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A CO2 detection system that enables in-situ and real-time monitoring of CO2 formation from carbon corrosion during start-stop potential cycling was developed. The set-up included a nondispersive infrared (NDIR) CO¬2 detector connected to the fuel cell cathode exhaust. For both Ketjen Black (KB) and Platinum/Ketjen Black (Pt/KB) (50 wt% carbon) cathodes, the amount of CO2 was found to increase with the number of potential cycles (up to 500 cycles) and the carbon loading. Pt was found to increase the initial rate (µg CO2/cycle) of CO2 formation, confirming the findings of earlier studies that Pt accelerates carbon corrosion. Preliminary calculations show that carbon loss is about 30% for both KB and Pt/KB cathodes under the potential cycling protocol used in this study. Pt only acts as a catalyst for the reaction, and it does not significantly affect the total carbon loss which is a function of the amount of corrodible carbon.

Ethanol presents several advantages over other alternative fuels. Its volumetric energy density (23.4 MJ/L) is slightly lower than gasoline (33.4 MJ/L), but much better than available with either methanol or hydrogen. If an ethanol is used in a proton exchange membrane (PEM) fuel cell the lowered energy density compared to gasoline in an internal combustion engine can in theory be overcome. This assumes that an electrochemical system can be developed that carries out the complete 12-electron oxidation of ethanol. To reach this goal, new catalyst systems must be developed. It is found that multicomponent catalysts such as platinum tin oxide (Pt/SnO2) and platinum tin oxide titanium dioxide (Pt/SnO2/TiO2) improve the conversion of ethanol to its 12-electron oxidation products. Catalysts of this type can be quickly prepared usingamicrowave-assisted polyol procedure. Elevation of the operating temperature of a PEM fuel cell using the indicated catalysts to 130åC facilities production of CO2 and provides an improved current-voltage response.

International audience; A highly active and durable non-platinum group metal (non-PGM) electrocatalyst was synthesized at high temperature from a catalyst precursor involving a ferrous iron salt and a nitrogen-containing charge-transfer salt as a precursor to form a nano-structured catalyst with performance level that makes it suitable for automotive applications. Such precursors have not been previously investigated for non-PGM catalysts. The synthesized material belongs to the class of metal-nitrogen-carbon catalysts and possesses an open-frame structure controlled by the silica-templating synthesis method. Thorough characterization using X-ray photoelectron, Mössbauer and in situ X-ray absorption spectroscopies demonstrates the successful formation of FeNxCy moieties that are active towards the oxygen reduction reaction. We report high kinetic current densities and high power performance in both rotating disk electrode and membrane electrode assembly studies. This Fe-N-C catalyst, jointly investigated by academic and industry partners, has shown high durability under different protocols, including that defined by the US Department of Energy Durability Working Group and Nissan’s load cycling protocol. In summary, the present Fe-N-C catalyst is highly active and durable, making it a viable alternative to Pt-based electrocatalysts for automobile fuel cell applications.

Introduction Conventional carbon supports suffer from catastrophic failure during start-up/shut-down events, which result in high cathode interfacial potentials, which, in turn, lead to carbon corrosion and catalyst degradation. Carbon corrosion is a major problem in fuel cells because it leads to loss of catalyst activity and collapse of electrode structure. Nissan, as an automotive OEM, has always approached the issue of catalyst support durability at the materials level, rather than at the systems-level, since system-level mitigation is an added cost to the balance of plant (BOP), and presents one additional factor that can fail during operation. NTCNA and IIT have been working on the development of high-surface-area, corrosion-resistant non-carbon supports, and we have previously demonstrated a class of highly stable non-carbon supports, e.g. ruthenium-titanium oxide (RTO) (1). In this work, we present the results of our work on a second class of non-carbon supports - tin-doped indium oxide (ITO). Materials and Methods RDE Testing – RDE tests were performed in a 3-compartment electrochemical cell containing 0.1 M HClO4 electrolyte. A glassy carbon disk (0.196 cm2) uniformly covered with Pt/C or Pt/ITO catalyst served as the working electrode. The counter and reference electrodes were Pt foil and RHE, respectively. Membrane Electrode Assembly (MEA) Fabrication - Catalyst inks were prepared by mixing Pt/C or Pt/ITO with water, n-propanol, and a Nafion ionomer dispersion. The mass-based ionomer/support (I/S) ratio in the ink was kept constant at 0.9. The cathode catalyst layers were formed on GDLs using an automated robotic spray system. MEAs (25 cm2) were prepared by hot pressing cathode GDEs (0.35 mgPt/cm2) and commercial anode GDEs (0.4 mgPt/cm2) onto Nafion® NR211 membranes. Results and Discussion Figure 1 shows the RDE performance of Pt/ITO vs. a commercially available Pt/C benchmark catalyst of comparable Pt particle size. The ECA obtained for Pt/ITO (22 m2/gPt) was lower than Pt/C (45 m2/gPt) due to the low surface area of ITO which causes Pt particle agglomeration. Even with a lower ECA, Pt/ITO shows promising performance since its mass activity of ~150 mA/mgPt matches that of the Pt/C benchmark catalyst. However, we have repeatedly observed that Pt/ITO performs very poorly in MEA testing. Figure 2 shows a typical H2/O2 polarization curve obtained for Pt/ITO at a high Pt loading of 0.35 mg/cm2. The only difference between the two MEAs is the cathode catalyst. Other than the dramatic difference between the two polarization curves, it can also be seen that Pt/ITO shows a very high HFR (high frequency resistance) of ~220 mΩ·cm2. The HFR represents the ohmic resistance due to proton transport in the membrane and the electronic contact resistances in the cell. The high HFR is attributed to the poor electronic conductivity of the ITO support since the two MEAs in Figure 2 have the same membrane, cell hardware, and cell components. It is hypothesized that hydroxylated species form on the ITO surface under fuel cell operating conditions. Hydroxide and oxy-hydroxide species may readily form on the surface of ITO due to hydrolysis reactions. Hydroxylated species such as In(OH)3 have low solubilities, hence they may remain adsorbed on the ITO surface, forming a passivating layer that will increase ohmic resistance (2). Furthermore, the Pourbaix diagram for indium shows that under fuel cell conditions, the formation of In3+ is favorable, and it is possible that In3+ can act as a poison that covers the Pt active sites. This is supported by the changes observed in the CV profile in MEA (loss of Hupd features and resistive behavior), suggesting some changes in the chemical properties of ITO and Pt poisoning. The promising RDE results did not translate to good performance in MEA, and this is hypothesized to be caused by cross-over hydrogen in MEA. H2 crossing over from anode to cathode may accelerate the formation of hydroxylated species. Experiments are underway to verify this. References 1. J. Parrondo, T. Han, E. Niangar, C. Wang, N. Dale, K. Adjemian and V. Ramani, Proceedings of the National Academy of Sciences, 111 (2014) 45-50. 2. B. Michael, P. A. Veneman, F. S. Marrikar, T. Schulmeyer, A. Simmonds, W. Xia, P. Lee, and N. R. Armstrong. Langmuir, 23(22), 11089-11099 (2007). Figure 1

The hydrogen/air proton-exchange membrane (PEM) fuel cell is a promising candidate for automotive power plants but Pt/C catalyst electrode cost and durability are still issues that require further study. In a series of previous papers and presentations [1-4], Pintauro and coworkers have shown that an electrospun nanofiber cathode, composed of Pt/C particles and a binder of Nafion + poly(acrylic acid), performs remarkably well in a hydrogen/air proton exchange membrane fuel cell. For example, a nanofiber electrode MEA with a 0.055 mgPt/cm2 cathode and 0.059 mgPt/cm2 anode produced more than 900 mW/cm2 at maximum power in a H2/air fuel cell at 80°C, 100% RH and high feed gas flow rates at 2 atm backpressure. In another study, electrospun nanofiber cathodes exhibited excellent durability, as determined from end-of-life polarization curves after an accelerated start-stop voltage cycling (carbon corrosion) test. For example, after 1,000 simulated start-stop cycles, a nanofiber MEA with Johnson Matthey Pt/C catalyst maintained 53% of its initial power at 0.65 V and 85% of its maximum power, as compared to a 28% power retention at 0.65 V and 58% maximum power for a sprayed electrode MEA. The excellent initial performance of nanofiber fuel cell electrodes was attributed to the unique nanofiber electrode morphology, with inter-fiber and intra-fiber porosity which results in better accessibility of oxygen to Pt catalyst sites and efficient removal of product water. The superior end-of-life performance of the nanofiber MEA after a carbon corrosion test was attributed to the combined effects of a high initial electrochemical cathode surface area, the retention of the nanofiber structure after testing (no collapse of the cathode, as confirmed by SEM imaging), and the rapid/effective expulsion of product water from the cathode which minimizes/eliminates flooding. In this presentation, the performance of Pt-alloy catalysts in electrospun nanofiber fuel cell cathodes will be discussed. The method for creating nanofiber mat cathodes with PtCo and PtNi powders, using a mixture of Nafion and poly(acrylic acid) as the cathode binder, will be described. These cathodes, with a Pt loading of 0.10 mg/cm2 were incorporated into a fuel cell membrane-electrode-assembly (MEA) with a Nafion 211 membrane and a Pt/C nanofiber anode (0.1 mg/cm2). Short-term fuel cell performance was assessed at 80oC with 100% RH using hydrogen and air at flow rates of 500 and 2,000 sccm, respectively. Power output was compared with an MEA containing conventional painted electrode gas diffusion electrodes, with neat Nafion binder and with Nafion + poly(acrylic acid) binder (same as the nanofibers). The performance of nanofiber MEAs was also examined and contrasted with that of a conventional electrode MEA after an accelerated carbon corrosion voltage cycling experiment, with 1,000 voltage cycles between 1.0 and 1.5V. Representative performance results for a nanofiber MEA with a PtCo cathode catalyst at a loading of 0.10 mg/cm2 are shown in Table 1. Under ambient pressure, the nanofiber morphology consistently provides a 25% improvement in power density at both 0.65V and at maximum power. This effect is even greater under backpressure where the improvement is consistently around a 35% increase in power density at both 0.65 and maximum power. In this case at 0.65V a power density above 1W/cm2 has been achieved. Additional results and analyses will be discussed in the presentation. Acknowledgments This work was funded in part by the National Science Foundation (NSF EPS-1004083) through the TN-SCORE program under Thrust 2. Figure 1

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