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...

Catalyst degradation results in performance losses of proton exchange membrane fuel cells (PEMFC) and is caused by electrochemical instability of commonly used platinum on carbon black (Pt/C). In this study, a comparison in durability of commercial Pt/C with a new Pt catalyst on a nanocomposite of fluorine-doped SnO 2 (FTO) and reduced graphene oxide (rGO) is carried out. Transmission electron microscopy (TEM) shows similar Pt distributions on support surfaces and Pt particle sizes so that a high comparability of support materials during durability investigation is ensured. High resolution TEM with EDS reveals dispersed Pt anchored at FTO-rGO interfaces. During stripping voltammetry Pt/FTO-rGO provides weaker CO sorption than Pt/C, indicating higher CO tolerances. Accelerated stress testing (0.05-1.47 V RHE) provokes Pt degradation on both supports in comparable rates. However, the FTO-rGO nanocomposite presents the more stable substrate in this study compared to carbon black. Identical location TEM illustrates stable FTO particles in size and position on rGO surface. Moreover, unchanged hydroquinone/quinone (HQ/Q) amounts and double layer capacitance in case of Pt/FTO-rGO were revealed by cyclic voltammetry. On the contrary, standard Pt/C shows significantly more generation of HQ/Q functionalities by a factor of 25 and thus higher carbon corrosion.

Fe-N-C materials are promising non-precious metal catalysts for the oxygen reduction reaction in fuel cells and batteries. However, during the synthesis of these materials less active Fe-containing nanoparticles are formed in many cases which lead to a decrease in electrochemical activity and stability. In this study, we reveal the significant properties of the carbon support required for the successful incorporation of Fe-N-related active sites. The impact of two carbon blacks and two activated biomass-based carbons on the Fe-N-C synthesis is investigated and crucial support properties are identified. Carbon supports having low portions of amorphous carbon, moderate surface areas (>800 m2/g) and mesopores result in the successful incorporation of Fe and N on an atomic level and improved oxygen reduction reaction (ORR) activity. A low surface area and especially amorphous parts of the carbon promote the formation of metallic iron species covered by a graphitic layer. In contrast, highly microporous systems with amorphous carbon provoke the formation of less active iron carbides and carbon nanotubes. Overall, a phosphoric acid activated biomass is revealed as novel and sustainable carbon support for the formation of Fe-Nx sites. Overall, this study provides valuable and significant information for the future development of novel and sustainable carbon supports for Fe-N-C catalysts.

Degradation of commonly used platinum on carbon black results into performance losses of proton exchange membrane fuel cells (PEMFC). A nanocomposite of fluorine-doped SnO 2 (FTO) and reduced graphene oxide (rGO) is used as Pt support and studied on electrochemical stability by potential cycling between 0.05-1.47 V RHE . Highly dispersed Pt with anchoring at FTO-rGO interfaces is observed by use of high resolution transmission electron microscopy (HR-TEM). Stripping voltammetry shows weaker CO binding on Pt/FTO-rGO than on Pt/C, indicating higher CO tolerances. During potential cycling, the catalyst shows a loss of electrochemical active surface and a reduced activity for oxygen reduction, whereas the support exhibits unchanged amounts of hydroquinone/quinone functionalities and stable double layer capacitance. Additionally, identical location TEM shows unchanged FTO particles on rGO surface, demonstrating electrochemical stability of FTO-rGO substrate. Thus, this composite material meets the stability criteria for catalyst support in PEM fuel cells.