Ionic conductivity in multiply substituted ceria-based electrolytes

The authors thank the University of St Andrews and the UK Engineering and Physical Sciences Research Council for the PhD studentship for AVC-A (grant code: EP/M506631/1).Cerias, appropriately doped with trivalent rare earth ions, have high oxide ion conductivity and are attractive SOFC (solid oxide fuel cell) electrolytes. Here, seven compositions of Ce0.8SmxGdyNdzO1.9 (where x, y and z = 0.2, 0.1, 0.0667 or 0 and x + y + z = 0.2) are synthesised using a low temperature method in order to determine the effect of multiple doping on microstructure and conductivity. Analysis using scanning and transmission electron microscopy, inductively coupled plasma mass spectrometry, X-ray diffraction and impedance spectroscopy is carried out. Crystallite sizes are determined in the powders and relative densities and grain size distributions were obtained in sintered pellets. Total, bulk and grain boundary conductivities are obtained using impedance spectroscopy and corresponding activation energies and enthalpies of ion migration and defect association are calculated. The highest total conductivity observed at 600 °C is 1.80 Sm−1 for Ce0.8Sm0.1Gd0.1O1.9 and an enhancement effect on conductivity for this combination of co-dopants between 300 °C and 700 °C relative to the singly doped compounds - Ce0.8Sm0.2O1.9 and Ce0.8Gd0.2O1.9 - is seen. This has interesting implications for their application as SOFC electrolytes, especially at intermediate temperatures.PostprintPeer reviewe

Substituted ceria materials for applications in solid oxide fuel cells

Cerias, appropriately doped with trivalent rare earth ions in particular, can have high oxide ion conductivity and are attractive as both SOFC (solid oxide fuel cell) electrolytes and anodes. Here, four groups of candidate electrolyte materials were synthesised using a low temperature method in order to determine the effect of multiple doping on their microstructure and ionic conductivity. In an initial study, seven compositions of Ce₀.₈SmₓGd[sub]yNd[sub]zO₁.₉ (where x, y and z = 0.2, 0.1, 0.0667 or 0 and x + y + z = 0.2) were synthesised and the properties of multiply-doped materials were compared with the corresponding singly-doped parent materials. The effect of co-doping with Gd and Sm was investigated in more detail by preparing and studying five compositions of Ce₁₋₂ₓSmₓGdₓO₂₋ₓ (where x = 0.125, 0.1, 0.0875, 0.075 or 0.05) and seven compositions of Ce₀.₈₂₅SmₓGd₀.₁₇₅₋ₓO₁.₉₁₂₅ (where x = 0.175, 0.14, 0.105, 0.0875, 0.07, 0.035 or 0). The effect of additional doping with a divalent ion- Ca²⁺- was studied in six compositions of Ce[sub](0.825+y)Sm[sub](0.0875-y)Gd[sub](0.0875-y)Ca[sub]yO₁.₉₁₂₅ (where y = 0, 0.00875, 0.0175, 0.02625, 0.035 or 0.04375). The materials were characterised using scanning and transmission electron microscopy, inductively coupled plasma mass spectrometry and X-ray diffraction. Crystallite sizes were determined in the powders and relative densities and grain size distributions were obtained in sintered pellets. Total, bulk and grain boundary conductivities were obtained using impedance spectroscopy and corresponding activation energies and enthalpies of ion migration and defect association were calculated. The most promising material for SOFCs operating at intermediate temperatures was found to be Ce₀.₈₂₅Sm₀.₀₈₇₅Gd₀.₀₈₇₅O₁.₉₁₂₅ which had a total conductivity at 600 °C of 2.23 S m⁻¹. Lastly, doped ceria materials, primarily Ce₀.₈Sm₀.₂O₁.₉, were employed as catalytic supports for Pd and PdO nanoparticles and these were investigated as SOFC anode materials

Oxygen ion conductivity in ceria-based electrolytes co-doped with samarium and gadolinium

The authors thank the University of St Andrews and the UK Engineering and Physical Sciences Research Council for the PhD studentship for AVC-A (grant code: EP/M506631/1). Electron microscopy was performed at the Electron Microscope Facility, University of St Andrews.In a systematic study, two compositional series of ceria-based oxides, both co-doped with Sm and Gd, were synthesised using a low temperature method and evaluated as oxygen ion-conducting electrolytes for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs). Series one, Ce1-2xSmxGdxO2-x, had equal concentrations of Sm and Gd but varying total dopant concentration. Series two, Ce0.825SmxGd0.175-xO1.9125, had a fixed total dopant concentration but the Sm:Gd concentration ratio was varied. The materials were characterised using scanning and transmission electron microscopy, inductively coupled plasma mass spectrometry and X-ray diffraction. Impedance spectra were recorded on dense pellets of these materials. From these, total, bulk and grain boundary conductivities and capacitances along with activation energies, pre-exponential constants and enthalpies of ion migration and defect association were obtained. These gave a detailed insight into the fundamental conduction processes in the materials. Ce0.825Sm0.0875Gd0.0875O1.9125 had the highest total ionic conductivity at temperatures of 550 °C and above and also demonstrated an enhanced conductivity with respect to its singly-doped parent compounds, Ce0.825Sm0.175O1.9125 and Ce0.825Gd0.175O1.9125, at 400 °C and above. This compares favourably with previously-reported values and has promising implications for the development of IT-SOFCs.PostprintPeer reviewe

Oxygen ion conductivity in ceria-based electrolytes co-doped with samarium and gadolinium

In a systematic study, two compositional series of ceria-based oxides, both co-doped with Sm and Gd, were synthesised using a low temperature method and evaluated as oxygen ion-conducting electrolytes for Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs). Series one, Ce1-2xSmxGdxO2-x, had equal concentrations of Sm and Gd but varying total dopant concentration. Series two, Ce0.825SmxGd0.175-xO1.9125, had a fixed total dopant concentration but the Sm:Gd concentration ratio was varied. The materials were characterised using scanning and transmission electron microscopy, inductively coupled plasma mass spectrometry and X-ray diffraction. Impedance spectra were recorded on dense pellets of these materials. From these, total, bulk and grain boundary conductivities and capacitances along with activation energies, pre-exponential constants and enthalpies of ion migration and defect association were obtained. These gave a detailed insight into the fundamental conduction processes in the materials. Ce0.825Sm0.0875Gd0.0875O1.9125 had the highest total ionic conductivity at temperatures of 550 °C and above and also demonstrated an enhanced conductivity with respect to its singly-doped parent compounds, Ce0.825Sm0.175O1.9125 and Ce0.825Gd0.175O1.9125, at 400 °C and above. This compares favourably with previously-reported values and has promising implications for the development of IT-SOFCs.</p

Ionic conductivity in multiply substituted ceria-based electrolytes

Cerias, appropriately doped with trivalent rare earth ions, have high oxide ion conductivity and are attractive SOFC (solid oxide fuel cell) electrolytes. Here, seven compositions of Ce0.8SmxGdyNdzO1.9 (where x, y and z = 0.2, 0.1, 0.0667 or 0 and x + y + z = 0.2) are synthesised using a low temperature method in order to determine the effect of multiple doping on microstructure and conductivity. Analysis using scanning and transmission electron microscopy, inductively coupled plasma mass spectrometry, X-ray diffraction and impedance spectroscopy is carried out. Crystallite sizes are determined in the powders and relative densities and grain size distributions were obtained in sintered pellets. Total, bulk and grain boundary conductivities are obtained using impedance spectroscopy and corresponding activation energies and enthalpies of ion migration and defect association are calculated. The highest total conductivity observed at 600 °C is 1.80 Sm−1 for Ce0.8Sm0.1Gd0.1O1.9 and an enhancement effect on conductivity for this combination of co-dopants between 300 °C and 700 °C relative to the singly doped compounds - Ce0.8Sm0.2O1.9 and Ce0.8Gd0.2O1.9 - is seen. This has interesting implications for their application as SOFC electrolytes, especially at intermediate temperatures

Substituted Ceria Materials for Applications in Solid Oxide Fuel Cells (thesis data)

The data files are embargoed until 16/06/202

Stratified analyses refine association between TLR7 rare variants and severe COVID-19

Summary: Despite extensive global research into genetic predisposition for severe COVID-19, knowledge on the role of rare host genetic variants and their relation to other risk factors remains limited. Here, 52 genes with prior etiological evidence were sequenced in 1,772 severe COVID-19 cases and 5,347 population-based controls from Spain/Italy. Rare deleterious TLR7 variants were present in 2.4% of young (<60 years) cases with no reported clinical risk factors (n = 378), compared to 0.24% of controls (odds ratio [OR] = 12.3, p = 1.27 × 10−10). Incorporation of the results of either functional assays or protein modeling led to a pronounced increase in effect size (ORmax = 46.5, p = 1.74 × 10−15). Association signals for the X-chromosomal gene TLR7 were also detected in the female-only subgroup, suggesting the existence of additional mechanisms beyond X-linked recessive inheritance in males. Additionally, supporting evidence was generated for a contribution to severe COVID-19 of the previously implicated genes IFNAR2, IFIH1, and TBK1. Our results refine the genetic contribution of rare TLR7 variants to severe COVID-19 and strengthen evidence for the etiological relevance of genes in the interferon signaling pathway

Whole-genome sequencing reveals host factors underlying critical COVID-19

: Critical COVID-19 is caused by immune-mediated inflammatory lung injury. Host genetic variation influences the development of illness requiring critical care1 or hospitalization2-4 after infection with SARS-CoV-2. The GenOMICC (Genetics of Mortality in Critical Care) study enables the comparison of genomes from individuals who are critically ill with those of population controls to find underlying disease mechanisms. Here we use whole-genome sequencing in 7,491 critically ill individuals compared with 48,400 controls to discover and replicate 23 independent variants that significantly predispose to critical COVID-19. We identify 16 new independent associations, including variants within genes that are involved in interferon signalling (IL10RB and PLSCR1), leucocyte differentiation (BCL11A) and blood-type antigen secretor status (FUT2). Using transcriptome-wide association and colocalization to infer the effect of gene expression on disease severity, we find evidence that implicates multiple genes-including reduced expression of a membrane flippase (ATP11A), and increased expression of a mucin (MUC1)-in critical disease. Mendelian randomization provides evidence in support of causal roles for myeloid cell adhesion molecules (SELE, ICAM5 and CD209) and the coagulation factor F8, all of which are potentially druggable targets. Our results are broadly consistent with a multi-component model of COVID-19 pathophysiology, in which at least two distinct mechanisms can predispose to life-threatening disease: failure to control viral replication; or an enhanced tendency towards pulmonary inflammation and intravascular coagulation. We show that comparison between cases of critical illness and population controls is highly efficient for the detection of therapeutically relevant mechanisms of disease