Sandwich structured membranes greatly increases lifetime of fuel cells

Monday 08 Oct 18

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PhD Defense

Arvind Kannan defended his thesis “Parametric development and durability of HTPEM Fuel Cells” the 24 August at DTU.

Principal supervisor: Professor Jens Oluf Jensen. Co-supervisors: Professor Qingfeng Li and senior researcher Lars Nilausen Cleemann

Examiners: Professor Niels J. Bjerrum, DTU Energy, Senior Engineer Søren Juhl Andreasen, Serenergy A/S, Denmark and Dr. Roswitha Zeis, Karlsruhe Institute of Technology (KIT), Germany.

Arvind Kannan recently defended his thesis. He showed that novel sandwich structured membranes led to a more than three fold enhancement of the durability of High Temperature Proton Exchange Membrane Fuel Cells (HTPEMFC).

Arvind Kannan recently defended his thesis “Parametric development and durability of HTPEM Fuel Cells” at DTU Energy in which he investigated acid transport and leaching pathways from membrane electrode assemblies (MEA) in High Temperature Proton Exchange Membrane Fuel Cells (HTPEMFC).

His aim was to develop materials to mitigate the loss of phosphoric acid – which provides the conductivity of the electrolyte – in the cells, thereby enhancing their durability.

“I showed that acid uptake and distribution in the gas diffusion layers adjoining the electrolyte can play a crucial role in extending the lifetime of HTPEMFC”, said Arvind Kannan.

"I showed that acid uptake and distribution in the gas diffusion layers adjoining the electrolyte can play a crucial role in extending the lifetime of HTPEMFC"
Arvind Kannan at his PhD defense, DTU Energy

Sandwiched membranes

But Arvind not only mapped how the acid is taken up in the gas diffusion layers. He also came up with a new method to counteract the degradation of the eletrolyte which results from the loss of acis. This has made it possible to increase the durability more than three fold.

The achievement was partly made by incorporating acid reservoirs within the membranes, thereby creating novel sandwich structured membranes. This concept showed significantly enhanced durability compared to the commercially available counterparts even with reduced overall thickness.

“The significant improvement in durability can be ascribed to higher acid content of the middle layer coupled with retention capability on the surface layers”, told Arvind Kannan.

Long-term durability of more than 10,000 hours with a degradation rate of less than 3 µVh-1 at 180 °C and 200 mA cm-2 was demonstrated with the sandwiched structured membranes.

Ex-situ better than in-situ

The influence of MEA fabrication factors on performance and applied contact pressure was also studied in the PhD project, and the performance behavior was presented in terms of cell potential and power density data, as a result of increasing cell compression.

“The degree of cell compression controls the gas diffusion layer thickness, contact resistance. Increased compressive force reduces the electrical contact resistance within the cell through improved interfacial contact and reduction of transport layer thickness”, said Arvind Kannan, concluding that cells made from ex-situ hot pressing resulted in a better performance than in-situ fabricated MEAs.

“However, increase of pressure with hot press can make the porosity in the electrodes collapse and lead to unfavorable distribution of acid, which can degrade the long term performance. It is expected that there exists an optimal balance between peak performance and long term durability.”

The studies by the DTU Team on phosphoric acid invasion through pore network modelling are expected to give better insights for further development of gas diffusion layer materials.

“Our test protocol with higher loads can help achieve faster development, and I believe that a multilayered membrane with inorganic phases such as mesoporous silica and alumna should be tried to improve robustness of the sandwiched structure”, said Arvind Kannan

The PhD project “Parametric development and durability of HTPEM Fuel Cells” was carried out in cooperation with Danish Power Systems and the technology group Freudenberg with financial support by the ForskEL program under energinet.dk.

What is HTPEMFC?

A fuel cell converts the chemically bound energy of a fuel directly into electricity. This allows fuel cells to have a higher efficiency than traditional generators and power plants.

At the Department of Energy Conversion and Storage we work on high-temperature polymer electrolyte membrane fuel cells (HT-PEMFC), where the electrolyte is polybenzimidazole doped with phosphoric acid to create ionic conductivity. This makes it possible to operate at above 100 °C since the membrane does not need to be humidified. This fact greatly simplifies both the water management and the thermal management of the system. Another notable advantage of high temperature PEMFC (HT-PEMFC) is the high tolerance towards fuel impurities like carbon monoxide and hydrogen sulphide. These properties make the auxiliary components of the fuel cell system simpler and cheaper. Two promising applications of HT-PEMFC are for transportation and for micro-CHP (combined heat and power) for single houses.

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16 DECEMBER 2018