Mass Transport in Gas‐Diffusion Electrodes: A Diagnostic Tool for Fuel‐Cell Cathodes

Perry, Mike; Newman, John; Cairns, Elton J.

doi:10.1149/1.1838202

Cited by 319 publications

(255 citation statements)

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“…[8b] At high overpotential range, steep slopes were obtained, probably indicating control by the combined effects of gas diffusion and ionic mass transport. [18] Comparing Cu/CNS to the control electrodes, a direct and intimate contact was introduced between Cu and CNS (Figure 2). Lim et al predicted a strong interaction between Cu nanoparticles and carbon, and we expect that to extend to CNS as well.…”

Section: Resultsmentioning

confidence: 99%

High‐Selectivity Electrochemical Conversion of CO₂ to Ethanol using a Copper Nanoparticle/N‐Doped Graphene Electrode

et al. 2016

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Though carbon dioxide is a waste product of combustion, it can also be a potential feedstock for the production of fine and commodity organic chemicals provided that an efficient means to convert it to useful organic synthons can be developed. Herein we report a common element, nanostructured catalyst for the direct electrochemical conversion of CO 2 to ethanol with high Faradaic efficiency (63 % at À1.2 V vs RHE) and high selectivity (84 %) that operates in water and at ambient temperature and pressure. Lacking noble metals or other rare or expensive materials, the catalyst is comprised of Cu nanoparticles on a highly textured, N-doped carbon nanospike film. Electrochemical analysis and density functional theory (DFT) calculations suggest a preliminary mechanism in which active sites on the Cu nanoparticles and the carbon nanospikes work in tandem to control the electrochemical reduction of carbon monoxide dimer to alcohol.

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Section: Resultsmentioning

confidence: 99%

High‐Selectivity Electrochemical Conversion of CO₂ to Ethanol using a Copper Nanoparticle/N‐Doped Graphene Electrode

et al. 2016

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“…Through-plane problem and the local impedance.-Model equations.-A system of CCL performance equations is [19][20][21][22] …”

Section: Modelmentioning

confidence: 99%

“…A core element of numerical impedance models is a strongly nonlinear transient model for the cathode catalyst layer performance. [19][20][21][22] A linearized and Fourier-transformed version of this model leads to the complex-valued boundary-value problem, which in the general case of arbitrary cell current can only be solved numerically. 23 The presence of the boundary-value problem solver makes the respective fitting code slow for massive processing of experimental results.…”

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confidence: 99%

A Model for PEM Fuel Cell Impedance: Oxygen Flow in the Channel Triggers Spatial and Frequency Oscillations of the Local Impedance

Kulikovsky

Shamardina

2015

J. Electrochem. Soc.

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A physical model for impedance of a PEM fuel cell cathode side is developed. The model takes into account oxygen flow in the cathode channel. Analytical solution to model equations reveals an effect of spatial oscillations of the local impedance Z loc along the channel coordinate z. The oscillations arise due to interference of the local and transported down the channel perturbations of the oxygen concentration. With the growth of the frequency of the exciting signal, the domain of spatial oscillations of Z loc shrinks toward the oxygen channel inlet; a process, analogous to the skin-effect in classic electrodynamics. An expression for the characteristic width of the skin-layer is derived. The spatial oscillations are accompanied by the oscillations of Z loc along the frequency axis ω. The amplitude of Z loc oscillations decreases exponentially along z and ω, with the characteristic scale of the exponent dependent on the oxygen diffusion coefficient D b in the gas-diffusion layer. This effect enables determination of D b from the local cell impedance measured close to the channel outlet at a real operating stoichiometry of the oxygen flow. Electrochemical impedance spectroscopy (EIS) is, perhaps, the most powerful tool for in situ characterization of fuel cells.1,2 In spite of impressive progress in developing physical models for PEMFC impedance, 3-15 cell and stack developers still routinely use simple transmission line models (TLMs) for understanding the impedance spectra.16,17 A great advantage of TLM is simplicity and fast operation, which enables rapid characterization of the cell components in terms of TLM resistivities and capacitances.18 However, relation of TLM parameters to the physical transport and kinetic coefficients of the cell is beyond the scope of this approach.A much more informative physical characterization of the cell can, in principle, be done with the physical impedance models; however, these models are typically slow for accurate least-squares (LS) fitting of experimental spectra. A core element of numerical impedance models is a strongly nonlinear transient model for the cathode catalyst layer performance.19-22 A linearized and Fourier-transformed version of this model leads to the complex-valued boundary-value problem, which in the general case of arbitrary cell current can only be solved numerically. 23 The presence of the boundary-value problem solver makes the respective fitting code slow for massive processing of experimental results.An alternative approach is based on analytical solutions for the impedance.22,24-26 Based on ideas developed in Refs. 27-29 this approach aims at deriving analytical solutions for the linearized version of the cell performance model. If the cell current density is small, these solutions can be obtained and a closed-form expression for the system impedance Z can be derived. Analytical relations for Z typically include the Tafel slope of the oxygen reduction reaction (ORR), the proton conductivity of the cathode catalyst layer (CCL), and the oxygen diffu...

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“…As noted in the literature, both proton or ionic transport and oxygen mass transfer can limit the reaction 7 rate. [12][13][14] One could expect that under saturated conditions, oxygen mass transfer is more limiting than proton conduction, and vice versa under low-relative-humidity conditions due to dry out of the membrane in the catalyst layer. Thus, although Figure 4 may suggest an infinitely thick catalyst is optimum, if one looks at thicker catalyst layers, a maximum exists even with the higher platinum loadings of the thicker layers.…”

Section: 11mentioning

confidence: 99%

Effects of Membrane- and Catalyst-Layer-Thickness Nonuniformities in Polymer-Electrolyte Fuel Cells

Weber

Newman

2007

J. Electrochem. Soc.

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In this paper, results from mathematical, pseudo 2-D simulations are shown for four different along-the-channel thickness distributions of both the membrane and cathode catalyst layer. The results and subsequent analysis clearly demonstrate that for the membrane thickness distributions, cell performance is affected a few percent under low relative-humidity conditions and that the position along the gas channel is more important than the local thickness variations.However, for the catalyst-layer thickness distributions, global performance is not impacted, although for saturated conditions there is a large variability in the local temperature and performance depending on the thickness. * Electrochemical Society Member ** Electrochemical Society Fellow z E-mail: azweber@lbl.gov 2 Introduction and ApproachAs polymer-electrolyte fuel cells (PEFCs) make the transfer from demonstration to production, manufacturing issues begin to become important. One such issue is that of materialproperty tolerances, and specifically layer thicknesses. While some thickness variation may be acceptable, the limits are not known. The variation or nonuniformity of layer thicknesses also brings fundamental questions that impact water and thermal management on the cell or global level, and it provides clues as to how durability and degradation may be initiated and proceed on the local level. In this paper, the effect of local variations in the membrane and cathode-catalystlayer thicknesses in terms of both the local and global performances is investigated.It is known that manufacturing and production processes inherently result in nonuniform material properties, especially thickness. This variability can be seen in scanning-electron micrographs of the membrane-electrode assembly such as that shown in Figure 1. From multiple micrographs taken from various parts of a PEFC, thickness distributions can be obtained. Figure 2 gives three distributions for both the membrane and cathode catalyst layer, hereby referred to as the catalyst layer, taken from three different PEFCs. A fourth distribution is that of uniform thickness (the solid lines in Figure 2) with values of 13.5 and 30 μm for the catalyst layer and membrane, respectively. In terms of the distributions, for the mathematical analysis, the gas channel was discretized into 32 segments, with every two segments having the same thickness.The distributions clearly show that there is a great deal of variability and randomness in the local thickness values; however, the average values for the different distributions are almost identical as seen in Table I. Table I also gives the standard deviations for each distribution and the cumulative ones, which are essentially normal distributions. 3The distributions are for virgin materials; however, it is not expected that they will change in relation to each other upon cell assembly and operation. This is because the gas-diffusion layers are the most compressible, and a simple stress analysis demonstrates that upon membrane swelling and hydration, it...

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Mass Transport in Gas‐Diffusion Electrodes: A Diagnostic Tool for Fuel‐Cell Cathodes

Cited by 319 publications

References 19 publications

High‐Selectivity Electrochemical Conversion of CO₂ to Ethanol using a Copper Nanoparticle/N‐Doped Graphene Electrode

High‐Selectivity Electrochemical Conversion of CO₂ to Ethanol using a Copper Nanoparticle/N‐Doped Graphene Electrode

A Model for PEM Fuel Cell Impedance: Oxygen Flow in the Channel Triggers Spatial and Frequency Oscillations of the Local Impedance

Effects of Membrane- and Catalyst-Layer-Thickness Nonuniformities in Polymer-Electrolyte Fuel Cells

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Mass Transport in Gas‐Diffusion Electrodes: A Diagnostic Tool for Fuel‐Cell Cathodes

Cited by 319 publications

References 19 publications

High‐Selectivity Electrochemical Conversion of CO2 to Ethanol using a Copper Nanoparticle/N‐Doped Graphene Electrode

High‐Selectivity Electrochemical Conversion of CO2 to Ethanol using a Copper Nanoparticle/N‐Doped Graphene Electrode

A Model for PEM Fuel Cell Impedance: Oxygen Flow in the Channel Triggers Spatial and Frequency Oscillations of the Local Impedance

Effects of Membrane- and Catalyst-Layer-Thickness Nonuniformities in Polymer-Electrolyte Fuel Cells

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High‐Selectivity Electrochemical Conversion of CO₂ to Ethanol using a Copper Nanoparticle/N‐Doped Graphene Electrode

High‐Selectivity Electrochemical Conversion of CO₂ to Ethanol using a Copper Nanoparticle/N‐Doped Graphene Electrode