Pt supported on carbon black, commonly used as PEM fuel cell catalyst, underlies electrochemical instabilities in terms of carbon corrosion and platinum degradation. To better understand the influence of the support on nature and extent of catalyst aging, Pt was synthesized on four different substrates: Carbon black, multiwalled carbon nanotubes (MWCNTs), reduced graphene oxide (rGO) and a nanocomposite of indium tin oxide with rGO (ITO-rGO). The four Pt catalysts and the separate supports were studied on their durability using an accelerated stress test (AST, −0.02-1.40 V SHE ). Comparable platinum degradation was shown by losses of electrochemically active surface area (EASA) and activity for oxygen reduction reaction (ORR) and by identical location transmission electron microscopy (IL-TEM). With respect to the supports, highest instability of carbon black was observed investigating the double layer capacitance and amounts of hydroquinone (HQ) species. MWCNTs showed the lowest degradation. Thus, AST provoked strongly different extents of support aging but similar Pt degradation. In view of complex FC catalyst degradation mechanism, only negligible Pt detachment caused by support degradation and rather dominating Pt dissolution and agglomerationadditionally evidenced by IL-TEM-is assumed here. Regarding ITO-rGO, neither carbon support nor platinum stabilization by ITO nanoparticles has been observed. Proton exchange membrane fuel cells (PEMFCs) are attractive for stationary, portable and automotive applications.1,2 Short response times and simple cell design with low weight and solid electrolyte membranes are some advantages of PEMFCs, especially for the automotive sector. Good performance and high lifetimes are two important criteria for commercialization of fuel cells. Low temperature PEMFCs can reach power densities about 680 mWcm −2 , 3 higher than the power densities of other fuel cell types.1 However, a challenge is the loss of performance with operation time.2,4 The better understanding of physical, thermal, mechanical, chemical and electrochemical processes, leading to the aging of fuel cell components, is indispensable and is therefore one main issue of current fuel cell research. 2,[5][6][7][8] Platinum supported on carbon black represents the commonly used catalyst in fuel cells. Under PEMFC conditions at low pH values and cell voltages of around 1.0 V during no-load or 1.4 V during startstop operation, 9 dissolution of platinum becomes relevant. Pt oxides are formed at potentials higher than 0.6 V SHE , 10 whereas Pt oxides or metallic Pt can dissolve.2 Dissolved Pt underlies Ostwald ripening or simply leaves the cell with the exhaust water stream. Pt ions can migrate into the membrane and be reduced to metallic platinum.
11Especially at potentials above 0.95 V SHE oxygen atoms can replace Pt atoms, so that potential cycling can lead to significant changes of the catalyst particle structure.
2Also instabilities of the catalyst support can result in a reduction of cell performance. Corrosion of carbo...
