Investigation of catalytic vs reactant transport effect of catalyst layers on proton exchange membrane fuel cell performance

- Evaluated catalytic (kinetic) vs mass diffusion effect on fuel cell performance.
- Better cell performance for catalyst layers with lower mass diffusion resistivity.
- Not necessarily better cell performance for better catalyst kinetic characteristics.
- Lower mass diffusion resistivity for catalyst layers made by spraying technique.
- Demonstrated the importance of diffusion effect, hence the catalyst layer structure.

For proton exchange membrane fuel cells (PEMFC), the importance of catalytic (kinetic) effect is widely recognized with less attention being paid to mass transport (diffusion) effect. In this study, the importance of kinetic and diffusion effect on PEMFC performance is investigated experimentally by using different catalysts and catalyst layer (CL) fabrication methods of spraying and brush-painting, both of which are commonly used, simple and low-cost with volume-production capability. It is found that as a catalyst, 20% Pt/C has better kinetic characteristics than 60% Pt/C in terms of smaller Pt particle size, better Pt dispersion, less Pt agglomeration, and larger active surface area. For the same Pt loading, the porosity is almost identical for the CLs made of the two catalysts by the two fabrication methods, but the diffusion resistivity for the CLs made of 60% Pt/C is smaller than its counterpart for the CLs made of 20% Pt/C, due to difference in the effective diffusion coefficient and CL thickness. As a result, the performance of the PEMFC made of 60% Pt/C is better than the corresponding PEMFC made of 20% Pt/C. Similarly, for PEMFCs made of the same catalyst, the diffusion resistivity is smaller for CLs made by spraying compared with brush-painting method, leading to better performance for the PEMFC made by spraying method. These results highlight the importance of diffusion effect, hence the structure of the CLs, in determining the PEMFC performance.