Papers by Ragnar Strandbakke
Journal of materials chemistry. A, 2024
Dalton Transactions, 2023
This study concerns energetics of formation and the stability in high water partial pressure of B... more This study concerns energetics of formation and the stability in high water partial pressure of BaLnCo2O6−δ, (Ln = La, Pr, Nd, and Gd) (BLnC) and BaGd1−xLaxCo2O6−δ, where x = 0.2, 0.5, and 0.7 (BGLC) double perovskite cobaltites.
Journal of materials chemistry. A, Materials for energy and sustainability, 2021
Molten-solid composite oxides are candidates as oxygen transport membranes (OTMs) at intermediate... more 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% V 2 O 5-ZrV 2 O 7 composite with a eutectic melting point at $670 C. When V 2 O 5 melts and increases the V 2 O 5 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 V 2 O 5 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% V 2 O 5-ZrV 2 O 7 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.
Solid State Ionics, Aug 1, 2017
La0.8Sr0.2MnO3- (LSM) and Ba0.5Sr0.5Co0.8Fe0.2O3- (BSCF) composite anodes deposited on proton-c... more La0.8Sr0.2MnO3- (LSM) and Ba0.5Sr0.5Co0.8Fe0.2O3- (BSCF) composite anodes deposited on proton-conducting BaCe0.2Zr0.7Y0.1O3- (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 ºC 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•cm 2 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.
Solid State Ionics, Apr 1, 2018
The combined impact of carbon type (anthracite coal, bituminous coal and pine charcoal) and in si... more The combined impact of carbon type (anthracite coal, bituminous coal and pine charcoal) and in situ, catalyst-aided, carbon gasification process on the electrochemical performance of a Direct Carbon Fuel Cell (DCFC) is explored. The effect of operation temperature (700-800 o C) and catalyst (Co/CeO 2) infusion to carbon feedstock under CO 2 atmosphere at the anode chamber is systematically investigated in a cell of the type: Carbon+CO 2 |Cu-CeO 2 /YSZ/Ag|Air. All fuel samples were characterized, in terms of chemical composition, crystallite structure (XRD), pore structure (BET), surface morphology (SEM), particle size distribution (PSD) and thermogravimetric analysis (TGA), in order to obtain a close relationship between the carbon characteristics and the DCFC performance. The results reveal that in the absence of catalyst, the optimum performance is obtained for the charcoal sample (P max ~12 mW/cm 2), due to its high oxygen and volatile matter contents. Catalyst infusion to carbon feedstock results in a considerable increase in the achieved cell power density up to 225%, depending on carbon type and temperature. The enhanced performance obtained by infusing Co/CeO 2 catalyst into carbon is ascribed to the pronounced effect of catalyst on in situ carbon gasification, through the reverse Boudouard reaction (C + CO 2 2CO), and the subsequent faster diffusion and electro-oxidation of formed CO at the anodic three-phase boundary.
Chemical Communications, 2020
Journal of the American Ceramic Society, Nov 11, 2019
The cubic Ba0.5La0.5CoO3-δ was synthesized using solid state reaction. The structural properties ... more The cubic Ba0.5La0.5CoO3-δ was synthesized using solid state reaction. The structural properties were determined by the simultaneous refinement of Synchrotron Powder Xray 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 θP = 198(3) K and µeff=2.11(2) µB. Electric measurements show the thermally activated
Journal of The Electrochemical Society, 2016
Composite electrodes of La 0.8 Sr 0.2 MnO 3 (LSM) / La 28-x W 4+x O 54+3x/2 (x=0.85, "LWO56") on ... more Composite electrodes of La 0.8 Sr 0.2 MnO 3 (LSM) / La 28-x W 4+x O 54+3x/2 (x=0.85, "LWO56") on LWO56 electrolytes have been characterized by use of electrochemical impedance spectroscopy vs pO 2 and temperature from 900 ⁰C, where LWO56 is mainly oxide ion conducting, to 450 ⁰C, where it is proton conducting in wet atmospheres. The impedance data are analyzed in a model which takes into account the simultaneous flow of oxide ions and protons across electrolyte and electrodes, allowing extraction of activation energies and pre-exponential factors for the partial electrode reactions of protons and oxide ions. One composite electrode was infiltrated with Pt nanoparticles with average diameter of 5 nm, lowering the overall electrode polarization resistance (R p) at 650 ⁰C from 260 to 40 Ω cm 2. The Pt-infiltrated electrode appears to be rate limited by surface reactions with activation energy of ~90 kJ mol-1 in the low temperature proton 2 transport regime and ~150 kJ mol-1 in the high temperature oxide ion transport regime. The charge transfer reaction, which makes a minor contribution to R p , exhibits activation energies of ~85 kJ mol-1 for both oxide ion and proton charge transfer.
Journal of the American Ceramic Society, Mar 1, 2010
Magrasó, A., Xuriguera, H., Varela, M., Sunding, MF, Strandbakke, R., Haugsrud, R. and Norby, T.(... more Magrasó, A., Xuriguera, H., Varela, M., Sunding, MF, Strandbakke, R., Haugsrud, R. and Norby, T.(2010), Novel Fabrication of Ca-Doped LaNbO 4 Thin-Film Proton-Conducting Fuel Cells by Pulsed Laser Deposition. Journal of the American Ceramic Society, 93: 1874 ...
Journal of Power Sources, 2022
Journal of Materials Chemistry A, 2021
Molten-solid composite oxides are candidates as oxygen transport membranes (OTMs) at intermediate... more Molten-solid composite oxides are candidates as oxygen transport membranes (OTMs) at intermediate temperatures. We report the electrical conductivity characteristics of a 30 mol% V2O5–ZrV2O7 composite with a eutectic melting point at ∼670 °C.
Solid State Ionics, 2021
Proton conducting oxide electrolytes find potential application in proton ceramic fuel cells and ... more 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 BaZrO 3 (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; (Ba 0.85 Sr 0.15)(Zr 0.7 Ce 0.1 Y 0.2)O 2.9 (BSZCY151020). High temperature XRD shows that this material has a cubic structure (space group Pm3m) 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 H 2. This electrolyte with increased TEC may find application in proton ceramic electrochemical cells in general and metal supported ones in particular.
Materials, 2020
The application of double perovskite cobaltites BaLnCo2O6−δ (Ln = lanthanide element) in electroc... more 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.
Acta Materialia, 2020
Abstract The structure of BaLnCo2O6-δ (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy) was studied by the mean... more Abstract 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.
Chemical Communications, 2020
OER electrocatalysts based on double perovskite cobaltites (Ln = Gd or Pr) with intrinsic catalyt... more OER electrocatalysts based on double perovskite cobaltites (Ln = Gd or Pr) with intrinsic catalytic activities exceeding that of IrO2.
Journal of the American Ceramic Society, 2019
The cubic Ba0.5La0.5CoO3-δ was synthesized using solid state reaction. The structural properties ... more The cubic Ba0.5La0.5CoO3-δ was synthesized using solid state reaction. The structural properties were determined by the simultaneous refinement of Synchrotron Powder Xray 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 θP = 198(3) K and µeff=2.11(2) µB. Electric measurements show the thermally activated
Nature Materials, 2019
Hydrogen production from water electrolysis is a key enabling energy storage technology for large... more Hydrogen production from water electrolysis is a key enabling energy storage technology for 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. The development of PCEs has however 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 cm 2 active area and a hydrogen production rate above 15 NmL•min-1. The novel steam anode Ba1-xGd0.8La0.2+xCo2O6-δ (BGLC) exhibits mixed p-type electronic and protonic conduction and low activation energy for water splitting, enabling total polarization resistances below 1 Ω•cm 2 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. High temperature electrolysers (HTEs) that utilize readily available steam and/or heat (renewable or industrial) as a supplementary energy source provide superior electrical efficiency compared to conventional water electrolysis. 1-4 HTEs developed to date comprise solid oxide electrolysers (SOEs) which utilize oxide ion conducting electrolytes and therefore produce hydrogen on the steam side cathode. The undiluted high pressure oxygen produced on the anode in SOEs presents a safety hazard. Their high operating temperature (typically 800°C)
International Journal of Hydrogen Energy, 2019
The current work explores the feasibility to improve the performance of a Direct Carbon Fuel Cell... more 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 o 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.
Solid State Ionics, 2018
The combined impact of carbon type (anthracite coal, bituminous coal and pine charcoal) and in si... more The combined impact of carbon type (anthracite coal, bituminous coal and pine charcoal) and in situ, catalyst-aided, carbon gasification process on the electrochemical performance of a Direct Carbon Fuel Cell (DCFC) is explored. The effect of operation temperature (700-800 o C) and catalyst (Co/CeO 2) infusion to carbon feedstock under CO 2 atmosphere at the anode chamber is systematically investigated in a cell of the type: Carbon+CO 2 |Cu-CeO 2 /YSZ/Ag|Air. All fuel samples were characterized, in terms of chemical composition, crystallite structure (XRD), pore structure (BET), surface morphology (SEM), particle size distribution (PSD) and thermogravimetric analysis (TGA), in order to obtain a close relationship between the carbon characteristics and the DCFC performance. The results reveal that in the absence of catalyst, the optimum performance is obtained for the charcoal sample (P max ~12 mW/cm 2), due to its high oxygen and volatile matter contents. Catalyst infusion to carbon feedstock results in a considerable increase in the achieved cell power density up to 225%, depending on carbon type and temperature. The enhanced performance obtained by infusing Co/CeO 2 catalyst into carbon is ascribed to the pronounced effect of catalyst on in situ carbon gasification, through the reverse Boudouard reaction (C + CO 2 2CO), and the subsequent faster diffusion and electro-oxidation of formed CO at the anodic three-phase boundary.
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Papers by Ragnar Strandbakke