Toward Optimizing Electrospun Nanofiber Fuel Cell Catalyst Layers: Polymer-Particle Interactions and Spinnability

Michael Ulsh, Sunilkumar Khandavalli, Nisha Sharma-Nene, Sadia Kabir, Samrat Sur, Jonathan Rothstein, Kenneth Neyerlin, Scott Mauger

Research output: Contribution to journalArticlepeer-review

14 Scopus Citations

Abstract

We investigate the effect of the poly(acrylic acid) (PAA) carrier polymer concentration on the microstructure and rheological properties of catalyst inks for electrospun polymer-electrolyte membrane fuel-cell catalyst layers. Characterization of an ink microstructure using oscillatory shear rheology showed that the catalyst particles (platinum on carbon) are significantly agglomerated in the absence of PAA or an ionomer. Both the ionomer and PAA promoted the stability of the particles against agglomeration via electrosteric stabilization by adsorbing onto the particle surface. Increasing the PAA concentration increased the stability of the particles (or reduced the agglomerated structure) due to increasing PAA coverage onto the free surface area of the particles. However, beyond a certain increase in concentration, PAA was found to predominantly remain as an excess free polymer in the ink due to an insufficient free/available surface area on the particles for further PAA coverage. Extensional rheology measurements demonstrated that PAA enhances the extensional viscosities of the inks. Consequently, increasing the PAA concentration in the ink promoted the evolution of uniform nanofibers. However, beyond a certain concentration, a significant increase in the shear viscosities of the inks led to defective fiber morphologies because of the onset of flow instabilities. Electrochemical performance comparisons between catalyst layers with different PAA concentrations showed maximum performance at the PAA concentration that led to the least agglomerated structure of the catalyst, most uniform fiber morphologies, and low concentrations of free (non-adsorbing) PAA in the electrode. These results provide a rationale for optimization of electrospun catalyst nanofibers for both spinnability and electrochemical performance.

Original languageAmerican English
Pages (from-to)2374-2384
Number of pages11
JournalACS Applied Polymer Materials
Volume3
Issue number5
DOIs
StatePublished - 14 May 2021

Bibliographical note

Publisher Copyright:
© 2021 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-79228

Keywords

  • catalyst inks
  • electrospinning
  • extensional rheology
  • fuel cells
  • nanofibers
  • poly(acrylic acid)

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