A polybenzimidazole polymer can support the formation of gold nanoparticles with well-defined sizes on graphene. Image: I²CNER, Kyushu University.
A polybenzimidazole polymer can support the formation of gold nanoparticles with well-defined sizes on graphene. Image: I²CNER, Kyushu University.

The widespread adoption of fuel cells relies on improving the performance of the catalysts they use. Gold nanoparticles have been cited as an ideal solution, but creating a uniform, useful catalyst with them has proven elusive. A team of researchers at Kyushu University's International Institute for Carbon-Neutral Energy Research (I2CNER) in Fukuoka, Japan, has now found a way to do this by developing a new type of catalyst support.

In a potential breakthrough for fuel cells reported in Scientific Reports, the researchers show how wrapping a graphene support in a specially prepared polymer provides an ideal foundation for making uniform, highly-active gold nanoparticle catalysts.

Fuel cells produce electricity directly from the oxidation of a fuel such as hydrogen at an anode and the reduction of oxygen at a cathode, with water the only by-product. Fuel cells produce no greenhouse gases and are widely seen as essential for a clean-energy future.

However, the rate at which electricity can be produced in fuel cells is limited, especially by the oxygen reduction reaction (ORR) at the cathode. Although current platinum-based catalysts accelerate this reaction, they tend to catalyze other reactions as well and are also sensitive to poisoning by the reactants, limiting their overall utility. Despite bulk gold being chemically inert, gold nanoparticles are surprisingly effective at catalyzing the ORR without the drawbacks associated with their platinum counterparts.

Actually creating uniformly-sized gold nanoparticle catalysts has proven problematic, however. Previous fabrication methods have produced catalysts with nanoparticle sizes that were either too large or too widely distributed for practical use. Meanwhile, efforts to regulate the particle size tended to restrict the gold's activity or produce less-stable catalysts.

"Creating small, well-controlled particles meant that we needed to focus on particle nucleation and particle growth," says lead and corresponding author Tsuyohiko Fujigaya. "By wrapping the [graphene] support in the polybenzimidazole polymer we successfully developed with platinum, we created a much better support environment for the gold nanoparticles."

The team also tested the performance of these novel catalyst structures, finding that they had the lowest overpotential ever reported for this type of reaction. "The overpotential is a bit like the size of the spark you need to start a fire," co-author Naotoshi Nakashima says. "Although we're obviously pleased with the catalysts' uniformity, the performance results show this really could be a leap forward for the ORR reaction and maybe fuel cells as well."

This story is adapted from material from I2CNER, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.