Mass-Transport Resistances of Acid and Alkaline Ionomer Layers: A Microelectrode Study Part 1 - Microelectrode Development

Gas permeability, the product of gas diffusivity and Henry's gas-absorption constant, of ionomer membranes is an important transport parameter in fuel cell and electrolyzer research as it governs gas crossover between electrodes and perhaps in the catalyst layers as well. During transient operation, it is important to divide the gas permeability into its constituent properties as they are individually important. Although transient microelectrode measurements have been used previously to separate the gas permeability into these two parameters, inconsistencies remain in the interpretation of the experimental techniques. In this work, a new interpretation methodology is introduced for determining independently diffusivity and Henry's constant of hydrogen and oxygen gases in ionomer membranes (Nafion 211 and Nafion XL) as a function of relative humidity using microelectrodes. Two time regimes are accounted for. At long times, gas permeability is determined from a twodimensional numerical model that calculates the solubilized-gas concentration profiles at a steady state. At short times, permeability is deconvoluted into diffusivity and Henry's constant by analyzing transient data with an extended Cottrell equation that corrects for actual electrode surface area. Gas permeability and diffusivity increase as relative humidity increases for both gases in both membranes, whereas Henry's constants for both gases decrease with increasing relative humidity. In addition, results for Nafion 211 membranes are compared to a simple phase-separated parallel-diffusion transport theory with good agreement. The two-time-regime analysis and the experimental methodology can be applied to other electrochemical systems to enable greater precision in the calculation of transport parameters and to further understanding of gas transport in fuel cells and electrolyzers.

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“…The experimental microelectrode cell has been described previously . A schematic is provided in Figure .…”

Section: Experimental Methodsmentioning

confidence: 99%

“…The experimental microelectrode cell has been described previously. 36 A schematic is provided in Figure 1. In brief, the cell is a twochambered, flow-through design with one chamber containing the working (micro-) and counter electrodes and one for a reversible hydrogen (RHE) reference electrode.…”

Section: Microelectrode Cell Designmentioning

confidence: 99%

Gas Mass-Transport Coefficients in Ionomer Membranes Using a Microelectrode

2022

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“…The first configuration that we will discuss involves a reliance on the application of a downforce on the ME into the membrane, which has been more commonplace in the literature for studies involving solid polymer electrolytes. [16][17][18][19] A sandwich structure is traditional for this configuration in that the ME is pressed into the membrane that is stacked on top of a porous electrode, typically a platinum mesh, or a solid electrode acting as the counter electrode. The membrane of interest generally acts as the electrolytic bridge to the reference electrode.…”

Section: Microelectrode Setup and Testingmentioning

confidence: 99%

Method—Using Microelectrodes to Explore Solid Polymer Electrolytes

Petrovick

Anderson

Kushner

et al. 2021

J. Electrochem. Soc.

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Solid polymer electrolytes are an emerging technology in electrochemistry driven by their use in energy applications such as fuel cells, electrolyzers, and solid-state batteries. Compared to traditional liquid electrolytes, solid polymer electrolytes provide safer, cheaper, and potentially improved device performance. However, there is a lack of standard experimental methods for studying solid electrolytes. Microelectrodes have inherent benefits capable of filling this experimental gap due primarily to their integration into model electrochemical cells with solid electrolytes that represent complex interfaces, enabling additional insight into reaction processes. In this tutorial review, we explore the use of microelectrodes to study solid polymer electrolytes, beginning with a brief history of the field including common experimental cell designs and their benefits and drawbacks. Methods of evaluating essential kinetic and mass-transport parameters are then examined. In addition, the key studies of the past 30 years utilizing microelectrode cells and solid polymer electrolytes are summarized, with important results highlighted and compared. Finally, future studies of solid polymer electrolytes with microelectrodes and potential new avenues of research are commented on.

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“…A homemade DC conductivity setup was used to measure the particle conductivity. 36 Briefly, the catalyst powder was sandwiched between copper electrodes and compressed to 200 lb/in 2 , the thickness was measured, and an I−V curve was generated from −50 to 50 mV using a potentiostat (SP300, BioLogic). The catalyst conductivity was extracted from the slope of the curve and the catalyst thickness.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…In both systems, Ir was subsequently deposited on the CCSs using the WI method. Conductivities were measured using an in-house assembled DC conductivity set-up, 36 and catalyst activities towards the oxygen evolution reaction (OER) were evaluated in rotating disk electrode (RDE) and in a PEMWE. Throughout, we compared the performance with state-of-the-art commercial catalysts and previous investigations using supported Ir catalysts from the literature.…”

Section: Introductionmentioning

confidence: 99%

Supported Oxygen Evolution Catalysts by Design: Toward Lower Precious Metal Loading and Improved Conductivity in Proton Exchange Membrane Water Electrolyzers

et al. 2020

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Reducing the precious metal content of water oxidation catalysts for proton-exchange-membrane water electrolysers remains a critical barrier to their large-scale deployment. Herein, we present an engineered architecture for supported iridium catalysts, which enables decreased precious metal content and improved activity and conductivity. The improvement in performance at lower precious metal loading is realized by the deposition of a conformal layer of platinum nanoparticles on titanium dioxide (TiO 2 ) using a facile photoreduction method to prepare conductive layer coated supports (CCSs). Platinum nanoparticles are homogeneously dispersed on TiO 2 , and the conductivity of the subsequent catalysts with 39 wt% precious group metal loadings are significantly higher than the commercial 75 wt% loaded IrO 2 -TiO 2 catalysts. The conformal conductive layer also maintains enhanced conductivity and electrochemical activity upon thermal annealing when compared to catalysts without the conductive layer and nonconformal heterogeneous conductive layer. The iridium mass activity from half-cell studies shows 141% improvement for CCS supported catalysts at 42% lower loadings compared to the commercial catalysts. The conductive layer also improves the single cell electrolyzer performance at similar catalyst loading in comparison to commercial state-of-the-art catalyst. We correlate the physical properties of the engineered catalysts with their electrochemical 2 performance in electrolyzers to understand structure-activity relationships, and we anticipate further performance improvements upon synthesis and materials optimizations.

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Mass-Transport Resistances of Acid and Alkaline Ionomer Layers: A Microelectrode Study Part 1 - Microelectrode Development

Cited by 6 publications

References 8 publications

Gas Mass-Transport Coefficients in Ionomer Membranes Using a Microelectrode

Gas Mass-Transport Coefficients in Ionomer Membranes Using a Microelectrode

Method—Using Microelectrodes to Explore Solid Polymer Electrolytes

Supported Oxygen Evolution Catalysts by Design: Toward Lower Precious Metal Loading and Improved Conductivity in Proton Exchange Membrane Water Electrolyzers

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