Governing Principles in Hydration of Mixed Conducting Oxides (completed)

• Strandbakke, Ragnar; Wachowski, Sebastian Lech; Balaguer, Maria; Vines, Lasse; Sky, Thomas Neset & Szpunar, Iga [Show all 12 contributors for this article] (2026). Governing principles of hydration of mixed proton conducting Co-based double perovskites. Nature Communications. 17, p. 1–10. doi: 10.1038/s41467-026-70212-w. Full text in Research Archive Show summary

  Proton ceramic electrochemical cells PCECs hold promise for efficient, sustainable production and use of hydrogen. The positive electrodes are mixed proton conducting perovskites that facilitate water splitting and oxygen reduction, but the factors that determine the protonation are poorly under stood. Here, we establish the governing principles of protonation through a study of hydration of 45 double perovskites with the general formula AIAIICo2O6 δ, having Ba or Ba+Sr on AI and a mix of rare earths (Y and lanthanides Ln =La,Pr,Nd,Sm,Gd,Dy,Tb,Lu)onAII. We show how hydration is coupled to the A-site basicity and disorder as well as population of electron holes in the Co-O bond (Co oxidation state), promoted by a closed or semiclosed Ln 4f shell, i.e., Ln =La,Gd,Lu.

• Miruszewski, Tadeusz; Strandbakke, Ragnar; Dzierzgowski, Kacper; Szpunar, Iga; Mielewczyk-Gryń, Aleksandra & Wachowski, Sebastian [Show all 7 contributors for this article] (2024). A modified DC Hebb–Wagner polarization method for determining the partial protonic electrical conductivity in mixed-conducting BaGd0.3La0.7Co2O6−δ. Journal of Materials Chemistry A. ISSN 2050-7488. p. 12891–13534. doi: 10.1039/d4ta00100a. Full text in Research Archive Show summary

  In this work, partial protonic conductivity in mixed conducting (BZCY721) and BaGd0.3La0.7Co2O6−δ (BGLC137) was studied. For this purpose, a modified DC Hebb–Wagner polarization method was used. A four-wire type of galvanic cell as well as a suitable calculation model was applied. The method was validated using proton conducting electrolyte – BaZr0.7Ce0.2Y0.1O3−δ – as a reference material. For the first time, protonic partial conductivity in BaGd0.3La0.7Co2O6−δ was determined. It was found that at 600 °C its total conductivity was ∼550 S cm−1, whereas the partial protonic conductivity under the same conditions was 4.4 × 10−5 S cm−1 (protonic transference number of 7.6 × 10−8). Therefore, the proposed measurement cell and the applied model allowed for the determination of a minor protonic conductivity in the BGLC137 electronic conductor.

• Mielewczyk-Gryń, Aleksandra; Yang, Shuhao; Balaguer, Maria; Strandbakke, Ragnar; Sørby, Magnus Helgerud & Szpunar, Iga [Show all 11 contributors for this article] (2023). Energetics of formation and stability in high pressure steam of barium lanthanide cobaltite double perovskites. Dalton Transactions. ISSN 1477-9226. 52(17), p. 5771–5779. doi: 10.1039/d2dt03989c. Full text in Research Archive
• Strandbakke, Ragnar; Wragg, David Stephen; Sørby, Magnus Helgerud; Guzik, Matylda; Gunnæs, Anette Eleonora & Szpunar, Iga [Show all 12 contributors for this article] (2022). Structural properties of mixed conductor Ba1−xGd1−yLax+yCo2O6−δ. Dalton Transactions. ISSN 1477-9226. 51(48), p. 18667–18677. doi: 10.1039/d2dt02277j. Full text in Research Archive Show summary

  Ba1−xGd1−yLax+yCo2O6−δ (BGLC) compositions with large compositional ranges of Ba, Gd, and La have been characterised with respect to phase compositions, structure, and thermal and chemical expansion. The results show a system with large compositional flexibility, enabling tuning of functional properties and thermal and chemical expansion. We show anisotropic chemical expansion and detailed refinements of emerging phases as La is substituted for Ba and Gd. The dominating phase is the double perovskite structure Pmmm, which is A-site ordered along the c-axes and with O vacancy ordering along the b-axis in the Ln-layer. Phases emerging when substituting La for Ba are orthorhombic Ba-deficient Pbnm and cubic LaCoO3-based R[3 with combining macron]c. When La is almost completely substituted for Gd, the material can be stabilised in Pmmm, or cubic Pm[3 with combining macron]m, depending on thermal and atmospheric history. We list thermal expansion coefficients for x = 0–0.3, y = 0.2.

• Andersen, Håkon; Xu, Kaiqi; Malyshkin, Dmitry; Strandbakke, Ragnar & Chatzitakis, Athanasios Eleftherios (2020). A highly efficient electrocatalyst based on double perovskite cobaltites with immense intrinsic catalytic activity for water oxidation. Chemical Communications. ISSN 1359-7345. 56(7), p. 1030–1033. doi: 10.1039/c9cc08765f. Full text in Research Archive
• Wachowski, Sebastian Lech; Szpunar, Iga; Sørby, Magnus Helgerud; Mielewczyk-Gryń, Aleksandra; Balaguer, Maria & Ghica, Corneliu [Show all 12 contributors for this article] (2020). Structure and water uptake in BaLnCo2O6−δ (Ln = La, Pr, Nd, Sm, Gd, Tb and Dy). Acta Materialia. ISSN 1359-6454. 199, p. 297–310. doi: 10.1016/j.actamat.2020.08.018. Full text in Research Archive Show summary

  The structure of BaLnCo2O6-δ (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy) was studied by the means of synchrotron radiation powder X-ray diffraction, neutron powder diffraction and Transmission Electron Microscopy (TEM), while water uptake properties were analysed with the use of thermogravimetry (TG) and water adsorption isotherms. The structure refinement revealed that the dominant phase in all compositions was orthorhombic with an ordering of the A-site cations along the c-axis and ordering of oxygen vacancies along the b-axis, which was also directly evidenced by TEM. It was shown that both unit cell volume and average Co-oxidation state at room temperature decrease linearly with decreasing Ln radius. TG water uptake experiments in humidified N2–O2 gas mixture at 300 °C revealed that among all compositions, only BaLaCo2O6-δ and BaGdCo2O6-δ exhibit significant water uptake. Surface water adsorption studies showed that the α, a normalised parameter reflecting the surface hydrophilicity, mostly independently of Ln radius was close to 0.5, which means that the surface is neither hydrophobic nor hydrophilic. The results indicated that water uptake observed at 300 °C is a bulk process, which cannot be described by standard hydration/hydrogenation reaction and it is related to the layered structure of the perovskite lattice and characteristic to La or Gd being present in the lattice.

• Bjørheim, Tor Svendsen; Hoedl, Maximilian; Merkle, Rotraut; Kotomin, Eugene & Maier, Joachim (2020). Proton, Hydroxide Ion, and Oxide Ion Affinities of Closed-Shell Oxides: Importance for the Hydration Reaction and Correlation to Electronic Structure. Journal of Physical Chemistry C. ISSN 1932-7447. 124(2), p. 1277–1284. doi: 10.1021/acs.jpcc.9b07570. Full text in Research Archive
• Szpunar, Iga; Strandbakke, Ragnar; Sørby, Magnus Helgerud; Wachowski, Sebastian Lech; Balaguer, Maria & Tarach, Mateusz [Show all 12 contributors for this article] (2020). High-temperature structural and electrical properties of BaLnCo2O6 positrodes. Materials. 13(18), p. 1–18. doi: 10.3390/ma13184044. Full text in Research Archive Show summary

  The application of double perovskite cobaltites BaLnCo2O6−δ (Ln = lanthanide element) in electrochemical devices for energy conversion requires control of their properties at operating conditions. This work presents a study of a series of BaLnCo2O6−δ (Ln = La, Pr, Nd) with a focus on the evolution of structural and electrical properties with temperature. Symmetry, oxygen non-stoichiometry, and cobalt valence state have been examined by means of Synchrotron Radiation Powder X-ray Diffraction (SR-PXD), thermogravimetry (TG), and X-ray Absorption Spectroscopy (XAS). The results indicate that all three compositions maintain mainly orthorhombic structure from RT to 1000 °C. Chemical expansion from Co reduction and formation of oxygen vacancies is observed and characterized above 350 °C. Following XAS experiments, the high spin of Co was ascertained in the whole range of temperatures for BLC, BPC, and BNC.

• Szpunar, Iga; Wachowski, Sebastian; Miruszewski, Tadeusz; Dzierzgowski, Kacper; Górnicka, Karolina & Klimczuk, Tomasz [Show all 12 contributors for this article] (2019). Electric and magnetic properties of Lanthanum Barium Cobaltite. Journal of The American Ceramic Society. ISSN 0002-7820. 103(3), p. 1809–1818. doi: 10.1111/jace.16865. Full text in Research Archive Show summary

  The cubic Ba0.5La0.5CoO3‐δ was synthesized using solid state reaction. The structural properties were determined by the simultaneous refinement of Synchrotron Powder X‐ray Diffraction and Neutron Powder Diffraction data. Iodometric titration was used to examine the oxygen stoichiometry and average cobalt oxidation state. Low‐temperature magnetic studies show soft ferromagnetic character of fully oxidized material, with θ P = 198(3) K and µ eff = 2.11(2) µ B. Electric measurements show the thermally activated nature of conductivity at low temperatures, whereas, due to the variable oxidation and spin state of cobalt, a single charge transport mechanism cannot be distinguished. Around room temperature, a wide transition from thermally activated conductivity to semi‐metallic behavior is observed. Under the inert atmosphere, the oxygen content lowers and the cation ordering takes place, leading to coexistence of two, ordered and disordered, phases. As a result of this change, thermally activated conductivity is observed also at high temperatures in inert atmosphere.

• Sun, Xinwei; Xu, Kaiqi; Fleischer, Christian; Liu, Xin; Grandcolas, Mathieu & Strandbakke, Ragnar [Show all 9 contributors for this article] (2018). Earth-abundant electrocatalysts in proton exchange membrane electrolyzers. Catalysts. 8:657(12), p. 1–41. doi: 10.3390/catal8120657. Full text in Research Archive Show summary

  In order to adopt water electrolyzers as a main hydrogen production system, it is critical to develop inexpensive and earth-abundant catalysts. Currently, both half-reactions in water splitting depend heavily on noble metal catalysts. This review discusses the proton exchange membrane (PEM) water electrolysis (WE) and the progress in replacing the noble-metal catalysts with earth-abundant ones. The efforts within this field for the discovery of efficient and stable earth-abundant catalysts (EACs) have increased exponentially the last few years. The development of EACs for the oxygen evolution reaction (OER) in acidic media is particularly important, as the only stable and efficient catalysts until now are noble-metal oxides, such as IrOx and RuOx. On the hydrogen evolution reaction (HER) side, there is significant progress on EACs under acidic conditions, but there are very few reports of these EACs employed in full PEM WE cells. These two main issues are reviewed, and we conclude with prospects for innovation in EACs for the OER in acidic environments, as well as with a critical assessment of the few full PEM WE cells assembled with EACs.

View all works in NVA

• Norby, Truls Eivind (2021). Electrode kinetics in fuel cells and electrolysers. Full text in Research Archive Show summary

  Fuel cells constitute the technology of choice to convert hydrogen to electricity, while electrolyzers will be a major technology for producing that hydrogen from electricity from renewable sources, notably indirect (hydroelectric, wind, wave) and direct (photovoltaic) solar energy. They are hence not directly the topic of a workshop on solar fuels, but photoelectrochemical (PEC) electrode kinetics is such a complex matter that it is useful to have electrode kinetics of fuel cells and electrolyzers as kind of reference. Both PEC and fuel cells and electrolyzers have in common that established state-of-the-art versions have aqueous liquid electrolytes, while solid-state electrolytes are of increasing interest. We will cover both, and dwell on various intermediate cases. While various charge carrying ions are in use in different ranges of temperature (O2-, CO32-, H+, OH-, H3O+), protonic electrolytes are most central to PEC and we will focus on them, with examples from proton ceramics, proton exchange membranes (PEMs), hydroxide ion conducting polymers, and surface protonic conduction. The electrode reaction comprises faradaic charge transfer over the electrolyte-electrode interface. This can be an electron transfer (redox) or – in the case of mixed ion electron conducting electrodes – ion transfer, in which case the electron transfer must take place somewhere else, e.g. on the electrode surface. The charge transfer – which is our means of driving the reaction with a voltage or recording a current in a chemically driven fuel cell – may be hindered by the supply of reactants, making adsorption and dissociation appear in the polarization resistance. In addition, diffusion in gas phase, over surfaces, and in the bulk of the electrode or electrolyte slows the reaction further and may eventually limit the current. While charge transfer takes place over the double layer capacitance of the electrolyte-electrode interface, the other processes may store reactants and products as much higher chemical capacitance, whereby the different processes have different time constants and may be separated in impedance spectroscopy. The talk will go through materials, processes, and methods, look to general principles that can be applied across systems and technologies, where possible also photoelectrochemical cells for solar hydrogen and artificial photosynthesis.

• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Sørby, Magnus Helgerud; Szpunar, Iga; Wachowski, Sebastian Lech & Mielewczyk-Gryń, Aleksandra [Show all 10 contributors for this article] (2020). Governing principles of hydration in mixed conducting oxides. Full text in Research Archive
• Norby, Truls Eivind (2019). Water and protonic conduction on surfaces of nanomaterials - role in catalytic processes. Full text in Research Archive Show summary

  Water vapour chemisorbs on surfaces as protons and hydroxide ions at elevated temperatures and physisorbs as molecular water at lower temperatures in ice-like thin and liquid-like thick layers, respectively. Also hydrogen adsorbs and dissociates. All adsorbates give rise to surface protonic conduction of different mechanisms and magnitude depending on temperature and acidity of the surface. The surface protonic conduction may be used in electrolytes for electrochemical cells, but in this talk focus is more on its effect in some catalytic processes in finely porous nanomaterials.

• Vøllestad, Einar; Sørby, Magnus Helgerud & Norby, Truls Eivind (2019). Defect chemistry of mixed conducting double perovskites. Full text in Research Archive
• Strandbakke, Ragnar; Vøllestad, Einar; Sørby, Magnus Helgerud & Norby, Truls Eivind (2019). Defect chemistry of mixed conducting double perovskites. Full text in Research Archive
• Strandbakke, Ragnar; Balaguer, Maria; Wachowski, Sebastian Lech; Mielewczyk-Gryn, Aleksandra; Carvalho, Patricia Almeida & Sørby, Magnus Helgerud [Show all 7 contributors for this article] (2019). Protonics, stability and electrochemistry of Ba1‑xGd1-yLax+yCo2O6-δ (BGLC). Full text in Research Archive
• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Vøllestad, Einar; Mielewczyk-Gryn, Aleksandra; Wachowski, Sebastian Lech & Lewandowska, Iga [Show all 9 contributors for this article] (2019). Defect chemistry of mixed conducting double perovskites. Full text in Research Archive
• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Sørby, Magnus Helgerud; Wachowski, Sebastian Lech; Mielewczyk-Gryn, Aleksandra & Balaguer, Maria [Show all 9 contributors for this article] (2019). Hydration and hydrogenation of mixed conducting BaGd1‑xLaxCo2O6‑δ (BGLC). Full text in Research Archive
• Bjørheim, Tor Svendsen; Maier, Joachim; Merkle, Rotraut; Kotomin, Eugene & Hoedl, Maximillian (2019). Defect thermodynamics and lattice site basicity of proton and mixed conducting oxides, Full text in Research Archive
• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Sørby, Magnus Helgerud; Szpunar, Iga; Wachowski, Sebastian Lech & Mielewczyk-Gryn, Aleksandra [Show all 9 contributors for this article] (2019). Protons in mixed conducting Ba1‑xGd1‑yLax+yCo2O6‑δ (BGLC). Full text in Research Archive
• Bjørheim, Tor Svendsen; Hoedl, Maximillian; Kotomin, Eugene; Merkle, Rotraut & Maier, Joachim (2018). Hydration thermodynamics and lattice site basicity of proton conducting and mixed conducting oxides. Full text in Research Archive
• Norby, Truls Eivind (2018). Electrodics for proton ceramic electrochemical cells (PCECs). Full text in Research Archive
• Wachowski, Sebastian; Levandowska, Iga; Sørby, Magnus Helgerud; Balaguer, Maria; Bjørheim, Tor Svendsen & Gazda, Maria [Show all 10 contributors for this article] (2018). Governing Principles in Hydration of Mixed Conducting Oxides: Structure and Hydration of BaLnCo2O6-d. Full text in Research Archive
• Balaguer, Maria; Tarach, Mateusz; Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Mielewczyk-Gryn, Aleksandra & Wachowski, Sebastian [Show all 11 contributors for this article] (2018). Hydration Stability of Mixed Conducting Layered Oxides. Full text in Research Archive
• Norby, Truls Eivind (2018). The chemistries of proton ceramic electrochemical cells. Full text in Research Archive
• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Mielewczyk-Gryn, Aleksandra; Wachowski, Sebastian; Lewandowska, Iga & Balaguer, Maria [Show all 10 contributors for this article] (2018). Governing Principles in Hydration of Mixed Conducting Oxides. Full text in Research Archive
• Strandbakke, Ragnar; Gunnæs, Anette Eleonora; Carvalho, Patricia A.; Mielewczyk-Gryn, Aleksandra; Wachowski, Sebastian & Balaguer, Maria [Show all 8 contributors for this article] (2018). Coupled hydration, cation reorganization and red-ox in MIEC perovskites. Full text in Research Archive
• Strandbakke, Ragnar; Vøllestad, Einar; Norby, Truls Eivind; Sartori, Sabrina; Guzik, Matylda Natalia & Lang, Julien (2017). Hydration and structural properties of mixed conductor Ba1‑xGd0.8La0.2+xCo2O6-δ (BGLC). Full text in Research Archive

View all works in NVA