Non-isothermal model for an industrial chlor-alkali cell with oxygen-depolarized cathode

Chavan, Naresh; Pinnow, Stefan; Polcyn, Gregor D.; Turek, Thomas

doi:10.1007/s10800-015-0831-2

Cited by 13 publications

(16 citation statements)

References 35 publications

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“…Different factors which are not included in the model might have contributed to this behavior: Although the experiments were conducted under temperature control, a moderate increase of the ODC temperature which would improve kinetics and transport processes, cannot be excluded. In that regard, heating effects can be caused by ohmic losses or the entropy effect, for instance . Also conceivable is the influence of the micro kinetics considering hydrogen peroxide formation and catalyst loading with hydrogen ions, which are not considered by the assumed lumped kinetics.…”

Section: Dynamic Analysismentioning

confidence: 99%

“…In that regard, heating effects can be caused by ohmic losses or the entropy effect, for instance. [39] Also conceivable is the influence of the micro kinetics considering hydrogen peroxide formation and catalyst loading with hydrogen ions, [40] which are not considered by the assumed lumped kinetics. The same effects may occur for the steady state results shown above.…”

Section: Dynamic Analysismentioning

confidence: 99%

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The Key Role of Water Activity for the Operating Behavior and Dynamics of Oxygen Depolarized Cathodes

et al. 2019

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Advanced chlor‐alkali electrolysis with oxygen depolarized cathodes (ODC) requires 30 % less electrical energy than conventional hydrogen‐evolution‐based technology. Herein, we confirm that the activities of hydroxide and water govern the ODC performance and its dynamics. Experimental characterization of ODC under varying mass transfer conditions on the liquid side reveals large differences in the polarization curves as well as in potential step responses of the electrodes. Under convective transport in the liquid electrolyte, the ODC is not limited by mass transfer in its current density at j>3.9 kA m−2, whereas transport limitations are already reached at j≈1.3 kA m−2 with a stagnant electrolyte. Since gas phase conditions do not differ significantly between the measurements, these results are in contrast the common assumption that oxygen supply determines ODC performance. A dynamic model reveals the strong influence of the electrolyte mass transfer conditions on oxygen availability and thus performance. Dynamic responses of the current density to step‐wise potential changes are dominated by the mass transport of water and hydroxide ions, which is by orders of magnitude faster with convective electrolyte flow. Without convective liquid electrolyte transport, a high accumulation of hydroxide ions significantly lowers the oxygen solubility. Thus, a fast mass transport of water and hydroxide is essential for high ODC performance and needs to be ensured for technical applications. The predicted accumulation of ions is furthermore validated experimentally by means of scanning electrochemical microscopy. We also show how the outlined processes can explain the distinctively different potential step responses with and without electrolyte convection.

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Section: Dynamic Analysismentioning

confidence: 99%

Section: Dynamic Analysismentioning

confidence: 99%

The Key Role of Water Activity for the Operating Behavior and Dynamics of Oxygen Depolarized Cathodes

et al. 2019

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“…In 2017, 89 million tons of chlorine were produced worldwide. [3] The centerpiece of this technique is the silver catalyst based gas diffusion cathode, [4] at which the oxygen reduction reaction (ORR) takes place [Eq. [1] An energy-saving alternative is given by advanced chlor-alkali electrolysisw ith oxygen depolarized cathodes (ODCs), which reduces the required energy by about 30 %.…”

Section: Introductionmentioning

confidence: 99%

“…[2] Here, in contrast to the standard process, no hydrogen is produced as ac oproduct, but oxygen is consumed at the cathode. [3] The centerpiece of this technique is the silver catalyst based gas diffusion cathode, [4] at which the oxygen reduction reaction (ORR) takes place [Eq. (1)]:…”

Section: Introductionmentioning

confidence: 99%

Processes and Their Limitations in Oxygen Depolarized Cathodes: A Dynamic Model‐Based Analysis

2019

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Oxygen depolarized cathodes (ODCs) are key components of alkaline fuel cells and metal–air batteries or of chlor‐alkaline electrolysis, but suffer from limited oxygen availability at the reaction zone. Dynamic analysis is a highly suitable approach to identify the underlying causes, especially the limiting steps and process interactions in such gas diffusion electrodes. Herein, a one‐dimensional, dynamic, three‐phase model for analyzing the oxygen reduction reaction in silver‐based ODCs is presented. It allows for a detailed evaluation of the electrochemical reaction, the mass transport processes, and their interaction. The model also reveals that the depletion of reactant oxygen in the liquid electrolyte is caused by the current‐dependent change of the gas–liquid equilibrium as the limiting subprocess. The phase equilibrium, in turn, depends on the slow mass transport of water and hydroxide ions in the liquid phase. Key parameters are the location or size of the gas–liquid interface within the electrode. Profiles of local concentrations and partial pressures of different species reveal a steep gradient of oxygen in the liquid phase, but no limitation in oxygen mass transport in the gas phase. Dynamic simulations with potential steps allowed the identification of different time constants to separate overlapping processes. Accordingly, the mass transport of water and hydroxide ions was identified as the slowest process that strongly influenced the dynamic response of all species, including oxygen, and of the current. The characteristic time constant of the mass transport of water and hydroxide ions across the liquid phase within the ODC is determined to be τmt,0.166667emnormalH2normalO ≈0.176 s, whereas the time constant of oxygen mass transport into the reaction zone is several magnitudes smaller: τmt,0.166667emnormalO2 ≈1.70×10−6 s. Finally, a sensitivity analysis confirms that the overall performance is best improved by adjusting mass transport properties in the liquid phase.

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“…Recent results by Botz et al for the same electrode showed that the local hydroxide and water activities have an additional important influence on the GDE performance [66]. The p2D model for the Ag-PTFE electrode developed by Pinnow et al was later extended to account for the distribution of concentrations and temperature along the height of the electrode [27].…”

Section: Pseudo-two-dimensional Gde Modelsmentioning

confidence: 99%

Modeling Oxygen Gas Diffusion Electrodes for Various Technical Applications

Kubannek

Turek

Krewer

2019

Chemie Ingenieur Technik

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In gas diffusion electrodes (GDEs), electrocatalysts are in contact with gas and electrolyte ensuring a large active threephase boundary. GDEs are used for important technical applications in energy transformation and chemical synthesis. This review gives an introduction into the vast range of existing models for GDEs and their specific purpose, with an emphasis on oxygen reduction electrodes. After introducing the processes occurring in GDEs, modeling approaches are described according to their dimensionality (from 0D to 3D to multiscale) and perspectives for future research are discussed.

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Non-isothermal model for an industrial chlor-alkali cell with oxygen-depolarized cathode

Cited by 13 publications

References 35 publications

The Key Role of Water Activity for the Operating Behavior and Dynamics of Oxygen Depolarized Cathodes

The Key Role of Water Activity for the Operating Behavior and Dynamics of Oxygen Depolarized Cathodes

Processes and Their Limitations in Oxygen Depolarized Cathodes: A Dynamic Model‐Based Analysis

Modeling Oxygen Gas Diffusion Electrodes for Various Technical Applications

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