An Electrolyte Distribution Model in Consideration of the Electrode Wetting in the Molten Carbonate Fuel Cell

Kawase, Makoto; Mugikura, Yoshihiro; Watanabe, Takao

doi:10.1149/1.1393282

Cited by 40 publications

(41 citation statements)

References 6 publications

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“…This was explained as related to the solubility of gas species in the electrolyte, and differences with respect to the contact angle at the three phase boundary inside the porous structure. In general, the temperature dependence of the contact angle in Li/Na electrolyte is larger (more negative) than that of Li/K electrolyte [5,7,24]. This supports the above explanation of the high temperature sensitivity of Li/Na cell performance.…”

Section: Effect Of Temperaturesupporting

confidence: 70%

Electrowetting of Molten Carbonate Electrolytes

Hsieh

Selman

2011

Fuel Cells

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The wetting characteristics of various molten carbonate electrolytes were experimentally measured and the dependence of the contact angle on polarisation was thoroughly examined for various temperatures and gas atmospheres. At open circuit under an atmosphere of CO2 and/or oxidant gases, addition of alkaline earth carbonates decreases the wettability of the electrolyte. Addition of alkaline earth carbonates also tends to decrease the temperature dependence of the contact angle. Upon polarisation, the contact angle shows a complex behaviour. In an oxidising atmosphere its dependence on potential is roughly symmetric (like an electrocapillary curve) but in a reducing atmosphere this is not the case. Generally, the contact angle increases upon cathodic polarisation but decreases in the anodic direction. These changes in contact angle are interpreted in terms of interfacial tensions. The complex dependence of contact angle on polarisation can be interpreted in terms of a superimposed electrocapillary and transport effects. As such, it may be affected by specifically adsorbed species at the electrode surface (especially complex oxides), by the basicity (oxide ion activity) of the melt, and by the potential‐induced segregation of the cationic species in the carbonate melt.

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Section: Effect Of Temperaturesupporting

confidence: 70%

Electrowetting of Molten Carbonate Electrolytes

Hsieh

Selman

2011

Fuel Cells

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“…The meniscus plays an important role in controlling the reaction rate. [8][9][10][11][12][13] Inaba et al reported that the hydrogen oxidation reaction (HOR) was affected by the shape of the meniscus, which determines the diffusion path of the dissolved gas.14 With an alkaline electrolyte, interesting interfacial phenomena have been observed. [15][16][17][18][19][20][21] In a previous study, we observed an in situ meniscus motion during the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) on a platinum electrode.…”

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confidence: 99%

Observation of Three-Phase Interface during Hydrogen Electrode Reactions in Unitized Regenerative Fuel Cell

Majima

Matsushima

Fukunaka

et al. 2014

J. Electrochem. Soc.

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The dynamic behavior of the meniscus of a potassium hydroxide and sulfuric acid droplet on a platinum electrode was studied using a charge-coupled device (CCD) camera and confocal laser microscopy. The three-phase interface was investigated during the hydrogen oxidation reaction (HOR) and the hydrogen evolution reaction (HER). Contact angle measurements revealed a spreading interface during the HER whereas the droplet shape remained unchanged during the HOR for both droplets. The overhead view revealed the formation of many fine droplets near the meniscus boundary during the HOR in the alkaline electrolyte, which agrees with previous results for the oxygen reduction reaction (ORR). The correlation of these observations with electrochemical data and differences in the results between the HOR and the HER suggest that the motion of the meniscus was induced by local pH and temperature gradients, presumably caused by a non-uniform reaction because of the limitations of the dissolved gas. Hydrogen is an attractive energy source as an alternative to fossil fuels. [1][2][3][4] Hydrogen can be produced from water and used in fuel cells. No toxic gases are generated and thus energy shortages and environmental problems can be prevented. Unitized regenerative fuel cells (URFCs) are ideal energy devices.5-7 They function by generating electricity as fuel cells and they produce hydrogen gas by water electrolysis. They are compact and economic because common electrodes may be used. However, URFCs require highly controlled wettability and this is dependent on the operational mode. A hydrophobic nature is desired for the fuel cell mode and a hydrophilic is required for water electrolysis. Therefore, intrinsic interfacial properties make it difficult to improve the energy conversion efficiency.The complex interface consists of an electrode (solid), an electrolyte (liquid), and a gas (air) and this is referred to as the three-phase interface, which is an essential part of the relevant electrochemical reaction. The meniscus plays an important role in controlling the reaction rate. [8][9][10][11][12][13] Inaba et al. reported that the hydrogen oxidation reaction (HOR) was affected by the shape of the meniscus, which determines the diffusion path of the dissolved gas.14 With an alkaline electrolyte, interesting interfacial phenomena have been observed. [15][16][17][18][19][20][21] In a previous study, we observed an in situ meniscus motion during the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) on a platinum electrode. 17 A spread of the three-phase interface during the ORR was observed and the role of hydroxide ions in determining the surface tension was investigated.To clarify the mechanism of this dynamic motion, in this study we measured the contact angle using different electrolytes and gas atmosphere used in a previous study. The relationship between the wettability and the electrochemical reaction of the HOR and the hydrogen evolution reaction (HER) is thus discussed in detail. ExperimentalThe experi...

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“…The effect of gas composition on the electrolyte distribution in the electrode is not considered in the evaluation of these experimental data, even though the electrolyte wetting properties of the Ni electrode strongly depend on gas composition. 20 The exchange current densities i 0 can be determined by solving Eq. 5, using the parameter values listed in Table IV.…”

Section: Resultsmentioning

confidence: 99%

Electrode Kinetics of the Ni Porous Electrode for Hydrogen Production in the Molten Carbonate Electrolysis Cell (MCEC)

Lindbergh

Lagergren³

2015

ECS Trans.

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The purpose of this study was to elucidate the kinetics of a porous nickel electrode for hydrogen production in a molten carbonate electrolysis cell. Stationary polarization data for the Ni electrode were recorded under varying gas compositions and temperatures. The slopes of these iR-corrected polarization curves were analyzed at low overpotential, under the assumption that the porous electrode was under kinetic control with mass-transfer limitations thus neglected. The exchange current densities were calculated numerically by using a simplified porous electrode model. Within the temperature range of 600-650 • C, the reaction order of hydrogen is not constant; the value was found to be 0.49-0.44 at lower H 2 concentration, while increasing to 0.79-0.94 when containing 25-50% H 2 . The dependence on CO 2 partial pressure increased from 0.62 to 0.86 with temperature. The reaction order of water showed two cases as did hydrogen. For lower H 2 O content (10-30%), the value was in the range of 0.47-0.67 at 600-650 • C, while increasing to 0.83-1.07 with 30-50% H 2 O. The experimentally obtained partial pressure dependencies were high, and therefore not in agreement with any of the mechanisms suggested for hydrogen production in molten carbonate salts in this study. Electrolysis in molten carbonate salts at high temperatures is a promising method for hydrogen and/or syngas (H 2 +CO) production, especially when combining it with renewable electricity resources such as solar energy and wind power. Due to the favorable thermodynamic and kinetic conditions, high-temperature electrolysis will attain higher overall efficiency and require lower applied voltage when compared to low-temperature electrolysis.1 Electrolysis in molten carbonates has been evidenced by some authors, mainly by converting CO 2 into CO.2-5 Peelen et al. 2 studied the electrochemical reduction of CO 2 into CO on a gold flag electrode in 62/38 mol% Li/K carbonate mixture in the temperature range 575-700• C. Kaplan et al.3-4 observed the conversion of CO 2 to CO by using a cell with a molten electrolyte consisting of lithium carbonate and lithium oxide, in which the electrodes were graphite (anode) and titanium (cathode), and the working temperature was 850-900• C. Chery et al. 5 presented thermodynamic calculations and experimental measurements on the reduction of CO 2 into CO on a gold flag or planar disk electrode with Li/K and Li/Na carbonate eutectics at temperatures from 575 to 650• C. However, most experiments were carried out on flag electrodes, which are different from porous electrodes when considering electrode surface and mass-transfer limitations. In our previous study 6 a cell operating at 650• C, with conventional molten carbonate fuel cell (MCFC) materials (Ni-based porous electrode and molten carbonate electrolyte), was investigated also for electrolysis. The cell was found to give lower polarization losses in MCEC mode than in MCFC mode, mainly due to the NiO electrode performing much better as anode in the electrolysis cell. Reversing...

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An Electrolyte Distribution Model in Consideration of the Electrode Wetting in the Molten Carbonate Fuel Cell

Cited by 40 publications

References 6 publications

Electrowetting of Molten Carbonate Electrolytes

Electrowetting of Molten Carbonate Electrolytes

Observation of Three-Phase Interface during Hydrogen Electrode Reactions in Unitized Regenerative Fuel Cell

Electrode Kinetics of the Ni Porous Electrode for Hydrogen Production in the Molten Carbonate Electrolysis Cell (MCEC)

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