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The development of Pt-free catalyst for anion exchange membrane fuel cells is limited by the sluggish hydrogen oxidation reaction (HOR) at the anode. Previously, the use of CeO2 as a catalyst promoter facilitated drastic ennoblement of Pd for the HOR kinetics in base media. However, further optimization and understanding of the Pd-CeO2 interaction, surface properties, and its influence on HOR are still needed. In this work, three types of Pd-CeO2/C catalysts are synthesized by a flame-based process, where the Pd-CeO2 interface and HOR activity are improved as compared to catalysts prepared by wet-chemistry processes. The correlation between the Pd-CeO2 interaction and HOR activity is established through comparisons with the three types of Pd-CeO2/C synthesized catalysts using electrochemical techniques and X-ray photoelectron spectroscopy.

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Cationic contamination is known to cause performance degradation and reduced lifetime in polymer electrolyte based electrochemical systems. Calcium is an important cationic impurity due to its prevalence in roadside particulates and as an airborne contaminant. The role of calcium ion (Ca 2+ ) is investigated in-situ by injecting a solution of calcium sulfate (CaSO 4 ) in deionized (DI) water into the cathode of a polymer electrolyte membrane (PEM) fuel cell through a nebulizer. Stability tests are conducted to determine the effects at various current densities with various Ca 2+ concentrations. It is found that 5 parts per million (ppm, molar ratio) eq. Ca 2+ in air is sufficient to lead to high cell performance loss at 1 A/cm 2 as well as severe membrane degradation. Precipitation of CaSO 4 is found at the contact regions between the gas diffusion layers (GDL) and bipolar plates of the cathode at all test conditions. The amount of precipitation becomes sufficient to cause mass transport issues.

The effects of lower equivalent weight ͑EW͒ perfluorosulfonic acid ͑PFSA͒ ionomers and Pt-Co/C catalyst on the cathode performance of proton exchange membrane fuel cells ͑PEMFCs͒ were investigated at two atmospheric pressure operating conditions: low temperature/high relative humidity ͑RH͒, 80°C/100% RH, and high temperature/low RH, 120°C/35% RH. Cell voltage at a current density of 400 mA/cm 2 was used for the performance comparison. The optimized content in the electrode changed with the ionomer EW, from 32% for 1100 EW Nafion, 28% for 920 EW Nafion to 25% for a developmental PFSA 800 EW ionomer. Compared to 1100 EW Nafion, 800 EW ionomer significantly improved the cell performance by 39 mV at 120°C/35% RH; however, at 80°C/100% RH, its effect was not apparent. The introduction of Pt-Co/C catalyst into the cathode increased the cell performance by 43 mV at 80°C/100% RH, which was much higher than a performance improvement at 120°C/35% RH. Compared to electrodes made of Pt/C and Nafion 1100 EW, the combination of 800 EW Ionomer and Pt-Co/C catalyst resulted in a 55 mV cell voltage increase at 80°C/100% RH and a 48 mV cell voltage increase at 120°C/35% RH.In proton exchange membrane fuel cells ͑PEMFCs͒, an effective cathode must provide transport for all involved species for effective oxygen reduction. The three required reactants are protons from the membrane to the catalyst layer, electrons from the current collector to the catalyst layer, and reactant oxygen and product water to and from the catalyst layer and the gas channels. 1 Optimization of PEMFC electrodes was previously described; 2 however, this optimization was targeted for low-temperature PEMFC operation. PEMFCs operated at elevated temperatures ͑Ͼ100°C͒ have a number of advantages. 3,4 However, operation of PEMFCs at high temperature and ambient pressure results in a low RH. The requirements of the cathode structure for two different operation conditions, low temperature/high RH and high temperature/low RH, may be different.Our previous study showed that the catalytic activity for the oxygen reduction increased with an RH increase until 60-70%. 5,6 Above 60-70% RH, the effect of the RH on the catalytic activity was not apparent. The variation of catalytic activity with RH is due to two changes: proton activity and oxide coverage on the platinum surface. 7,8 Higher proton activity accelerates the oxygen reduction reaction; however, increased oxide coverage suppresses oxygen reduction because the reactive sites on the platinum surface are blocked by oxygenated species. 9 To increase the proton activity at high temperature and low RH, low equivalent weight perfluorosulfonic acid ͑PFSA͒ ionomers ͑800 EW and 920 EW͒ were introduced into the electrodes in this study. It was hoped that the increased proton activity could improve the oxygen reduction rate. Some platinum alloys have shown higher activity for oxygen reduction than platinum because the platinum coverage with oxidized species is inhibited by the introduced second metal. 10,11 Carbon-supported P...

An important step in achieving fundamental understanding of fuel cell failure mechanisms and development of technology to mitigate these failures is accomplished by analysis of directed lifetime and failure test results. Several lifetime, accelerated stress, and drive cycle test protocols have been developed and carried out. The two major ASTs that have been developed to evaluate membrane degradation are 1) Open circuit voltage tests, which are designed to accelerate chemical degradation, and 2) Relative humidity cycling tests, which are designed to accelerate mechanical degradation. The results from these tests have been compared to field tests. The ultimate goal is to use the laboratory tests to predict data in the field. An overall predictive decay model is being developed through a combination of specific modeling and tests.

Significant effort has been devoted to reduce the cathode platinum loading for proton exchange membrane fuel cells (PEMFCs). To achieve this, it is imperative to have a comprehensive understanding of the polarization behavior for the low-Pt-loading electrodes, and to reduce the polarization loss due to oxygen transport limitation. Herein, a systematic breakdown of six types of polarization sources is presented to elaborate the effect of cathode Pt loading and the catalyst layer fabrication process. Four modifications are applied to accommodate low cathode Pt loading. GORE PRIMEA catalyst-coated membranes (CCMs) were used as a baseline and tested with 0.4 and 0.1 mg cm −2 cathode Pt loading. A novel electrode fabrication method, reactive spray deposition technology (RSDT), was employed to fabricate 0.1 mg cm −2 Pt loading cathode using Ketjen black carbon as catalyst supports. Non-electrode concentration overpotential is determined by the cathode Pt loading and the type of diffusion medium, while cathode electrode concentration overpotential is determined by the ionomer thin film and ionomer/Pt interface which are dependent on the fabrication process. It is shown that the RSDT process can improve fuel cell performance at 0.1 mg cm −2 cathode Pt loading by reducing the cathode electrode concentration overpotential.