Nagoya University develops water-soluble fullerene derivatives that dramatically improve fuel cell durability

A research group led by Professor Yutaka Matsuo and Designated Professor Masaya Kawasumi from the Graduate School of Engineering at Nagoya University has developed a technology that dramatically improves the durability of polymer electrolyte membranes (PEMs), which are the heart of proton exchange membrane fuel cells (PEMFC), using uniquely developed water-soluble fullerene derivatives. The research was published in Communications Materials.

PEMFCs, which generate electricity using hydrogen as fuel, are expected to be utilized in various fields such as automobiles and stationary power sources as clean power that does not emit carbon dioxide. The PEM, which is the heart of these fuel cells, requires excellent proton conductivity and mechanical and chemical stability. However, degradation is a problem due to reactive oxygen species generated during long-term operation, particularly hydroxyl radicals and peroxyl radicals, which cause membrane decomposition, thinning, and pinhole formation. While fullerenes possess powerful radical scavenging capabilities, they have poor compatibility with water and electrolyte membranes, causing aggregation within the membrane, which posed challenges for practical application.

The research group adopted an approach of synthesizing novel fullerene derivatives that are soluble in water and alcohol and uniformly dispersing them in Nafion membranes. Through regioselective introduction of functional groups such as phenol groups and carboxylic acid groups to the spherical carbon structure of fullerenes, they achieved high water solubility compared with conventional hydroxylated fullerenes (fullerenols) while maintaining the π-conjugated structure and also improved affinity with Nafion. This enabled fullerene derivatives to be stably retained in Nafion's ion clusters and allowed membrane formation with uniform dispersion throughout the entire membrane.

It was confirmed these fullerene derivatives have the property of strongly chelating cerium ions and that Ce introduced into the membrane does not leak out during washing or operation and maintains its radical scavenging ability over long periods of time. In fact, in chemical durability evaluations through the Fenton tests, conventional Nafion membranes rapidly decomposed and released large amounts of fluoride ions, whereas hybrid membranes containing fullerene derivatives and Ce showed approximately 90% reduction in fluoride ion release.

Significant improvements were also observed in durability tests during fuel cell operation using membrane electrode assemblies (MEA). Under accelerated test conditions of high temperature, low humidity, and high voltage, conventional Nafion membranes began to show performance degradation at approximately 100 hours. In contrast, the PhCOOH-5-OH/Ce/Nafion hybrid membrane developed by the group maintained stable open circuit voltage (OCV) for over 1050 hours, achieving a life more than 10 times longer than conventional membranes. Additionally, the F-ion release rate in discharged water was 1/50 that of membranes without fullerene derivatives. It is also suggested that there is a mechanism where at this time, a catalytic cycle - i.e., the fullerene cation species generated are reduced by hydrogen molecules and slight leak currents, and radicals are captured again - is repeated, whereby membrane stability is maintained over long periods.

The fabricated hybrid membranes also demonstrated performance equal to or superior to conventional membranes in terms of proton conductivity and mechanical properties. It was revealed that hydroxyl groups and carboxylic acid groups in the fullerene derivatives enhance water retention and promote proton conduction, while also improving the tensile strength and elastic modulus of the membrane through interactions with Nafion molecular chains. Specifically, the PhCOOH-5-OH/Nafion membrane recorded a tensile strength of 25.5 MPa and proton conductivity of 0.12 S/cm, providing sufficient performance as a practical material.

This achievement realizes a fundamental improvement in chemical durability, which was a challenge for PEMFC electrolyte membranes, and represents an important milestone toward the realization of a hydrogen society through future commercialization and multi-purpose deployment of fuel cells. Beyond contributing to improved fuel cell durability and multi-purpose deployment to heavy-duty trucks, ships, railways, construction machinery, and other applications that require longer-term durability, radical control technology using water-soluble fullerene derivatives is expected to find applications in a wide range of fields including membrane separation, catalysis, and medical materials, not limited to fuel cell materials.

Journal Information
Publication: Communications Materials
Title: Water-soluble fullerene derivatives as radical scavengers for highly durable proton exchange membrane fuel cells
DOI: 10.1038/s43246-025-00845-9