Analysis of models for carbon monoxide poisoning of high performance membrane electrode assemblies in proton exchange membrane fuel cells.

摘要

Rate constants for H2 and CO oxidation were estimated for predicting rates of CO poisoning in a Proton Exchange Membrane Fuel Cell (PEMFC) with high performance Membrane Electrode Assemblies (MEAs). These estimates were determined from a regression to anode overpotential data collected at 70 and 90°C. The Langmuir isotherm model for homogenous adsorption was used for the CO adsorption equilibrium and the Heyrowski-Volmer mechanism for H2 oxidation on a Pt/Ru-C catalyst. The parameters estimated from this work will be used for predicting rates of CO poisoning and recovery on these high performance MEAs.; Recent data for CO poisoning and recovery determined at 70°C, 101 kPa and 70 and 90°C, 202 kPa were modeled with transient surface balance equations. This transient model consists of an anode overpotential transient equation which accounts for the change in anode overpotential with CO coverage as well as transient response of the system to CO during poisoning and recovery. The CO adsorption coefficient as well as the density of catalysis sites was estimated from a best fits to the recovery data.; Rate constants for H2 and CO oxidation by O2 during air-bleed were estimated from previously published anode overpotential results. These estimations were achieved through a best fit of current density expressions derived from a series of case studies described in detail below. This work was motivated by observed lack of recovery in cell performance at high CO concentrations (ex. 10,000 ppm CO/H2) even when up to 15% air-bleed was employed. The O2 adsorption step in the CO oxidation process was studied by varying the oxidation parameters which revealed favorable results when taking it as the rate limiting step.; Finally Regional Analysis was used to determine the adsorption properties for CO on Pt-C and Pt/Ru-C directly from anode polarization data from a PEMFC. The information generated from this method allows for the study of various adsorption isotherm models for the homogeneous adsorption of CO and also the estimation of their respective isotherm parameters including the adsorption energy. In this work, the CO isotherm parameters were provided for the analysis of both metals in the alloy. Also a proposed model for CO oxidation on a Pt/Ru-C electrode was proposed.