ac Impedance Study of a Proton Exchange Membrane Fuel Cell Stack Under Various Loading Conditions

摘要

This paper presents the ac impedance study and analysis of a proton exchange membranen(PEM) fuel cell operated under various loading conditions. Ballard’s 1.2 kW Nexa™ fuelncell used for this study is integrated with a control system. The PEM fuel cell stack wasnoperated using room air and pure hydrogen (99.995%) as input. Impedance data werencollected for the fuel cell to study the behavior of the stack and groups of cells undernvarious loads. Single cell impedance analysis was also performed for individual cellsnplaced at different locations in the stack. The ac impedance analysis, also known asnelectrochemical impedance analysis, showed low frequency inductive effects and massntransport losses due to liquid water accumulation at high current densities. Results shownthat the stack run time to achieve steady state for impedance measurements is important.nUsing impedance plots, the average Ohmic resistance for the whole stack was estimatednto be 41 mu0001, the same value obtained when summing the resistance value of all individualncells. Impedance analysis for groups of cells at different locations in the stacknshows changes in both polarization resistance and capacitive component only in the lownfrequency region. At high frequencies, single cell inductive and capacitive behavior variednas a function of location in the stack. The effects of artifacts on the high frequencynloop and on the high and low frequency intercept loops are also discussed.