am8b15039_si_001.pdf (171.65 kB)
Rheological Investigation on the Microstructure of Fuel Cell Catalyst Inks
journal contribution
posted on 2018-12-09, 17:13 authored by Sunilkumar Khandavalli, Jae Hyung Park, Nancy N. Kariuki, Deborah J. Myers, Jonathan J. Stickel, Katherine Hurst, K. C. Neyerlin, Michael Ulsh, Scott A. MaugerWe present a rheological investigation
of fuel cell catalyst inks. The effects of ink parameters, which include
carbon black-support structure, Pt presence on carbon support (Pt–carbon),
and ionomer (Nafion) concentration, on the ink microstructure of catalyst
inks were studied using rheometry in combination with ultrasmall-angle
X-ray scattering (USAXS) and dynamic light scattering (DLS). Dispersions
of a high-surface-area carbon (HSC), or Ketjen black type, demonstrated
a higher viscosity than Vulcan XC-72 carbon due to both a higher internal
porosity and a more agglomerated structure that increased the effective
particle volume fraction of the inks. The presence of Pt catalyst
on both the carbon supports reduced the viscosity through electrostatic
stabilization. For carbon-only dispersions (without Pt), the addition
of ionomer up to a critical concentration decreased the viscosity
due to electrosteric stabilization of carbon agglomerates. However,
with Pt–carbon dispersions, the addition of ionomer showed
contrasting behavior between Vulcan and HSC supports. In the Pt–Vulcan
dispersions, the effect of ionomer addition on the rheology was qualitatively
similar to Vulcan dispersions without Pt. The Pt–HSC dispersions
showed an increased viscosity with ionomer addition and a strong shear-thinning
nature, indicating that Nafion likely flocculated the Pt–HSC
aggregates. These results were verified using DLS and USAXS. Further,
the observations of the effect of ionomer:carbon ratio and a comparison
between carbons of different surface areas provided insights on the
microstructure of the catalyst ink corresponding to the optimized I/C ratio for fuel cell performance reported
in the literature.