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Research Papers

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

[+] Author and Article Information
N. V. Dale, M. D. Mann

Department of Chemical Engineering, University of North Dakota, Grand Forks, ND 58202

H. Salehfar, A. M. Dhirde, T. Han

Department of Electrical Engineering, University of North Dakota, Grand Forks, ND 58202

J. Fuel Cell Sci. Technol 7(3), 031010 (Mar 11, 2010) (10 pages) doi:10.1115/1.3207871 History: Received August 07, 2008; Revised February 28, 2009; Published March 11, 2010; Online March 11, 2010

This paper presents the ac impedance study and analysis of a proton exchange membrane (PEM) fuel cell operated under various loading conditions. Ballard’s 1.2 kW Nexa™ fuel cell used for this study is integrated with a control system. The PEM fuel cell stack was operated using room air and pure hydrogen (99.995%) as input. Impedance data were collected for the fuel cell to study the behavior of the stack and groups of cells under various loads. Single cell impedance analysis was also performed for individual cells placed at different locations in the stack. The ac impedance analysis, also known as electrochemical impedance analysis, showed low frequency inductive effects and mass transport losses due to liquid water accumulation at high current densities. Results show that the stack run time to achieve steady state for impedance measurements is important. Using impedance plots, the average Ohmic resistance for the whole stack was estimated to be 41mΩ, the same value obtained when summing the resistance value of all individual cells. Impedance analysis for groups of cells at different locations in the stack shows changes in both polarization resistance and capacitive component only in the low frequency region. At high frequencies, single cell inductive and capacitive behavior varied as a function of location in the stack. The effects of artifacts on the high frequency loop and on the high and low frequency intercept loops are also discussed.

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References

Figures

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Figure 1

Typical Nyquist plot for PEM fuel cell showing all four losses

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Figure 2

PEM fuel cell stack used in the experiments

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Figure 3

Experimental setup for ac impedance study of 1.2 kW PEM fuel cell

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Figure 4

Effect of ac signal amplitude on EIS spectra for 47 cell Nexa™ stack at 10 A dc

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Figure 5

Impedance data recorded at different stack run times for 10 A dc with an ac signal of 10% of dc

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Figure 6

Current dependence of Nyquist plot for the current range from 1 A dc to 15 A dc with an ac signal amplitude of 10% of dc

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Figure 7

Bode magnitude plot for the current range of 1–15 A dc with an ac signal amplitude of 10% of dc

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Figure 8

Current dependence of Nyquist plot for the current range of 20–40 A dc with an ac signal amplitude of 10% of dc

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Figure 9

Bode magnitude plot for the current range of 20–39 A dc with an ac signal amplitude of 10% of dc

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Figure 10

Nyquist plot for group of ten cells at different positions in the stack

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Figure 11

Bode magnitude plot for group of ten cells at different positions in the stack

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Figure 12

Nyquist plot for group of five cells at either end of the fuel cell stack

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Figure 13

Nyquist plot for single cells at different locations in the fuel cell stack

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Figure 14

Bode phase plot for single cells at different locations in the fuel cell stack

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Figure 15

Effect of load connections on high frequency impedance loop

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