Transport in Low Pt-Loading Cathodes: The Impact of Electrode and Catalyst Support Morphology

Abstract

This tutorial will focus on recent learning by the polymer electrolyte fuel cell (PEFC) research community on the impact of electrode and catalyst support structure on the transport processes and voltage losses in low Pt-loading cathodes. This includes the porous electrode structure, but also the catalyst support morphology and how carbon supports of varying surface area impact the catalyst utilization and local transport losses. The tutorial will cover the distinct differences between medium surface area supports (e.g., Vulcan carbon black) where the Pt primarily resides on the exterior of the carbon versus high surface area supports (e.g., Ketjen black) that feature a high proportion of internal Pt. The discussion on morphology will include the current understanding of ionomer distributions within the electrode and over the catalyst and support surfaces. The tutorial will also cover the current understanding of oxygen and proton transport mechanisms at the catalyst and support length-scales, with particular attention paid to the transport of reactants through non-electroneutral water domains to the internal catalyst surfaces embedded within the porous carbon support. Maintaining the active surface area and catalytic activity of the catalyst is paramount to achieving good high current density durability, thus the tutorial will also cover aspects of Pt migration and alloying element dissolution that relate to low Pt-loading and catalyst support selection. Figure 1