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Nagoya University researchers introduced a phosphonic acid polymer with hydrophobic spacers for fuel cells, achieving high-temperature and low-humidity operation without PFAS-related environmental concerns. The design offers improved conductivity and stability, advancing clean energy solutions. Credit: Atsushi Noro
Researchers at Nagoya University developed a phosphonic acid polymer with hydrophobic spacers for fuel cell electrolytes, enabling high-temperature, low-humidity operation.
A research group led by Atsushi Noro at Nagoya University in Japan has introduced a groundbreaking design for fuel cell electrolytes, featuring a phosphonic acid polymer with hydrocarbon spacers. This innovative approach enables fuel cells to function efficiently at high temperatures (above 100°C) and low humidity, overcoming significant barriers to widespread adoption. The findings were published in the journal ACS Applied Polymer Materials.
Fuel cells generate electricity by electrochemically combining hydrogen and oxygen, producing only water as a byproduct, making them a clean energy solution. However, the use of perfluorosulfonic acid polymers—classified as per- and polyfluoroalkyl substances (PFAS)—in conventional fuel cells has raised concerns. These substances persist in the environment and accumulate in living organisms, leading to regulatory restrictions in many countries.
Advantages and Challenges of Phosphonic Acid Polymers
Unlike PFAS, phosphonic acid hydrocarbon polymers do not contain fluorine, making them less likely to persist in the environment. These polymers also exhibit moderate chemical stability under high-temperature and low-humidity conditions. Despite these advantages, poor conductivity and the hydrophilic nature of phosphonic acid groups, which attract water, limit their use, potentially leading to dissolution in humid environments.
New design of phosphonic acid polymer with hydrocarbon spacers, and the conductivity of the membrane at 120° C and under 20% RH. Credit: Atsushi Noro and Takato Kajita
To overcome these challenges, Noro introduced a hydrophobic spacer between the polymer backbone and the phosphonic acid groups of a phosphonic acid hydrocarbon polymer. This enabled water insolubility, chemical stability, and moderate conductivity, even at high temperatures and low humidities. Additionally, the hydrophobic spacer effectively repelled water, ensuring that the material’s stability was maintained.
Improved Membrane Performance
The new membrane demonstrated significantly higher water insolubility in hot water compared to polystyrene phosphonic acid membrane without hydrophobic spacers and a commercially available membrane of cross-linked sulfonated polystyrene.
“Under conditions of 120°C and 20% relative humidity, the conductivity of the developed membrane reached 40 times higher than polystyrene phosphonic acid membrane and 4 times higher than cross-linked sulfonated polystyrene membrane,” Noro said.
“Finding a fuel cell that operates under low-humidity and high-temperature conditions offers many advantages for fuel cell vehicles,” Noro continued. “First, the reactions at the electrodes of a fuel cell proceed more rapidly at higher temperatures, enhancing the overall performance of the fuel cell and improving power generation efficiency. Second, there is reduced carbon monoxide (CO) poisoning of the electrodes, as trace amounts of CO in the hydrogen fuel tend to adsorb onto the catalyst at lower temperatures, but not at higher temperatures. Third, the fuel cell benefits from more efficient heat dissipation at high temperatures, allowing simpler cooling system designs and no external humidification, enabling lighter and more compact systems.”
This study received support from the New Energy and Industrial Technology Development Organization (NEDO). According to the NEDO Roadmap for Fuel Cell and Hydrogen Technology Development, the proposed design concept for electrolyte membranes presented in this study marks a major contribution to developing next-generation fuel cells that support the shift to a net-zero carbon society. Patent applications for materials related to the suggested design concept have been filed in Japan and several other countries.
Reference: “Polymer Electrolyte Membranes of Polystyrene with Directly Bonded Alkylenephosphonate Groups on the Side Chains” by Takenori Nakayama, Takato Kajita, Mio Nishimoto, Haruka Tanaka, Katsumi Sato, Mayeesha Marium, Albert Mufundirwa, Hiroyuki Iwamoto and Atsushi Noro, 10 December 2024, ACS Applied Polymer Materials.
DOI: 10.1021/acsapm.4c02688
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