Influence of Anode Flow Rate and Cathode Oxygen Pressure on CO Poisoning of Proton Exchange Membrane Fuel Cells

Abstract

The anode flow rate of a proton exchange membrane ͑PEM͒ fuel cell involving Pt anode electrocatalyst is found to strongly influence the single cell performance when H 2 containing trace amounts of CO is used as the feed. The performance drops dramatically due to CO poisoning as the anode flow rate increases until a large overpotential is reached when it levels off. This effect of the flow rate on the extent of poisoning is found to be reversible and is explained as depending on the actual concentration of CO in the anode chamber which in turn depends on the feed content, the flow rate, and CO oxidation kinetics on Pt. Further, it is found that oxygen permeating across the PEM from the cathode side also appreciably affects the anode overpotential by providing another route for CO oxidation. A CO inventory model is provided that explains the observed phenomena in a PEM fuel cell operating with H 2 /CO as anode feed and a cathode feed with different oxygen pressures.Proton exchange membrane ͑PEM͒ fuel cells power plants for stationary and mobile applications are planned to be operated on reformate gas feed that would inevitably contain trace amounts of CO. 1,2 Extensive investigations have been performed to evaluate the CO tolerance of the PEM fuel cells with different electrocatalysts and under different conditions. It has been reported that the fuel cell temperature and CO content of the gas mixture are the key parameters that determine the performance of a given catalyst. 3-8 The poisoning effect of CO has also been investigated in electrochemical cells incorporating liquid electrolytes such as H 3 PO 4 or H 2 SO 4 . 9-12 These investigations provide much insight into the effect of CO poisoning on the performance of PEM fuel cells. The present work is motivated by our desire to systematically study the mechanisms and kinetics of standard fuel cell catalyst, such as Pt and PtRu, at real PEM fuel cell conditions. During the study of CO poisoning on PEM fuel cell performance with Pt anode catalyst, we found the strong influence of certain operating parameters, namely the anode flow rate and cathode oxygen partial pressure, which have not so far been documented.The performance of a single fuel cell is normally studied in the laboratory under a constant flow rate or stoichiometry. Though PEM fuel cell anodes fed with pure H 2 are often operated near a stoichiometry of one, reformate gas mixtures from catalytic reformers require higher flow rates, because considerable amounts of CO 2 and N 2 are also present in the gas mixtures, with H 2 concentrations ranging from 40 to 75% depending upon the reforming system and specific process. 13 It is shown in this work that the anode flow rate and cathode oxygen partial pressure are very important operating parameters influencing the extent of CO poisoning when operating with a feed containing essentially pure H 2 along with trace amounts of CO. We report here for the first time, experimental results on the effect of anode flow rate and cathode oxygen partial pressure on the per...

Complex Oscillatory Response of a PEM Fuel Cell Fed with H[sub 2]/CO and Oxygen

“…The decrease due to the presence of CO is smaller than that found in a pure platinum catalyst. 39 The decrease in this case, however, is not monotonic; instead, an oscillatory response sets in and the cell voltage switches between two limits. As the cell current increases, these two limits decrease accordingly.…”

Electrochemical Impedance Spectroscopy (EIS) Characterization of Reformate-operated High Temperature PEM Fuel Cell Stack

“…Degradation due to CO is mainly associated with reduced free reaction sites due to its adsorption on the Pt electrode surface [6,17,21]. It is an effect that can be reversed after reconditioning of the stack [44]. However, prolonged exposure to CO may cause irreversible degradation [11].…”

Effect of Fuel Impurities on Fuel Cell Performance and Durability

“…This model has been extended and modified several times by o ther researchers. [22][23][24] Meanwhile, the transient process of poisoning in a hydrogen/oxygen fuel cell has also been experimentally studied using cell polarization measurements. [25][26][27] Wang et.…”