Structural change of carbon supported Pt nanocatalyst subjected to a step-like potential cycling in PEM FC

• We studied structural changes in aged Pt nanocatalysts worked in PEM FC.
• Combined HRTEM, XRD and XAFS analysis was applied.
• In the first stage of FC work small particle dissolution was a dominant process.
• Then dissolution–precipitation process was coupled with particle coalescence.
• Short-range structural order plays a minor role in the catalyst activity enhancement.

In this paper we present detailed X-ray absorption fine structure (XAFS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigations of the changes in the local geometric and electronic structure of Pt nanoparticles used as a cathode catalyst in proton exchange membrane fuel cell (PEMFC), working under controlled potential cycling conditions. The body of the results obtained suggests that in the first stage of PEMFC operation, small particle dissolution was a dominant process. Subsequent 100 h of work led to the progressive agglomeration of nanoparticles followed by a pronounced growth of the mean nanoparticle size. At the same time, high-quality XAFS spectra analysis demonstrated that negligible changes in structural local ordering and a slight increase in Pt 5d-electron density occurred during the whole FC operation period under consideration.