Title: Investigation of the Microstructure and Rheology of Iridium Oxide Catalyst Inks for Low-Temperature Polymer Electrolyte Membrane Water Electrolyzers

Abstract

Here, we present an investigation of the structure and rheological behavior of catalyst inks for low-temperature polymer electrolyte membrane water electrolyzers. The ink consists of iridium oxide (IrO₂) catalyst particles and a Nafion ionomer dispersed in a mixture of 1-propanol and water. The effects of ionomer concentration and catalyst concentration on the microstructure of the catalyst ink were studied. Studies on dilute inks (0.1 wt % IrO₂) using zeta potential and dynamic light scattering measurements indicated a strong adsorption of the ionomer onto the catalyst particles which resulted in an increase in the ..zeta..-potential and the z-average diameter. Steady-shear and dynamic-oscillatory-shear rheological measurements of concentrated IrO₂ dispersions (35 wt % IrO₂) indicated that the particles are strongly agglomerated in the absence of the ionomer. The addition of even a small amount of the ionomer (2.4 wt % with respect to total solids) caused the rheology to transition from shear thinning to Newtonian because of the reduction in agglomerated structure due to stabilization of the aggregates by the ionomer, consistent with the behavior of dilute inks. At intermediate ionomer loadings, between 2.4 and 9 wt %, the viscosity increased with increasing ionomer wt %, though remained Newtonian, predominantly due to themore » increasing ionomer volume fraction in the ink. For ionomer loadings greater than 9 wt %, the particles were found to be flocculated, likely induced by a dispersed ionomer. The flocculated inks exhibited strong shear-thinning and gel-like behaviors in steady-shear and oscillatory-shear rheology. The onset of flocculation was found to be sensitive to the catalyst concentration, where below 35 wt % of IrO₂, flocculation was not observed. The rheological observations were further verified by ultra-small-angle X-ray scattering.« less

Authors:

Khandavalli, Sunilkumar  ^[1];

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Park, Jae Hyung ^[2]; Kariuki, Nancy N. ^[2]; Zaccarine, Sarah F. ^[3]; Pylypenko, Svitlana  ^[3];

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Myers, Deborah J. ^[2]; Ulsh, Michael J.  ^[1];

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Mauger, Scott A.  ^[1]

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+ Show Author Affiliations

1. National Renewable Energy Laboratory (NREL), Golden, CO (United States)
2. Argonne National Lab. (ANL), Lemont, IL (United States)
3. Colorado School of Mines, Golden, CO (United States)

Publication Date:

2019-11-07

Research Org.:

National Renewable Energy Lab. (NREL), Golden, CO (United States); Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Transportation Office. Fuel Cell Technologies Office; USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities Division

OSTI Identifier:

1578258

Alternate Identifier(s):

OSTI ID: 1606551

Report Number(s):

NREL/JA-5900-74843
Journal ID: ISSN 1944-8244; TRN: US2102202

Grant/Contract Number:  

AC36-08GO28308; AC02-06CH11357

Resource Type:

Accepted Manuscript

Journal Name:

ACS Applied Materials and Interfaces

Additional Journal Information:

Journal Volume: 11; Journal Issue: 48; Journal ID: ISSN 1944-8244

Publisher:

American Chemical Society (ACS)

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; low-temperature polymer electrolyte membrane exchange water electrolysis; rheology; catalyst inks; iridium oxide; ionomer; catalyst layer