Transient carbon monoxide poisoning kinetics during warm-up period of a high-temperature PEMFC – Physical model and parametric study

Abstract

This paper investigates the anode electrokinetics during the start-up or warm-up period of a high-temperature proton exchange membrane fuel cell (HT-PEMFC) from a temperature above 100°C, to the desired temperature of 180°C, where carbon monoxide (CO) contaminated hydrogen (H2) is used as the fuel. The heating strategy considered in this study involves an initial heating of the HT-PEMFC by an external source to a temperature above 100°C, after which current is drawn, where electrochemical reaction heating is expected to contribute to the heating process. Thus, a numerical transient three-dimensional model is derived addressing the anode electrokinetics under a specific temperature increase rate during the warm-up process. Operational parameters such as temperature increase rate, initial start-up temperature, CO volume fraction and extracted current density are varied and their effects on the CO and hydrogen coverage fractions on the electrode, the anode overpotential and the cell potential with respect to time, are studied. The results indicate that parameters such as temperature increase rate, initial start-up temperature, CO volume fraction and extracted current density would significantly affect the anode overpotential and the cell potential. Specifically, it is critical to reduce the extracted current density and CO volume fraction, and increase the temperature increase rate, to avoid a sudden shoot up of the anode overpotential that can result in the premature shutdown of the fuel cell. Having a low initial start-up temperature does result in a higher base value of the anode overpotential. The results also indicate that if the fuel cell reaches 130±5°C before the anode overpotential is overly high, then the fuel cell would not shut down prematurely due to the high anode overpotential.