At the Hong Kong University of Science and Technology (HKUST), scientists have fabricated an innovative iron-based cathode material to achieve record performance for proton ceramic fuel cells.
This marks a major step forward in the development and commercialization of this encouraging renewable energy technology.
Fuel cells, which tend to use the chemical energy of hydrogen or other fuels to produce electricity cleanly and efficiently. Energy sources that have been the subject of intense development around the world to combat energy shortages and climate change.
A new technology has been developed in the field, known as proton ceramic fuel cells (PCFCs), which are based on proton-conducting ceramic electrolytes. Furthermore, they have the advantages of high efficiency, low pollutant emissions and the adaptability to work well not only with hydrogen but also with other gases such as methane, biogas and ammonia. Typically, they are used for distributed power generation, such as off-grid power generation.
But the wide commercialization of PCFCs has been hampered by the need for more cost-effective and high performance cathode materials.
Currently, cobalt-based perovskites are known to be the most widely used cathode materials, as cobalt has the potential to easily decrease and increase its oxidation number. This leads to excellent oxygen reduction reaction activity which appears to be crucial for cathode performance.
But these materials are expensive, cause pollution in mines, and require complicated preparation procedures that are inconsistent with mass production. In addition, lithium-ion batteries, typically used in electric vehicles, are in great demand.
Preferably, the cobalt requires substitution with transition metals of reduced cost but similar reactivity. Iron comes close to cobalt on the periodic table and shares several similar chemical properties, but it’s cheap.
Additionally, iron-based materials are usually known to be worse catalysts, resulting in poor performance. Therefore, material compositions should be refined to determine the best performing material.
In this direction, a research group led by Professor Francesco Ciucci of the Department of Mechanical and Aerospace Engineering and of the Department of Chemical and Biological Engineering integrated molecular orbital analyses, simulations of first principles and experiments.
This was done to devise new inexpensive ceramics that make use of low-cost elements, such as barium (Ba), zirconium (Zr) and iron (Fe), resulting in PCFC with record-breaking performance.
The research group developed the cathode materials starting from the fundamental physico-chemical principles and from the density functional theory. With the help of calculation-driven optimization, Ba0.875Fe0.875Zr0.125O3-δ (D-BFZ) was determined as the most encouraging cathode material.
Thus, experiments demonstrated that D-BFZ exhibited unusual electrochemical activity to react with oxygen, resulting in a high peak power density, among the best in the field, and outstanding operational stability.
Furthermore, D-BFZ could be produced using a synthesis method that is simple and suitable for mass production. This is a significant step towards identifying commercially viable PCFCs.
PCFC technology could transform itself and there are many exciting opportunities to develop it further. We will continue to leverage first-law calculations and experiments to improve the performance of PCFCs.
Francesco Ciucci, Professor, Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology
Ciucci added: “If used reversibly, PCFCs will have a huge impact on hard-to-decarbonise sectors, such as steel, ammonia production and heavy transportation.”
The research team, led by Professor Ciucci, included doctoral students Yuhao Wang, Matthew James ROBSON and Alessio BELOTTI; postdoctoral fellow Dr. Yufei Song; PhD students Dr. WANG Jian (class of 2018) and Dr. LIU Jiapeng (class of 2020); former postdoctoral fellows Dr. WANG Zheng and Dr. ZHANG Zhiqi; and also collaborators from Ulsan National Institute of Science and Technology and Seoul National University in South Korea, Nanjing Tech University in China, and Curtin University in Australia.
Wang, Z. et al. (2022) Rational design of perovskite ferrites as cathodes of high performance proton conduction fuel cells. Catalysis of nature. doi.org/10.1038/s41929-022-00829-9.