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

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 catalystmore » 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.« less

Authors:

Khandavalli, Sunilkumar  ^[1];

• Search DOE PAGES for author "Khandavalli, Sunilkumar"
• Search DOE PAGES for ORCID "0000-0003-3179-5718"

Sharma-Nene, Nisha ^[1]; Kabir, Sadia ^[1]; Sur, Samrat ^[2]; Rothstein, Jonathan P. ^[2]; Neyerlin, Kenneth C.  ^[1];

• Search DOE PAGES for author "Neyerlin, Kenneth C."
• Search DOE PAGES for ORCID "0000-0002-6753-9698"

Mauger, Scott A.  ^[1];

• Search DOE PAGES for author "Mauger, Scott A."
• Search DOE PAGES for ORCID "0000-0003-2787-5029"

Ulsh, Michael  ^[1]

• Search DOE PAGES for author "Ulsh, Michael"
• Search DOE PAGES for ORCID "0000-0003-3725-8032"

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+ Show Author Affiliations

1. National Renewable Energy Lab. (NREL), Golden, CO (United States)
2. Univ. of Massachusetts, Amherst, MA (United States)

Publication Date:

Fri Apr 09 00:00:00 EDT 2021

Research Org.:

National Renewable Energy Laboratory (NREL), Golden, CO (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE)

OSTI Identifier:

1779800

Report Number(s):

NREL/JA-5900-79228
Journal ID: ISSN 2637-6105; MainId:33454;UUID:c2fe02fe-38af-48f2-a59c-ab3e2c5afdb1;MainAdminID:21274

Grant/Contract Number:  

AC36-08GO28308

Resource Type:

Accepted Manuscript

Journal Name:

ACS Applied Polymer Materials

Additional Journal Information:

Journal Volume: 3; Journal Issue: 5; Journal ID: ISSN 2637-6105

Publisher:

ACS Publications

Country of Publication:

United States

Language:

English

Subject:

25 ENERGY STORAGE; electrospinning; poly(acrylic acid); extensional rheology; fuel cells; catalyst inks; nanofibers