Impact of Pt spatial distribution on the relative humidity tolerance of Pt/C catalysts for fuel cell applications.

The distribution of platinum group metal (PGM) nanoparticle catalysts throughout the porous structure of the carbon support has been widely reported to have a significant impact on the performance of the catalyst. For catalysts having Pt primarily on the outer surface of the carbon, low mass activity but excellent performance at high current densities is often observed. Conversely, when Pt is deposited within the pores of the carbon, high mass activity but poor performance at high current density is observed. This relationship has been well studied, and the mechanism has been clearly elucidated. A key method in the literature to study Pt distribution has been the 'Pt accessibility' tests, which are based on monitoring roughness factor (cm2Pt/cm2 membrane electrode assembly (MEA)) vs. relative humidity (RH). While these tests have now been correlated with performance, most of the polarization testing during these studies is performed under one single RH condition. In this work, the relationship between Pt spatial distribution and RH tolerance is probed to gain further insight into how the materials-level properties of the catalyst impact MEA-level characteristics. This work provides an additional design tool that can be used by MEA designers when selecting catalysts for their specific application. [Display omitted] • Study of relative humidity tolerance as a function of Pt spatial distribution. • New mechanism proposed to explain the relative humidity/performance relationship. • Recommendations provided for the design and selection of Pt/C catalysts. [ABSTRACT FROM AUTHOR]