Investigation of the Effect of Airborne Contaminants on PEM Fuel Cell Stack Performance and Degradation Using Electrochemical Impedance Spectroscopy, AVL Thda™ and FTIR Gas Analyzer

Abstract

Air pollution is still a bitter truth in many locations in the world. In highly populated regions like metropolitan areas as well as in agricultural areas there are various airborne contaminants which can be harmful to organisms. Also fuel cells, especially PEMFC are sensitive to airborne contaminants.In most mobile and stationary PEM fuel cell systems, ambient air is used as oxidant gas at the cathode of the fuel cell. It is cost and weight saving because there is no need to install additional tank for pure oxygen and to refill it, but the performance of fuel cell can suffer beyond the oxygen gain from airborne contaminants, which also have the potential to accelerate degradation. To prevent that airborne contaminants reach the fuel cell cathode, air filter systems consisting of particle filter and additional activated carbon filter are installed at the cathode inlet.The focus here is on the investigation of the use of AVL THDAtm method to detect effects of airborne contaminants. THDA (total harmonic distortion analysis) is a patented online fuel cell monitoring method based on analyzing harmonic distortion effects of voltage drifts instead of single cell voltage measurement. So far it was successfully demonstrated for the detection of water issues like flooding and drying, and for low media supply issues on both cathode and anode side [1, 2].For the development and validation of the method, experiments with a PEMFC stack are going to be done on a fuel cell testbed equipped with an AVL X-Ion impedance analyzer. Specific air pollutant gases ammonia (NH3), sulfur dioxide (SO2) and nitrogen oxides (NOx) are going to be mixed into the cathode air in the ppb range. Their effects on PEMFC stack performance are going to be investigated with electrochemical impedance spectroscopy (EIS) and total harmonic distortion analysis. The cathode exhaust gas is also going to be analyzed by an FTIR gas analyzer.It is planned to test the PEMFC stack under different operating conditions, with various parameters and different cathode gas mix ratios while monitoring possible conversion of impurities via FTIR and the stack state of health using THDA and conventional technologies to understand the link between the effect of airborne contaminants on fuel cell stack performance, on its lifetime and to determine possible early indicators in the THDA signals.