Analysis of carbon-supported platinum through potential cycling and potential-static holding

• Pt/C in CCM-based MEA under potential cycling and potential holding was studied.
• In-situ electrochemical tests and ex-situ SEM/TEM/XPS characterization were conducted.
• “Pt band” occurred in the membrane and Pt particles can reach hundreds of nanometers.
• Carbon surface oxidation current appeared as well as different carbon surface groups.

The stability of platinum and carbon support in catalyst-coated membrane (CCM) was investigated by a potential cycling between 0.7 and 0.9 V and a potential-static holding at 1.2 V, 1.3 V and 1.5 V in single cells. Clear cell performance deterioration can be observed by polarization curves during accelerated stress tests, along with electrochemical surface area (ESA) loss of Pt catalysts by cyclic voltammogram (CV). The X-ray diffraction (XRD) results of CCM before and after tests show that a distinct Pt agglomeration occurred from approximate 3 nm–8 nm in diameter, which is in accord with the observation of Pt/C by transmission electron microscopy (TEM). It is also interesting to note that, redeposited Pt particles in the membrane could be as large as hundreds of nanometers from TEM images of CCM microtomy. X-ray photoelectron spectroscopy (XPS) of carbon 1S indicates that the corrosion of carbon support is highly dependent on the holding potential, and enormous surface groups, such as carboxyl, lactones and ether were generated after tests. Meanwhile, a severer ESA loss of Pt after carbon corrosion under high potential holdings happens than that of potential cycling. The results indicate that both Pt and carbon support in the catalyst are important to maintain a long-term stable operation for fuel cells.

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