A thermogravimetric analysis/mass spectroscopy study of the thermal and chemical stability of carbon in the Pt/C catalytic system

Vulcan XC72 carbon powder and Pt/Vulcan XC72 catalytic powder were characterized by transmission electron microscopy (TEM) and their reactivity under controlled atmospheres was studied as a function of the temperature. Under air atmosphere, production of water was detected by thermogravimetric analysis coupled with mass spectroscopy (TGA-MS) measurement at m/z 18, which evidenced that hydrogenated surface functions were present on the carbon substrate. Under argon atmosphere, the comparison of TGA-MS measurements performed at m/z 18 and m/z 44 with TEM and XRD results, together with XPS measurements, indicated that platinum surface oxides are rather Pt(OH)2 than PtO or PtO2 species. Such reactive surface species is involved in the degradation mechanism of carbon support under air and inert atmospheres. Under H2(3%)/Ar atmosphere, hydrocarbon production coming from “reforming” reactions of the carbon support started at very low temperatures (below 373 K). TEM images of the same catalytic powder region before and after thermal treatment at 423 K under reducing atmosphere clearly displayed consumption of the carbon substrate. The reaction products may not only affect the intrinsic properties of the support but also the catalytic properties of platinum particles: reaction products could poison the anodic catalyst.