Scientists in Tokyo have synthesized a new thin film that could make energy production more efficient and cleaner

Solid oxide fuel cells (SOFCs) are clean and highly efficient power generation systems, which can generate electrical energy but are limited by their high operating temperatures and infrequent applications. Researchers from the Tokyo University of Science led by Dr Tohru Higuchi, in their new study, explore how the efficiency of SOFCs can be increased by lowering their operating temperature and could be an alternative to nuclear and thermal power generation in the future.

In this post-industrialization age, electricity has become the backbone of our society. However, using fossil fuels to generate it is not the best option because of their limited availability and harmful nature. In the last two decades, significant efforts have been made to develop techniques to foster sustainable energy. Against this backdrop, solid oxide fuel cells (SOFCs) have risen as a clean and highly efficient alternative that can generate electrical energy. However, a major drawback of SOFCs is their high operating temperatures, restricting their widespread usage.

Various previous studies have attempted to overcome this drawback by improving conductivity at high temperatures using fluorite type oxides like CeO_2-δ. Normally, these fluorite oxides are available in porous form, and their mechanism of conductivity is believed to be dependent on the surface adsorption of water molecules, which is the process of adhesion of atoms or molecules to a surface.

A team of scientists from Tokyo University of Science, led by Dr Tohru Higuchi, took this research one step forward. In their new study published in Nanoscale Research Letters, the researchers explored the effect of "doping," which is the process of adding impurities to alter their conductivity, on these oxides, which are a very good candidate for SOFCs. Researchers "doped" the oxide with a metal called Samarium (Sm). Then, they deposited thin films of this doped oxide on a substrate of Aluminium oxide (Al₂O₃) in a specific direction known to enhance the conductivity. Dr Higuchi considers this an advantage, stating, "When considering practical devices, thin film forms are more suitable than porous or nanocrystalline forms."

Then, the research team characterized the crystalline quality and electronic structure of the novel film. They also compared the difference in conductivity between this novel film and thick ceramic oxides commonly used in the industry. Their findings revealed that the ceramic sample exhibited poor crystallinity and had poor proton conductivity compared to the thin film sample.

What's more, the "resistivity"―or the resistance to electrical flow―of the thin film was found to decrease with increasing humidity due to the "proton conduction" in fluorite type oxides, as explained by Grotthuss mechanism. A water molecule consists of two atoms of oxygen and one atom of hydrogen. The molecules of water have bonds between them, called "hydrogen bonds." The Grotthuss mechanism (or the "hop-turn" mechanism) allows the water molecules to be split into ions that increase the conductivity, and hence they move from one hydrogen bond to another. The novel film was found to exhibit surface protonic conduction in the low temperature region below 100°C.

This novel film, with its high conductivity at room temperatures, is sure to have several applications in the future. As far as SOFCs are concerned, Dr Higuchi concludes, "Our study on electrolyte membranes presents radical findings that can help lower the operating temperature of SOFCs, and may be an alternative system for making more practical devices using fluorite type oxides in SOFCs, and open up new avenues for nuclear and thermal power generation in the future."

　　　　　　 　　　　　　 　　　　　　 　　　　　　

Reference
Titles of original papers	:	Surface Proton Conduction of Sm-Doped CeO2-δ Thin Film Preferentially Grown on Al2O3 (0001)
Journal	:	Nanoscale Research Letters
DOI	:	10.1186/s11671-020-3267-5

About The Tokyo University of Science

Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.

With a mission of "Creating science and technology for the harmonious development of nature, human beings, and society", TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.

About Associate Professor Tohru Higuchi from Tokyo University of Science
Tohru Higuchi is a member of the Department of Applied Physics in the Tokyo University of Science. An alumnus of the Tokyo University of Science, his research mainly focuses on functional material science specializing in thin film/surface and interfacial physical properties and Inorganic industrial materials. He has contributed to over 200 papers and is the recipient of received several awards. Most recently, he received the honor of Outstanding Research Achievement and Contribution to GREEN-2019 for his contributions to energy conscious research.
https://www.tus.ac.jp/en/fac/p/index.php?3402