Breakthrough Fuel Cell Design Tackles Environmental and Operational Barriers
A team of researchers from Nagoya University, led by Atsushi Noro, has developed an innovative fuel cell electrolyte that incorporates a phosphonic acid polymer with hydrophobic hydrocarbon spacers. This new design allows fuel cells to operate efficiently at high temperatures (above 100°C) and low humidity, overcoming significant challenges that have previously hindered their wider adoption.
Fuel cells produce electricity by electrochemically combining hydrogen and oxygen, generating only water as a byproduct, making them an environmentally friendly energy source. However, conventional fuel cells often use perfluorosulfonic acid polymers, which belong to the class of per- and polyfluoroalkyl substances (PFAS). These compounds are persistent in the environment and accumulate in living organisms, raising environmental concerns and leading to regulatory restrictions in numerous countries.
Benefits and Limitations of Phosphonic Acid Polymers
Phosphonic acid hydrocarbon polymers offer several advantages over PFAS, as they do not contain fluorine and are less likely to persist in the environment. These polymers also demonstrate moderate chemical stability in high-temperature, low-humidity conditions. However, despite these benefits, they face challenges, such as poor conductivity and the hydrophilic nature of the phosphonic acid groups, which attract water. This can result in potential dissolution in humid environments, limiting their widespread use.
Overcoming Challenges with Hydrophobic Spacer Innovation
To address the limitations of phosphonic acid polymers, Noro introduced a hydrophobic spacer between the polymer backbone and the phosphonic acid groups. This modification enabled the polymer to remain water-insoluble, chemically stable, and moderately conductive, even under high-temperature and low-humidity conditions. The hydrophobic spacer also effectively repelled water, ensuring the material’s long-term stability.
Enhanced Membrane Performance
The newly developed membrane demonstrated significantly improved water insolubility in hot water compared to a polystyrene phosphonic acid membrane without hydrophobic spacers and a commercially available cross-linked sulfonated polystyrene membrane.
Under conditions of 120°C and 20% relative humidity, the membrane's conductivity was 40 times higher than that of the polystyrene phosphonic acid membrane and four times higher than the cross-linked sulfonated polystyrene membrane, according to Noro.
Advantages for Fuel Cell Applications
Noro emphasized the benefits of fuel cells that operate efficiently in low-humidity, high-temperature environments. At higher temperatures, reactions at the electrodes of a fuel cell occur more rapidly, improving overall performance and power generation efficiency. Additionally, the higher temperature reduces carbon monoxide (CO) poisoning of the electrodes, as CO tends to adsorb onto catalysts at lower temperatures but not at elevated temperatures. Furthermore, heat dissipation is more efficient at high temperatures, simplifying cooling system designs and eliminating the need for external humidification, which results in lighter and more compact systems.
This research was supported by the New Energy and Industrial Technology Development Organization (NEDO). According to the NEDO Roadmap for Fuel Cell and Hydrogen Technology Development, this electrolyte membrane design is a significant step toward next-generation fuel cells and supports the transition to a net-zero carbon society. Patent applications for materials related to this design have been filed in Japan and several other countries.
