(641f) Platinum Reduction in the Cathode of a PEM Fuel Cell with Multiple Catalyst Layers

Bhattacharyya, D., West Virginia University
Srinivasarao, M., Indian Institute of Technology
Rengaswamy, R., Texas Tech University
Narasimhan, S., Indian Institute of Technology

To make the polymer electrolyte membrane fuel cells (PEMFC) commercially viable, further reduction in its cost and improvement in its performance are required. The major cost component of a PEMFC is that of the Pt catalyst. More amount of Pt is typically used on the cathode side because of the sluggish oxygen reduction reaction. In this work, use of multiple catalyst layers (CL) is considered in place of traditionally used single catalyst layer for reduction in Pt loading without deteriorating the cell performance. 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 for minimizing the Pt loading. 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. It has been shown that such layered construction can result in a significant improvement in the cell performance1. In this work, the overall Pt loading is minimized by optimizing the design variables of each of the CLs. The design variables are chosen such that they can be achieved experimentally. For the optimization study, a detailed steady state model of a PEMFC cathode with multiple CLs is developed1,2. 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 CL. The fidelity of the model is also varied to study the effect of modeling various mechanisms on the values of the optimized decision variables. The tradeoff between the cell performance and the Pt loading will also be presented.

1. Srinivasarao,M; Bhattacharyya, D; Rengaswamy, R; Narasimhan, S; Performance analysis of a PEM fuel cell cathode with multiple catalyst layers, International Journal of Hydrogen Energy, doi:10.1016/j.ijhydene.2010.03.092, 2010

2. Srinivasarao,m; Bhattacharyya, D; Rengaswamy, R; Narasimhan, S; Parametric study of the cathode and the role of liquid saturation on the performance of a polymer electrolyte membrane fuel cell ? A numerical approach, Journal of Power Sources, doi:10.1016/j.jpowsour.2010.03.003, 2010