonina Björg; Haugsrud, Reidar; Vøllestad, Einar & Polfus, Jonathan (2024). Oxygen Exchange Kinetics of BaGd0.3La0.7Co26-d Air/Steam Electrode for Proton Ceramic Electrochemical Cells. Full text in Research Archive
• Gudmundsdottir, Jonina Björg; Haugsrud, Reidar; Vøllestad, Einar & Polfus, Jonathan (2024). Oxygen Exchange Kinetics of BaGd0.3La0.7Co2O6-d Air/Steam Electrode for Proton Ceramic Electrochemical Cells. Full text in Research Archive
• Vøllestad, Einar (2024). Approaching a mechanistic understanding of PCEC electrodics. Full text in Research Archive
• Småbråten, Didrik Rene (2024). Atomistic modelling of functional materials. Full text in Research Archive
• Småbråten, Didrik Rene (2024). Modelling of electrode surface chemistry and kinetics on the atomic scale. Full text in Research Archive
• Gudmundsdottir, Jonina Björg (2023). Oxygen on the IrO2 (110) Surface - A DFT Study. Full text in Research Archive
• Gudmundsdottir, Jonina Björg; Vøllestad, Einar; Haugsrud, Reidar & Polfus, Jonathan (2023). Oxygen Exchange Kinetics of BaGd0.3La0.7Co2O6-d. Full text in Research Archive
• Småbråten, Didrik Rene & Polfus, Jonathan (2023). DFT on electrodes for high-temperature electrolysis. Full text in Research Archive
• Vøllestad, Einar (2022). A discussion on the electrochemistry of PCEC electrodes. Full text in Research Archive
• Gudmundsdottir, Jonina Björg; Thoreton, Vincent; Vøllestad, Einar & Polfus, Jonathan (2022). Oxygen Exchange Kinetics of BaGd0.3La0.7Co2O6-d Steam Electrodes for Proton Ceramic Electrochemical Cells. Full text in Research Archive
• Polfus, Jonathan; Småbråten, Didrik Rene & Liu, Xin (2022). Linking Atomistic and Electrochemical Modelling of Proton Ceramic Electrochemical Cells. Full text in Research Archive

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