International audienceA 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

We report a unique and highly stable electrocatalyst-platinum (Pt) supported on titanium-ruthenium oxide (TRO)-for hydrogen fuel cell vehicles. The Pt/TRO electrocatalyst was exposed to stringent accelerated test protocols designed to induce degradation and failure mechanisms identical to those seen during extended normal operation of a fuel cell automobile-namely, support corrosion during vehicle startup and shutdown, and platinum dissolution during vehicle acceleration and deceleration. These experiments were performed both ex situ (on supports and catalysts deposited onto a glassy carbon rotating disk electrode) and in situ (in a membrane electrode assembly). The Pt/TRO was compared against a state-of-the-art benchmark catalyst-Pt supported on high surfacearea carbon (Pt/HSAC). In ex situ tests, Pt/TRO lost only 18% of its initial oxygen reduction reaction mass activity and 3% of its oxygen reduction reaction-specific activity, whereas the corresponding losses for Pt/HSAC were 52% and 22%. In in situ-accelerated degradation tests performed on membrane electrode assemblies, the loss in cell voltage at 1 A · cm −2 at 100% RH was a negligible 15 mV for Pt/TRO, whereas the loss was too high to permit operation at 1 A · cm −2 for Pt/HSAC. We clearly show that electrocatalyst support corrosion induced during fuel cell startup and shutdown is a far more potent failure mode than platinum dissolution during fuel cell operation. Hence, we posit that the need for a highly stable support (such as TRO) is paramount. Finally, we demonstrate that the corrosion of carbon present in the gas diffusion layer of the fuel cell is only of minor concern.noncarbon catalyst supports | PEFC | start-stop protocol | TiO 2 -RuO 2 | carbon corrosion C arbon has traditionally been the most common material of choice for polymer electrolyte fuel cell (PEFC) electrocatalyst supports (1) due to its low cost, high abundance, high electronic conductivity (30 S · cm −1 ), and high Brunauer, Emmett, and Teller (BET) surface area (200-300 m 2 · g −1 ), which permits good dispersion of the platinum (Pt) catalyst (2-4). The (in) stability of the carbon-supported platinum electrocatalyst is a key issue that currently precludes widespread commercialization of PEFCs for automotive applications. Carbon is known to undergo electrochemical oxidation to carbon dioxide, as shown in Eq. 1. The standard electrode potential for this reaction is 0.207 V vs. standard hydrogen potential (SHE; all potentials henceforth reported vs. SHE, unless otherwise stated). Under normal PEFC operating conditions, the electrode potential is <0.1 V at the anode and between 0.6 V and 0.8 V at the cathode. Despite the fact that the cathode potential is usually significantly higher than the standard potential for carbon oxidation (with an effective overpotential of 0.4-0.6 V), the actual rate of carbon oxidation is very slow due to intrinsic kinetic limitations; in other words, a very low standard heterogeneous rate constant (5).During operation of automotive PEFC stacks, fuel/air ...

A series of electrospun nanofiber mat electrodes with two different commercial Pt/C catalysts and a binder of Nafion and poly(acrylic acid) were fabricated and evaluated. The electrodes were assembled into membrane-electrode-assemblies (MEAs) using Nafion 211 as the membrane. Variations in catalyst type, nanofiber composition (the ratio of Pt/C to Nafion), and fiber diameter had little or no impact on hydrogen/air fuel cell power output. 25 cm 2 nanofiber and sprayed gas diffusion electrode MEAs were compared in terms of beginning of life (BoL) and end of life (EoL) performance after automotive-specific load cycling (Pt dissolution) and start-stop cycling (carbon corrosion) cathode durability protocols. Nanofiber electrode MEAs (0.10 mg/cm 2 Pt loading for the anode and cathode) were clearly superior to sprayed MEAs; they produced more power at BoL and maintained a higher percentage of their power after the carbon corrosion durability protocol, resulting in much higher EoL fuel cell performance. On the other hand, there was no effect of electrode morphology on MEA durability for the Pt dissolution test. The higher MEA power output after carbon corrosion with electrospun electrodes is attributed to better oxygen and water transport within the nanofiber electrode and a higher electrochemical surface area for the fiber cathode. The hydrogen/air proton-exchange membrane fuel cell is a promising candidate for emission-free automotive power plants due to its high power output, efficiency of energy conversion, and quick start-up. The successful integration of a sizable fleet of Electric Vehicles into the transportation sector would greatly diminish localized air pollution and alleviate our dependency on depleting oil reserves. Presently, mass commercialization of fuel cell vehicles is challenging due in large part to issues related to the cost and durability of membraneelectrode-assemblies (MEAs). 1A principal strategy to reduce the cost of MEAs is to minimize the amount of the platinum catalyst in the electrodes without sacrificing power generation. In this regard, recent R&D efforts have been directed at the investigation of platinum metal alloys, 2 core-shell nanostructures, 3 and the use of platinum-free metal-nitrogen-carbon catalysts. 4,5 Although these studies have shown some promise in terms of catalytic activity and potential cost savings, they do not currently meet automotive power density and durability targets.Carbon support corrosion in Pt/C catalysts during fuel cell startup/shut-down is another ongoing issue that has drawn considerable research attention. In particular, when a hydrogen-air mixture is present in the anode during start-up, the cathode potential spikes as high as 1.5 V vs. SHE, resulting in severe carbon corrosion of the cathode catalyst layer. 6 Researchers have worked to mitigate carbon corrosion at the materials level by investigating catalyst that can better withstand the harsh automotive operating environment. Current efforts are focused on metal oxides and thermally treated carbon sup...

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.

High surface area indium tin oxide (ITO) catalyst support materials were synthesized by using co-precipitation method to get uniform and small particle size. Colloidal deposition was used to deposit platinum onto the ITO support. The ITO support demonstrated exceptional electrochemical stability in RDE tests with less than 10% double layer pseudo capacitance loss compared with a 270% change for Vulcan XC-72R carbon under the standard support stability protocol (start-stop). 40%Pt/ITO catalyst showed higher durability than the commercial Pt/C when tested using the support stability protocol. The ECSA change for 40%Pt/ITO was similar to 46%Pt/C (TKK) under catalyst stability protocol (load cycling) but it showed less than 4% ECSA change compared with 40% loss for commercial catalyst under support stability protocol. The baseline mass activities (RDE) for the two catalysts (Pt/ITO and Pt/C) were similar. However, the fuel cell performance in the MEA was very poor for 40%Pt/ITO catalyst and XPS and EDX techniques revealed the formation of indium hydroxide and support degradation upon fuel cell operation, though these modes were not evident upon testing in an RDE.