Manufacturers integrate these catalysts in complex assemblies called catalyst layers. Until now, they had to do so without a detailed picture of the resulting structure, as traditional imaging processes almost always cause some degree of damage. Vasiliki Tileli, head of the Laboratory for in-situ nanomaterials characterization with electrons in the School of Engineering, has found a way around this challenge. By imaging catalysts and their environment at below-freezing temperatures using cryogenic transmission electron tomography and processing the images with deep learning, she and her colleagues have succeeded in revealing, for the first time, the nanoscale structure of catalyst layers.

“We’re still far away from PEMFCs without platinum, which is very expensive, so in the short term, we need to reduce platinum loading to make this technology viable for mass production. It’s therefore imperative to understand how platinum sits in relation to other materials within the catalyst layer, to increase the surface area contact required for chemical reactions to take place,” Tileli explains.

“That’s why it’s quite an achievement to image these catalysts in three dimensions; before, it was impossible to have the right contrast between the different catalyst layer components.” The work has recently been published in the journal Nature Catalysis.

Better preservation; higher resolution

During imaging using conventional electron microscopy, delicate catalyst layer samples often become damaged by electron beams, causing materials to shrink or deform. By carrying out the imaging in-situ at cryo-temperatures, Tileli and her team were able to preserve most of the catalyst layer’s morphology. Then, they used a machine learning algorithm to more accurately denoise and classify the images, allowing them to achieve a higher image resolution than had ever previously been possible.

Crucially, the scientists were able to reveal the heterogenous thickness of a porous polymer layer on the catalysts called ionomer. Ionomer thickness strongly influences how well platinum catalysts perform.

“The ionomer must have a certain thickness for the catalytic reactions to happen efficiently. Because we could do a full reconstruction of catalyst layers with limited damage to the structure, we could show, for the first time, how much platinum is covered with ionomer and the thickness of that coverage,” Tileli explains.

Such information could be a gold mine for catalyst manufacturers, who could use it to produce catalysts with more platinum particles that are covered by the right amount of ionomer — and that therefore perform optimally.

“The cryo-aspect is the key component of this study. Ionomers are like proteins: they are soft, and require freezing conditions to stabilize and protect their structure,” Tileli says.

“I think this advanced technique will therefore be useful not just for facilitating the mass manufacturing of PEMFCs through optimized platinum use, but also for many different materials science and energy applications — for example, battery storage, water electrolysis, and energy conversion systems in general.”

The World Health Organization describes metabolic syndrome as the constellation of three or more of the following: abdominal obesity, insulin resistance, hypertension, and hyperlipidemia. The prevalence of metabolic syndrome in US middle-aged adults is 30%, increasing to 50% in adults older than 60 years. In Finland, the prevalence of metabolic syndrome is 30% in men and 25% in women. Metabolic syndrome increases the risk of worsening obesity, type 2 diabetes, cardiovascular disease, and premature death.

Already among children aged 6 — 12 years, the prevalence of metabolic syndrome is approximately 3% while among adolescents aged 13 — 18 years, the prevalence is approximately 5% globally. Among children who are overweight, the prevalence of metabolic syndrome is 12% but 29% among children who are obese. This trend in the prevalence of metabolic syndrome is consistent across the globe; hence the need to identify novel causes and prevent or reverse the disease.

A new risk factor for childhood and adolescent metabolic disease such as obesity and insulin resistance is arterial stiffness. This risk factor is being established as a potential cause of type 2 diabetes among adults globally. However, it is not clear whether arterial stiffness causes metabolic syndrome.

The current study included 3,862 adolescents (1,719 males and 2,413 females) aged 17 years who were followed up until age 24 years. These adolescents had dual-energy Xray absorptiometry measurement for trunk fat mass and skeletal muscle mass, as well as fasting blood samples such as glucose, insulin, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglyceride, and high sensitivity C-reactive protein, in addition to smoking status, socio-economic status, family history of cardiovascular disease, and moderate-to-vigorous physical activity. Arterial stiffness was measured with carotid-femoral pulse wave velocity and the presence of any three of high blood pressure, high trunk fat mass, high fasting glucose, high fasting triglyceride, or low fasting high-density lipoprotein cholesterol was considered to describe metabolic syndrome.

The prevalence of metabolic syndrome in the study was 5% in males and 1.1% in females at age 17 years but 8.8% in males and 2.4% in females at age 24 years. This significant sex-difference in the prevalence of metabolic syndrome is due to a higher proportion of males having elevated systolic blood pressure, hyperglycemia, elevated triglyceride, and reduced high-density lipoprotein cholesterol compared to females. However, females had significantly higher trunk fat mass than males.

During the 7-year follow-up, worsening arterial stiffness was associated with a 9% risk of metabolic syndrome in males but there was no statistically significant risk among females. It was also observed that arterial stiffness potentially caused metabolic syndrome; however, metabolic syndrome did not cause arterial stiffness. The pathway through which arterial stiffness caused metabolism syndrome could be partly explained by an increase in fasting insulin (12% contribution) and low-density lipoprotein cholesterol (9% contribution).

“We are seeing for the first time that arterial stiffness in adolescents is an unknown risk factor for metabolic syndrome which may initiate a cascade of disease processes that might lead to type 2 diabetes, cardiovascular disease, and premature death. Early intervention might likely reduce high fasting insulin and low-density lipoprotein cholesterol thereby cutting off 20% of the potential causal effect of arterial stiffness on metabolic syndrome,” says Andrew Agbaje, a physician and clinical epidemiologist at the University of Eastern Finland.

“Pending when randomized clinical trials will be successful in reversing and treating arterial stiffness, it is expedient for caregivers, pediatricians, public health experts, and policymakers to focus on ways to reduce high fasting insulin or insulin resistance and low-density lipoprotein cholesterol, particularly from adolescence through improvement in diet and physical activity,” Agbaje continues.

Dr Agbaje’s research group (urFIT-child) is supported by research grants from Jenny and Antti Wihuri Foundation, the Finnish Cultural Foundation Central Fund, the Finnish Cultural Foundation North Savo Regional Fund, the Orion Research Foundation sr, the Aarne Koskelo Foundation, the Antti and Tyyne Soininen Foundation, the Paulo Foundation, the Yrjö Jahnsson Foundation, the Paavo Nurmi Foundation, the Finnish Foundation for Cardiovascular Research and the Foundation for Pediatric Research.

“We’re trying to measure the composition of gases inside galaxies,” said Yuguang Chen, a postdoctoral researcher working with Professor Tucker Jones in the Department of Physics and Astronomy at the University of California, Davis.

Most elements other than hydrogen, helium and lithium are produced inside stars, so the composition and distribution of heavier elements — especially the ratio of oxygen to hydrogen — can help astronomers understand how many and what kinds of stars are being formed in a distant object.

Astronomers use two methods to measure oxygen in a galaxy, but unfortunately, they give different results. One common method, collisionally excited lines, gives a strong signal, but the results are thought to be sensitive to temperature changes, Chen said. A second method uses a different set of lines, called recombination lines, which are fainter but not thought to be affected by temperature.

The recombination line method consistently produces measurements about double those from collisionally excited lines. Scientists attribute the discrepancy to temperature fluctuations in gas clouds, but this has not been directly proven, Chen said.

Chen, Jones and colleagues used optical and infrared astronomy to measure oxygen abundance in dwarf galaxy Markarian 71, about 11 million light years from Earth. They used archived data from the recently retired SOFIA flying telescope and the retired Herschel Space Observatory, as well as making observations with telescopes at the W.M. Keck Observatory in Mauna Kea, Hawaii.

SOFIA (Stratospheric Observatory For Infrared Astronomy) was a telescope mounted in a Boeing 747 aircraft. By flying at 38,000 to 45,000 feet, the aircraft could get above 99% of the water vapor in Earth’s atmosphere, which effectively blocks infrared light from deep space from reaching ground level. A joint project of NASA and the German space agency, SOFIA made its last operational flight in September 2022 and is now headed for a museum display in Tucson.

The Herschel Space Observatory, named after astronomers William and Caroline Herschel, was an infrared space telescope operated by the European Space Agency. It was active from 2009 to 2013.

A surprising result

With data from these instruments, Chen and Jones examined oxygen abundance in Markarian 71 while correcting for temperature fluctuations. They found that the result from collisionally excited infrared lines was still 50% less than that from the recombination line method, even after eliminating the effect of temperature.

“This result is very surprising to us,” Chen said. There is no consensus on an explanation for the discrepancy, he said. The team plans to look at additional objects to figure out what properties of galaxies correlate with this variation, Chen said.

One of the goals of the James Webb Space Telescope, launched in 2022, is to make infrared observations of the composition of distant galaxies in the first billion years of the universe. The new results provide a framework for making these measurements with the JWST and the Atacama Large Millimeter Array in Chile.

Additional co-authors on the paper are: Ryan Sanders and Erin Huntzinger, UC Davis; Dario Fadder, Jessica Sutter and Robert Minchin, SOFIA Science Center, NASA Ames Research Center; Peter Senchyna, Observatories of the Carnegie Institute for Science, Pasadena; Daniel Stark and Benjamin Weiner, Steward Observatory, University of Arizona; Justin Spilker, Texas A&M University; and Guido Roberts-Borsani, UCLA. The work was financially supported in part by NASA. SOFIA was jointly operated by the Universities Space Research Association, Inc., and the Deutsches SOFIA Institut.

The W.M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA, with financial support from the W.M. Keck Foundation. The researchers would like to thank the Hawaiian community for the privilege of allowing them to conduct observations on Mauna Kea, which plays a significant cultural and religious role.