Dictating Pt-Based Electrocatalyst Performance in Polymer Electrolyte Fuel Cells, from Formulation to Application

Timothy Van Cleve, Sunilkumar Khandavalli, Svitlana Pylypenko, Min Wang, Scott Mauger, Michael Ulsh, Kenneth Neyerlin, Anamika Chowdury, Samantha Medina, Karren More, Nancy Kariuki, Deborah Myers, Adam Weber

Research output: Contribution to journalArticlepeer-review

87 Scopus Citations

Abstract

In situ electrochemical diagnostics designed to probe ionomer interactions with platinum and carbon were applied to relate ionomer coverage and conformation, gleaned from anion adsorption data, with O2 transport resistance for low-loaded (0.05 mgPt cm-2) platinum-supported Vulcan carbon (Pt/Vu)-based electrodes in a polymer electrolyte fuel cell. Coupling the in situ diagnostic data with ex situ characterization of catalyst inks and electrode structures, the effect of ink composition is explained by both ink-level interactions that dictate the electrode microstructure during fabrication and the resulting local ionomer distribution near catalyst sites. Electrochemical techniques (CO displacement and ac impedance) show that catalyst inks with higher water content increase ionomer (sulfonate) interactions with Pt sites without significantly affecting ionomer coverage on the carbon support. Surprisingly, the higher anion adsorption is shown to have a minor impact on specific activity, while exhibiting a complex relationship with oxygen transport. Ex situ characterization of ionomer suspensions and catalyst/ionomer inks indicates that the lower ionomer coverage can be correlated with the formation of large ionomer aggregates and weaker ionomer/catalyst interactions in low-water content inks. These larger ionomer aggregates resulted in increased local oxygen transport resistance, namely, through the ionomer film, and reduced performance at high current density. In the water-rich inks, the ionomer aggregate size decreases, while stronger ionomer/Pt interactions are observed. The reduced ionomer aggregation improves transport resistance through the ionomer film, while the increased adsorption leads to the emergence of resistance at the ionomer/Pt interface. Overall, the high current density performance is shown to be a nonmonotonic function of ink water content, scaling with the local gas (H2, O2) transport resistance resulting from pore, thin film, and interfacial phenomena.

Original languageAmerican English
Pages (from-to)46953-46964
Number of pages12
JournalACS Applied Materials and Interfaces
Volume11
Issue number50
DOIs
StatePublished - 18 Dec 2019

Bibliographical note

Publisher Copyright:
© 2019 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-74854

Keywords

  • in situ electrochemical diagnostics
  • ink formulation and processing
  • ionomer coverage
  • oxygen transport resistance
  • Pt/C catalyst inks

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