A novel design concept for fuel cell electrolytes

By Amit Malewar 14 Dec, 2024

Collected at: https://www.techexplorist.com/novel-design-concept-fuel-cell-electrolytes/94661/

Fuel cells generate electricity by electrochemically reacting hydrogen and oxygen, producing only water as a byproduct, which makes them a clean energy source. However, using perfluoro sulfonic acid polymers containing sulfonic acid groups—a type of per- and polyfluoroalkyl substance (PFAS)—in fuel cells has raised concerns.

PFAS can accumulate in the environment and living organisms, increasing regulatory scrutiny in many countries.

In contrast, phosphonic acid hydrocarbon polymers do not contain fluorine, making them less likely to persist in the environment. These polymers also offer moderate chemical stability under high-temperature and low-humidity conditions.

However, their use is limited by poor conductivity and their hydrophilic nature, meaning they attract water. This can lead to dissolution in humid environments, restricting their potential in fuel cell applications.

To overcome these challenges, a research group led by Atsushi Noro at Nagoya University in Japan has announced a novel design concept for fuel cell electrolytes. Their research uses a phosphonic acid polymer with hydrocarbon spacers.

The team improved a phosphonic acid hydrocarbon polymer by introducing a hydrophobic spacer between the polymer backbone and the phosphonic acid groups. This modification made the polymer water-insoluble, chemically stable, and moderately conductive, even under high temperatures and low humidity. The hydrophobic spacer also helped repel water, preserving the material’s stability.

The new polymer electrolyte membrane showed much higher water insolubility in hot water than a polystyrene phosphonic acid membrane without hydrophobic spacers and a commercially available cross-linked sulfonated polystyrene membrane.

Noro said, “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.”

A fuel cell that operates under low-humidity and high-temperature conditions offers several advantages, especially for fuel cell heavy-duty vehicles:

1. Reactions at the electrodes happen faster at higher temperatures, improving the fuel cell’s overall performance and power generation efficiency.
2. There is less carbon monoxide (CO) poisoning of the electrodes, as trace amounts of CO in the hydrogen fuel tend to stick to the catalyst at lower temperatures but not at higher temperatures.
3. High temperatures allow for better heat dissipation, which leads to simpler cooling system designs and eliminates the need for external humidification. This makes the system lighter and more compact.

According to the New Energy and Industrial Technology Development Organization (NEDO), the proposed design concept marks a major contribution to developing next-generation fuel cells that support the shift to a net-zero carbon society.

Journal Reference:

1. Takenori NakayamaTakato, KajitaMio Nishimoto, Haruka Tanaka, Katsumi Sato, Mayeesha Marium, Albert Mufundirwa, Hiroyuki Iwamoto, Atsushi Noro. Polymer Electrolyte Membranes of Polystyrene with Directly Bonded Alkylenephosphonate Groups on the Side Chains. ACS Applied Polymer Materials. DOI: 10.1021/acsapm.4c02688