Electrochemical Studies on High Durable Carbon Supported Fuel Cell Catalysts

Fuel cell cost reduction demands improved catalyst performance and durability. Platinum (Pt) particle size, crystallite geometry, metal dispersion on carbon support, conductivity, and porosity of the catalyst layer are key features that determine the catalytic activity in fuel cell operating environment. These properties can be controlled by proper design of the catalyst synthesis process with suitable carbon support¹. The fundamental properties of the carbon support can have great influence on fuel cell catalyst at low temperature PEMFC as well as high temperature PAFC systems. Pt catalysts supported on high surface area carbon supports result in smaller Pt crystallites with increased electrochemically active surface area but it results in lower durability due to carbon corrosion. The durability of Pt catalyst at cathode is considered as one of the key challenges for fuel cell system reliability. The major degradation in fuel cell performance is due to loss of electrochemical surface area of Pt catalyst due to carbon corrosion². This phenomenon is attributed to Oswald ripening (Pt particles detached from carbon support to form larger aggregates), which contributes to the loss in fuel cell performance. In the present study we have prepared fuel cell catalysts with three high durable carbon (HDC) supports with varying surface areas and graphitization. The carbon corrosion behavior of catalysts was studied using cyclic voltammetry. With high durable carbon support, optimization of electrode structure with PTFE binder is crucial for improved performance and to mitigate carbon corrosion. The electrodes are prepared with different loadings of PTFE content and characterized by measuring electrochemical surface area and linear sweep voltammetry (Figure 1). The carbon corrosion experiments are conducted in 0.5M H₂SO₄ by sweeping the voltage from 0.4 to 1.0 using Ag/AgCl as reference electrode. After every 1000 cycles, electrochemical surface area is measured (Figure 2). An optimum surface area and graphitization is required to balance the performance and durability.

Reference:

1. Chunzhi He, Sanket Desai, Garth Brown, and Srinivas Bollepalli, The Electrochemical Society Interface, 41-45, Fall 2005.
2. R. Borup, J. Meyers, B. Pivovar, Y.S. Kim, R. Mukundan, N. Garland, D. Myers, M. WilSon, F. Garzon, and D. Wood, Chem. Rev., 107, 3904 (2007)