Carbon Loss in the Cathode Catalyst Support of
Proton Exchange Membrane Fuel Cells

Andrew Maslyn
OPT407: Electron Microscopy
Spring 2011
Final Project

Figure 1University of Rochester
Dept. of Chemical Engineering

Figure 1General Motors
Electrochemical Energy Research Lab

Intro to Fuel Cells and Carbon Corrosion
Sample Preparation and Imaging Methods
Thickness Measurement Results and Discussion
Structural Analysis Results and Discussion
References and Acknowledgements

Intro to Fuel Cells and Carbon CorrosionFigure 1

Proton exchange membrane fuel cells are energy conversion devices which harness electrochemistry to convert hydrogen into electrical current.  Due to their high efficiency and zero emission capabilities, they have attracted the interest of automotive companies as replacements to the classical internal combustion engine.  As a result, substantial research has gone into improving performance while decreasing cost and improving durability, and this work continues [4].

A PEM fuel cell is made up of an anode where hydrogen oxidation takes place and a cathode where oxygen reduction takes place.  These two electrodes are separated by a proton exchange membrane which serves two key functions; first, it acts as a medium for the transport of protons from the anode to cathode, and second it creates a barrier to gas cross-over between the two electrodes. A generalized diagram of a PEM fuel cell can be seen to the right along with the reactions which take place at each electrode.

Figure 1

As previously mentioned, durability is a key concern for the commercialization of fuel cell vehicles, specifically electrode voltage performance loss.  The electrode is generally made up of catalyst particles (in most cases platinum) dispersed on a carbon support. The carbon support creates a porous structure for the transfer of gases and water to and from the catalyst sites. It also acts to increase the mass specific surface area of the catalyst, allowing for more effective use of the catalyst.

Performance loss in the cathode is driven mainly by platinum catalyst degradation or carbon support corrosion.  Vehicle start-up, cathode potential cycling, vehicle shut-down and even vehicle off time with air present on the cathode can lead to significant carbon weight loss [3].  Since carbon loss and performance loss are not linearly related, as shown at the left, it is difficult to predict how much carbon loss can be tolerated in the cathode. For this reason carbon weight loss must be understood and mitigated as much as possible in future vehicle systems to ensure performance loss is minimal.




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