Research Papers

Effect of Membrane Electrode Assembly Bonding Technique on Fuel Cell Performance and Platinum Crystallite Size

[+] Author and Article Information
Steven Buelte

Research Scientist
Center for Automation Technologies and Systems,
Rensselaer Polytechnic Institute,
110 8th Street,
Troy, NY 12180
e-mail: Steve.buelte@gmail.com

Daniel Walczyk

Professor of Mechanical Engineering
Center for Automation Technologies and Systems,
Rensselaer Polytechnic Institute,
110 8th Street,
Troy, NY 12180
e-mail: walczd@rpi.edu

Ian Sweeney

Center for Automation Technologies and Systems,
Rensselaer Polytechnic Institute,
110 8th Street,
Troy, NY 12180
e-mail: ian.swy@gmail.com

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF FUEL CELL SCIENCE AND TECHNOLOGY. Manuscript received May 8, 2013; final manuscript received August 4, 2013; published online January 2, 2014. Editor: Nigel M. Sammes.

J. Fuel Cell Sci. Technol 11(3), 031002 (Jan 02, 2014) (10 pages) Paper No: FC-13-1046; doi: 10.1115/1.4025525 History: Received May 08, 2013; Revised August 04, 2013

Major efforts are underway to reduce fuel cell manufacturing costs, thereby facilitating widespread adoption of fuel cell technology in emerging applications, such as combined heat and power and transportation. This research investigates new methods for fabricating membrane electrode assemblies (MEAs), which are at the core of fuel cell technology. A key manufacturing step in the production of fuel cell MEAs is bonding two electrodes to an ionically conductive membrane. In particular, new MEA bonding methods are examined for polybenzimidazole-based phosphoric acid (PBI/PA) fuel cells. Two new methods of bonding PBI/PA fuel cell MEAs were studied with the goal of reducing cycle time to reduce manufacturing costs. Specifically, the methods included ultrasonic bonding and thermally bonding with advance process control (APC thermal). The traditional method of thermally bonding PBI MEAs requires 30 seconds, whereas the new bonding methods reduce the cycle time to 2 and 8 seconds, respectively. Ultrasonic bonding was also shown to significantly reduce the energy consumed by the bonding process. Adverse effects of the new bonding methods on cell performance and structure were not observed. Average cell voltages at 0.2 A/cm2 for ultrasonic, APC thermal, and thermally bonded MEAs were 650 mV, 651 mV, and 641 mV, respectively. The platinum crystallite size was found to be the same before and after ultrasonic bonding using XRD. Furthermore, changes in the electrode pore structure were not observed in SEM images taken after ultrasonic bonding. The test results show that it is possible to reduce manufacturing costs by switching to faster methods of bonding PBI phosphoric acid fuel cell MEAs.

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Fig. 1

Conceptual diagram of MEA bonding

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Fig. 2

Fixture and process for aligning MEA subcomponents

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Fig. 3

The thermal bonding process, where MEAs are thermally pressed at 140 °C for 30 seconds to 75% of the combined starting thickness of the subcomponents

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Fig. 4

Ultrasonic bonding system. A pneumatic cylinder drives the anvil up to compress the MEA between the horn and the anvil. The convertor, booster, and horn assembly vibrates vertically at 20 kHz, causing rapid heating of the MEA material interfaces.

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Fig. 5

APC thermal bonding apparatus

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Fig. 6

Cell hardware and serpentine gas flow fields: two-channel anode flow field (left) and three-channel cathode flow field (right)

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Fig. 7

The Ohmic loss is added to the cell voltage at each current density to remove this loss from the V/I curve. The Ohmic loss is calculated by multiplying the impedance measured at 1000 Hz by the corresponding current.

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Fig. 8

Electrochemical parameter extraction form Ohmic loss corrected V-log(I) plots for a cell operated on air and oxygen

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Fig. 9

Effect of incomplete Ohmic loss correction on a V-log(I) plot

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Fig. 10

Effect of electronic shorts (low electronic resistance) on the Tafel slope. The table on the figure shows calculated Tafel slopes based on measured baseline slope of 95 mV/decade and an assumed range of electronic shorting resistances.

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Fig. 11

XRD data acquired before and after ultrasonic and thermal MEA bonding shows no change in crystallite size. The platinum (111) peak is seen between 38° and 44°. The intensity is not normalized on the plot on the left and is normalized by a factor of 1.02, 1.05, and 1.07 for the 2000-J ultrasonic, 5000-J ultrasonic, and thermally bonded electrodes, respectively.

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Fig. 12

SEM images taken before (left) and after (right) ultrasonic bonding




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