Dealing with degradation in solid oxide electrochemical cells: novel materials and spectroscopic probes

In this PhD thesis, we have focused on two of the main issues regarding solid oxide fuel cells and electrolysers. On the one hand, the high temperatures at which they work (800-1000ºC) is detrimental for their long-term performance, and novel combinations of electrolyte and oxygen electrode materials have been tested in order to establish their suitability to work in intermediate temperature (600-800ºC) solid oxide fuel cells. On the other hand, degradation issues affect these devices greatly when working in the electrolyser mode, often assigned to the development of high oxygen partial pressures within the electrolyte. Regarding this topic, we have developed an analytical procedure to monitor the oxygen activity inside a YSZ electrolyte using redox dopants as spectroscopic probes and used it in cells tested in different conditions in the electrolysis mode.First, an aluminium-doped lanthanum silicate compound (LSAO) with the apatite structure was chosen as electrolyte, and eight different strontium and cobalt-free compounds with a perovskite structure with the general formula LaMxN1-xO3 (where M: Fe, Mn, Cr; and N: Ni, Cu) were selected to be tested with the apatite electrolyte. The solid-state synthesis of the apatite and perovskite-type compounds was optimised, achieving perovskite compounds free from secondary phases or decomposition, both in powder form and also after sintering them in pellet form, as it was proven by X-ray diffraction and Raman spectroscopy. The chemical compatibility of the electrolyte and electrode materials was tested by mixing and heating the powders at temperatures above the operational and sintering ones, and no reaction between the compounds took place, as proven again by X-ray diffraction. The thermomechanical compatibility between sintered materials was tested by dilatometry, and no big differences could be found regarding the thermal expansion behaviour of the apatite and perovskites in a wide range of temperatures.Then, the electrochemical performance of the compounds was tested by electrochemical impedance spectroscopy. The LSAO ionic conductivity at intermediate temperatures (9.4·10-3 S·cm-1 at 800ºC) was close to the one shown by a conventional YSZ electrolyte, and the electrical conductivity of the oxygen electrode materials ranged from 10 to 100 S·cm-1 at 800ºC, with activation energies in the high temperature range between 0.1 and 0.3 eV. Among the perovskite materials, the ones containing manganese and copper showed the highest electrical conductivities and the lowest activation energies. The iron-containing compounds (LFN and LFC) exhibited a different activation behaviour with temperature than the rest of the compounds.The following step consisted on manufacturing symmetrical cells with the apatite electrolyte and perovskite electrodes. For that purpose, slurries of the electrode materials were prepared and the electrolyte pellet was coated with them by dip-coating and sintered. The microstructure of the cells was checked in terms of electrode thickness, porosity, particle size, and adherence of the electrodes. Among the compositions tested, LFC showed the lowest ASR with just 4.3 Ω·cm2 at 700ºC, value comparable to the state-of-the-art oxygen electrodes. When applying a small DC bias, the activation energies of the electrodes decreased, as well as their polarization resistances. Promising results were found in this thesis about novel electrolyte/electrode combinations for IT-SOFC, with room for improvement regarding electrode microstructure and the fabrication of composite electrodes with the LFC material.In order to examine the degradation issues concerning SOEC devices, the research began with finding a suitable spectroscopic probe that allowed us to track the oxygen activity in the cells. First, the optical signals in a YSZ electrolyte doped with redox ions were investigated. The objective was to select the ones suitable to track the oxygen activity, allow for a detection in the backscattering configuration and be operative at high temperatures. The samples tested in this part of the thesis were either commercial or solidified on purpose YSZ single-crystals doped with Ce, Mn, Mn-Nd, V or Tb; or polycrystalline ceramics of Tb or Pr-doped YSZ.Among the commercial samples, it was found that YSZ-Ce showed strong change in its optical signal upon redox treatment, and the Ce3+ backscattering signal could be used to monitor the oxygen activity, although the signal disappeared at temperatures above 300ºC. In the case of YSZ-Mn and YSZ-V, even though a change in the optical signal upon oxidation/reduction could be found, there were no backscattering signals that could be used for tracking the oxygen activity. The luminescence of minority rare earth dopants in these samples (Pr3+, Er3+ or Nd3+) was measured and a change in the backscattering signal could be observed upon redox treatment. Nevertheless, the quantification of these signals would have been complicated due to a possible interaction with the major dopants, and these commercial samples were not used to track the oxygen activity within the electrolyte.In the case of praseodymium-doped YSZ, a change in optical signal was observed by diffuse reflectance, and bands due to Pr3+ and Pr4+ could be found. In the case of backscattering signal, Pr3+ ions exhibited an intense luminescence band which decreases upon oxidation to Pr4+, and this signal held up to 700ºC. This could be useful to make in-situ or in-operando measurements of the oxygen activity inside the electrolyte. Nevertheless, ion-ion interaction and concentration quenching of the luminescence band prevented an easy quantification of the oxygen activity, and this probe was also discarded.Terbium-doped YSZ was found suitable in order to track the oxygen activity within YSZ. Changes in optical and luminescence signals could be observed and attributed to different oxidation states of terbium (Tb3+ and Tb4+) upon redox treatments. Tb3+ was not affected by concentration quenching and a quantitative analysis could be carried out. It was found that Tb4+ absorbance was proportional to PO2^(1⁄4), as expected for the electron trapping model. A relation between the Tb3+ luminescence intensity and the oxygen partial pressure could be found, and it proved to be useful in the high PO2 range (10-4-100 bar). Terbium was therefore the selected probe in order to carry out the electrochemical experiments to detect degradation mechanisms in electrolysers.3%Tb-doped 8YSZ shows appropriate oxide ion conductivity to be used as the electrolyte in solid oxide cells. Then, an electrolyte-supported solid oxide cell was prepared using a LSM/YSZ composite for the oxygen electrode and a NiO/YSZ composite for the fuel electrode, and its electrochemical properties were tested in a bicameral cell at 800ºC. Using EIS and changing the atmosphere in the oxygen side, the electrochemical properties of the system were described, and the polarization resistance of each electrode was assigned. After those measurements, several experiments were carried out polarising different cells using a range of biases in the electrolyser mode. When a steady-state was reached around 48 hours after applying a constant voltage, cells were quenched to freeze the high temperature polarization state.The post-mortem cells were analysed in terms of the Tb3+ luminescence across the electrolyte thickness. The luminescence values were transformed into oxygen partial pressures using the relation mentioned above and profiles of the oxygen activity within the electrolyte could be obtained. These measurements were noisy and a couple of corrections were made in order to obtain a suitable signal. An edge-correction due to the loss of signal near the electrodes and a saturation correction due to microstructural aspects of the cell were applied. The method presented here has potential to visualize PO2 profiles in SOEC. Further experiments should be done in order to achieve higher accuracies.Finally, numerical solutions to the transport equations for describing the oxygen activity within the electrolyte were found and compared with the experimental results. It was found that the simulations assuming polarization resistances as derived from EIS spectra at the beginning of the CA experiments did not agree with the oxygen activity profiles obtained from the luminescence experiments. By analysing the SEM micrographs of the post-mortem cells, we could find that the most degradation had occurred near the fuel electrode. The nickel particles tended to agglomerate, especially for high polarization biases, and the porosity of the electrode decreased with applied bias. Besides, cracks within the electrolyte were found near this electrode and even a complete delamination of the fuel electrode was observed for the highest polarization experiment. These observations allowed us to assign a higher polarization resistance to the fuel electrode and then the numerical model results were closer to the results of the luminescence measurements. In order to get better insights of the degradation conditions of the cell while working on electrolyser mode, more experiments should be done.<br /

La lección del Nunca Más. Una aproximación interdisciplinar al contenido y alcance jurídico internacional de la obligación estatal de garantizar la no repetición a través de la educación en memoria. Informe Final

Conceptualmente, el proyecto giró en torno a las garantías de no repetición, es decir: medidas orientadas a evitar futuros incumplimientos del Derecho internacional, de muy diversa naturaleza, pues virtualmente pueden consistir en cualquier cosa (siempre que no resulte abusiva), aunque las más habituales en la práctica internacional son la adopción/derogación/reforma de legislación o de medidas administrativas y las medidas de carácter institucional (relativas a la existencia, organización o funcionamiento de órganos del Estado). Cuando un Estado incumple una obligación internacional –y, por tanto, comete un hecho internacionalmente ilícito–, la principal consecuencia que surge para él es la obligación de reparar, en cualquier de sus tres formas –restitución (o, en su caso, compensación por equivalencia), indemnización o satisfacción (reparación moral)–. Además, en circunstancias excepcionales, tendría también la obligación de ofrecer garantías de no repetición1. Esas “circunstancias excepcionales” vienen en esencia delimitadas por la existencia de violaciones graves de normas imperativas de Derecho internacional, como ocurre cuando se lesionan de manera flagrante o sistemática derechos humanos fundamentales, prácticas que a su vez están tipificadas como crímenes internacionales (genocidio o crímenes contra la humanidad). Por tanto, cuando en el interior de un Estado se cometen atrocidades de esa naturaleza, bien por parte de las propias autoridades estatales, bien por parte de actores no estatales cuyo comportamiento no ha sido prevenido o reprimido por el Estado, surgiría para este la obligación de ofrecer garantías de no repetición

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio

Effects of synthetic conditions on the structural, stability and ion conducting properties of Li0.30(La0.50Ln0.50)0.567TiO3 (Ln= La, Pr, Nd) solid electrolytes for rechargeable lithium batteries

The structure, thermal stability, morphology and ion conductivity of titanium perovskites with the general formula Li3xLn2/3−xTiO3 (Ln = rare earth element; 3x= 0.30) are studied in the context of their possible use as solid electrolyte materials for lithium ion batteries. Materials are prepared by a glycine-nitrate method using different sintering treatments, with a cation-disorder-induced structural transition from tetragonal to cubic symmetry, detected as quenching temperature increases. SEM images show that the average grain size increases with increasing sintering temperature and time. Slightly higher bulk conductivity values have been observed for quenched samples sintered at high temperature. Bulk conductivity decreases with the lanthanide ion size. A slight conductivity enhancement, always limited by grain boundaries, is observed for longer sintering times. TDX measurements of the electrolyte/cathode mixtures also show a good stability of the electrolytes in the temperature range of 30-1100ºC.This research has been funded by the Consejería de Industria, Innovación, Comercio y Turismo (SAIOTEK 2012 programmes), by Dpto. Educación, Política Lingüística y Cultura of the Basque Goverment (Grupos de Investigación del Sistema Universitario Vasco 2013 – 2018; IT-630-13), by Ministerio de Ciencia e Innovación (MAT2010-15375 and MAT2012-30763) and by Ministerio de Economía y Fondos Feder (MAT2010-19837-C06-06). The authors thank SGIker technical support (UPV/EHU, MEC, GV/EJ and European Social Fund). L.O.S.M. acknowledges the Departamento Ciencias, PUCP, for the allocation of research time

Prospects of new planar optical waveguides based on eutectic microcomposites of insulating crystals: The ZrO 2 (c)-CaZrO 3 erbium doped system

A new approach to produce structured optical materials is described. The method relies on the capability of growing eutectic crystals of wide optical band gap materials by directional solidification procedures. The laser float zone technique was used to produce ordered arrays of alternate lamellae with thickness of the order of microns of erbium doped CaZrO 3 and calcia stabilized zirconia single crystals. The later, having a higher refractive index, exhibited planar waveguiding effects as it has been proved experimentally.Peer ReviewedPostprint (published version

Comparison of Imported Plasmodium ovale curtisi and P. ovale wallikeri Infections among Patients in Spain, 2005–2011

Sequencing data from Plasmodium ovale genotypes co-circulating in multiple countries support the hypothesis that P. ovale curtisi and P. ovale wallikeri are 2 separate species. We conducted a multicenter, retrospective, comparative study in Spain of 21 patients who had imported P. ovale curtisi infections and 14 who had imported P. ovale wallikeri infections confirmed by PCR and gene sequencing during June 2005–December 2011. The only significant finding was more severe thrombocytopenia among patients with P. ovale wallikeri infection than among those with P. ovale curtisi infection (p = 0.031). However, we also found nonsignificant trends showing that patients with P. ovale wallikeri infection had shorter time from arrival in Spain to onset of symptoms, lower level of albumin, higher median maximum core temperature, and more markers of hemolysis than did those with P. ovale curtisi infection. Larger, prospective studies are needed to confirm these findings. Download MP3  Length: 1:2

Subcutaneous anti-COVID-19 hyperimmune immunoglobulin for prevention of disease in asymptomatic individuals with SARS-CoV-2 infection: a double-blind, placebo-controlled, randomised clinical trialResearch in context

Summary: Background: Anti-COVID-19 hyperimmune immunoglobulin (hIG) can provide standardized and controlled antibody content. Data from controlled clinical trials using hIG for the prevention or treatment of COVID-19 outpatients have not been reported. We assessed the safety and efficacy of subcutaneous anti-COVID-19 hyperimmune immunoglobulin 20% (C19-IG20%) compared to placebo in preventing development of symptomatic COVID-19 in asymptomatic individuals with SARS-CoV-2 infection. Methods: We did a multicentre, randomized, double-blind, placebo-controlled trial, in asymptomatic unvaccinated adults (≥18 years of age) with confirmed SARS-CoV-2 infection within 5 days between April 28 and December 27, 2021. Participants were randomly assigned (1:1:1) to receive a blinded subcutaneous infusion of 10 mL with 1 g or 2 g of C19-IG20%, or an equivalent volume of saline as placebo. The primary endpoint was the proportion of participants who remained asymptomatic through day 14 after infusion. Secondary endpoints included the proportion of individuals who required oxygen supplementation, any medically attended visit, hospitalisation, or ICU, and viral load reduction and viral clearance in nasopharyngeal swabs. Safety was assessed as the proportion of patients with adverse events. The trial was terminated early due to a lack of potential benefit in the target population in a planned interim analysis conducted in December 2021. ClinicalTrials.gov registry: NCT04847141. Findings: 461 individuals (mean age 39.6 years [SD 12.8]) were randomized and received the intervention within a mean of 3.1 (SD 1.27) days from a positive SARS-CoV-2 test. In the prespecified modified intention-to-treat analysis that included only participants who received a subcutaneous infusion, the primary outcome occurred in 59.9% (91/152) of participants receiving 1 g C19-IG20%, 64.7% (99/153) receiving 2 g, and 63.5% (99/156) receiving placebo (difference in proportions 1 g C19-IG20% vs. placebo, −3.6%; 95% CI -14.6% to 7.3%, p = 0.53; 2 g C19-IG20% vs placebo, 1.1%; −9.6% to 11.9%, p = 0.85). None of the secondary clinical efficacy endpoints or virological endpoints were significantly different between study groups. Adverse event rate was similar between groups, and no severe or life-threatening adverse events related to investigational product infusion were reported. Interpretation: Our findings suggested that administration of subcutaneous human hyperimmune immunoglobulin C19-IG20% to asymptomatic individuals with SARS-CoV-2 infection was safe but did not prevent development of symptomatic COVID-19. Funding: Grifols