Boosting fuel cell efficiency with water vapor

Hydration doubles oxide-ion conductivity in Ba7Nb4MoO20, a promising material for low-temperature solid oxide fuel cells

Institute of Science Tokyo

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Ba7Nb4MoO20, a ceramic electrolyte with potential for low-temperature fuel cells, becomes nearly twice as conductive when exposed to water vapor at 500 °C. The improvement is driven by enhanced oxide-ion mobility in the material and could lead to more efficient and durable fuel cells.

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Credit: Institute of Science Tokyo

Hydration significantly boosts ion conductivity in Ba7Nb4MoO20, a promising ceramic electrolyte candidate for low-temperature solid oxide fuel cells. But its origin and mobile ionic species were unresolved issues. Researchers at Institute of Science Tokyo found that exposure to water vapor enhances oxide-ion mobility by increasing interstitial oxygen ions, nearly doubling the oxide-ion conductivity at 500 °C. The findings of this study could advance the development of efficient and durable fuel cells for clean energy applications.   

Fuel cells generate electricity by combining hydrogen and oxygen, producing only water as a byproduct. Once used to provide power and drinking water for space missions, fuel cells are now being explored as a source of low-emission energy. Fuel cells are classified by the type of electrolyte used; each type has specific advantages and drawbacks. One category includes solid oxide fuel cells and proton ceramic fuel cells, which use ceramics as electrolytes. These fuel cells operate at high temperatures—as high as 1,000 °C—eliminating the need for expensive precious metal catalysts. However, high temperatures also accelerate material degradation; therefore, it is crucial to develop highly conductive electrolytes at lower temperatures.

A recent study led by Professor Masatomo Yashima at Institute of Science Tokyo (Science Tokyo), Japan, in collaboration with researchers from Imperial College London and Kyushu University, highlights Ba7Nb4MoO20 as a promising electrolyte material. The team found that the material's oxide-ion conductivity and diffusivity significantly improved when exposed to water vapor, offering a pathway toward more efficient, lower-temperature fuel cells. The findings were published online on July 18, 2025, in the Journal of Materials Chemistry A, where the paper was selected as a HOT Paper in honor of its impact and contribution.

Yashima says, “A new ‘smart material’ has been discovered that enhances the oxygen-ion mobility within ceramics while absorbing water.”

Ba7Nb4MoO20 is a hexagonal perovskite-related oxide where oxide ions (O2-) migrate through the interstitial sites in an oxygen-deficient cubic close packed (CCP) layer in its crystal structure. Materials exhibiting this interstitialcy diffusion mechanism have shown high ionic conductivity under both wet and dry conditions. However, the impact of hydration on O2- transport and conductivity of Ba7Nb4MoO20 was not well understood.

To solve this problem, the researchers synthesized Ba7Nb4MoO20 pellets and investigated their transport properties under dry and wet conditions at different temperatures. They measured the electromotive force using both oxygen and vapor water concentration cells to assess the contributions of O2- and H+ to the electrical conductivity. They also performed tracer diffusion experiments to track the diffusion of oxide ions within the material.

When exposed to water vapor, the material’s conductivity increased significantly compared to dry air, and the O2- was identified as the dominant charge carrier. At 500 °C, the oxygen diffusivity nearly doubled, and the material’s total conductivity in humid air (5.3 × 10‒4 S cm‒1) was more than twice that in dry conditions (2.5 × 10‒4 S cm‒1).

This behavior was attributed to an increase in interstitial oxygen atoms due to the absorption of water vapor. Using molecular dynamics simulations with neural network potential, the researchers found that the hydration introduces additional O2- ions, which occupy interstitial sites and form (Nb/Mo)2O9 dimers within the lattice. The disappearance and reforming of the  dimers enhance O2- mobility, improving the material’s O2- conductivity.

This study addresses a key knowledge gap in interstitial oxygen conductors by revealing how hydration enhances O2- conductivity and mobility in Ba7Nb4MoO20. These findings could lead to the development of more durable and efficient fuel cells that operate at lower temperatures, helping to overcome a major barrier to their wider adoption.

“Understanding O2- and H+ conduction in ceramic oxide-ion, proton, and dual-ion conductors is vital for clean energy,” says Yashima. “This breakthrough in materials science is expected to greatly advance the development of ion conductors, which are essential for clean energy technologies such as fuel cells and steam electrolysis cells. These technologies are key components for building a sustainable next-generation society and achieving the United Nations Sustainable Development Goals.”

 

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About Institute of Science Tokyo (Science Tokyo)
Institute of Science Tokyo (Science Tokyo) was established on October 1, 2024, following the merger between Tokyo Medical and Dental University (TMDU) and Tokyo Institute of Technology (Tokyo Tech), with the mission of “Advancing science and human wellbeing to create value for and with society.”

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Journal

Journal of Materials Chemistry A

DOI

10.1039/D5TA04728E 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Hydration-Driven Enhancement of Interstitialcy Oxide-Ion Diffusion

 

Coastline of lakes an important part of global carbon cycle

Uppsala University

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A lake in Sweden, Uppsala

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Credit: Sandra Gunnarsson

Lakes have long been viewed as sources of carbon dioxide emissions, but new research suggests they may actually act as carbon sinks. A study led by Uppsala University reveals that lake shorelines store more carbon than previously believed, highlighting the need to include these littoral zones in calculations of the continental carbon balance.

The ‘coastlines’ of lakes, called littoral zones, are often surrounded by aquatic plants that are among the fastest growing plants in the world. They take up a large amount of carbon from the atmosphere and high quantities of carbon from remaining plant material are stored in the sediments. Although the total littoral zone of lakes around the world is four times longer than the coastline of the oceans, the role of lake shorelines has not been considered in global carbon budgets, until now.

A new publication by Uppsala University is the first to include littoral zone plants in lake carbon budgets and reveals that, rather than releasing carbon to the atmosphere, lakes may actually be a carbon sink.

“We were planning to write a conceptual paper about how aquatic plants in the littoral zone are overlooked in lake carbon cycling. But after doing some initial calculations quantifying the role of these plants, we quickly realised that littoral zones could be a significant player in the global carbon budget! So, our conceptual paper eventually turned into the first global carbon budget to include the critical contribution of aquatic plants from lake littoral zones,” says Charlotte Grasset, first author of the study and researcher at Uppsala University.

Lakes switched from net carbon source to net carbon sink

Using existing data and a simple model connecting littoral zones to the lake centre, the authors did the first global-scale quantification of the contribution of littoral zones to the carbon budget of lakes.

“We find that adding the littoral zone vegetation to the global carbon budget of lakes substantially changes the carbon accounting of lakes. Depending on the values used, we found that when littoral zones were included, lakes switched from a net carbon source to a net carbon sink; that is, the carbon stored annually in lake sediments was greater than the carbon released to the atmosphere,” says Grasset.

Restoring lakeshores for climate and biodiversity gain

The authors all conclude that there is still much work to be done. Although their estimates are based on the best data and information currently available, more measurements are required to improve these initial findings for lakes. This includes a better understanding of the areal extent of vegetated littoral zones in lakes, more refined estimates of carbon gas exchange between the aquatic plants, sediments, atmosphere and the lake’s centre.

“We hope this study will stimulate future research on the critical role of lake littoral zones in carbon budgets, and of the possible role of restoring the lake littoral as a nature-based solution,” says Grasset.

Given that plants in marine coastal habitats known as ‘blue carbon’ have been considered as a nature-based solution for over 15 years, the authors argue that it is time to start focusing some of that attention on lake littoral zones, not only for better carbon accounting, but to improve lake water quality and restore aquatic biodiversity.

Strandsjön, Lake in Sweden. 

Credit

Charlotte Grasset

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Journal

Nature Geoscience

DOI

10.1038/s41561-025-01739-8 

Article Title

Contribution of lake littoral zones to the continental carbon budget

Article Publication Date

14-Aug-2025

 

Associate professor Guo-Ming Weng’s group published a research article on simultaneous methane conversion and hydrogen production in Science Bulletin

Science China Press

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Figure 1 | Schematic diagram of the pH-asymmetric electrolyzer coupling EOM with HER.

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Credit: ©Science China Press

The authors fabricated a NiO/Ni heterostructure electrocatalyst on nickel foam via a thermal oxidation strategy. By optimizing electrolysis parameters such as current density, electrolysis time, and electrolyte pH gradient, they significantly enhanced EOM performance. In a pH-asymmetric 0.1 M NaOH||0.1 M HCl system, the catalyst achieved a high liquid product formation rate of 2.7 mmol gNiO–1 h–1 at 0.4 mA and a remarkable 90.1% Faradaic efficiency for liquid products at 0.1 mA. Notably, by harnessing electrochemical neutralization energy, the EOM||HER system stably operated at an ultralow cell voltage of 1.86 V, saving up to 37% energy compared to conventional electrolyzers, while simultaneously producing high-purity hydrogen at the cathode (Figure 2).

Through comprehensive in situ characterization and control experiments, the authors unraveled the reaction mechanism and identified key active species in EOM. In situ Raman spectroscopy revealed potential-dependent evolution of surface species, confirming NiOOH (NiIII–OŸ–NiIII–O–) as the crucial intermediate for methane activation (Figure 3). 18O isotope labeling and kinetic isotope effect experiments demonstrated that the oxygen atoms in products originated directly from OH– in the electrolyte, with the reaction proceeding via a proton-coupled electron transfer mechanism. Combined XPS depth profiling and electrochemical active species studies revealed that dynamic formation and maintenance of highly active Ni3+ species at the heterointerface are essential for efficient EOM, directly impacting the selectivity towards low-carbon alcohols.

Density functional theory (DFT) calculations further elucidated how the NiO/Ni interface promotes methane activation and regulates product selectivity (Figure 4). Simulations indicated that applying an external field (1.45 V vs. RHE) substantially enhances CH₄ adsorption on Ni sites, changing the Gibbs free energy from endergonic (+1.16 eV) to exergonic (–0.29 eV). Reaction pathway analysis showed that *CH4 dehydrogenation to *CH3 is the rate-determining step of EOM. At low applied potentials, *CH3 tends to hydroxylate directly into methanol, while at higher potentials, it favors further dehydrogenation via the *OCH2 intermediate to form ethanol. However, the high desorption energy barrier of ethanol (0.91 eV) leads to an extended residence time on active sites, thereby facilitating its deep oxidation to acetic acid. This also accounts for the phenomenon that ethanol is prone to deep oxidation to acetic acid. Moreover, the charge redistribution at the heterointerface enhances the electron affinity of Ni3+-O· active centers, boosting *CH4 polarization, which matches the experimentally observed high EOM efficiency and potential-dependent selectivity.

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Journal

Science Bulletin

DOI

10.1016/j.scib.2025.05.031 

Figure 2 | (a) Synthesis scheme of NiO/Ni with SEM images and EDS elemental maps; (b) Faradaic efficiency of EOM liquid products under different applied currents; (c) Energy consumption analysis and energy savings for different electrolyzer configurations.

Figure 3 | EOM mechanism analyses over NiO/Ni. (a) In-situ Raman spectroscopic analysis of the NiO/Ni catalyst and the local magnification of NiO/Ni Raman spectrum (b) at different potentials in 0.1 M NaOH aqueous electrolyte. The corresponding LSV profile is shown in the right panel and the potential of each spectrum is labeled between the spectra and the LSV curve vs. Ag/AgCl. (c) The valence band edge (Eedge) in UPS spectra of NiO/Ni catalysts before and after electrolysis. The inset shows the productivity of oxygenates at different applied currents. (d) MS spectrum for the CH3CH2OH product in 18O-containing electrolyte over NiO/Ni at 1 mA for 24 h and typical MS spectrum for CH3CH2OH. (e) The Ni 2p (e) and the O 1s (f) XPS spectra of NiO/Ni electrolysis at the applied currents of 1mA and 0.2 mA.

Figure 4 | Schematic mechanism and DFT energy profiles for EOM. (a) Proposed reaction mechanism on NiO/Ni; (b) The energy barriers for methanol and ethanol formation.

Credit

©Science China Press

 

Livestock played a role in prehistoric plague infections

An ancient Yersinia pestis genome recovered from sheep sheds new light on a mysterious infectious disease that plagued prehistoric Eurasia for over 2000 years

Max Planck Institute for Evolutionary Anthropology

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Archaeological sheep bones unveiled at a Bronze Age site in the Eurasian steppe. Archaeological sheep bones unveiled at a Bronze Age site in the Eurasian steppe. Ancient animal bones are the key to understanding the origins of zoonotic infectious diseases.

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Credit: © Björn Reichhardt

To the point

• Role of livestock in spreading the plague: Yersinia pestis has been identified in a 4,000-year-old sheep, indicating that livestock played a role in spreading an early form of plague that once circulated throughout Eurasia during the Late Neolithic and Bronze Age (LNBA) periods.

• Spillover from unknown reservoir: Genetic analysis reveals that humans and sheep were infected by nearly identical plague strains. The disease was contracted through spillover from an unknown wild animal reservoir, and sheep grazing over large pastures likely increased human exposure to the pathogen.

• Distinct plague evolution: The LNBA plague lineage, found in both sheep and humans, lacked the genetic machinery necessary for flea transmission. This lineage exhibited parallel genetic changes under strong evolutionary constraints, suggesting different disease dynamics compared to later historic plagues.

• Historical context: The increase in livestock herding during the Bronze Age may have led to greater contact between humans, animals, and wild reservoirs of the plague. This underscores the importance of animal domestication and husbandry in the emergence and spread of major zoonotic diseases.

Around 5,000 years ago, a mysterious form of plague spread throughout Eurasia, only to disappear 2,000 years later. Known only from ancient DNA, this enigmatic ‘LNBA plague’ lineage has left scientists puzzled about its likely zoonotic origin and transmission. In a new study published in Cell, this ancient plague is identified in an animal for the first time - a 4,000-year-old domesticated sheep excavated at the pastoralist site Arkaim in the Western Eurasian Steppe. Different lines of evidence suggest that plague infections in both human and sheep stem from spillover of a still unknown wild reservoir, and that widespread sheep herding during the Bronze Age brought steppe pastoralist communities into closer contact with this reservoir. This study reveals the connections between domesticated animals and the spread of one of the world's most infamous bacteria, providing insight into how the pathogen was so successful in infecting people across thousands of kilometers over thousands of years.

Zoonotic origins of prehistoric plague infections

The majority of human pathogens known today have a zoonotic origin, meaning they jumped from animals into humans - a process known as spillover. A growing body of evidence suggests that many of the infectious diseases they cause emerged within the last 10,000 years - overlapping with the domestication of livestock and pets and pointing to our increasingly close relationships with these animals as the source of these diseases in humans. The study of pathogens from ancient animals using ancient DNA methods offers a unique opportunity to investigate the emergence of human infectious disease, but remains largely unexplored to date.

Plague is among the most deadly zoonotic diseases known. Spread by fleas living on rats, it has killed millions of people throughout history - most notably during the 14th century Black Death in which more than a third of the population of Europe perished. However, before major historical pandemics, a genetically distinct, prehistoric form of plague circulated throughout Eurasia, beginning around 5,000 years ago. Known today as the Late Neolithic Bronze Age (LNBA) lineage, it infected human populations for nearly 3,000 years before vanishing, presumably going extinct. Surprisingly, the LNBA lineage lacks the key genetic toolkit for flea transmission of both historic and modern plaque strains, making its manner of transmission enigmatic. Other animals must have been involved in its spread, but which? “One of the first steps in understanding how a disease spreads and evolves is to find out where it's hiding, but we haven’t done that yet in the ancient DNA field” says lead author Ian Light-Maka, a PhD candidate focused on the long-term evolution of pathogens. “We have over 200 Y. pestis genomes from ancient humans, but humans aren’t a natural host of plague,” says Light-Maka.

Sheep remains from Arkaim reveal the first prehistoric Y. pestis genome in livestock

To try to solve the puzzle of how the infection persisted and spread over thousands of years in Eurasia, an international team of researchers from the Max Planck Institute of Infection Biology, Harvard University, the University of Arkansas, Max Planck Institute of Evolutionary Anthropology, and Seoul National University investigated the bones and teeth of Bronze Age livestock at the pastoralist site Arkaim (Russia), a Eurasian Steppe site belonging to the Sintashta-Petrovka culture known for its innovations in cattle, sheep, and horse husbandry. There they identified a 4,000-year-old sheep infected with the same LNBA lineage of Y. pestis that was infecting people at the time.

“Arkaim was part of the Sintashta cultural complex and offered us a great place to look for plague clues: they were early pastoralist societies without the kind of grain storage that would attract rats and their fleas - and prior Sintashta individuals have been found with Y. pestis infections. Could their livestock be a missing link?” says Dr. Taylor Hermes, Assistant Professor of Anthropology at the University of Arkansas and co-author of the study.

Sheep posed elevated Y. pestis infection risk in pastoralist societies

Comparing the ancient Y. pestis genome from the sheep to other ancient and modern genomes revealed that the sheep Y. pestis genome was a very close match to one that had infected a human at a nearby site at around the same time. “If we didn't know it was from a sheep, everyone would have assumed it was just another human infection – it's almost indistinguishable,” says Dr. Christina Warinner, Landon T. Clay Professor of Scientific Archaeology at Harvard University and a group leader at the MPI-EVA. This shows that humans and their animals were both being infected with the same population of Y. pestis, but who was infecting whom? Archaeological and comparative approaches may provide some answers. From parts of the world where Y. pestis is still endemic, it is known that sheep can become infected through direct contact with carcasses of infected animals such as rodents, the natural reservoir of the pathogen, and this can spark local plague outbreaks in humans if the sheep are not properly butchered or cooked. Such a scenario could have also spread LNBA plague in prehistory, linking human and sheep infections. “The Sintashta-Petrovka culture is famous for their extensive herding over vast pastures aided by innovative horse technologies, and this provided plenty of opportunity for their livestock to come into contact with wild animals infected by Y. pestis,” says Christina Warinner. “From then on it is just one more short hop into humans.”

Signatures of natural selections suggest the prehistoric Y. pestis reservoir remains unknown

Analyzing the new sheep Y. pestis genome with those available from humans enabled a better reconstruction of the evolutionary dynamics of this ancient, presumably extinct, plague lineage. In contrast to the Y. pestis lineages known today, which are geographically variable and distinct, the ancient LNBA lineage was highly similar across its nearly 6,000 kilometers range at any given time. Differences in the life cycle and possibly natural selection could have played a role, since in many well-known pathogens, like SARS-CoV-2 causing COVID-19, new variants can emerge and become widespread if they are better at infecting and transmitting disease. However, rather than finding such variants, the study unexpectedly found the opposite: the ancient lineage was evolving under strong constraints. Notably, a subset of genes were found to mutate repeatedly and independently, but these parallel changes were only seen for the infections that do not have direct descendants, possibly a kind of genetic footprint of past spillovers.

“We can show that the ancient lineage evolved under elevated pressure, which is in contrast to the Y. pestis still found today. Moreover, the ancient sheep as well as human infections are likely isolated spillovers from the unknown reservoir, which remains at large. Finding that reservoir would be the next step,” says Dr. Felix M. Key, senior author and head of the Evolutionary Pathogenomics Lab at the MPIIB. Despite these new insights, major questions still remain unsolved, like how the pathogen spread so far and wide over short periods of time. Sheep and humans are unlikely to have been the main agents spreading the disease since there are examples of nearly identical LNBA Y. pestis genomes at the same time but thousands of kilometers apart, too far for sick humans or terrestrial animals to travel. Luckily, the search for pathogens in ancient animal remains is just beginning - archaeological digs can yield tens of thousands of animal bones, and results from past excavations are waiting in storerooms to be studied further. “I think”, Key says, “there will be more and more interest in analyzing these collections - they give us insights that no human sample can.”

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Journal

Cell

DOI

10.1016/j.cell.2025.07.029 

Article Title

Bronze Age Yersinia pestis genome from sheep sheds light on hosts and evolution of a prehistoric plague lineage

Article Publication Date

11-Aug-2025

4,000-year-old sheep tooth from which the Y. pestis genome was recovered.

Excavations on the Eurasian Steppe have yielded thousands of animal bones from Bronze Age livestock.




A herd of sheep grazes in a steppe landscape near Arkaim, where herders would have managed similar flocks 4,000 years ago.


Credit
© Taylor Hermes




Co-author Dr. Taylor Hermes overlooks a herd of sheep in central Eurasia, where the innovation of horseback riding allowed herders to manage more livestock over larger pastures. It also likely brought these herds into closer contact with wild reservoirs of pathogens.


Credit

© Emma Davolt