Transition Metal Oxides as Reconfigured Fuel Cell Anode Catalysts for Improved CO Tolerance: Polarization Data

Abstract

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...

A review of performance degradation and failure modes for hydrogen-fuelled polymer electrolyte fuel cells

“…In another method, oxygen is bled into the H 2 feed in order to oxidize CO to CO 2 before it reaches the anode catalyst layer [31]. A more recent method includes the use of a 'reconfiguration anode', where a catalytic material which uses cobalt, iron, and copper is applied to the gas-facing side of the anode GDL to oxidize the CO in the fuel feed before it permeates into the anode catalyst layer [32]. A comprehensive review of articles discussing PEFC contamination to date has been carried out by Cheng et al [33].…”

Transient behavior of CO poisoning of the anode catalyst layer of a PEM fuel cell

“…Greek letters ε porosity η overpotential (V) θ CO coverage ratio of CO on Pt catalyst site θ H coverage ratio of hydrogen on Pt catalyst site ξ molar area density of Pt catalyst sites (C cm −2 ) φ potential (V) Subscripts CO carbon monoxide H 2 hydrogen gas ss steady state Superscripts in inlet at catalyst layer (z = 0) 0 initial state use of a precious metal, some researchers adopted some methods to restore the cell performance during the operation process, including oxidant-bleeding [14][15][16], self-oxidation [2,17], and current-pulsing [17,18]. In theoretical studies, Springer et al [19] derived a mathematical model to describe CO adsorption, desorption and charge fluxes on the Pt catalyst site.…”

Components for PEM Fuel Cells: An Overview

“…In this context, several approaches have been attempted to reduce the CO poisoning [104][105][106]. [117].…”