Online Carbon Corrosion Analysis of a Novel, Alloyed PtTi/C in PEM Fuel Cells Using a Non-Dispersive-Infrared System
Authors: Merzdorf Thomas , Kühl Stefanie , Herzog Antonia , Strasser Peter 
Published: February 2020

Moving on from a fossil fuel based society towards renewable energies presents many difficulties, which need to be addressed by researchers and industries. Hydrogen production, storage and usage will take a big role in the economy of the future and electrolyzer as well as fuel cells are the focal point of a hydrogen based economy.[1-2] In this work, we will focus on the durability of fuel cell catalysts, which is one of the most severe problems. The catalyst, consisting of platinum based nanoparticles on a carbon based support, is degrading in different manners during his lifetime. For the active area, the platinum or platinum alloy nanoparticles will suffer through Ostwald ripening, agglomeration in general, particle movement and detachment from the support.[3] The carbon support corrodes while being exposed to higher potentials.[4-5] Thus, potential control in fuel cell devices in combination with more stable materials are crucial for the success of fuel cells in future technologies. A focus of the research is the modification of carbon support materials, to enable improved attachment of the nanoparticles on the support and to prevent carbon corrosion, which increases the stability especially at high potentials. New measurement strategies are required, which enable the identification of the occurring processes in the fuel cell and provide a deeper insight into degradation mechanisms.
Testing different carbon supported catalysts based on the DOE support degradation protocol gives first insights in the stability of the carbon. However, since multiple degradation processes happen at potentials above 1 V as mentioned above, further online analysis is needed to identify the degradation of the MEA based on corroding carbon.
Herein, we present measurements performed with a fuel cell test stand equipped with an ND-IR, which is connected to the cathode exhaust. Therefore, this setup allows for online quantification of CO and CO2 in the exhaust gas stream. Figure 1 shows the results obtained with an AST based on a DOE protocol for support degradation. Several characteristic features are observable. On the first sight, the eight air polarization curves are visible with increased oxygen amount. Furthermore, sharp CO and CO2 peaks are predominantly visible during the cycling under nitrogen. The measured and calculated amount of carbon has multiple possible origins: the support, the ionomer, the membrane, the gas diffusion layers, the flow fields and the tubing of the test stand. From blank tests we concluded, that the signal is from the carbon support and the ionomer. Integrating the signal gives a calculated amount of 1.6 mg carbon. On the MEA, a total of 3.72 mg carbon support is situated on the cathode side.
Our goal is to obtain a deeper understanding of the carbon corrosion processes occurring during fuel cell testing. Therefore, we show the degradation of different carbon supports. Changing the ionomer content gives us the opportunity to calculate the contribution of the ionomer during the degradation. Furthermore, post mortem cross section SEM analysis provides microscopic insight in the changes happening during the AST such as film thickness and particle distribution. Combining the better understanding of the degradation of carbon supports with new Pt based nanocatalysts will provide active and stable fuel cell catalysts to further move into the hydrogen society.

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Figure 1: Data obtained from an AST performed with our fuel cell test stand (10 cm², 0.15 mg Pt/cm²) equipped with an ND-IR. The graph shows the results of the DOE protocol for support degradation (5000 cycles, 1.0 – 1.5 V, polarization curves between cycling)

Figure 1