Electrochemical Reactors

Vogt, Helmut; Kreysa, G.; Vasudevan, Subramanyan; Wüthrich, Rolf; Ziki, Jana D. Abou; El-Haddad, R.

doi:10.1002/14356007.l09_l01.pub2

Cited by 2 publications

(4 citation statements)

References 211 publications

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“…As the current density increases, the concentration of dissolved hydrogen becomes high enough to activate nucleation sites, which enable the evolution of gas bubbles at the electrode. 50 Therefore, the fraction of product leaving the electrode in dissolved form decreases with higher current densities, which consequently limits the flux of dissolved hydrogen across the separator. Furthermore, it is assumed that an increase in pressure moves the gas evolution efficiency toward higher current densities, which would explain the later plateau formation.…”

Section: Resultsmentioning

confidence: 99%

“…49 For the nucleation sites to become active a sufficient deviation from equilibrium concentration of the generated product is mandatory. 50 Therefore, the electrolyte becomes supersaturated, which describes a higher concentration of dissolved hydrogen within the electrode boundary or catalyst layer than it would be expected through Henry's law (Eq. 13).…”

Section: Crossover Mechanismsmentioning

confidence: 99%

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Hydrogen Crossover in PEM and Alkaline Water Electrolysis: Mechanisms, Direct Comparison and Mitigation Strategies

Trinke

Haug

Brauns

et al. 2018

J. Electrochem. Soc.

178

126

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This study provides a direct comparison of hydrogen crossover in PEM (Nafion 117) and alkaline water electrolysis (Zirfon) at a temperature of 60 • C applying state-of-the-art separating unit materials. To this end, occurring crossover mechanisms are described first, before experimental data of the anodic hydrogen content are shown in dependence of current density, system pressure and process management strategy. The results suggest that permeation in PEM electrolyzers is mainly governed by diffusion due to a supersaturated concentration of dissolved hydrogen within the catalyst layer, showing a share of 98% of the total permeation flux at 1 A cm −2 and atmospheric pressure. Permeation in alkaline electrolyzers also exhibits a significant influence of supersaturation, but the overall crossover is mainly influenced by mixing the electrolyte cycles, which makes up a share of 90% at 0.7 A cm −2 and 1 bar. Generally it becomes evident that hydrogen permeation across the separating unit is more than one order of magnitude smaller in alkaline electrolysis, which is mainly a consequence of the significantly lower hydrogen solubility in concentrated KOH electrolyte. Finally, this study concludes with an assessment of the impact of separating unit thickness and provides mitigation strategies to reduce hydrogen crossover.

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Section: Resultsmentioning

confidence: 99%

Section: Crossover Mechanismsmentioning

confidence: 99%

Hydrogen Crossover in PEM and Alkaline Water Electrolysis: Mechanisms, Direct Comparison and Mitigation Strategies

Trinke

Haug

Brauns

et al. 2018

J. Electrochem. Soc.

178

126

View full text Add to dashboard Cite

show abstract

“…Simultaneous operation of more than one working electrode within one electrochemical cell is well-known from scientific research, e.g., bipotentiostat operation, but to our knowledge it has not yet been used for electrochemical storage and conversion systems. 16−18…”

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confidence: 99%

“…The proposed configuration consists of multiple electrodes based on nickel and iron, having different functions, and thus permits the decoupling of material usage for the battery and for the hydrogen storage. Simultaneous operation of more than one working electrode within one electrochemical cell is well-known from scientific research, e.g., bipotentiostat operation, but to our knowledge it has not yet been used for electrochemical storage and conversion systems. − …”

mentioning

confidence: 99%