Pt nano-catalyst with graphene pockets enhances fuel cell durability and efficiency

The manufacturing and deployment of hybrid and electric vehicles is on the rise, contributing to ongoing efforts to decarbonize the transport industry. While cars and smaller vehicles can be powered using lithium batteries, electrifying heavy-duty vehicles, such as trucks and large buses, has so far proved much more challenging.

Fuel cells, devices that generate electricity via chemical reactions, are promising solutions for powering heavy-duty vehicles. Most of the fuel cells employed so far are so-called proton exchange membrane fuel cells (PEMFCs), cells that generate electricity via the reaction of hydrogen and oxygen, conducting protons from their anode to their cathode utilizing a solid polymer membrane.

Despite their potential, many existing fuel cells have limited lifetimes and efficiencies. These limitations have so far hindered their widespread adoption in the manufacturing of electric or hybrid trucks, buses and other heavy-truck vehicles.

A research group at the University of California, Los Angeles (UCLA), led by Professor Yu Huang, recently designed a new platinum (Pt)-based nano-catalyst, a material that speeds up chemical reactions and could help to improve the efficiency and durability of fuel cells. This catalyst, presented in a paper published in Nature Nanotechnology, consists of Pt nanoparticles, protected by graphene nanopockets and supported on a form of carbon known as Ketjenblack.

“Our research emerged from an urgent need to decarbonize heavy-duty vehicles (HDVs), such as long-haul trucks, which require extended operational range and durability,” Huang, senior author of the paper, told Phys.org. “Fuel cells represent a promising solution for electrifying HDVs due to their superior system-level mass-specific energy density compared to batteries. However, a major obstacle is catalyst stability.”

Platinum and other alloy metals typically used to fabricate catalysts for PEMFCs tend to gradually dissolve and some of their atoms are redeposited onto other particles, causing them to become larger. This process reduces the area of the catalyst that can speed up reactions in fuel cells, ultimately causing their performance to decline over time.

“Motivated by this challenge, our team at UCLA developed a Pt-based catalyst with an innovative protective yet permeable structure,” said Huang. “Our primary goal was to design a catalyst architecture that effectively prevents metal dissolution and maintains high catalytic activity over prolonged use.”

The Pt-based nano-catalyst developed by Huang and her colleagues has a unique design that slows down its degradation over time. The catalyst consists of ultrafine Pt nanoparticles encased within thin and protective layers of graphene, known as graphene nanopockets.

“These graphene nanopockets protect the platinum nanoparticles from dissolving and coalescing (clumping together),” explained Zeyan Liu, co-first author of the article. “Additionally, these protected nanoparticles are confined within the pores of a carbon support, significantly enhancing stability and durability under harsh operational conditions.”

This recent study introduced an alternative catalyst that could boost the performance and durability of fuel cells, as it does not rapidly deteriorate like many catalysts introduced in the past. In initial tests, the new Pt-based nano-catalyst yielded very promising results, as fuel cells incorporating it presented unprecedented stabilities, while also maintaining a high catalytic activity and efficiency.

“The catalyst demonstrated exceptional performance, including an initial mass activity of 0.74 A mg⁻¹ and a rated power density of 1.08 W cm⁻²,” said Bosi Peng, co-first author of the paper. “Remarkably, the catalyst experienced less than 1.1% power loss after undergoing a rigorous accelerated stress test of 90,000 voltage cycles. These metrics suggest a projected fuel cell lifetime exceeding 200,000 hours, significantly surpassing current Department of Energy targets for heavy-duty fuel cells.”

In the future, the new catalyst designed by Huang and her colleagues could be used to develop new highly performing and durable hydrogen-based fuel cells. These fuel cells could in turn be used to power various heavy-truck vehicles, thus contributing to ongoing efforts aimed at reducing carbon emissions.

“Our study represents a significant step forward in reducing emissions and enhancing fuel economy in transportation sectors that heavily contribute to energy consumption and environmental impact,” added Huang. “Beyond further enhancing platinum catalyst activity and durability, we aim to focus future research on optimizing the entire catalyst electrode structure to further improve the performance of the fuel cell.

“Developing advanced carbon support materials, innovative electrode architecture and improved ionomer components will be equally critical, as they significantly influence high-current-density performance and overall fuel cell stability.”

Huang’s research group at UCLA is now conducting further research aimed at improving and advancing fuel cells. Their efforts are currently focused on the improvement of membrane electrode assemblies, the central component of PEMFCs.

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