Rheological Investigation on the Microstructure of Fuel Cell Catalyst Inks

Khandavalli, Sunilkumar; Park, Jae Hyung; Kariuki, Nancy N.; Myers, Deborah J.; Stickel, Jonathan J.; Hurst, Katherine E.; Neyerlin, Kenneth C.; Ulsh, Michael; Mauger, Scott A.

doi:10.1021/acsami.8b15039

“…For instance, Soboleva et al systematically investigated the effects of ionomer loading on the water sorption and electrochemical activities of two types of carbon [32]. Khandavalli et al provided insights on the rheological behavior of ink varying I/C ratio and carbon-support type [33]. Similarly, different solvent selection has been explored, which results in maximum stability [22,28], and electrochemical performance [14,34].…”

Section: Introductionmentioning

confidence: 99%

“…But DLS very often requires high degree of dilution or is feasible for monodispersed systems only, which consequently provides misleading particle sizing analysis [43]. Small-angle or wide-angle x-ray scattering analysis is a powerful technique for characterizing inks [16,33,44], however, associated with challenging data interpretation [45] and higher operating costs. Despite the options available in store, a gap in tools and technologies to study ink dispersions in their native state and at operational concentration levels exists.…”

Section: Introductionmentioning

confidence: 99%

On the State and Stability of Fuel Cell Catalyst Inks

Bapat

¹

,

Giehl²,

Kohsakowski³

et al. 2021

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0

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Catalyst layers (CL) as an active component of the catalyst coated membrane (CCM) form the heart of proton electrolyte membrane fuel cells (PEMFC). For optimum performance of the fuel cell, obtaining suitable structural and functional characteristics for the CL is crucial. Direct tuning of the microstructure and morphology of the CL is non-trivial; hence catalyst inks as catalyst layer precursors need to be modulated, which are then applied onto a membrane, to form the CCM. Obtaining favorable dispersion characteristics forms an important prerequisite in engineering catalyst inks for large scale manufacturing. In order to facilitate a knowledge-based approach for developing fuel cell inks, this work introduces new tools and methods to study both the dispersion state and stability characteristics, simultaneously. Catalyst inks were prepared using different processing methods which include stirring and ultrasonication. The proposed tools are used to characterize and elucidate the effects of the processing method. Structural characterization of the dispersed particles and their assemblages was carried out by means of transmission electron microscopy. Analytical centrifugation (AC) was used to study the state and stability of inks. Herein, we introduce new concepts, S score and stability trajectory, for a time-resolved assessment of inks in their native state using AC. The findings were validated and rationalized using transmittograms as a direct visualization technique. The flowability of inks was investigated by rheological measurements. It was found that probe sonication only up to an optimum amplitude leads to a highly stable colloidal ink.

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“…x-ray scattering analysis is a powerful technique for characterizing inks [16,33,44], however, associated with challenging data interpretation [42] and higher operating and investment costs.…”

Section: Introductionmentioning

confidence: 99%

On the State and Stability of Fuel Cell Catalyst Inks

Bapat¹,

Giehl²,

Kohsakowski³

et al. 2020

Preprint

0

View full text Add to dashboard Cite

Catalyst layers (CL) as an active component of the catalyst coated membrane (CCM) form the heart of proton electrolyte membrane fuel cells (PEMFC). For optimum performance of the fuel cell, obtaining suitable structural and functional characteristics for the CL is crucial. Direct tuning of the microstructure and morphology of the CL is non-trivial; hence catalyst inks as catalyst layer precursors need to be modulated, which are then applied onto a membrane, to form the CCM. Obtaining favorable dispersion characteristics forms an important prerequisite in engineering catalyst inks for large scale manufacturing. In order to facilitate a knowledge-based approach for developing fuel cell inks, this work introduces new tools and methods to study both the dispersion state and stability characteristics, simultaneously. Catalyst inks were prepared using different processing methods which include stirring and ultrasonication. The proposed tools are used to characterize and elucidate the effects of the processing method. Structural characterization of the dispersed particles and their assemblages was carried out by means of transmission electron microscopy. Analytical centrifugation (AC) was used to study the state and stability of inks. Herein, we introduce new concepts, S score and stability trajectory, for a time-resolved assessment of inks in their native state using AC. The findings were validated and rationalized using transmittograms as a direct visualization technique. The flowability of inks was investigated by rheological measurements. It was found that probe sonication only up to an optimum amplitude leads to a highly stable colloidal ink.

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“…The knowledge of its native dispersion state over time is important for the optimization of ink processing, and consequent large-scale manufacturing of fuel cells. The size and concentration of particles, along with their interactions, affect macroscopic properties such as stability, 3,4 aggregation, 5,6 rheology, [7][8][9] and electrochemical performance. 6,10 However, ink formulation and processing is primarily governed by empiricism and important process-structure-property relationships remain to be adequately explored.…”

mentioning

confidence: 99%

“…6,10 However, ink formulation and processing is primarily governed by empiricism and important process-structure-property relationships remain to be adequately explored. 6,9,11 Recent advances in analytical centrifugation (AC), employing STEP-technology™ (Space-Time Extinction Profiles) 12 (shown in Figure 1), permit direct measurement of sedimentation dynamics of particle systems in a facile manner, with low cost and preparation demands. Monitoring the progression of particles in a centrifugal field is attractive for several applications, such as (a) evaluation of processstructure relations, 13 (b) comparison of emulsifying properties, 14,15 and (c) assessment of emulsion/dispersion stability.…”

mentioning

confidence: 99%

Exhibitive Nano-to-Micron Scale Sedimentation Dynamics of Colloidal Formulations Through Direct Visualization

Bapat

¹

,

Segets²

2020

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0

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The study of sedimentation behavior of nanoparticle dispersions is important for revealing particle size and colloidal stability characteristics. Quantitative appraisal of real-world colloidal systems in their native state, is key for replacing prevailing empiricism in formulation science by knowledge-based design. Herein, we choose fuel cell inks as one case-example amongst many other possibilities to present a new visualization technique, called Transmittogram. This technique readily depicts the time-resolved settling behavior of solid-liquid dispersions, measured by analytical centrifugation (AC). Although AC enables the causal examination of agglomeration, settling, and creaming behavior of dispersions, along with its consequent effect on structure formation and product properties, the understanding of the main transmission readout is often non-intuitive and complex. Transmittograms are, therefore, the missing link for straightforward data interpretation. First, we illustrate the utility of transmittogram analysis using model silica nanoparticle systems and further validate it against known characteristics of the system. Then, we demonstrate the application of transmittograms to characterize fuel cell inks, showing the strength of the approach in deconvoluting and distilling information to the reader. Finally, we discuss the potential of the technique for routine analysis using analytical centrifugation.

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Rheological Investigation on the Microstructure of Fuel Cell Catalyst Inks

Cited by 113 publications

References 64 publications

On the State and Stability of Fuel Cell Catalyst Inks

On the State and Stability of Fuel Cell Catalyst Inks

On the State and Stability of Fuel Cell Catalyst Inks

Exhibitive Nano-to-Micron Scale Sedimentation Dynamics of Colloidal Formulations Through Direct Visualization

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