A team of researchers has created an innovative design for the electrolytes utilized in fuel cells. This new material adheres to environmental standards and shows moderate conductivity even in extreme conditions, achieving conductivity levels that are four times higher than the traditional cross-linked sulfonated polystyrene material. Their research plays a vital role in advancing the development of next-generation fuel cells and aids in the pursuit of net-zero carbon objectives.
The research team, led by Atsushi Noro from Nagoya University in Japan, has unveiled a groundbreaking design for fuel cell electrolytes, which uses a phosphonic acid polymer enhanced with hydrocarbon spacers. This new design enables fuel cells to function efficiently under high temperature (over 100°C) and low humidity conditions, thus overcoming significant obstacles to their widespread adoption. Their findings are documented in the journal ACS Applied Polymer Materials.
Fuel cells generate electricity by electrochemically combining hydrogen and oxygen, emitting only water as a byproduct, which underscores their potential as a clean energy source. However, the conventional use of perfluorosulfonic acid polymers — a category of per- and polyfluoroalkyl substances (PFAS), is facing criticism. The environmental impact of PFAS and their tendency to accumulate in living beings have led to regulatory actions in various countries.
In contrast to PFAS, phosphonic acid hydrocarbon polymers are free from fluorine, reducing their likelihood of environmental persistence. These polymers also display moderate chemical stability in high-temperature and low-humidity settings. Nevertheless, challenges such as poor conductivity and the hydrophilic characteristics of phosphonic acid groups, which draw in water, can limit their application and may risk dissolution in moist environments.
To tackle these issues, Noro introduced a hydrophobic spacer between the polymer backbone and the phosphonic acid groups of the phosphonic acid hydrocarbon polymer. This development enhanced water insolubility, chemical stability, and moderate conductivity, even at elevated temperatures and low humidity. Furthermore, the hydrophobic spacer effectively repelled water, ensuring the material’s stability was preserved.
The newly developed membrane demonstrated a significantly higher level of water insolubility in hot water compared to both the polystyrene phosphonic acid membrane without hydrophobic spacers and a commercially available cross-linked sulfonated polystyrene membrane.
“At a temperature of 120°C and 20% relative humidity, the conductivity of our membrane reached 40 times that of the polystyrene phosphonic acid membrane and 4 times that of the cross-linked sulfonated polystyrene membrane,” Noro noted.
“Developing a fuel cell that can operate in low-humidity and high-temperature environments provides several benefits for fuel cell vehicles,” he added. “First, reactions at the fuel cell electrodes occur more rapidly at elevated temperatures, leading to improved overall performance and power generation efficiency. Second, there is a reduced risk of carbon monoxide (CO) poisoning of the electrodes; low levels of CO present in hydrogen fuel can cling to the catalyst at lower temperatures, but this is less of a concern at higher temperatures. Third, high temperatures allow for better heat dissipation, which simplifies cooling system design and eliminates the need for external humidification, resulting in lighter and more compact systems.”
This research received backing from the New Energy and Industrial Technology Development Organization (NEDO). As indicated in the NEDO Roadmap for Fuel Cell and Hydrogen Technology Development, the newly proposed electrolyte membrane design represents a significant advancement towards creating next-generation fuel cells that facilitate the transition to a carbon-neutral society. Patent applications related to this innovative design are currently being pursued in Japan and several other countries.
