(354d) The Impact of Inorganic Electrocatalyst Surface Ligands on Humidification Requirements in Operating Proton Exchange Membrane Fuel Cells

Despite significant advances in the development of electrocatalysts with unprecedented Pt mass-specific electrocatalytic activity, the high cost of this precious metal remains an obstacle to proton exchange membrane fuel cell (PEMFC) fuel cell commercialization. A primary reason for this is that high-power applications drive thermodynamic irreversibilities beyond the catalytically-driven reaction kinetics associated with fundamental benchtop screening studies. Key among these irreversibilities is the transport of product liquid water that can obstruct gaseous reactant access to the electrocatalyst yet is at the same essential to membrane proton transport. Unlike industrial PEMFC, fundamental benchtop studies employ reagents dissolved in liquid electrolytes.

In this work, we address the question of how the interfacial chemistry of electrocatalyst nanoparticles used in electrodes can influence water management in industrial PEMFC. Our work employs both carbon supported and unsupported (carbon free) platinum-bismuth alloy nanoparticles (PtBi NP) since these have been shown to exhibit superior oxygen reduction reaction (ORR) activity and durability in fundamental benchtop investigations. For example, after 10000 potential cycles in accelerated durability testing, the PtBi NP demonstrate no degradation in mass activity, half-wave potential, Tafel slope and electrochemical surface area (ECSA). We employ a unique inorganic redox synthesis scheme to introduce hydrophilic stannous chloride ligands onto the surface of these nanoparticles with a well-characterized structure and charge density. Alloy nanoparticle surface hydrophilicity is shown to be key to optimizing the humidification and performance of an operating low temperature hydrogen-air PEMFC while maintaining durability at 25 cm2 scale.