ACS Nano http://doi.org/5fx (2015)

Proton exchange membrane fuel cells could potentially be used as portable power sources with high energy densities. However, the cells typically rely on catalysts made of expensive noble metals such as platinum, which limits their widespread commercialization. This has led to an extensive search for cheaper materials, but an alternative approach is to try to improve the long-term efficiency of platinum-based catalysts. Heeyeon Kim, Alex Robertson and colleagues have now shown that the lifetime of platinum nanoparticle catalysts can be increased by coating them with a porous layer of graphene.

The researchers — who are based at the Korean Institute of Energy Research, the University of Oxford and KAIST in South Korea — synthesized graphene-encapsulated nanoparticles in a one-step procedure in which carbon and platinum precursors were simultaneously vapourized at temperatures ranging from 400 °C to 1,100 °C; the resulting structures were then characterized using aberration-corrected transmission electron microscopy. At such temperatures, catalytic growth of graphene occurs on platinum surfaces and by limiting the temperature to around 400 °C, nanoparticles with graphene shells that were only 1–2 layers thick could be formed.

The shells were found to protect the nanoparticles from the operating conditions of the fuel cell, but at the same time degrade the catalytic performance. However, the growth of complete graphene shells could be inhibited by adding nitrogen precursors during synthesis and the resulting platinum nanoparticles, which had porous graphene shells, were found to offer both high performance and increased resilience.