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Unraveling the inner workings of solid oxide fuel cells through the integration of computational data and hands-on experimentation

Solid oxide fuel cells, or SOFC, is a type of electrochemical device that generates electricity using hydrogen as fuel, with the only 'waste' product being water. Naturally, as we strive to reduce our carbon output and mitigate the casualties of the climate crisis, both business and academia have taken a major interest in the development of SOFCs.

In what can potentially accelerate the development of more efficient SOFCs, a research team in Fukuoka, Japan, led by Kyushu University has uncovered the chemical inner workings of a perovskite-based electrolyte they developed for SOFCs. The duo combined synchrotron radiation analysis, large-scale supercomputer simulations, machine learning, and thermogravimetric analysis, to uncover the active site where hydrogen atoms are introduced within the perovskite lattice in its process to produce energy. The results were published in the journal Chemistry of Materials. 

At the fundamental level, a fuel cell is just a device that generates electricity by facilitating the split of a hydrogen atom into its positively charged proton and negatively charged electron. The electron is used to generate electricity, and then comes together with a proton and oxygen and produces water as a 'waste' product.

The material at the literal center of all this is the electrolyte. This material acts as an atomic sieve that facilitates the transfer of specific atoms across the fuel cell. Depending on the type of fuel cell, those atoms could be protons or oxygen.

While SOFCs may be an uncommon term to many people, the technology has already been commercialized in generators for single-family homes. Nonetheless, they remain expensive, with one of the most significant obstacles being their high operating temperature.

"Conventional SOFCs need to be at 700-1000℃ for the electrolyte to perform efficiently," explains Professor Yoshihiro Yamazaki at Kyushu University's Platform of Inter-/Transdisciplinary Energy Research, who led the research. "Naturally, there's a global race to develop SOFC electrolytes that can operate at lower temperatures of around 300-450℃. One such promising materials are perovskites."

Perovskites are a category of material with a specific crystalline structure that allows them to possess unique physical, optical, and even electrical properties. Moreover, since they can be artificially synthesized with different atoms, a large body of research focuses on developing and testing a near-infinite number of possible perovskites.

One such case is in developing better SOFC electrolytes.

"In our past work, we developed a Barium and Zirconium based perovskite with the chemical composition BaZrO3. By replacing the Zr site with a high concentration of Scandium, or Sc, we succeeded in making a high-performance electrolyte that can function at our target temperature of 400℃," explains Yamazaki. "Of course, that was only a part of what we wanted to find. We also were investigating a question that hadn't been solved for over three decades: where in the electrolyte's lattice do the protons get introduced?"

Probing the inner workings of SOFCs had been difficult due to its high operating temperature and changing pressure from the water, the fuel cell's source of hydrogen.

To get around these issues, the team conducted X-ray absorption spectroscopy experiments on their perovskite electrolyte using synchrotron radiation—the electromagnetic radiation emitted from particle accelerators—while the fuel cell was active at around 400℃.

"These results gave us insight into where in the material's chemical structure the protons would be incorporated. From there we applied machine learning, and using a supercomputer calculated possible structural configurations of the material," continued Yamazaki. "By carefully comparing the predicted results with experimental data we were able to clarify the structural changes the electrolyte undertakes when active."

 "Now that we have the fundamental inner workings of the electrolyte we can being optimizing its nanostructures and even propose new materials that can lead to more efficient fuel cells and even ones that work at wider temperature ranges," concludes Yamazaki.

Molecular supercomputer modeling suggests structural consequences of an early protein mutation that promoted the viral transmission

The rapid spread of COVID-19 may have been partly due to changes in the structure of the SARS-CoV-2 virus wrought by an early mutation in its genome, a detailed analysis by RIKEN researchers suggests. The finding could help inform the development of next-generation vaccines and antiviral drugs.

Alpha, Delta, Omicron, and other variants of concern have been making news throughout the COVID-19 pandemic. But the most significant mutation may have occurred in the early days of the pandemic, and it might have enabled the virus to spread so rapidly.

Yuji Sugita of the RIKEN Center for Computational Science (R-CCS) and Hisham Dokainish, who was at R-CCS at the time of the study, investigated the effect of mutations on the viral structure. They did this by simulating the atomic positions of molecules found in different forms of the virus’s important spike protein—a tool coronaviruses use to bind and enter human cells.

They found that the substitution of a single amino acid altered this protein’s shape, helping SARS-CoV-2 to adapt to human hosts. This finding demonstrates how even tiny mutations—swapping a single amino acid in this case—can greatly affect protein dynamics.

To understand why the mutation proved so advantageous to the virus, the pair ran detailed simulations of the protein’s structure and stability. Their analysis, done using the RIKEN Fugaku supercomputer, one of the fastest in the world, revealed how the mutation (known as D614G) breaks an ionic bond with a second subunit of the Spike protein. It also changes the shape of a nearby loop structure, which alters the orientation of the entire protein, locking it into a form that makes it easier for the virus to enter cells (Fig. 1).

“A single and local change in an interaction within the molecule caused by a single mutation could affect the global structure of the spike protein,” explains Sugita, who is additionally affiliated with the RIKEN Center for Biosystems Dynamics Research. The resulting mutant proved better at replicating and transmitting between human hosts, and the D614Glineage quickly outcompeted its ancestral lineages and spread across the globe. It remains a fixture of every dominant variant that has followed.

Sugita’s team is now performing similar investigations of adaptive viral mutations that arose later in the course of the pandemic, including those found in the Omicron variant.

“Information obtained from our molecular dynamics simulations should help increase the opportunities for us to find effective drugs and other medicines,” he says.

Researchers generate a vector vortex light beam and imprint its spatial structure onto spins inside a semiconductor solid

Spin, a quantum property of particles, can be controlled using light waves to store information. This is conventionally achieved using a uniformly polarized light beam. Recently, researchers from Japan successfully generated a structured light beam with spatially variant polarization and transferred its structure to electron spins confined within a semiconductor solid. Additionally, they simultaneously generated two spin waves with inverted phases using this beam. Their results have important implications in optical communications and information storage.

Light is composed of electric and magnetic fields that oscillate perpendicular to each other. When these oscillations are restricted, say, along a plane, it results in polarized light. Polarized light is of great importance in optical communications and can similarly revolutionize how information is stored.

Current electronic devices store information in the form of electronic charges. However, spin-a uniquely quantum property of electrons offers an alternative. The spin can be controlled using polarized light to store information. A polarized light beam interacts with electron spins within a semiconductor to generate spin-polarized electrons, i.e., spins aligned along a specific direction. So far, only uniformly polarized light, i.e., light with a spatially uniform polarization, has been exploited to control electron spins. If, however, the polarization has an additional spatial structure (variation), it can produce spatially structured electron spins, opening up new ways to store information.

To this end, a group of researchers, led by Junior Associate Professor Jun Ishihara from and including Graduate Student Takachika Mori, Graduate Student (at the time of the research) Takuya Suzuki, and Professor Kensuke Miyajima from Tokyo University of Science (TUS), Japan, has now devised a method for generating such spatially structured electron spins using a structured light with spatially varying polarization profile. The study was done in collaboration with research groups from Chiba University, Tohoku University, and Tsukuba University in Japan.

"In this work, we generated a doughnut-shaped structured light-a vector optical vortex beam with an orbital angular momentum (OAM)-from a basic Gaussian beam using vortex half-wave plate and quarter-wave plate devices. We then used this beam to excite the electron spins confined within a gallium arsenide/aluminum gallium arsenide semiconductor quantum well. These spins, in turn, formed a helical spatial structure in a circle," explains Dr. Ishihara.

Interestingly, while the beam with an OAM number equal to one produced a helix with two spin periods-spin up and spin down around the circle, an OAM number of two resulted in a helix with four such alterations. These observations indicated that the spatial polarization structure of the optical vortex, determined by the OAM, was transferred to the electron spins inside the semiconductor. In addition, increasing the OAM number was suggested to enable higher information storage capacity, characterized by a higher spin repetition rate around the circle.

Moreover, the researchers utilized the effective magnetic field of the spin-orbit interaction acting on electron spins in the quantum well to simultaneously generate two spin waves with opposite phases in the vertical direction using a single beam. This suggested that various spin states with spatial structures could be produced by exploiting the effective magnetic fields (a characteristic of solids) alongside structured light beams.

With such exciting results, the researchers discuss the future prospects of their work. "The conversion of the spatial polarization structure of light into a spatial structure of spin along with the generation of new spin spatial structures in combination with effective magnetic fields in solids are expected to lead to elemental technologies for higher-order quantum media conversion and information capacity enhancement using spin textures," says Dr. Ishihara.