Renewable Energy Global Innovations features: Synthesis of inorganic-organic hybrid membranes consisting of organotrisiloxane linkages and their fuel cell properties

Significance Statement

Perfluorosulfonic polymers, for instance, Naflon, are preferable candidates for membranes used in polymer electrolyte fuel cells owing to their high proton conductivity, excellent mechanical strength, and chemical stability for temperatures below 100°C.  Nevertheless, the operating conditions need to be optimized to maintain 100% relative humidity at about 80 °C as well as low carbon-monoxide concentration in hydrogen gas. The functioning of polymer electrolyte fuel cells at higher temperatures raises the tolerance concentration of carbon monoxide poisoning for the platinum catalysts.

The increased operation temperature enhances the cell efficiency and simplifies the management system. For this reason, there is an urgent need for membrane electrolytes exhibiting high proton conductivities as well as intermediate temperatures. Inorganic-organic hybrid membranes possess the advantages of inorganic as well as organic phases. This is in the sense that functionality and flexibility of organics are blended with the thermal, mechanical, and chemical stability of inorganics. Therefore, the inorganic-organic hybrid membrane is preferable for implementation at intermediate temperatures.

Copolymerization of suitable monomers is a clear-cut approach for the formation of covalent bonds in the hybrid membranes. Researchers led by Professor Toshinobu Yogo at Nagoya University in Japan, demonstrated the one-pot synthesis of inorganic-organic hybrid membranes through copolymerization of N-vinylbenzotriazole, 1,5-divinyl-3-phenylpentamethyltrisiloxane, and 2-hydroxyethyl methacrylate acid phosphate. The research team did not require any hydrolysis-condensation for the preparation of the silicon-oxygen-silicon linkages reference to the fact that trisiloxane linkage was used for the inorganic backbone of the hybrid membrane. Their research work is published in Polymer.

The authors adopted the ac impedance method to measure proton conductivity of the hybrid membranes. They did this at various temperatures and relative humidity in a sealed vessel. They equilibrated the measurement cell at a desired relative humidity for one night at about 40 °C before measurement.

The Toshinobu Yogo and his team constructed inorganic-organic membranes from trisiloxane as well as aliphatic polymer chains bond with phosphonic acid groups, which were later copolymerized through one-pot method. The authors observed that the membranes were self-standing, possessed high thermal stability, high formability, and were homogeneous. The trisiloxane linkage in the hybrid membrane enhanced the thermal and oxidation stability of the membrane.

The hybrid membrane in the ratio 1:9:5 was found to have a high elastic modulus as compared to that of membranes with 2:8:5 and 3:7:5. The proton conductivity of the hybrid membranes was observed to rise with increasing temperature and relative humidity up to 130 °C. 1:9:5-ratio membrane was operated at 140 °C, 30% relative humidity for about 30 hours and indicated a peak power of about 7.8mWcm^-2 at 10 hours. Reference to chemical design, one-pot synthesis of the hybrid membranes is presented as a versatile synthetic process for the polymer electrolyte fuel cells used at low relative humidity as well as intermediate temperatures.

About The Author

Masaya Takemoto received his B. Eng. (2013) and M. Eng. (2015) degrees in crystalline materials chemistry from Nagoya University. His research interests include processing and characterization of energy and energy-saving materials. Currently, he is working for an energy-related company.

About The Author

Koichiro Hayashi received the B. Eng. (2005), M. Eng. (2007), and Dr. Eng. (2010) degrees in materials chemistry from Nagoya University. He worked as an assistant professor at the Tokushima University (2010-2014) and Nagoya University (2014-2017). Currently, he is an assistant professor at Kyushu University.

His interests include the development of multifunctional organic-inorganic nanomaterials and their applications to medical and dental fields.

About The Author

Shin-ichi Yamaura is an Associate Professor at The Polytechnic University of Japan since 2015. He received his PhD degree from Tohoku University, Sendai, Japan in 1999. He worked as an assistant professor and as an associate professor in the Institute for Materials Research, Tohoku University from 2000 to 2015.

His research interests include the preparation, process, characterization and functional property of amorphous/nanostructured alloys for hydrogen-related applications and also grain boundary engineering focused on grain boundary character that can be described as CSL Σ-value.

About The Author

Wei Zhang is a Professor in School of Materials Science and Engineering at Dalian University of Technology, China. He received his PhD degree from Tohoku University (Japan) in 1998. He has been a Lecturer at Dalian University of Technology, a research fellow at Japan Science and Technology Agency, and an associate professor in Institute for Materials Research, Tohoku University.

His research interests include the preparation, processes, characterization, and properties of amorphous and nanostructured alloys. He has published more than 290 articles including 7 book chapters.

About The Author

Wataru Sakamoto is an associate professor at Institute of Materials and Systems for Sustainability, Nagoya University. He received B.S. and M.S. degrees in applied chemistry from Nagoya University in 1989 and 1991, respectively. He worked from 1991 to 1994 at Matushita Electric Industrial (now Panasonic) Co., Ltd. He earned his Doctorate of Engineering from Nagoya University in 2000. He was appointed an associate professor in the Center for Integrated Research in Science and Engineering (now named Institute of Materials and Systems for Sustainability), Nagoya University, in February 2002. His research interests are novel processing and properties evaluation of electroceramics and functional nanostructured materials.

About The Author

Toshinobu Yogo is a professor at Institute of Materials and Systems for Sustainability, Nagoya University. He received B.S. and M.S. degrees in synthetic chemistry from Nagoya University.  He received his PhD degree from Hokkaido University (Japan) in 1980.

His research interests include the synthesis and characterization of functional nanomaterials and nano-structured hybrid materials.

Reference

Masaya Takemoto, Koichiro Hayashi, Shin-ichi Yamaura, Wei Zhang, Wataru Sakamoto, and Toshinobu Yogo. Synthesis of inorganic-organic hybrid membranes consisting of organotrisiloxane linkages and their fuel cell properties at intermediate temperatures. Polymer, volume 120 (2017), pages 264-271.

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