Bulk Properties of the Oxygen Reduction Catalyst SrCo_(0.9)Nb_(0.1)O_(3-δ)

The perovskite SrCo_(0.9)Nb_(0.1)O_(3−δ) (SCN) has excellent electrochemical activity toward oxygen reduction, and it is also valuable as a possible model material for other state-of-the-art perovskite catalysts based on strontium and cobalt, such as Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3−δ) (BSCF). Here we report thermogravimetric, conductivity, and diffraction measurements from SCN. We find that the thermodynamic stability limits of SCN are slightly more favorable than those reported for BSCF, although both materials exhibit a slow oxidative partial decomposition under likely operating conditions. In SCN, this decomposition is thermodynamically preferred when the average formal oxidation state of cobalt is greater than ∼3.0+, but due to sluggish kinetics, metastable SCN with higher cobalt valence can be observed. The oxygen stoichiometry 3−δ varies from 2.45 to 2.70 under the conditions studied, 500–1000 °C and 10^(–4)–1 bar O_2, which encompass both stable and metastable behavior. The electronic conductivity is p-type and thermally activated, with a value at 600 °C in air of 250 S cm^(–1), comparable to that of La_(0.8)Sr_(0.2)MnO_(3−δ). The polaron migration enthalpy decreases linearly from 0.30 to 0.05 eV as 3−δ increases from 2.52 to 2.64. Thermal and chemical expansivities are also reported

Probing the reaction pathway in (La_(0.8)Sr_(0.2))_(0.95)MnO_(3+δ) using libraries of thin film microelectrodes

Libraries of (La_(0.8)Sr_(0.2))_(0.95)MnO_(3+δ) (LSM) thin film microelectrodes with systematically varied thickness or growth temperature were prepared by pulsed laser deposition, and a novel robotic instrument was used to characterize these libraries in automated fashion by impedance spectroscopy. The measured impedance spectra are found to be described well by an electrochemical model based on a generalized transmission model for a mixed conducting oxide, and all trends are consistent with a reaction pathway involving oxygen reduction over the LSM surface followed by diffusion through the film and into the electrolyte substrate. The surface activity is found to be correlated with the number of exposed grain boundary sites, which decreases with either increasing film thickness (at constant growth temperature) or increasing film growth temperature (at constant thickness). These findings suggest that exposed grain boundaries in LSM films are more active than exposed grains towards the rate-limiting surface process, and that oxygen ion diffusion through polycrystalline LSM films is faster than many prior studies have concluded

Platinum-decorated carbon nanotubes for hydrogen oxidation and proton reduction in solid acid electrochemical cells

Pt-decorated carbon nanotubes (Pt-CNTs) were used to enhance proton reduction and hydrogen evolution in solid acid electrochemical cells based on the proton-conducting electrolyte CsH_2PO_4. The carbon nanotubes served as interconnects to the current collector and as a platform for interaction between the Pt and CsH_2PO_4, ensuring minimal catalyst isolation and a large number density of active sites. Particle size matching was achieved by using electrospray deposition to form sub-micron to nanometric CsH_2PO_4. A porous composite electrode was fabricated from electrospray deposition of a solution of Pt-CNTs and CsH_2PO_4. Using AC impedance spectroscopy and cyclic voltammetry, the total electrode overpotential corresponding to proton reduction and hydrogen oxidation of the most active electrodes containing just 0.014 mg cm^(−1) of Pt was found to be 0.1 V (or 0.05 V per electrode) at a current density of 42 mA cm^(−2) for a measurement temperature of 240 °C and a hydrogen-steam atmosphere. The zero bias electrode impedance was 1.2 Ω cm2, corresponding to a Pt utilization of 61 S mg^(−1), a 3-fold improvement over state-of-the-art electrodes with a 50× decrease in Pt loading

Scanning impedance probe for high-​throughput electrochemical characterization of solid state electrodes

We have developed a robotic instrument that can measure the electrochem. impedance of hundreds of thin-film microelectrodes in automated fashion. By measuring electrodes with systematically varied area, thickness, surface decoration, and compn., it is possible to probe reaction pathways, decouple bulk and surface properties, and rapidly screen hundreds of chem. compns. to discover trends and identify new high performing catalysts. Here we introduce the capabilities of this new instrument by using it to measure geometrically graded microdot electrodes of the solid-oxide fuel-cell (SOFC) cathode material (La_(0.8)Sr_(0.2))0.95MnO3-δ (LSM). We collect A.C. impedance spectra from several hundred microdots with diams. ranging from 30 to 500 μm and thicknesses from 30 to 300 nm over the temp. and oxygen partial pressure ranges of 700 to 800 °C and 3.2 × 10^(-4) to 1 atm, resp. Automated data anal. using a phys. motivated equiv. circuit model yields phys. parameters for each dot at each measurement condition. The LSM surface reaction resistance and bulk ionic resistance both exhibited a power law dependence on dot diam. with an exponent close to -2, indicative of a surface reaction pathway that encompasses the entirety of the dot surface. The slight deviation from -2 is attributed to local cooling of the sample by the microprobe tip, which slightly increases the resistances for smaller diam. microelectrodes. A surprising increase in surface reaction resistance with microelectrode thickness was obsd., tentatively assigned to an obsd. increase in film roughness with thickness. The results set the stage for exploration of a wide range of gradient types, from compn. to growth temp. to catalyst coating, while the use of impedance spectroscopy implies that a broad range of properties, from ionic cond. to material nonstoichiometry, can be extd

Bulk Properties of the Oxygen Reduction Catalyst SrCo_0.9Nb_0.1O_3−δ

The perovskite SrCo_0.9Nb_0.1O_3−δ (SCN) has excellent electrochemical activity toward oxygen reduction, and it is also valuable as a possible model material for other state-of-the-art perovskite catalysts based on strontium and cobalt, such as Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF). Here we report thermogravimetric, conductivity, and diffraction measurements from SCN. We find that the thermodynamic stability limits of SCN are slightly more favorable than those reported for BSCF, although both materials exhibit a slow oxidative partial decomposition under likely operating conditions. In SCN, this decomposition is thermodynamically preferred when the average formal oxidation state of cobalt is greater than ∼3.0+, but due to sluggish kinetics, metastable SCN with higher cobalt valence can be observed. The oxygen stoichiometry 3−δ varies from 2.45 to 2.70 under the conditions studied, 500–1000 °C and 10^–4–1 bar O₂, which encompass both stable and metastable behavior. The electronic conductivity is p-type and thermally activated, with a value at 600 °C in air of 250 S cm^–1, comparable to that of La_0.8Sr_0.2MnO_3−δ. The polaron migration enthalpy decreases linearly from 0.30 to 0.05 eV as 3−δ increases from 2.52 to 2.64. Thermal and chemical expansivities are also reported

Genome-wide meta-analysis identifies 127 open-angle glaucoma loci with consistent effect across ancestries

10.1038/s41467-020-20851-4Nature Communications121125

Chromosome Xq23 is associated with lower atherogenic lipid concentrations and favorable cardiometabolic indices

Abstract Autosomal genetic analyses of blood lipids have yielded key insights for coronary heart disease (CHD). However, X chromosome genetic variation is understudied for blood lipids in large sample sizes. We now analyze genetic and blood lipid data in a high-coverage whole X chromosome sequencing study of 65,322 multi-ancestry participants and perform replication among 456,893 European participants. Common alleles on chromosome Xq23 are strongly associated with reduced total cholesterol, LDL cholesterol, and triglycerides (min P = 8.5 × 10−72), with similar effects for males and females. Chromosome Xq23 lipid-lowering alleles are associated with reduced odds for CHD among 42,545 cases and 591,247 controls (P = 1.7 × 10−4), and reduced odds for diabetes mellitus type 2 among 54,095 cases and 573,885 controls (P = 1.4 × 10−5). Although we observe an association with increased BMI, waist-to-hip ratio adjusted for BMI is reduced, bioimpedance analyses indicate increased gluteofemoral fat, and abdominal MRI analyses indicate reduced visceral adiposity. Co-localization analyses strongly correlate increased CHRDL1 gene expression, particularly in adipose tissue, with reduced concentrations of blood lipids

Genetic architecture of human plasma lipidome and its link to cardiovascular disease

Abstract Understanding genetic architecture of plasma lipidome could provide better insights into lipid metabolism and its link to cardiovascular diseases (CVDs). Here, we perform genome-wide association analyses of 141 lipid species (n = 2,181 individuals), followed by phenome-wide scans with 25 CVD related phenotypes (n = 511,700 individuals). We identify 35 lipid-species-associated loci (P <5 ×10−8), 10 of which associate with CVD risk including five new loci-COL5A1, GLTPD2, SPTLC3, MBOAT7 and GALNT16 (false discovery rate<0.05). We identify loci for lipid species that are shown to predict CVD e.g., SPTLC3 for CER(d18:1/24:1). We show that lipoprotein lipase (LPL) may more efficiently hydrolyze medium length triacylglycerides (TAGs) than others. Polyunsaturated lipids have highest heritability and genetic correlations, suggesting considerable genetic regulation at fatty acids levels. We find low genetic correlations between traditional lipids and lipid species. Our results show that lipidomic profiles capture information beyond traditional lipids and identify genetic variants modifying lipid levels and risk of CVD