Reaction kinetics of protons and oxide ions in LSM/lanthanum tungstate cathodes with Pt nanoparticle activation

Composite electrodes of La0.8Sr0.2MnO3 (LSM)/La28–xW4+xO54+3x/2 (x = 0.85, “LWO56”) on LWO56 electrolytes have been characterized by use of electrochemical impedance spectroscopy vs. pO2 and temperature from 900°C, where LWO56 is mainly oxide ion conducting, to 450°C, 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 (Rp) at 650°C from 260 to 40 Ω cm2. 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 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 Rp, exhibits activation energies of ∼85 kJ mol−1 for both oxide ion and proton charge transfer

Tailoring the properties of a-site substituted Ba1-xGd0.8La0.2+xCo2O6-δ

The double perovskite BaGd0.8La0.2Co2O6-δ (BGLC) shows excellent performance as oxygen electrode for Proton Ceramic Fuel Cells (PCFCs) and electrolyzer cells (PCEC), with polarization resistances in wet oxygen of 0.04 and 10 Ωcm2 at 650 and 350 ⁰C, respectively [1]. Compared with other reported PCFC cathodes [2], BGLC performs better both at high and low temperature. The excellent performance of BGLC in proton ceramic cells is rationalized by a suggested partial proton conductivity at intermediate temperatures, supported by significant hydration up to 400°C observed by thermogravimetric studies. However, the chemical stability of BGLC in high steam pressures under PCEC operation remains a concern due to its highly basic A-site. Thus, tailoring the A-site stoichiometry by partial substitution of Ba with La may be a viable route for further optimizing the balance between chemical stability and electrochemical performance. In the literature we find numerous defect chemical models describing REBaCo2O5.5+δ-type double perovskites, but these are typically limited to describing the oxygen non-stoichiometry. Little can be found which relates defect chemistry to electrochemical performance, electrical conductivity or hydration behavior. Thus, this contribution aims to develop a global defect chemical model of the system Ba1‑xGd0.8La0.2+xCo2O6-δ (x = 0-0.5) by investigating its structural and functional properties as a function of Ba-site substitution. The complex structural behavior of Ba-site substituted BGLC is elucidated by combining synchrotron and neutron diffraction data with high temperature XRD to describe the local Co-O environment and the degree of cation and anion ordering as a function of temperature and pO2. The implications of A-site stoichiometry on proton incorporation are further investigated by thermogravimetric hydration studies supported by neutron powder diffraction of dry and deuterated samples. Finally, these properties are linked to oxygen non-stoichiometry, electrical conductivity and electrochemical performance to develop and validate our general defect chemical model for the system Ba1‑xGd0.8La0.2+xCo2O6-δ (x = 0-0.5). Please click Additional Files below to see the full abstract

Defect chemistry of mixed conducting double Perovskites

Barium Gadolinium Lanthanum Cobaltites with the general formula Ba1-xGd0.8-yLa0.2+x+yCo2O6-δ (BGLC) are reported as Mixed Proton and Electron Conducting materials (MPECs), and have been utilized as positrode (positive electrode) materials for Proton Ceramic Electrochemical Cells (PCECs) [1]. A defect chemical model, treating various charge carrying defects in BGLC was published in 2017 [2] and in this work we expand the model to also comprise formation of protons in BGLC. Protons can be incorporated by two different reactions, in a ratio depending on measurement conditions and the oxidation state of the material. Low temperatures and high pO2 leaves BGLC oxidized, and with increasing electron hole concentration, the hydrogenation reaction is promoted with respect to hydration. Hydrogenation is confirmed by use of isothermal Dry-H2O-D2O switches in thermogravimetric measurements, revealing a larger concentration of protons than expected from hydration only (Figure 1, left). The reduction of BGLC by hydrogenation is slowly counteracted by oxygen uptake combined with an expected cation reordering, bringing the material back to its initial oxidation state after equilibration in wet conditions. By combining oxidation and hydration thermodynamics, hydrogenation entropy and enthalpy can be obtained, making it possible to model proton concentrations from hydration and hydrogenation separately by use of advanced defect chemistry (Figure 1, right). Hydration is proposed to be facilitated by a minor concentration of oxygen vacancies in the O-Co-O layers, where acidic vacancies may accommodate basic hydroxyl groups. These vacancies are neighboured by more basic oxide ions in the O-Ba-O and O-Ln-O layers which in turn may accommodate protons. Please click Additional Files below to see the full abstract

Effect of fuel thermal pretreament on the electrochemical performance of a direct lignite coal fuel cell

Proceedings of the 20th International Conference on Solid State Ionics SSI-20The impact of fuel heat pretreatment on the performance of a direct carbon fuel cell (DCFC) is investigated by utilizing lignite (LG) coal as feedstock in a solid oxide fuel cell of the type: lignite | Co–CeO2/YSZ/Ag | air. Four LG samples are employed as feedstock: (i) pristine lignite (LG), and differently heat treated LG samples under inert (He) atmosphere at (ii) 200 °C overnight (LG200), (iii) 500 °C for 1 h (LG500) and (iv) 800 °C for 1 h (LG800). The impact of several process parameters, related to cell temperature (700–800 °C), carrier gas type (He or CO2), and molten carbonate infusion into the feedstock on the DCFC performance is additionally explored. The proximate and ultimate analysis of the original and pretreated lignite samples show that upon increasing the heat treatment temperature the carbon content is monotonically increased, whereas the volatile matter, moisture, sulfur and oxygen contents are decreased. In addition, although volatiles are eliminated upon increasing the treatment temperature and as a consequence more ordered carbonaceous structure remained, the heat treatment increases the reactivity of lignite with CO2 due mainly to the increased carbon content. These modifications are reflected on the achieved DCFC performance, which is clearly improved upon increasing the treatment temperature. An inferior cell performance is demonstrated by utilizing inert He instead of reactive CO2 atmosphere, as purging gas in the anode compartment, while carbonate infusion always results in ca. 70–100% increase in power output (15.1 mW cm− 2 at 800 °C). The obtained findings are discussed based also on AC impedance spectroscopy measurements, which revealed the impact of LG physicochemical characteristics and DCFC operating parameters on both ohmic and electrode resistances.The authors would like to acknowledge financial support from the European project “Efficient Conversion of Coal to Electricity — Direct Coal Fuel Cells”, which is funded by the Research Fund for Carbon & Steel (RFCR CT-2011-00004).Peer reviewe

Mixed proton and electron conducting double perovskite anodes for stable and efficient tubular proton ceramic electrolysers.

[EN] 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 cm(2) active area and a hydrogen production rate above 15 Nml min(-1). The novel steam anode Ba1-xGd0.8La0.2+xCo2O6-delta exhibits mixed p-type electronic and protonic conduction and low activation energy for water splitting, enabling total polarization resistances below 1 Omega cm(2) at 600 degrees 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.The work leading to these results has received funding from the Research Council of Norway (grant 236828) and from the European Union's Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement 621244 ('ELECTRA') and Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement 779486 ('GAMER'). This Joint Undertaking receives support from the European Union's Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe research.Vøllestad, E.; Strandbakke, R.; Tarach, M.; Catalán-Martínez, D.; Fontaine, M.; Beeaff, D.; Clark, DR.... (2019). Mixed proton and electron conducting double perovskite anodes for stable and efficient tubular proton ceramic electrolysers. Nature Materials. 18(7):752-759. https://doi.org/10.1038/s41563-019-0388-2S75275918

Energetics of formation and stability in high pressure steam of barium lanthanide cobaltite double perovskites

[EN] This study concerns energetics of formation and the stability in high water partial pressure of BaLnCo(2)O(6-delta), (Ln = La, Pr, Nd, and Gd) (BLnC) and BaGd1-xLaxCo2O6-delta, where x = 0.2, 0.5, and 0.7 (BGLC) double perovskite cobaltites. Those materials are extensively studied due to their potential applications as a positrode in electrochemical devices. Therefore, their stability under such conditions is a key issue. All investigated materials are thermodynamically stable relative to binary oxides and exhibit strongly exothermic enthalpies of formation. Moreover, BaGd0.3La0.7Co2O6-delta and BaGd0.8La0.2Co2O6-delta remain the main perovskite structure up to 3 bars of water vapor at 400 degrees C. At higher steam pressure, reaching 10 bar at 300 degrees C, the partial decomposition to constituent oxides and hydroxides was observed. The BGLC compounds exhibit higher negative formation enthalpies in comparison to single-Ln compositions, which does not translate into higher chemical stability under high steam pressures since the BLnC series retained the main perovskite structure at higher temperatures as well as in higher water vapor pressures.The research has been supported by the National Science Centre Poland (2016/22/Z/ST5/00691), the Spanish Ministry of Science and Innovation (PCIN-2017-125, RTI2018-102161, and IJCI-2017-34110), and the Research Council of Norway (grant no. 272797 "GoPHy MiCO") through the M-ERA.NET Joint Call 2016. We also acknowledge Solaris National Radiation Centre Poland for access to the PIRX (XAS/PEEM) beamline time (proposal no 201036). Dr Chiu C. Tang at beamline I11 at Diamond Light Source, Didcot, UK is gratefully acknowledged SR-PXD measurements. The calorimetry at Arizona State University received financial support from the U.S. Department of Energy, Office of Basic Energy Sciences, grant DE-SC0021987.Mielewczyk-Gryn, A.; Yang, S.; Balaguer Ramirez, M.; Strandbakke, R.; Sorby, MH.; Szpunar, I.; Witkowska, A.... (2023). Energetics of formation and stability in high pressure steam of barium lanthanide cobaltite double perovskites. Dalton Transactions. 52(17):5771-5779. https://doi.org/10.1039/d2dt03989c57715779521

Oxide nanoparticle exsolution in Lu-doped (Ba,La)CoO3

This study investigated Lu doping of BaLaCoO and its influence on the exsolution of oxide nanoparticles (NPs). As a result of Lu doping, we observed the phase segregation into the main BaLaCoLuO (BLCO-Lu) phase and the secondary BaLaCoLuO (BCO-Lu) phase. We noticed the exsolution of BCO-Lu nanoparticles on the main BLCO-Lu phase. Moreover, the BLCO-Lu phase exsolved in the form of nanoparticles on the adjacent BCO-Lu grains. That shows that the phases are covered with mutually exsolved oxide NPs. In addition, trace amounts of the BaLuCoO phase are detected. We noticed that the exsolved oxides even in the as-prepared sample were fine (average size of 18 nm), and well distributed with a dense population of NPs above 280 per 1 μm. Furthermore, we showed that the size and shape of the exsolved oxide NPs can be controlled by varying the annealing temperature. For example, at 800 °C the exsolved oxides segregate and form two different shapes; spherical and cuboidal, with an average size of 31 nm and NP population of about 23 NPs per μm. Meanwhile, with lowering the temperature to 400 °C the oxides form only spherical and quite evenly distributed NPs with the occurrence of 137 NPs per 1 μm. The obtained results open the possibility of tailoring a novel, more catalytically active material for future applications in electrochemical devices.Project FunKeyCat is supported by the National Science Centre, Poland under the M-ERA.NET 2, which has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no 685451. The Research Council of Norway is also acknowledged for support to the Norwegian Center for Transmission Electron Microscopy (NORTEM) (no. 197405/F50)

Structural properties of mixed conductor Ba1−xGd1−yLax+yCo2O6−δ

BaGdLaCoO (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 LaCoO-based R3̄c. When La is almost completely substituted for Gd, the material can be stabilised in Pmmm, or cubic Pm3̄m, depending on thermal and atmospheric history. We list thermal expansion coefficients for x = 0-0.3, y = 0.2.The research has been supported by the National Science Centre Poland (2016/22/Z/ST5/00691), the Spanish Ministry of Science and Innovation (PCIN-2017-125, RTI2018-102161 and IJCI-2017-34110), and the Research Council of Norway (Grant no. 272797 “GoPHy MiCO”) through the M-ERA.NET Joint Call 2016. The authors acknowledge the skilful assistance from the staff of the Swiss–Norwegian Beamline (SNBL) at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. Dr. Cheng Li at POWGEN, SNS, Oak Ridge, US and Dr. Chiu C. Tang at beamline I11 at Diamond, Didcot, UK are gratefully acknowledged for PND and SR-PXD measurements, respectively

Fru Pigalopp som feministisk aktivist? En feministisk diskursanalyse av Vivian Zahl Olsens tegninger

Denne oppgaven handler om Vivian Zahl Olsens tegninger av fru Pigalopp, alle hentet fra boken og tv-serien om Travelt-folket fra 1974. Fru Pigalopp er fremstilt som en bestemt, men morsom figur som gjennom fortellingen observerer og kommenterer fenomener hun opplever gjennom sin egen versjon av en sommerferie. Ferien viker ikke nevneverdig fra en vanlig 70-talls ferietur, men fru Pigalopp reagerer på ting som vanligvis oppfattes som helt normale og hverdagslige. Opplevelsene holder hun sammen med sin egen livsfilosofi som gjenspeiles i tegningenes spenn mellom alvor og sprell. Den «pigaloppske» livsfilosofien blir utdypet gjennom oppgaven da essensen blir billedliggjort gjennom tegningene. Vivian Zahl Olsens tegninger er fargerike og fantasifulle og bærer en naivitet som er interessant å se som motpol til den underliggende kompleksiteten som tegningene kun antyder i overflaten. Det teoretiske grunnlaget har tatt for seg redegjørelser av ulike feministiske diskurser som tegningene er knyttet opp imot og et underliggende spørsmål for oppgaven har vært: Er fru Pigalopp relevant som et nytt og progressivt symbol for kvinnebevegelsens perspektiver? Feminismen som metode poengterer at de ikke finnes mono-kausale sannheter, men at man må se på hele nettverk av diskurser for å skape helthetlige syn der forskjellige forklaringsmodeller konstituerer en slags virkelighet. Analysens hovedoppgave ble å synliggjøre hvorvidt det var mulig å lese tegningene som en type feministisk aktivisme. Tegningene tar for seg en representert sosial verden i møte med fenomener knyttet til 70-tallet. Iscenesettelser av subjektet og fremmedgjøring er begreper som går igjen. Ved å lese Vivian Zahl Olsens tegninger gjennom en feministisk diskursiv analyse forbi kunstnerens eller oppdragsgivers intensjon ble resultatet at tegningene viser både feministisk aktivisme på et grunnleggende plan og at tegningene fremstiller kvinnen forbi en tillært femininitet. I dette lå det også en mulighet for en frigjøring av kvinnefremstillinger og kjønnsrollediskursen. 70-årene ble desenniet som inneholdt store endringer sosialt, kulturelt og politisk, og dette representeres i tegningene av fru Pigalopp. Hennes feministiske aktivisme ble tydeliggjort gjennom å se hvordan linjer, farger og former kom til syne over komplekse og mangfoldige sammenhenger. Analysen viser at fru Pigalopps aktivisme ikke fremstilles med opposisjon som virkemiddel. Der 70-tallsfeminismen var preget av kamp, er fru Pigalopps feministiske aktivisme preget av et autonomt utgangspunkt der frihet fra patriarkatets objektiviserende forenklingssystemer kom til syne. Gjennom dette tydeliggjøres et nytt perspektiv innenfor 70-tallsfeminismen