Researchers from Queen Mary University of London and University College London (UCL) have produced graphene via a special, scalable technique and used it to develop hydrogen fuel cell catalysts. In an open-access paper published in the RSC journal Nanoscale, the researchers report that this new type of graphene-based catalyst was more durable than commercially available catalysts and matched their performance.
Platinum is the most widely used catalyst for fuel cells, but its high cost is a big problem for the commercialization. To address this issue, commercial catalysts are typically made by decorating tiny nanoparticles of platinum onto a cheaper carbon support—however the poor durability of the material greatly reduces the lifetime of current fuel cells.
Previous research has suggested graphene could be an ideal support material for fuel cells due to its corrosion resistance, high surface area and high conductivity. However, the graphene used in the majority of experiments to-date contains many defects, meaning that the predicted improved resistance has not yet been achieved.
The technique described in the study produces high-quality graphene decorated with platinum nanoparticles in a one-pot synthesis. This process could be scaled up for mass production, opening up the use of graphene-based catalysts for widespread energy applications.
Herein we describe a scalable synthesis for Pt nanoparticle-coated graphene whereby PtCl2 is reduced directly by negatively charged single layer graphene sheets in solution. The resultant nanoparticles are of optimal dimensions and can be uniformly dispersed, yielding high catalytic activity, remarkable stability, and showing a much smaller decrease in electrochemical surface area compared with an optimised commercial catalyst over 30 000 cycles. The stability is rationalised by identical location TEM which shows minimal nanoparticle agglomeration and no nanoparticle detachment.—Angel et al.
Transmission Electron Micrograph of graphene decorated with platinum nanoparticles. The dark spots are the platinum nanoparticles and the grey sheet they lie on is the graphene support material. Image credit: Patrick Cullen / Gyen Ming Angel
We’ve shown that by using graphene instead of the typical amorphous carbon as a support material we can create ultra-durable catalysts.—Professor Dan Brett, Professor of Electrochemical Engineering at UCL
The researchers confirmed the durability of the graphene-based catalyst using a type of test based on those recommended by the US Department of Energy (DOE), known as accelerated stress tests. Accelerated stress tests deliberately stress the catalyst rapidly over many cycles in a short space of time, allowing scientists to assess the stability of new materials without having to use them in an operational fuel cell over a period of months or years.
Using these tests, the scientists showed that loss in activity over the same testing period was around 30% lower in the newly developed graphene-based catalyst, compared with commercial catalysts.
The DOE sets tests and targets for fuel cell durability, with one accelerated stress test to simulate normal operating conditions and one to simulate the high voltages experienced when starting up and shutting down the fuel cell. Most research studies in the graphene space only evaluate using one of the recommended tests. However, since we have high-quality graphene in our material, we have managed to achieve high durability in both tests and under long testing periods, which is important for the future commercialisation of these materials. We look forward to incorporating our new catalyst into commercial technology and realizing the advantages of longer-life fuel cells.—Gyen Ming Angel, UCL PhD student and lead author
Graphene is made from a single layer of carbon atoms arranged in a hexagonal lattice. Despite its relatively simple structure, graphene is thought to have remarkable properties including high electrical conductivity, high transparency and high flexibility.
Gyen Ming A. Angel, Noramalina Mansor, Rhodri Jervis, Zahra Rana, Chris Gibbs, Andrew Seel, Alexander F.R. Kilpatrick, Paul R. Shearing, Christopher A. Howard, Dan J. L. Brett and Patrick L. Cullen (2020) “Realising the electrochemical stability of graphene: scalable synthesis of ultra-durable platinum catalyst for the oxygen reduction reaction” Nanoscale doi: 10.1039/D0NR03326J