ragnarst

• 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, s. 1–9. doi: 10.1016/j.electacta.2026.149534. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Strandbakke, Ragnar; Wachowski, Sebastian Lech; Balaguer, Maria; Vines, Lasse; Sky, Thomas Neset & Szpunar, Iga [Vis alle 12 forfattere av denne artikkelen] (2026). Governing principles of hydration of mixed proton conducting Co-based double perovskites. Nature Communications. 17, s. 1–10. doi: 10.1038/s41467-026-70212-w. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Carrillo, Alfonso; Balaguer, M.; Solis, Cecilia; Lopez-Garcia, Andres; Haas, Sylvio & Fabuel, Maria [Vis alle 13 forfattere av denne artikkelen] (2025). Evaluating oxide nanoparticle exsolution on A-site deficient PrBaCo2O6-δ electrodes. Journal of Physics: Energy. 7(2), s. 1–15. doi: 10.1088/2515-7655/ada8de. Fulltekst i vitenarkiv Vis sammendrag

  Nanoparticle exsolution is a powerful technique for functionalizing redox oxides in energy applications, particularly at high temperatures. It shows promise for solid oxide fuel cells and electrolyzers. However, exsolution of other chemistries like metal oxides is not well studied, and the mechanism is poorly understood. This work explores oxide exsolution in PrBa1−xCo2O6−δ (x = 0, 0.05, 0.1, 0.15) double perovskites, practiced electrodes in proton ceramic fuel cells and electrolyzers. Oxide exsolution in PrBa1−xCo2O6−δ aimed at boosting the electrocatalytic activity and was evaluated by varying intrinsic materials-related properties, viz. A-site deficiency and external parameters (temperature, under fixed time, and pO2 = 10−5 atm conditions). The materials were analyzed with conventional characterization tools and synchrotron-based small-angle x-ray scattering. Unlike metal-nanoparticle exsolution, increasing the A-site deficiency did not enhance the extent of oxide-nanoparticle exsolution, whereas larger nanoparticles were obtained by increasing the exsolution temperature. Combined Raman spectroscopy and electron microscopy analysis revealed that BaCoO3, Co3O4, and amorphous BaCO3 nanoparticles were formed on the surface of the double perovskites after the reductive treatments. The present results demonstrate the complexity of oxide-nanoparticle exsolution in comparison with metal-nanoparticle exsolution. Further materials screening and mechanistic studies are needed to enhance our understanding of this method for functionalizing proton ceramic electrochemical cells (PCEC) electrodes.

• 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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Balcerzak, Daria; López-García, Andrés; Carrillo, Alfonso J.; Balaguer, María; Alfaro, Jose Manuel Serra & Norby, Truls [Vis alle 9 forfattere av denne artikkelen] (2025). Tailoring oxide nanoparticle exsolution in La0.5Ba0.5-yCo1-xFexO3-δ. Journal of the European Ceramic Society. ISSN 0955-2219. 45(10), s. 1–12. doi: 10.1016/j.jeurceramsoc.2025.117347. Fulltekst i vitenarkiv Vis sammendrag

  We show that oxide nanoparticles (NPs) exsolve on La0.5Ba0.5-yCo1-xFexO3-δ (x = 0–1, y = 0 or 0.01) in oxidizing conditions. The phenomenon occurs only in Co-containing materials and depends on pO2 and pH2O pressures. Under dry conditions, the smallest NPs average about 30 nm, with 200–300 NPs/µm2 at pO2= 5 × 10−5 atm. For pO2= 1 atm, NP size increases to 100–200 nm, and population drops to a few to about 20 NPs/µm2 depending on A-site nonstoichiometry and x. In humid conditions, the smallest NPs around 50 nm, with a peak of 100 NPs/µm2 exsolve for pO2= 1. Transmission electron microscopy shows that exsolved NPs in La0.5Ba0.5-yCoO3-δ are Ba-O-rich. We propose defect chemistry models, indicating that exsolution is driven by oxidation reactions forming A-site vacancies, increasing exsolved material with higher pO2. We suggest that adsorbed water under humid conditions blocks nucleation sites, altering observed trends.

• Wachowski, Sebastian Lech; Szpunar, Iga; Pospiech, Joanna; Balcerzak, Daria; Mielewczyk-Gryn, Aleksandra & Nadolska, Malgorzata [Vis alle 12 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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

• Pośpiech, Joanna; Nadolska, Małgorzata; Cieślik, Mateusz; Sobczyk, Tomasz; Chmielewski, Marek & Mielewczyk-Gryń, Aleksandra [Vis alle 9 forfattere av denne artikkelen] (2024). Additive manufacturing of Proton-Conducting Ceramics by robocasting with integrated laser postprocessing. Applied Materials Today. ISSN 2352-9407. 40. doi: 10.1016/j.apmt.2024.102398. Fulltekst i vitenarkiv Vis sammendrag

  A hybrid system combining robocasting and NIR laser postprocessing has been designed to fabricate layers of mixed proton-electron conducting Ba0.5La0.5Co1-xFexO3-δ ceramic. The proposed manufacturing technique allows for the control of the geometry and microstructure and shortens the fabrication time to a range of a few minutes. Using 5 W laser power and a scanning speed of 500 mm·s−1, sintering of a round-shaped layer with an 8 mm radius was performed in less than 2 s. The single phase of the final product was confirmed by X-ray diffraction. Various ceramic-to-polymer weight ratios were tested, showing that various porosities of microstructures of ∼30 - 35 % and ∼19 % can be obtained with 2:1 and 4:1 loading respectively.

• Miruszewski, Tadeusz; Strandbakke, Ragnar; Dzierzgowski, Kacper; Szpunar, Iga; Mielewczyk-Gryń, Aleksandra & Wachowski, Sebastian [Vis alle 7 forfattere av denne artikkelen] (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. s. 12891–13534. doi: 10.1039/d4ta00100a. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Balcerzak, Daria; Szpunar, Iga; Strandbakke, Ragnar; Saeed, Sarmad W.; Bazioti, Calliope & Mielewczyk-Gryń, Aleksandra [Vis alle 12 forfattere av denne artikkelen] (2023). Oxide nanoparticle exsolution in Lu-doped (Ba,La)CoO₃. CrysteEngComm. 25(30), s. 4316–4316. doi: 10.1039/d3ce00422h. Fulltekst i vitenarkiv Vis sammendrag

  This study investigated Lu doping of Ba 0.5 La 0.5 CoO 3 and its influence on the exsolution of oxide nanoparticles (NPs).

• Mielewczyk-Gryń, Aleksandra; Yang, Shuhao; Balaguer, Maria; Strandbakke, Ragnar; Sørby, Magnus Helgerud & Szpunar, Iga [Vis alle 11 forfattere av denne artikkelen] (2023). Energetics of formation and stability in high pressure steam of barium lanthanide cobaltite double perovskites. Dalton Transactions. ISSN 1477-9226. 52(17), s. 5771–5779. doi: 10.1039/d2dt03989c. Fulltekst i vitenarkiv
• Dayaghi, Amir Masoud; Polfus, Jonathan M.; Strandbakke, Ragnar; Pokle, Anuj; Almar, Laura & Escolastico, Sonia [Vis alle 10 forfattere av denne artikkelen] (2023). Effects of sintering additives on defect chemistry and hydration of BaZr0.4Ce0.4(Y,Yb)0.2O3−δ proton conducting electrolytes. Solid State Ionics. ISSN 0167-2738. 401. doi: 10.1016/j.ssi.2023.116355. Fulltekst i vitenarkiv
• Balcerzak, Daria; Szpunar, Iga; Strandbakke, Ragnar; Saeed, Sarmad Waheed; Bazioti, Kalliopi & Mielewczyk-Gryń, Aleksandra [Vis alle 12 forfattere av denne artikkelen] (2023). Oxide nanoparticle exsolution in Lu-doped (Ba,La)CoO3. CrysteEngComm. 25(30), s. 4306–4316. doi: 10.1039/d3ce00422h. Fulltekst i vitenarkiv
• Sobhana, Dilimon Vijayan; Strandbakke, Ragnar & Norby, Truls (2022). Impedance spectroscopy study of Au electrodes on Gd-doped CeO<inf>2</inf> (GDC) – Molten Li<inf>2</inf>CO<inf>3</inf>+Na<inf>2</inf>CO<inf>3</inf> (LNC) composite electrolytes. Journal of Power Sources. ISSN 0378-7753. 522. doi: 10.1016/j.jpowsour.2022.230986. Fulltekst i vitenarkiv Vis sammendrag

  We herein report an impedance spectroscopy study of Au electrodes on Gd-doped CeO2 (GDC) – molten Li2CO3+Na2CO3 (LNC) composite electrolytes in O2 and O2+CO2 atmospheres. Complementary measurements of Au on GDC alone are provided for supporting insight. We find that the adsorption of CO2 on GDC in O2+CO2 atmospheres effectively blocks oxygen adsorption and severely slows oxygen reduction kinetics. The conductivity of the composite is dominated by the GDC phase in the solid-solid temperature region, while the LNC phase dominates above its melting point, and no further enhancement e.g. by interfacial effects are found. The incorporation of LNC melt into GDC results in a significant reduction in the polarisation resistance of Au electrodes in O2 atmospheres, as the melt mediates the reaction by a peroxide mechanism. In O2+CO2 atmospheres, however, the polarisation resistance of Au electrodes on GDC-LNC membranes is significantly higher, higher even than that on GDC. This we assign again to the blocking adsorption of CO2 (or carbonate) on the surfaces of ceria and the sluggish transport and reactions now mediated by carbonate-carried oxide species (CO42−) instead of peroxide species.

• Strandbakke, Ragnar; Wragg, David Stephen; Sørby, Magnus Helgerud; Guzik, Matylda; Gunnæs, Anette Eleonora & Szpunar, Iga [Vis alle 12 forfattere av denne artikkelen] (2022). Structural properties of mixed conductor Ba1−xGd1−yLax+yCo2O6−δ. Dalton Transactions. ISSN 1477-9226. 51(48), s. 18667–18677. doi: 10.1039/d2dt02277j. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Zhu, Junjie; Gudmundsdottir, Jonina Björg; Strandbakke, Ragnar; Both, Kevin Gregor; Aarholt, Thomas & Carvalho, Patricia Almeida [Vis alle 12 forfattere av denne artikkelen] (2021). Double Perovskite Cobaltites Integrated in a Monolithic and Noble Metal-Free Photoelectrochemical Device for Efficient Water Splitting. ACS Applied Materials & Interfaces. ISSN 1944-8244. 13(17), s. 20313–20325. doi: 10.1021/acsami.1c01900. Fulltekst i vitenarkiv Vis sammendrag

  Water photoelectrolysis has the potential to produce renewable hydrogen fuel, therefore addressing the intermittent nature of sunlight. Herein, a monolithic, photovoltaic (PV)-assisted water electrolysis device of minimal engineering and of low (in the μg range) noble-metal-free catalysts loading is presented for unassisted water splitting in alkaline media. An efficient double perovskite cobaltite catalyst, originally developed for high-temperature proton-conducting ceramic electrolyzers, possesses high activity for the oxygen evolution reaction in alkaline media at room temperatures too. Ba1–xGd1–yLax+yCo2O6−δ (BGLC) is combined with a NiMo cathode, and a solar-to-hydrogen efficiency of 6.6% in 1.0 M NaOH, under 1 sun simulated illumination for 71 h, is demonstrated. This work highlights how readily available earth-abundant materials and established PV methods can achieve high performance and stable and monolithic photoelectrolysis devices with potential for full-scale applications.

• Emhjellen, Linn Katinka Susanne Shi; Strandbakke, Ragnar & Haugsrud, Reidar (2021). Electrical transport in a molten-solid V2O5–ZrV2O7 composite. Journal of Materials Chemistry A. ISSN 2050-7488. 9(34), s. 18537–18545. doi: 10.1039/D1TA03750A. Fulltekst i vitenarkiv Vis sammendrag

  Molten-solid composite oxides are candidates as oxygen transport membranes (OTMs) at intermediate temperatures (500–700 °C). Effects of the constituent phases and interphases on surface reactions and transport processes in these composites are elusive. Here we contribute fundamental insight to such materials systems, applying electrochemical impedance spectroscopy (EIS) and electromotive force (emf) measurements to investigate the electrical conductivity characteristics of a 30 mol% V2O5–ZrV2O7 composite with a eutectic melting point at ∼670 °C. When V2O5 melts and increases the V2O5 volume percolation, the electrical conductivity increases by a factor of 10 and the activation energy increases from 0.21 to ∼0.7 eV. The oxygen red-ox reaction at the surface changes from being rate limited by charge transfer processes to mass transfer processes as a consequence of fast oxygen exchange in molten V2O5 as compared to the all-solid composite. These effects coincide with the ionic transport number rising from essentially zero to ∼0.4, reflecting a significant increase in the relative oxide ion conductivity. Oxygen permeation across a 30 mol% V2O5–ZrV2O7 membrane was estimated to be in the same order as for several dual-phase membranes, but one magnitude lower than for single-phase mixed conducting membranes at intermediate temperatures.

• Dayaghi, Amir Masoud; Haugsrud, Reidar; Stange, Marit Synnøve Sæverud; Larring, Yngve; Strandbakke, Ragnar & Norby, Truls Eivind (2021). Increasing the thermal expansion of proton conducting Y-doped BaZrO3 by Sr and Ce substitution. Solid State Ionics. ISSN 0167-2738. 359. doi: 10.1016/j.ssi.2020.115534. Fulltekst i vitenarkiv Vis sammendrag

  Proton conducting oxide electrolytes find potential application in proton ceramic fuel cells and electrolyzers operating at intermediate temperatures, e.g. 400–600 °C. However, state-of-the-art proton conducting ceramics based on Y-doped BaZrO3 (BZY) have lower thermal expansion coefficient (TEC) than most commonly applied or conceived supporting electrode structures, making the assembly vulnerable to degradation due to cracks or spallation. We have increased the TEC of 20 mol% Y-doped BZY (BZY20) by partially substituting Ba and Zr with Sr and Ce, respectively, to levels which still maintain the cubic structure and sufficiently minor n-type conduction; (Ba0.85Sr0.15)(Zr0.7Ce0.1Y0.2)O2.9 (BSZCY151020). High temperature XRD shows that this material has a cubic structure (space group ) in the temperature range of 25–1150 °C and a linear TEC of ~10 × 10−6 K−1, as compared to the ~8 × 10−6 K−1 for BZY. It exhibited a DC conductivity of ~5 mS cm−1 at 600 °C in wet H2. This electrolyte with increased TEC may find application in proton ceramic electrochemical cells in general and metal supported ones in particular.

• 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), s. 1030–1033. doi: 10.1039/c9cc08765f. Fulltekst i vitenarkiv
• Wachowski, Sebastian Lech; Szpunar, Iga; Sørby, Magnus Helgerud; Mielewczyk-Gryń, Aleksandra; Balaguer, Maria & Ghica, Corneliu [Vis alle 12 forfattere av denne artikkelen] (2020). Structure and water uptake in BaLnCo2O6−δ (Ln = La, Pr, Nd, Sm, Gd, Tb and Dy). Acta Materialia. ISSN 1359-6454. 199, s. 297–310. doi: 10.1016/j.actamat.2020.08.018. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Szpunar, Iga; Strandbakke, Ragnar; Sørby, Magnus Helgerud; Wachowski, Sebastian Lech; Balaguer, Maria & Tarach, Mateusz [Vis alle 12 forfattere av denne artikkelen] (2020). High-temperature structural and electrical properties of BaLnCo2O6 positrodes. Materials. 13(18), s. 1–18. doi: 10.3390/ma13184044. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Vøllestad, Einar; Strandbakke, Ragnar; Tarach, Mateusz; Catalán-Martinez, David; Fontaine, Marie-Laure & Beeaff, Dustin [Vis alle 9 forfattere av denne artikkelen] (2019). Mixed proton and electron conducting double perovskite anodes for stable and efficient tubular proton ceramic electrolysers. Nature Materials. ISSN 1476-1122. 18(7), s. 752–759. doi: 10.1038/s41563-019-0388-2. Fulltekst i vitenarkiv Vis sammendrag

  Hydrogen production from water electrolysis is a key enabling energy storage technology for the large-scale deployment of intermittent renewable energy sources. Proton ceramic electrolysers (PCEs) can produce dry pressurized hydrogen directly from steam, avoiding major parts of cost-driving downstream separation and compression. However, the development of PCEs has suffered from limited electrical efficiency due to electronic leakage and poor electrode kinetics. Here, we present the first fully operational BaZrO3-based tubular PCE, with 10 cm2 active area and a hydrogen production rate above 15 Nml min−1. The novel steam anode Ba1−xGd0.8La0.2+xCo2O6−δ exhibits mixed p-type electronic and protonic conduction and low activation energy for water splitting, enabling total polarization resistances below 1 Ω cm2 at 600 °C and Faradaic efficiencies close to 100% at high steam pressures. These tubular PCEs are mechanically robust, tolerate high pressures, allow improved process integration and offer scale-up modularity.

• Szpunar, Iga; Wachowski, Sebastian; Miruszewski, Tadeusz; Dzierzgowski, Kacper; Górnicka, Karolina & Klimczuk, Tomasz [Vis alle 12 forfattere av denne artikkelen] (2019). Electric and magnetic properties of Lanthanum Barium Cobaltite. Journal of The American Ceramic Society. ISSN 0002-7820. 103(3), s. 1809–1818. doi: 10.1111/jace.16865. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Kaklidis, N.; Strandbakke, Ragnar; Arenillas, A.; Menendez, Javier A; Konsolakis, M. & Marnellos, G.E. (2019). The synergistic catalyst-carbonates effect on the direct bituminous coal fuel cell performance. International Journal of Hydrogen Energy. ISSN 0360-3199. 44(20), s. 10033–10042. doi: 10.1016/j.ijhydene.2019.02.038. Fulltekst i vitenarkiv Vis sammendrag

  The current work explores the feasibility to improve the performance of a Direct Carbon Fuel Cell (DCFC): CO2 + bituminous coal|Co-CeO2/YSZ/Ag|Air by infusing a gasification catalyst (Co/CeO2) and/or Li-K carbonates mixture into the carbon fuel. The different fuel feedstock mixtures were characterized by various methods, involving chemical composition and proximate analysis, particle size distribution (PSD), X-ray diffraction (XRD), N2 adsorption-desorption (BET method), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), to gain insight into the effect of catalyst and/or carbonates addition to fuel mixture physicochemical characteristics. An increase of the power output up to ca. 20 and 80% is achieved for carbon/catalyst and carbon/catalyst/carbonates mixtures, respectively, in comparison to bare carbon at 700 °C, demonstrating the pronounced effect of catalyst as well as its potential synergy with carbonates. It was also shown that the achieved maximum power density is directly associated with the CO formation rate, implying the importance of in situ formed CO on the electrochemical performance. The obtained findings are further discussed based also on the corresponding AC impedance spectroscopy studies, which revealed the beneficial effect of fuel feedstock additives (catalyst and/or carbonates) on ohmic and electrode polarization resistances. The present results clearly revealed the feasibility to improve the DCFC performance by concurrently infusing a gasification catalyst and carbonates mixture into fuel feedstock.

• Konsolakis, M.; Kaklidis, N.; Kyriakou, V.; Garagounis, I.; Kraia, Tzouliana & Arenillas, A. [Vis alle 9 forfattere av denne artikkelen] (2018). The combined impact of carbon type and catalyst-aided gasification process on the performance of a Direct Carbon Solid Oxide Fuel Cell. Solid State Ionics. ISSN 0167-2738. 317, s. 268–275. doi: 10.1016/j.ssi.2018.01.026. Fulltekst i vitenarkiv
• Sun, Xinwei; Xu, Kaiqi; Fleischer, Christian; Liu, Xin; Grandcolas, Mathieu & Strandbakke, Ragnar [Vis alle 9 forfattere av denne artikkelen] (2018). Earth-abundant electrocatalysts in proton exchange membrane electrolyzers. Catalysts. 8:657(12), s. 1–41. doi: 10.3390/catal8120657. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Bausa, Nuria; Solis, Cecilia; Strandbakke, Ragnar & Serra, José Manuel (2017). Development of composite steam electrodes for electrolyzers based on barium zirconate. Solid State Ionics. ISSN 0167-2738. 306, s. 62–68. doi: 10.1016/j.ssi.2017.03.020. Fulltekst i vitenarkiv Vis sammendrag

  La0.6Sr0.4Co0.2Fe0.8O3 − δ (LSCF), La2NiO4 + δ (LNO), La0.87Sr0.13CrO4 (LSC), La0.8Sr0.2MnO3 − δ (LSM) and Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF) composite anodes deposited on proton-conducting BaCe0.2Zr0.7Y0.1O3 − δ (BCZY27) electrolytes were studied as steam electrolysis anodes in symmetric cells. The effect of the electrode composition and microstructure on the electrochemical behavior was investigated using impedance spectroscopy in the 800–500 °C range under 3 bar of pressure of wet air (75% of steam). The first screening revealed that 50–50 (vol%) LSCF/BCZY27 composite anodes show the best performance, reaching polarization resistances < 0.68 Ω·cm2 at 700 °C and high steam pressure (0.75 bar of air and 2.25 bar of steam). The performance of the LSCF/BCZY27 composite was further improved by changing the ratio of the different phases. Finally the anode operation conditions (steam, oxygen and total pressures) were systematically varied in order to identify and characterize the different electrochemical processes that take place in the anode under realistic operation.

• Kraia, Tzouliana; Wachowski, Sebastian Lech; Vøllestad, Einar; Strandbakke, Ragnar; Konsolakis, M. & Norby, Truls Eivind [Vis alle 7 forfattere av denne artikkelen] (2017). Electrochemical performance of Co3O4/CeO2 electrodes in H2S/H2O atmospheres in a proton-conducting ceramic symmetrical cell with BaZr0.7Ce0.2Y0.1O3 solid electrolyte. Solid State Ionics. ISSN 0167-2738. 306, s. 31–37. doi: 10.1016/j.ssi.2017.04.010. Fulltekst i vitenarkiv Vis sammendrag

  The electrochemical performance of Co3O4/CeO2 mixed oxide materials as electrodes, when exposed to H2S/H2O atmospheres, was examined employing a proton conducting symmetrical cell, with BaZr0.7Ce0.2Y0.1O3 (BZCY72) as the solid electrolyte. The impact of temperature (700–850 °C) and H2S concentration (0–1 v/v%) in steam-rich atmospheres (90 v/v% H2O) on the overall cell performance was thoroughly assessed by means of electrochemical impedance spectroscopy (EIS) studies. The performance of the Co3O4/CeO2 electrode was significantly enhanced by increasing the H2S concentration and temperature. The obtained results were interpreted on the basis of EIS results and physicochemical characterization (XRD, SEM) studies of fresh and used electrodes. Notably, it was found that the mass transport processes, mainly associated with the adsorption and diffusion of the intermediate species resulting by the chemical and half-cell reactions taking place during cell operation, dominate the electrode polarization resistance compared with the charge transfer processes. Upon increasing temperature and H2S concentration, the electrode resistance is substantially lowered, due to the in situ activation and morphological modifications of the electrode, induced by its interaction with the reactants (H2S/H2O) and products (H2/SO2) mixtures.

• Vøllestad, Einar; Schrade, Matthias; Segalini, Julie; Strandbakke, Ragnar & Norby, Truls Eivind (2017). Relating defect chemistry and electronic transport in the double perovskite Ba1-xGd0.8La0.2+xCo2O6-d (BGLC). Journal of Materials Chemistry A. ISSN 2050-7488. 5(30), s. 15743–15751. doi: 10.1039/c7ta02659e. Fulltekst i vitenarkiv Vis sammendrag

  Rare earth double perovskites comprise a class of functional oxides with interesting physiochemical properties both for low- and high-temperature applications. However, little can be found relating electrical properties with equilibrium thermodynamics of non-stoichiometry and defects. In the present work, a comprehensive and generally applicable defect chemical model is developed to form the link between the defect chemistry and electronic structure of partially substituted BGLC (Ba1−xGd0.8La0.2+xCo2O6−δ, 0 ≤ x ≤ 0.5). The equilibrium oxygen content of 4 different compositions is determined as a function of pO2 and temperature by thermogravimetric analysis, and combined with defect chemical modelling to obtain defect concentrations and thermodynamic parameters. Oxidation enthalpies determined by TG-DSC become increasingly exothermic (−50 to −120 kJ mol−1) with increased temperature and oxygen non-stoichiometry for all compositions, in excellent agreement with the thermodynamic parameters obtained from the defect chemical model. All compositions display high electrical conductivities (500 to 1000 S cm−1) with shallow pO2-dependencies and small and positive Seebeck coefficients (3 to 15 μV K−1), indicating high degree of degeneracy of the electronic charge carriers. The complex electrical properties of BGLC at elevated temperatures is rationalized by a two-band conduction model where highly mobile p-type charge carriers are transported within the valence band, whereas less mobile “n-type” charge carriers are located in narrow Co 3d band.

• Strandbakke, Ragnar; Vøllestad, Einar; Robinson, Shay Alexander; Fontaine, Marie-Laure & Norby, Truls Eivind (2017). Ba0.5Gd0.8La0.7Co2O6-δ infiltrated in porous BaZr0.7Ce0.2Y0.1O3 backbones as electrode material for proton ceramic electrolytes. Journal of the Electrochemical Society. ISSN 0013-4651. 164(4), s. F196–F202. doi: 10.1149/2.0141704jes. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Dyrlie, Oddvar; Hage, Fredrik Sydow & Norby, Truls (2016). Reaction kinetics of protons and oxide ions in LSM/lanthanum tungstate cathodes with Pt nanoparticle activation. Journal of the Electrochemical Society. ISSN 0013-4651. 163(6), s. F507–F515. doi: 10.1149/2.0881606jes. Fulltekst i vitenarkiv
• Kaklidis, N.; Kyriakou, V.; Marnellos, G.E.; Strandbakke, Ragnar; Arenillas, A. & Menendez, JA [Vis alle 7 forfattere av denne artikkelen] (2016). Effect of fuel thermal pretreament on the electrochemical performance of a direct lignite coal fuel cell. Solid State Ionics. ISSN 0167-2738. 288, s. 140–146. doi: 10.1016/j.ssi.2015.12.003. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Cherepanov, Vladimir A.; Zuev, Andrey Yu.; Tsvetkov, Dmitry S.; Argirusis, Christos & Sourkouni, Georgia [Vis alle 8 forfattere av denne artikkelen] (2015). Gd- and Pr-based double perovskite cobaltites as oxygen electrodes for proton ceramic fuel cells and electrolyser cells. Solid State Ionics. ISSN 0167-2738. 278, s. 120–132. doi: 10.1016/j.ssi.2015.05.014. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Strandbakke, Ragnar; Vøllestad, Einar; Singh, Kalpana & Norby, Truls (2025). Influence of bias on electrode reactions for Proton Ceramic Cells. Vis sammendrag

  In this work, we investigate electrode overpotential of positrodes under anodic and cathodic operation. We study how the impedance of several state-of-the-art positrode materials is affected by applied bias and propose a model for decoupling the kinetic and mass transfer contributions to the total electrode polarisation. Furthermore, we investigate how partial electronic conductivity – affected by applied bias – disguise the true electrode impedance. The model is tested for two different electrolytes – BaZr0.7Ce0.2Y0.1O3 (BZCY721) and BaZr0.4Ce0.4Y0.2O3 (BZCY442) – displaying different ionic- to electronic transference numbers and revealing the true influence of p-type conductivity on measured impedance under anodic and cathodic bias. The results enable decoupling of three main charge carriers – electron holes, protons and oxygen vacancies – and show how the partial currents are affected by temperature, pO2 and pH2O. Moreover, the kinetic part of the overpotential is revealed as more influential than previously interpreted from the small low-capacitance charge transfer reaction at the electrolyte-electrode interface as seen by EIS at OCV. The results are obtained by applying voltage over BZCY button-cells with three-electrode configuration in symmetrical atmosphere, and stepwise modelling of electrolyte and electrode impedances for three charge carriers. We propose a correction for the effect of the counter electrode overpotential on p-type conductivity, enabling full modelling of electrode impedance under bias

• Singh, Kalpana; Stefan, Elena; Grandcolas, Mathieu; Stange, Marit Synnøve Sæverud; Vøllestad, Einar & Strandbakke, Ragnar [Vis alle 10 forfattere av denne artikkelen] (2025). Innovative Design of CRM-lean Steam Electrode Architectures for Proton Conducting Ceramic Electrolysis. Fulltekst i vitenarkiv
• Vøllestad, Einar; Fontaine, Marie-Laure; Singh, Kalpana; Småbråten, Didrik Rene & Strandbakke, Ragnar (2025). Quantifying Spatial Extension of Reaction Zone on Model BaGd0.3La0.7Co2O6−δ Positrode Systems. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• Småbråten, Didrik Rene; Polfus, Jonathan; Strandbakke, Ragnar; Singh, Kalpana; Veenstra, Peter & Fontaine, Marie-Laure (2023). DFT modelling of thermodynamic and kinetic parameters in electrochemical proton ceramic conducting cells. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• Strandbakke, Ragnar (2023). Hydration, stability and electrochemistry of electrode materials for proton ceramic electrochemical cells. Fulltekst i vitenarkiv
• Chatzitakis, Athanasios; Zhu, Junjie; Gudmundsdottir, Jonina Björg; Strandbakke, Ragnar; Both, Kevin Gregor & Aarholt, Thomas [Vis alle 12 forfattere av denne artikkelen] (2022). A monolithic and noble metal-free photoelectrochemical device of minimal engineering for efficient, unassisted water splitting. Fulltekst i vitenarkiv
• Dayaghi, Amir Masoud; Polfus, Jonathan; Strandbakke, Ragnar; Vøllestad, Einar; Haugsrud, Reidar & Norby, Truls (2022). Effects of NiO, ZnO and CuO sintering additives on the hydration of BaZr0.4Ce0.4(Y,Yb)0.2O3-δ proton conducting electrolytes. Fulltekst i vitenarkiv
• Singh, Kalpana; Norby, Truls & Strandbakke, Ragnar (2022). Effect of partial conductivities on the polarisation resistance of positrodes for proton ceramic fuel cells and electrolysers. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Singh, Kalpana & Norby, Truls (2022). Effect of partial conductivities on the polarisation resistance of positrodes for proton ceramic fuel cells and electrolysers. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Balaguer, María; Carrillo, Alfonso; Wachowski, Sebastian Lech; Mielewczyk-Gryń, Aleksandra & Szpunar, Iga [Vis alle 13 forfattere av denne artikkelen] (2021). Hydration and electrochemistry of mixed conducting cobaltites. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Balaguer, María; Carrillo, Alfonso; Wachowski, Sebastian Lech; Mielewczyk-Gryń, Aleksandra & Szpunar, Iga [Vis alle 14 forfattere av denne artikkelen] (2021). Hydration and electrochemistry of mixed conducting cobaltites. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Sørby, Magnus Helgerud; Szpunar, Iga; Wachowski, Sebastian Lech & Mielewczyk-Gryń, Aleksandra [Vis alle 10 forfattere av denne artikkelen] (2020). Governing principles of hydration in mixed conducting oxides. Fulltekst i vitenarkiv
• Saeed, Sarmad Waheed & Strandbakke, Ragnar (2020). Resent Activities in FunKeyCat. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Saeed, Sarmad Waheed & Carrillo, Alfonso (2019). Exsolution activities in the FunKeyCat project: Exsolving oxide nano-catalysts from cathode materials. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Vøllestad, Einar; Sørby, Magnus Helgerud & Norby, Truls Eivind (2019). Defect chemistry of mixed conducting double perovskites. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Balaguer, Maria; Wachowski, Sebastian Lech; Mielewczyk-Gryn, Aleksandra; Carvalho, Patricia Almeida & Sørby, Magnus Helgerud [Vis alle 7 forfattere av denne artikkelen] (2019). Protonics, stability and electrochemistry of Ba1‑xGd1-yLax+yCo2O6-δ (BGLC). Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Vøllestad, Einar; Mielewczyk-Gryn, Aleksandra; Wachowski, Sebastian Lech & Lewandowska, Iga [Vis alle 9 forfattere av denne artikkelen] (2019). Defect chemistry of mixed conducting double perovskites. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Sørby, Magnus Helgerud; Wachowski, Sebastian Lech; Mielewczyk-Gryn, Aleksandra & Balaguer, Maria [Vis alle 9 forfattere av denne artikkelen] (2019). Hydration and hydrogenation of mixed conducting BaGd1‑xLaxCo2O6‑δ (BGLC). Fulltekst i vitenarkiv
• Saeed, Sarmad Waheed & Strandbakke, Ragnar (2019). FunKeyCat - An Overview. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Sørby, Magnus Helgerud; Szpunar, Iga; Wachowski, Sebastian Lech & Mielewczyk-Gryn, Aleksandra [Vis alle 9 forfattere av denne artikkelen] (2019). Protons in mixed conducting Ba1‑xGd1‑yLax+yCo2O6‑δ (BGLC). Fulltekst i vitenarkiv
• Wachowski, Sebastian; Levandowska, Iga; Sørby, Magnus Helgerud; Balaguer, Maria; Bjørheim, Tor Svendsen & Gazda, Maria [Vis alle 10 forfattere av denne artikkelen] (2018). Governing Principles in Hydration of Mixed Conducting Oxides: Structure and Hydration of BaLnCo2O6-d. Fulltekst i vitenarkiv
• Balaguer, Maria; Tarach, Mateusz; Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Mielewczyk-Gryn, Aleksandra & Wachowski, Sebastian [Vis alle 11 forfattere av denne artikkelen] (2018). Hydration Stability of Mixed Conducting Layered Oxides. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Wragg, David; Carvalho, Patricia; Mielewczyk-Gryn, Aleksandra; Wachowski, Sebastian & Balaguer, Maria [Vis alle 8 forfattere av denne artikkelen] (2018). Coupled hydration and red-ox in MIEC BGLC perovskites. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Mielewczyk-Gryn, Aleksandra; Wachowski, Sebastian; Lewandowska, Iga & Balaguer, Maria [Vis alle 10 forfattere av denne artikkelen] (2018). Governing Principles in Hydration of Mixed Conducting Oxides. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Gunnæs, Anette Eleonora; Carvalho, Patricia A.; Mielewczyk-Gryn, Aleksandra; Wachowski, Sebastian & Balaguer, Maria [Vis alle 8 forfattere av denne artikkelen] (2018). Coupled hydration, cation reorganization and red-ox in MIEC perovskites. Fulltekst i vitenarkiv
• 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). Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Vøllestad, Einar & Norby, Truls Eivind (2017). Development of oxygen-side electrodes for proton conducting fuel cells and electrolysers. Fulltekst i vitenarkiv
• 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). Fulltekst i vitenarkiv
• Fontaine, Marie-Laure; Xing, Wen; Bredesen, Rune; Denonville, Christelle; Polfus, Jonathan M. & Strandbakke, Ragnar [Vis alle 10 forfattere av denne artikkelen] (2016). Proton conducting electrolysers with tubular segmented-in-series cells for hydrogen production. Fulltekst i vitenarkiv
• Norby, Truls; Strandbakke, Ragnar; Chen, Min; Robinson, Shay Alexander & Kjølseth, Christian (2016). Fundamentals of electrodes for ceramic proton conducting electrolytes. Fulltekst i vitenarkiv
• Vøllestad, Einar; Strandbakke, Ragnar; Beeaff, Dustin & Norby, Truls (2016). Proton Ceramic Steam Electrolysers. Fulltekst i vitenarkiv
• Fontaine, Marie-Laure; Denonville, Christelle; Strandbakke, Ragnar; Vøllestad, Einar; Norby, Truls & Bredesen, Rune [Vis alle 8 forfattere av denne artikkelen] (2016). Proton conducting electrolytes integrated in tubular segmented-in-series cells for pressurized hydrogen production. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Vøllestad, Einar; Prato, Rafael Alberto; Wragg, David; Sartori, Sabrina & Norby, Truls (2016). Structural and electrochemical properties of hydrated mixed conductor Ba1-xGd0.8La0.2+xCo2O6-d. Fulltekst i vitenarkiv
• Vøllestad, Einar; Strandbakke, Ragnar; Beaff, Dustin & Norby, Truls (2016). Proton Ceramic Steam Electrolysers. Fulltekst i vitenarkiv
• Vøllestad, Einar; Fontaine, Marie-Laure; Denonville, Christelle; Strandbakke, Ragnar; Norby, Truls & Vigen, Camilla Kaori [Vis alle 7 forfattere av denne artikkelen] (2016). Development of tubular proton conducting electrolysers. Fulltekst i vitenarkiv
• Norby, Truls; Fontaine, Marie-Laure; Strandbakke, Ragnar; Denonville, Christelle; Vøllestad, Einar & Vigen, Camilla Kaori [Vis alle 8 forfattere av denne artikkelen] (2016). Development of tubular proton conducting electrolysers. Fulltekst i vitenarkiv
• Vøllestad, Einar; Strandbakke, Ragnar & Norby, Truls (2016). Tailoring the properties of BGLC double perovskites. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Vøllestad, Einar; Prato, Rafael Alberto; Wragg, David & Norby, Truls (2016). Structural and electrochemical properties of hydrated mixed conductor Ba1-xGd0.8La0.2+xCo2O6-d. Fulltekst i vitenarkiv
• Fontaine, Marie-Laure; Denonville, Christelle; Strandbakke, Ragnar; Serra, José Manuel; Beeaff, Dustin R. & Vigen, Camilla Kaori [Vis alle 8 forfattere av denne artikkelen] (2016). Development of Tubular Proton Ceramic Electrolysers (PCEs). Fulltekst i vitenarkiv
• Norby, Truls; Strandbakke, Ragnar; Vøllestad, Einar; Chen, Min; Robinson, Shay Alexander & Kjølseth, Christian (2016). Proton ceramic electrodics. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Vøllestad, Einar & Norby, Truls (2015). Investigation of BaGd0.8La0.2Co2O6-δ as Oxygen Electrode Material for Proton Conducting Fuel Cells and Electrolyzer Cells. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Vøllestad, Einar & Norby, Truls (2015). Characterization of electrodes on ionic conductors with transport of more than one type of charge carriers. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Vøllestad, Einar & Norby, Truls (2015). Characterization of double perovskite electrodes on ionic conductors with transport of more than one type of charge carriers. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Vøllestad, Einar & Norby, Truls (2015). Investigation of Ba1-xGd0.8La0.2+xCo2O6-δ as Oxygen Electrode Material for Proton Conducting Fuel Cells and Electrolyzer Cells. Fulltekst i vitenarkiv
• Evans, Anna; Xing, Wen; Strandbakke, Ragnar & Norby, Truls (2015). Transport properties of molten carbonates and ceria-carbonate composites. Fulltekst i vitenarkiv
• Evans, Anna; Strandbakke, Ragnar; Patricio, Sonia; Marques, Fernando & Norby, Truls (2015). Ionic transport in ceramic-carbonate composites. Fulltekst i vitenarkiv
• Vøllestad, Einar & Strandbakke, Ragnar (2015). Den nye vannkraften. Aftenposten Viten. ISSN 2464-3033. Fulltekst i vitenarkiv
• Vøllestad, Einar; Strandbakke, Ragnar; Fontaine, Marie-Laure & Norby, Truls (2015). Infiltrated Double Perovskite Electrodes for Proton Conducting Steam Electrolysers. Fulltekst i vitenarkiv
• Vøllestad, Einar; Strandbakke, Ragnar & Norby, Truls (2015). Infiltrated Double Perovskite Electrodes for Proton Conducting Steam Electrolysers. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Vøllestad, Einar & Norby, Truls (2015). Characterization of ionic transport and electrode kinetics in systems with multiple charge carriers. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Norby, Truls; Zuev, Andrey; Cherepanov, Vladimir & Argirusis, Christos (2014). Model and methodology for investigation of oxygen electrodes on BZCY* electrolytes. Fulltekst i vitenarkiv
• Norby, Truls; Strandbakke, Ragnar; Evans, Anna & Xing, Wen (2014). Characterisation of transport in oxides with more than one ionic charge carrier. Fulltekst i vitenarkiv
• Norby, Truls; Strandbakke, Ragnar; Cherepanov, Vladimir; Zuev, Andrey & Argirusis, Christos (2014). Model and methodology for investigation of oxygen electrodes on BZCY electrolytes. Fulltekst i vitenarkiv
• Strandbakke, Ragnar; Evans, Anna & Norby, Truls (2014). Investigation of the ionic transport in ceramic-carbonate composites. Fulltekst i vitenarkiv
• Strandbakke, Ragnar (2013). Gd and Pr-based double perovskite cobaltites as air side electrodes for Proton Conducting Solid Oxide Fuel Cells / Electrolyzer Cells. Fulltekst i vitenarkiv
• Strandbakke, Ragnar (2013). Recent developments in air side electrodes for PC-SOFC / PC-SOEC. Fulltekst i vitenarkiv
• Abbas, Haider; Haugsrud, Reidar & Strandbakke, Ragnar (2022). Defect and transport in Ba7M’4-x MoxO20+z (M’=Nb,Ta). Universitetet i Oslo. Fulltekst i vitenarkiv
• Svee, Tord; Norby, Truls; Haugsrud, Reidar; Strandbakke, Ragnar; Thoreton, Vincent & Clar, Daniel (2021). Surface kinetics of BaGd1-xLaxCo2O6-𝛿 for use as an anode material in proton ceramic electrolyser cells. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  The main topic of this thesis is the surface kinetics of BaGdxLa1-xCo2O6-δ (BGLC), a mixed ionic electronic conducting double perovskite, with operation temperatures between 400-700 °C that shows potential for use as an anode in Proton Conducting Ceramic Electrolysers (PCEC). While showing promise the material is still limited by its surface reactions, notably adsorption and dissociation. To test the variation in surface kinetics with the ratio of lanthanides on the A’-site, five compositions with differing lanthanide content was synthesised with a sol-gel synthesis path: BGLC19 (BaGd0.1La0.9Co2O6-δ), BGLC37 (BaGd0.3La0.7Co2O6-δ), BGLC55 (BaGd0.5La0.5Co2O6-δ), BGLC73 (BaGd0.7La0.3Co2O6-δ) and BGLC91 (BaGd0.9La0.1Co2O6-δ). Acceptable phase purity was determined through X-ray diffractometry (XRD), the batches sieved into four different grain size ranges, with diameters of 63-45 μm being used for all later experiments. Scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis were applied to examine the morphology and determine the specific surface area of the samples. Pulse isotope exchange (PIE) and gas phase analysis (GPA) were used to examine the surface kinetics of the samples. The PIE data also allows us to extract the adsorption and incorporation energy of gas species from the total activation energy. Comparative measurements in 21% oxygen at 400 °C for BGLC19 with GPA and PIE resulted in surface exchange coefficients for oxygen of 6.8×10-5 mol m-2 s -1 (PIE) and 1.3×10-5 mol m-2 s -1 (GPA), with the difference being attributed to exchange rates in GPA being limited by gas diffusion in the chamber. An experiment was also performed with PIE on BGLC19 in 21% and 2% oxygen, resulting in surface exchange coefficients of 6.8×10-5 mol m-2 s -1 (21%) and 1.2×10-4 mol m-2 s -1 (2%) at 400 °C. The total activation energy E0 for oxygen exchange was lower in 2% oxygen (0.84 eV in 2% vs 1.1 eV in 21%), but with a slightly higher adsorption energy Eads (0.79 eV in 2% vs 0.62 eV in 21%). Measurements were also performed with PIE in 2% oxygen across compositions, with BGLC55 showing the lowest incorporation energy Einc for oxygen at 0.82 eV but with the highest E0 (0.91 eV) and Eads (0.92 eV) of the set. BGLC73 displayed the lowest values for total activation and adsorption energies at 0.62 eV (E0) and 0.69 eV (Eads). The highest surface exchange rates for oxygen were measured for BGLC19, BGLC73 and BGLC91 at over 1×10-4 mol m-2 s -1 , while the values for BGLC37 and BGLC55 were around 6×10-4 mol m-2 s -1 . 3 PIE experiments involving the exchange of water vapour were also performed on BGLC37 and BGLC91, with BGLC73 exchanging the most water up to 450 °C. With unclear data and very little to no D2O measured by the mass spectrometer, these experiments remain inconclusive.

• Johansen, Hege Westvold; Haugsrud, Reidar & Strandbakke, Ragnar (2020). Defects and transport in donor doped LaNbO4. Universitetet i Oslo. Fulltekst i vitenarkiv
• Andersen, Håkon; Norby, Truls Eivind & Strandbakke, Ragnar (2020). Functional Properties and Electrochemical Performance of New Positrode Materials for Proton Ceramic Electrochemical Cells. Universitetet i Oslo. Fulltekst i vitenarkiv
• Pedersen, Madeeha Khalid; Norby, Truls Eivind & Strandbakke, Ragnar (2019). Fundamentals of Positrodes for Proton Ceramic Electrochemical Cells. Universitetet i Oslo. Fulltekst i vitenarkiv
• Emhjellen, Linn Katinka; Haugsrud, Reidar; Bjørheim, Tor Svendsen & Strandbakke, Ragnar (2017). Defects and Transport in SrFe1-xMoxO3-δ. Universitetet i Oslo. Fulltekst i vitenarkiv
• Modestino, Rafael Albert Prato; Haugsrud, Reidar; Strandbakke, Ragnar & Vøllestad, Einar (2016). TRANSPORT PROPERTIES AND SURFACE KINETICS OF Ba0.8+xGd0.8La0.2+xCo2O6-d. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  The main topics of this thesis are the surface kinetics and bulk diffusion of oxygen in Ba(1-x)Gd0.8La(0.2+x)Co2O(6-d) (BGLC). Previous work has identified BGLC as very promising electrode material for SOFC’s and electrolyzers. With conductivities in the range of ~1000 S/cm and polarization resistances in the order of 10^-2 Ocm2 around operating temperatures (i.e. 500-700 ºC). BGLC is in line to surpass current state of the art materials. Yet in order to introduce a new electrode, thorough characterization needs to be performed on its physicochemical properties. BGLC has been identified as double perovkite (double on the c-axis) by x-ray diffractometry (XRD), and synchotron measurements, in the form of AA'B2O(6-d). Cobalt occupies the B sites at the cell’s corners, with octahedral coordination of oxygen atoms, while barium and the lanthanides occupy the center of each square cell. Such a structure is highly defective; the heterovalency between barium and the lanthanides introduces oxygen vacancies in the material. The perfect structure is defined at BaGd0.8La0.2Co2O6 in order to establish a defect model. It is suggested that cobalt ions of differing valence (+2, +3 and +4) are evenly distributed through the material, and that the oxygen sites are ordered in layers surrounding the different cations. From this starting point, effects of temperature and atmosphere on the structure and properties of BGLC is studied. High temperature in-situ XRD in the temperature range from 25 to 800 ºC shows little change in the structure. As opposed to other perovskites (ex.: GdBaCo2O6-d), BGLC remains stable through operating temperatures. Lanthanum can be used to dope the barium sites without compromising stability, leading to more compositions. Synchotron data shows the majority of oxygen vacancies aggregated in the lanthanide layer (O1 site), a reduced amount in the cobalt layer (O2 site), and no vacancies present in the barium layer (O3 site). Such a flexible structure can be reduced or oxidized easily. Changes in temperature using a thermal balance revealed the oxygen non-stoichiometry as function of temperature down to [O] ~4.9. The same experiments were performed isothermally with changing pO2. The defect model proposed is able to model the data closely for BGLC and related double perovskites. These oxygen vacancies allow for ionic diffusion through the material. The transport regimes were divided in two: surface exchange of oxigen, and bulk diffusion (self-, chemical, and tracer). Thermogravimetry (TG), isotope exchange gas phase analysis (GPA) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) were employed to measure the diffusion coefficients (D) and surface coefficient (k) of BGLC at various temperatures between 350 to 800 ºC. Dchem was measured to 10^-6 to 10^-7 cm2/s at relatively low temperatures of 600 – 500 ºC with an equally low activation energy of ~0.74 eV. This leads to an oxide ion conductivity of 10^-2 to 10^-3 S/cm at operating conditions. The values were found to be competitive with state-of-the-art materials in literature. The pre-exponential values and activation energies are in close agreement to related double perovskites such as GdBaCo2O6-d and PrBaCo2O6-d. The oxygen surface exchange was studied using GPA, where a mass spectrometer tracks the concentration of species in the gas phase of a reaction chamber. Various reaction sequences are proposed for the oxygen exchange process of adsorption-dissociation-association-desorption. The desorption/adsorption steps were found to be rate limiting for this material. The surface exchange coefficient, k, is characterized by 6.0*10^-2 Exp(-66570/RT), a high value for k0 and low Ea for perovskites, but on par with novel double-perovskites. An imporant of feature of BGLC is the relatively high proton content (~1 mol%) under wet atmosphere. The hydration properties are included and modeled in the defect structure. The different basicity in the oxygen sites defined (O1, O2 and O3) is used to elucidate the hydration of the material. O3, the always-filled oxygen site is considered the main site for protonation due to its basicity (relative to the other oxygen sites). The adjacent vacancies in O2, a unique feature to BGLC, then allow for hydration. TGA hydration data resulted in an extracted entropy and enthalpy of hydration of ~ -120 J/molK and -46 kJ/mol respectively for all compositions of BGLC. Thourough agreement between the techniques used allow the characterization of the material properties, and the development of BGLC as future cathode material.

• Strandbakke, Ragnar; Norby, Truls Eivind & Haugsrud, Reidar (2014). Oxygen electrodes for ceramic fuel cells with proton and oxide ion conducting electrolytes. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  The overall aim of this work is to contribute to a better understanding of the reactions taking place at the oxygen electrode in proton ceramic fuel cells (PCFCs) and, moreover, to develop new materials with improved performance for this electrode. PCFCs and their cathode reactions are the main focus of the study, but these reactions are often running in parallel with reactions associated with other charge carriers that also need to be addressed. Most proton conducting ceramics exhibit also transport of oxide ions, and although small at intermediate temperatures, the relative contribution from partial oxide ion conductivity increases with temperature and eventually dominates at higher temperatures. Hence, characterization of the performance of a PCFC cathode may at higher temperatures in reality be affected by or even directly reflect the cathode reactions of an oxide ion conducting solid oxide fuel cell (SOFC) rather than that of a PCFC. The crossover between SOFCs and PCFCs with respect to the oxygen electrode reactions is emphasized in this work. The first manuscript presents status and challenges of PCFC research undertaken in Norway by the start of 2010. The work comprises manufacturing of single cells and cell stacking, focusing on the performance, the mechanical and thermal properties, as well as, the chemical stability of the different PCFC component materials. State-of-the-art cathode material at that time, La0.8Sr0.2MnO3 (LSM), showed a polarization resistance (Rp) of 30 Ωcm2 800°C on proton conducting Ca doped LaNbO4 electrolyte, revealing the necessity for a significant improvement in the cathode performance. New materials had to be found and their microstructural design optimized, based on the requirements specific for the proton conductor oxygen reaction. Reaction kinetics, with particular emphasis on the features specific for the PCFC oxygen electrode is investigated in manuscripts II, III and V. In manuscript IV, the experimental conditions are such that the SOFC reactions dominate the electrode process. The electrolyte/electrode interfacial exchange of protons instead of oxide ions distinguishes PCFCs from oxide ion conducting SOFCs and entails that water is formed on the oxygen side of the electrolyte. A major challenge with the PCFC cathode candidate materials studied so far is the confinement of the electrochemical process to pass the electrolyte / electrode / gas triple phase boundary (tpb), instead of utilizing the whole electrode area as for the best mixed conducting SOFC electrodes. The challenges related to tpbs as a bottleneck are addressed by microstructural improvements. Moreover, a novel material with simultaneous transport of electrons and protons is introduced that will enable also the PCFC cathode reactions to occur over the electrode surface, thereby extending the tpb reaction zone. The effect of water formation on the cathode reaction is studied in detail on a Pt model electrode. The results show higher reaction rates upon increased water vapor partial pressure, pH2O. Since the Pt electrode is rate limited by surface diffusion both under dry and wet conditions, the pH2O effect is explained by the formation of surface hydroxyls with high surface mobility relative to the adsorbed oxide ions which dominate under drier conditions. The presence of surface hydroxyls is confirmed by X-ray photoelectron spectroscopy. Water is looped in the oxygen reaction series, acting both as reactant and product. In manuscript V and in the results part of the thesis it is shown that ambient water vapor gives the same positive effect for the mixed conducting electrodes BaGd0.8La0.2Co2O6-δ (BGLC) and BaPrCo2O6- (BPC) when operated on a BaZr0.7Ce0.2Y0.1O3 (BZCY72) proton conducting electrolyte. At higher temperatures where BZCY72 is mainly oxide ion conducting, water vapor on the other has an adverse effect on the electrode reaction rate for the same mixed conducting electrodes. With the mixed oxide ion-p-type electron conductor La2NiO4+δ (LNiO) as electrode and La27.16W4.85O55.27, (La/W ≈ 5.6; LWO56) as electrolyte (manuscript IV), the electrode performance was independent of pH2O under conditions where oxide ion conductivity dominates in the electrolyte (above 700°C). Three well-established routes to improve the electrode microstructure were followed in this work; (i) addition of nano-sized catalysts by infiltration, (ii) improvement of the functional layer close to the electrolyte and (iii) manufacturing of composite electrodes by mixing electrode and electrolyte materials. The two first methods showed promising results: Addition of Pt nanoparticles in the LSM electrode lowered significantly the polarization resistance; from 260 to 40 Ωcm2 at 650°C. Characterization of the microstructure of BGLC and BPC electrodes showed that a fine-grained functional layer was successfully manufactured. The composite electrode approach did, however, not prove to enhance the performance of an electrode rate limited by surface reactions. The materials investigated in this work range from well-known pure electron conductors such as Pt and LSM, used first and formerly for the detailed characterization of the electrode reactions, via the promising mixed conducting candidate LNiO, to the novel mixed conducting double perovskites BGLC, BPC and their B-site iron-substituted variants BaGdCo1.8Fe0.2O6-δ (BGCF) and BaPrCo1.4Fe0.6O6-δ (BPCF). For Pt and LSM, high capacitance processes like surface diffusion is limiting the overall electrode reaction rate. For the mixed conducting electrodes LNiO and BGLC, the oxide ion transfer is shown to happen through the electrode interior. The latter also shows indications of partial bulk proton conductivity concluded based on the pH2O dependencies encountered for Rp and supported by hydration of the material at low temperatures with a hydration enthalpy of -50 kJ/mol. Bulk proton transport would facilitate the low temperature PCFC cathode reaction and widen the triple phase reaction zone improving the electrode performance. The behavior of these mixed conducting double perovskites, especially BGLC but possibly also BPC, with polarization resistances measured to 0.05 and 0.09 Ωcm2 at 650°C for BGLC and BPC, consequently gives indications of the first established mixed proton / electron conducting materials with sufficient electrochemical performance on a proton conducting electrolyte. To account correctly for mixed conductivity in the electrolyte is challenging when studying electrode reactions. In manuscript III and V, a model for the separation of the measured polarization resistance into the contributions from more than one charge carrier is developed. The model accounts also for the effect of parallel non-faradaic current during high temperature measurements under oxidizing conditions. The results of the modelling show that the measured polarization resistance for the system investigated here and reported above for 650°C is underestimated by approximately one order of magnitude. The same underestimation would apply to any other oxygen electrode measured on BZCY72 if the effect of electrolyte p-type partial conductivity was not properly addressed. In a running fuel cell or electrolyzer cell, the fuel-side reducing conditions are expected to induce a blocking layer for electronic conductivity in the electrolyte. The "true" polarization resistance will therefore be higher when the partial short circuit is absent. At lower temperatures, this effect of parallel non-faradaic current is less pronounced during half-cell electrode characterization. BGLC exhibits a total polarisation resistance for proton transport of only 10 Ωcm2 at 350°C, with an activation energy of 50 kJmol-1 ascribed mainly to the surface electrode reaction. Based on this, there is reason to believe that further improvements of the cathode performance can be achieved by enhanced microstructural processing, such as infiltration of BGLC in a BZCY backbone.

• Sass, Tobias; Norby, Truls Eivind & Strandbakke, Ragnar (2013). Yttrium Doped Barium Zirconate: Electrical Properties and Electrodes. Universitetet i Oslo. Fulltekst i vitenarkiv

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