Performance analysis of a PEM fuel cell cathode with multiple catalyst layers

The cathode catalyst layer (CL) of a PEM fuel cell (PEMFC) plays an important role in the performance of the cell because of the rate limiting mechanisms that take place in it. For enhancing the performance of a PEMFC, the use of multiple, ultra thin CLs instead of a single CL is considered in the present work. Since the concentration of oxygen decreases in a CL from the diffusion medium-CL interface towards the polymer membrane, the CL adjacent to the diffusion medium should be of higher porosity than the other CLs. Similarly, the CL adjacent to the polymer membrane should contain more ionomer than the other CLs. Furthermore, liquid water should be removed without causing significant mass transport and/or ohmic losses. Therefore, the design parameters of a CL can be varied spatially to minimize losses in a PEMFC. However, such a continuously graded CL is difficult to manufacture due to lack of commercially available techniques and associated costs. As an alternative, a combination of layers can be synthesized where each layer is manufactured with different design parameters. This approach provides the opportunity to optimize the design parameters of each layer. With this objective in mind, a detailed steady state model of a PEMFC cathode with multiple layers is developed. The model considers liquid water in all the layers. The catalyst layer microstructure is modeled as a network of spherical agglomerates. For improved water management, a thin micro-porous layer is considered between the gas diffusion layer (GDL) and the first catalyst layer. The performance curves for various combinations of the design parameters are shown and the results are analyzed. The results show that there exists an optimum combination of design parameters for each catalyst layer that can significantly improve the performance of a PEMFC.