Clean energy technologies, pivotal for sustainable societies, are increasingly focusing on efficient and robust electrochemical devices like solid-oxide fuel cells (SOFCs) and proton ceramic fuel cells (PCFCs). These devices are at the forefront of green power generation, but their wider adoption has been hampered by several challenges. SOFCs, for instance, require high operating temperatures, which can degrade their materials over time. Conversely, PCFCs struggle with chemical stability and require energy-intensive manufacturing processes.
The Tokyo Tech-led study, published in Chemistry of Materials, introduces a potential solution by investigating dual-ion conductors, materials that can efficiently transport both protons and oxide ions. This property could allow for lower operational temperatures and better overall performance in electrochemical devices. While similar materials like Ba7Nb4MoO20 have been studied before, their practical applications have been limited due to insufficient conductivity and an incomplete understanding of their ion transport mechanisms.
Professor Masatomo Yashima, leading the research team, collaborated with the Australian Nuclear Science and Technology Organisation (ANSTO), the High Energy Accelerator Research Organization (KEK), and Tohoku University. The team's exploration centered around perovskite oxides with higher molybdenum (Mo) content, focusing on Ba7Nb3.8Mo1.2O20.1. Their findings were striking: "Ba7Nb3.8Mo1.2O20.1 exhibited bulk conductivities of 11 mS/cm at 537 degrees under wet air and 10 mS/cm at 593 degrees under dry air. Total direct current conductivity at 400 degrees in wet air of Ba7Nb3.8Mo1.2O20.1 was 13 times higher than that of Ba7Nb4MoO20, and the bulk conductivity in dry air at 306 degrees is 175 times higher than that of the conventional yttria-stabilized zirconia (YSZ)," highlights Prof. Yashima.
Further investigation into the material's ion-transport mechanisms was conducted using advanced techniques such as ab initio molecular dynamics (AIMD) simulations, neutron diffraction experiments, and neutron scattering length density analyses. These studies revealed that the high oxide-ion conductivity of Ba7Nb3.8Mo1.2O20.1 is attributed to a unique phenomenon: the formation of M2O9 dimers by sharing an oxygen atom, facilitating ultrafast oxide-ion movement. Additionally, the material's proton conduction efficiency is enhanced by the hexagonal close-packed BaO3 layers.
These insights into the ion migration mechanisms in Ba7Nb3.8Mo1.2O20.1 not only shed light on the science of dual-ion conductors but also provide a foundation for the rational design of future materials in this domain. Prof. Yashima concludes with optimism, "The present findings of high conductivities and unique ion migration mechanisms in Ba7Nb3.8Mo1.2O20.1 will help the development of science and engineering of oxide-ion, proton, and dual-ion conductors."
The team's discoveries represent a significant stride in the quest for more efficient and sustainable energy technologies. The unique properties of Ba7Nb3.8Mo1.2O20.1 pave the way for the development of advanced electrochemical devices, potentially revolutionizing how we approach energy generation and storage in the future.
Research Report:Dimer-Mediated Cooperative Mechanism of Ultrafast-Ion Conduction in Hexagonal Perovskite-Related Oxides
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