Gas Diffusion Electrodes for Efficient Manufacturing of Chlorine and Other Chemicals

Kintrup, Juergen; Millaruelo, M.; Trieu, Vinh; Bulan, Andreas; Mojica, Ernesto Silva

doi:10.1149/2.f07172if

Cited by 37 publications

(38 citation statements)

References 14 publications

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“…[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 %. In 2017, 89 million tons of chlorine were produced worldwide.…”

Section: Introductionmentioning

confidence: 99%

“…By using traditional NaCl membrane electrolysis, this corresponds to ac onsumption of 195 800 GWh electrical energy per year and the emission of 82 million tons of CO 2 . [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 %. [2] Here, in contrast to the standard process, no hydrogen is produced as ac oproduct, but oxygen is consumed at the cathode.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

2019

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“…This high energy demand is in turn responsible for a major share of CO 2 emissions. In order to reduce the electrical energy demand of the chlor‐alkali electrolysis process and thus the corresponding CO 2 emissions, significant progress has been made by replacing the so far used hydrogen‐evolving cathodes by oxygen depolarized cathodes (ODC) . In this manner electric energy savings of up to 30 % can be achieved under industrially relevant conditions (80–90 °C, 30 wt.% NaOH electrolyte) .…”

Section: Introductionmentioning

confidence: 99%

“…In order to reduce the electrical energy demand of the chlor-alkali electrolysis process and thus the corresponding CO 2 emissions, significant progress has been made by replacing the so far used hydrogen-evolving cathodes [8][9][10][11][12] by oxygen depolarized cathodes (ODC). [13][14][15][16][17][18][19] In this manner electric energy savings of up to 30 % can be achieved under industrially relevant conditions (80-90°C, 30 wt.% NaOH electrolyte). [20] Since the oxygen reduction reaction (ORR) has a higher standard electrode potential compared to the hydrogen evolution reaction (HER) [Eqs.…”

Section: Introductionmentioning

confidence: 99%

Improvement of Oxygen‐Depolarized Cathodes in Highly Alkaline Media by Electrospinning of Poly(vinylidene fluoride) Barrier Layers

et al. 2020

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Oxygen‐depolarized cathodes (ODC) were developed for chlor‐alkali electrolysis to replace the hydrogen evolution reaction (HER) by the oxygen reduction reaction (ORR) providing electrical energy savings up to 30 % under industrially relevant conditions. These electrodes consist of micro sized silver grains and polytetrafluoroethylene, forming a homogeneous electrode structure. In this work, we report on the modification of ODCs by implementing an electrospun layer of hydrophobic poly(vinylidene fluoride) (PVDF) into the ODC structure, leading to a significantly enhanced ORR performance. The modified electrodes are physically characterized by liquid flow porometry, contact angle measurements and scanning electron microscopy. Electrochemical characterization is performed by linear sweep voltammetry and chronopotentiometry. The overpotential for ORR at application near conditions could be reduced by up to 75 mV at 4 kA m−2 and 135 mV at a higher current density of 9.5 kA m−2. Consequently, we propose that modifying ODCs by electrospinning is an effective and cost‐efficient way to further reduce the energy demand of the ORR in highly alkaline media.

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“…[6,7] In the industrial process, and likewise on the laboratory scale, the O 2 availability can be increased by providing gaseous O 2 to the backside of the GDE, which directly delivers the O 2 to the catalytically actives ites of the electrode at the three-phase boundary between the solid catalyst, liquid electrolyte, and gaseous O 2 in the intraporous electrode space. [6] The local concentration of O 2 is drastically increased in at hin layer above the catalystm aterial [2,8,9] by lowering the diffusion path length from the gas phase to the solid catalyst surface.…”

Section: Introductionmentioning

confidence: 99%

Catalytic Reactivation of Industrial Oxygen Depolarized Cathodes by in situ Generation of Atomic Hydrogen

et al. 2019

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Electrocatalytically active materials on the industrial as well as on the laboratory scale may suffer from chemical instability during operation, air exposure, or storage in the electrolyte. A strategy to recover the loss of electrocatalytic activity is presented. Oxygen‐depolarized cathodes (ODC), analogous to those that are utilized in industrial brine electrolysis, are analyzed: the catalytic activity of the electrodes upon storage (4 weeks) under industrial process conditions (30 wt % NaOH, without operation) diminishes. This phenomenon occurs as a consequence of surface oxidation and pore blockage, as revealed by scanning electron microscopy, focused ion beam milling, X‐ray photoelectron spectroscopy, and Raman spectroscopy. Potentiodynamic cycling of the oxidized electrodes to highly reductive potentials and the formation of “nascent” hydrogen re‐reduces the electrode material, ultimately recovering the former catalytic activity.

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Gas Diffusion Electrodes for Efficient Manufacturing of Chlorine and Other Chemicals

Cited by 37 publications

References 14 publications

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

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

Improvement of Oxygen‐Depolarized Cathodes in Highly Alkaline Media by Electrospinning of Poly(vinylidene fluoride) Barrier Layers

Catalytic Reactivation of Industrial Oxygen Depolarized Cathodes by in situ Generation of Atomic Hydrogen

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