Characterization of Potential Catalysts for Carbon Monoxide Removal from Reformate Fuel for PEM Fuel Cells
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Characterization of Potential Catalysts for Carbon Monoxide Removal from Reformate Fuel for PEM Fuel Cells
Peter A. Adcock, Eric L. Brosha, Fernando H. Garzon, and Francisco A. Uribe Materials Science and Technology Division, Los Alamos National Laboratory Los Alamos, NM 87545, USA ABSTRACT We are developing a fuel-cell-integrated system for enhancing the effectiveness of an air-bleed for CO-tolerance of hydrogen and reformate PEM fuel cells, with minimal increase in stack cost or specific volume. This is called the reconfigured anode (RCA) system [1]. We report here on properties of several potential catalysts for this system. The materials were characterized by X-ray powder diffraction (XRD), energy dispersive X-ray spectrometry (EDS), and thermal analysis techniques. Surface area was determined using the Brunauer-Emmett-Teller (BET) technique. The XRD results were interpreted using full-profile analysis. In ongoing work, reactivity with CO is being quantified under various conditions, using gas chromatographic (GC) analysis. The results are discussed in terms of effects of the presence of an RCA catalyst on fuel cell performance, using a small air-bleed.
INTRODUCTION Practical PEM fuel cells for automotive and large stationary applications are expected to operate on reformate, obtained by reforming gasoline, diesel, natural gas, or methanol fuels. A very troublesome impurity in reformate is residual carbon monoxide, CO, which poisons the platinum catalyst surface [2]. CO is still present at a significant level even if water gas shift and preferential oxidation reactors are included. In the on-board reformate production option, complex processing to remove CO would have a high capital cost, volume and weight penalty. To improve the CO-tolerance of Pt-catalyzed anodes, Los Alamos National Laboratory is developing the reconfigured anode (RCA) system for in-cell CO conversion without a significant increase in stack volume or cost. This system relies on adding a small air-bleed to the humidified anode gas stream. We reported previously that oxides of metals having two stable, low oxidation states showed promise for CO removal from hydrogen and reformate streams at 80 ˚C [1]. Oxides of Co, Fe, and Cu were studied most extensively, and there was interest also in the manganese based cryptomelane KMn8O16 with potassium exchanged by cobalt [3]. This paper now presents a characterization of some of these catalyst materials as tested in fuel cell experiments.
EXPERIMENTAL Catalyst Preparation The acetate decomposition method was reported previously [1] for carbon-supported copper oxide. The mixing ratios and firing temperatures, Tmax, for each catalyst are given in Table 1. The method for ink preparation was reported previously [1]. The preparation of cryptomelanes was based on a literature method [4] with the following modifications. Sulfuric acid was substituted for nitric acid. Cobalt(II) sulfate was used in place of cobalt(II) nitrate.
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Table 1. Details of Preparation of Each Supported Catalyst Meta
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