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Innovation in Fuel Cell Electrolytes: A New Research Breakthrough

A research team, under the leadership of Atsushi Noro from Nagoya University in Japan, has unveiled a groundbreaking design for fuel cell electrolytes. This approach features a phosphonic acid polymer integrated with hydrocarbon spacers, allowing fuel cells to function efficiently in high-temperature settings (exceeding 100°C) combined with low-humidity environments. This development addresses significant hurdles that have hindered the widespread adoption of fuel cell technology. The findings of this research were published in ACS Applied Polymer Materials.

Fuel cells generate electricity through the electrochemical reaction of hydrogen and oxygen, emitting only water as a byproduct, which emphasizes their potential as a clean energy source. However, the prevalent use of perfluorosulfonic acid polymers, classified under per- and polyfluoroalkyl substances (PFAS), has raised environmental concerns due to their persistence and accumulation in biological systems. These drawbacks have led to increased regulatory scrutiny in various countries.

In contrast to PFAS, phosphonic acid hydrocarbon polymers are devoid of fluorine, significantly reducing their environmental persistence. These polymers demonstrate adequate chemical stability under the aforementioned extreme conditions. Nonetheless, challenges such as subpar conductivity and the hydrophilic nature of their phosphonic acid groups, which attract moisture, can impede their utility. This attraction may result in the polymers dissolving in humid settings.

In response to these challenges, Noro’s team incorporated hydrophobic spacers between the polymer backbone and the phosphonic acid groups. This innovation enhanced water insolubility, established chemical stability, and ensured moderate conductivity at elevated temperatures and reduced humidity levels. The hydrophobic nature of the spacers effectively repelled water, contributing to the overall stability of the material.

Experimental results demonstrated that the new membrane displayed significantly improved water insolubility in heated water when compared to both a polystyrene phosphonic acid membrane that lacked hydrophobic spacers and a commercially available cross-linked sulfonated polystyrene membrane.

“In conditions of 120°C and 20% relative humidity, the conductivity of our developed membrane reached a remarkable level—40 times superior to that of the polystyrene phosphonic acid membrane and four times that of the cross-linked sulfonated polystyrene membrane,” Noro reported.

Noro further emphasized, “The ability to design a fuel cell that operates at low humidity and high temperatures comes with numerous benefits for fuel cell vehicles. Elevated temperatures accelerate the reactions at the electrodes, thereby enhancing the fuel cell’s overall performance and efficiency in power generation. Moreover, this approach minimizes the risk of carbon monoxide (CO) poisoning of the electrodes; the trace amounts of CO present in hydrogen fuel tend to adhere to the catalyst at lower temperatures, which is not the case at higher temperatures. Additionally, fuel cells can dissipate heat more effectively at elevated temperatures, paving the way for simpler cooling systems without the need for external humidification, resulting in lighter and more compact designs.”

The study was supported by the New Energy and Industrial Technology Development Organization (NEDO). According to the NEDO Roadmap for Fuel Cell and Hydrogen Technology Development, the electrolyte membrane design concept introduced in this research represents a key advancement towards next-generation fuel cells that could facilitate a transition to a net-zero carbon society. Patent applications concerning the materials linked to this innovative design have been submitted in Japan and several other countries.

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