A research team from Tokyo University of Science has developed a novel hole-proton mixed-conductor material, which has led to a breakthrough in PC-SOFCs. Their research, which was published in the Journal of the Physical Society of Japan, may lead to significant developments in the field of energy technologies.
In the midst of the ongoing energy and climate crises, the urgency to find efficient ways of producing clean energy to replace fossil fuels has never been greater. Fuel cells have emerged as one of the most promising research directions. These electrochemical devices generate electricity directly from chemical reactions, which can be environmentally friendly in both their reactants and byproducts.
Among the various types of fuel cells, solid oxide fuel cells (SOFCs) have garnered significant interest from researchers. These cells operate without a liquid electrolyte, enhancing safety and simplifying manufacturing. However, a significant drawback of conventional SOFCs is their high operating temperature, typically exceeding 700 °C. This requirement limits their applicability, reduces efficiency and power output, and often affects durability. As a promising alternative, proton-conducting SOFCs (PC-SOFCs) that can operate at lower temperatures are being explored.
In this context, a research team led by Professor Tohru Higuchi from Tokyo University of Science has made a significant breakthrough in PC-SOFCs by developing a novel hole-proton mixed-conductor material. Their findings, published in the Journal of the Physical Society of Japan on June 18, 2024, could drive crucial advancements in energy technologies.
The new material is a perovskite-type oxide ceramic with the formula BaCe0.4Pr0.4Y0.2O3−δ (BCPY). The dopants Pr and Y ions were chosen based on previous research by the team, which showed that BaCe0.9Y0.1O3−δ and BaPrO3−δ demonstrated proton and hole (a type of positive charge carrier) conduction, respectively. They hypothesized that co-doping with both Pr and Y would result in high proton-hole mixed conductivity, and their research has validated this theory.
According to Professor Higuchi, such a material might be utilized in the anode electrode of PC-SOFCs.
The Pt metal electrode used in other fuel cells has issues, such as a large drop in power output because electrochemical reactions occur only at the three-phase interface where the fuel gas/electrode/electrolyte intersect. To solve this issue, a dense membrane with mixed conduction could be useful for improving the performance of PC-SOFC by expanding the electrochemical reaction area.
Tohru Higuchi, Professor, Tokyo University of Science
Using a sputtering technique, the researchers created thin films of BCPY and meticulously examined its conduction properties to identify evidence of mixed proton-hole conduction. They developed a quantitative evaluation method to measure oxygen vacancies using X-ray absorption spectroscopy and defect chemistry analysis.
Through these and additional experiments, including synchrotron radiation photoelectron spectroscopy for electronic band structure analysis, they found substantial evidence that mixed hole-proton conductivity can occur on the surface of the proposed electrode material.
Significantly, at 300 °C, BCPY electrodes demonstrated a high conductivity of more than 10−2 S.K/cm, indicating a promising future for both PC-SOFCs and other technologies.
If we can further confirm that BCPY thin films do enable hole-proton mixed conductivity, BCPY may become a novel oxide material for not only PC-SOFC anode electrode membranes but also electric-double-layer-transistors.
Tohru Higuchi, Professor, Tokyo University of Science
This transistor technology can address the scalability and miniaturization challenges of conventional transistors, which is crucial for the development of artificial intelligence systems and the enhancement of computational capacity in personal electronic devices.
This study offers valuable insights into new electrode materials for PC-SOFCs. Continued advancements in this field could enable electrochemical energy generation to power homes and cars with cleaner electricity, paving the way for more sustainable societies.
Journal Reference:
Notake, G., et al. (2024) Surface Hole-Proton Mixed Conduction of BaCe0.4Pr0.4Y0.2O3−δ Thin Film with Large Amounts of Oxygen Vacancies. Journal of the Physical Society of Japan. doi.org/10.7566/jpsj.93.074706.