In situ probing of magnetron sputtered Pt-Ni alloy fuel cell catalysts during accelerated durability test using EC-AFM

As-deposited Pt-Ni and annealed Pt-Ni alloy catalyst films prepared by magnetron co-sputtering were investigated in order to quantify their ageing during accelerated durability test. The parameters of the durability test were chosen to simulate severe potential conditions that may occur at start-up/shut-down cycles of a fuel cell. Using in situ electrochemical atomic force microscopy complemented with ex situ energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, synchrotron radiation photoelectron spectroscopy and X-ray diffraction provided step-by-step correlation of chemical and morphology changes induced by catalyst's aging processes. We show that the as-deposited Pt-Ni films face severe chemical stability problem which leads to almost complete destruction of the alloy during the durability test. On the other hand Pt-Ni films annealed in vacuum are more resistive to morphological and chemical changes. It was confirmed that upon annealing due to redistribution of Pt and Ni atoms Pt-skin is formed on catalyst surface, which is responsible for a better stability during the aging test.

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