The water transport and SO 2 crossover in the hybrid sulfur cycle electrolyzer were quantified for a poly͑phenylene͒-based proton exchange membrane and compared to the performance of industry-standard Nafion membranes. While Nafion exhibits good performance, there exists the possibility of a significant SO 2 crossover, which can modify the electrode composition, consume current that should be used for hydrogen production, introduce SO 2 to the hydrogen stream, and result in a loss of sulfur from the system. Recent research has focused on poly͑phenylene͒-based membranes that have exhibited high current density with good stability ͑both chemical and temperature͒ while limiting SO 2 crossover. In this paper, we extend our previous water-transportmodeling work on Nafion membranes to this polymer electrolyte and directly compare the two in terms of electrolyzer performance and SO 2 crossover. We show the ability of poly͑phenylene͒ membranes to operate at elevated temperatures with improved performance over lower temperatures; the high temperature performance exceeds that of Nafion membranes.
We are developing a fuel-cell-integrated approach for enhancing the effectiveness of air-bleed for CO tolerance of hydrogen and reformate polymer exchange membrane fuel cells ͑PEMFCs͒, called the ''reconfigured anode'' ͑RCA͒ ͓F. A. Uribe, J. A. Valerio, F. H. Garzon, and T. A. Zawodzinski,7, A376 ͑2004͔͒. It consists of a small modification to the backing cloth placed on the anode side of each membrane electrode assembly in a stack. A catalyst layer is placed on the gas-feed side of the cloth to catalyze oxidation of CO, utilizing the oxygen introduced in a small air-bleed. The purpose is to enhance the effectiveness of the air-bleed to achieve a high CO tolerance. We synthesized model RCA catalysts based on transition metal oxides, which were characterized using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, thermogravimetric analysis, and Brunauer-Emmett-Teller techniques. Here we present performance data from polarization curves measured on fuel cells with air bleed using these model RCA catalysts. The results indicate that by using an RCA and air-bleed it is possible to raise the CO tolerance of a Pt/C anode to the same level as that of an anode with a Pt-Ru/C catalyst with similar platinum loading and without other means of CO mitigation. The RCA represents a built-in safety net for CO transients, which could be applied to PEMFCs destined to operate on a reformer-derived, hydrogen-rich fuel stream.During the transition to a hydrogen economy, early practical polymer exchange membrane fuel cells ͑PEMFCs͒ for automotive and large stationary applications are expected to operate on reformate, 2 obtained by reforming fuels such as gasoline, diesel, natural gas, or methanol. Assuming cell operation below 100°C, residual carbon monoxide is well known to poison the platinum catalyst surface at levels as low as 10 ppm. 2 For development of PEMFC systems, the CO problem will not be eliminated until totally durable PEMFC systems for operation at 130-160°C and/or economical and green hydrogen production and storage are demonstrated. Although there are major efforts channeled into these areas, it remains of interest what to do about CO mitigation in proven, low-temperature PEMFCs, both for Pt/C and for more tolerant alloys. Under these conditions, the case for on-board reforming of gasoline for automobiles is currently less than compelling, chiefly because of the need for several bulky stages of CO cleanup. In gasoline reforming, relatively simple water gas shift reactors typically achieve a CO level of 5000-10000 ppm. Further reduction in the CO level may require several stages of preferential oxidation ͑PROX͒. The complex processing needed to remove CO to Ͻ10 ppm would have a high capital cost, volume, and weight penalty. Hence, it would be desirable to simplify the required on-board fuel processing. This, in turn, would be aided by raising the limit on CO in reformate feed to fuel cells from 10 ppm by one to three orders of magnitude.In methanol reforming, the amount of CO produced is...
The impact of humidity and temperature on a zinc oxide based transparent conducting oxide (TCO) was assessed under accelerated aging conditions. An in situ electroanalytical method was used to monitor the electrical properties for a conducting zinc oxide under controlled atmospheric (humidity, temperature and irradiation) conditions.A review of thin film photovoltaic (PV) literature has shown one major failure mode of cells/modules is associated with the ingress of water into modules in the field. Water contamination has been shown to degrade the performance of the TCO in addition to corroding interconnects and other conductive metals/materials associated with the module. Water ingress is particularly problematic in flexible thin film PV modules since traditional encapsulates such as poly(ethyl vinyl acetate) (EVA) have high water vapor transmission rates. The accelerated aging studies of the zinc oxide based TCOs will allow acceleration factors and kinetic parameters to be determined for reliability purposes.
Micro-scale aqueous steam reforming of glucose is suggested as a novel method of H 2 production for micro fuel cells. Compact fuel cell systems are a viable alternative to batteries as a portable electrical power source. Compared with conventional lithium polymer batteries, hydrocarbon powered fuel cells are smaller, weigh less, and have a much higher energy density. The goal of this project is to develop a hydrocarbon powered microfuel processor capable of driving an existing microfuel cell, and this interim report provides a summary of the engineering information for microscale reforming of carbohydrates and the summarizes the work completed as of September 2006. Work on this program will continue. Gas analysis of the gas evolved from glucose breakdown using a quadrupole mass spectrometer is now possible due do significant modifications to the vacuum chamber and to the mass spectrometer electronics. Effective adhesion of Pt/Al 2 O 3 to 316SS microstructured catalyst plates is still under investigation. Electrophoretic and dip coat methods of catalyst deposition have produced coatings with poor adhesion and limited available Pt surface area.
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