Thermodynamics of Electrochemical Systems

Kjelstrup, Signe; Bedeaux, Dick

doi:10.1007/978-3-662-46657-5_4

“…The emf -measurements take place under reversible conditions, and one can safely assume equilibrium at the membrane solution interfaces. This makes it convenient to deal with the membrane as a discrete system [ 57 ]. The entropy production has contributions from the membrane transport of heat, mass, and charge.…”

Section: The Electromotive Force Of the Ag|agcl-cellmentioning

confidence: 99%

“…Non-equilibrium thermodynamics [ 28 , 53 , 54 , 55 , 56 , 57 ] can be used to describe the conversion of thermal to electric energy. Two sets of variables are then relevant: the practical set according to Katchalsky and Curran [ 53 ], which consists of measurable variables, and the set most often used of ionic variables.…”

Section: Introductionmentioning

confidence: 99%

Perspectives on Thermoelectric Energy Conversion in Ion-Exchange Membranes

Barragán

¹

,

Kristiansen

²

,

Kjelstrup

³

2018

Entropy

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By thermoelectric power generation we mean the creation of electrical power directly from a temperature gradient. Semiconductors have been mainly used for this purpose, but these imply the use of rare and expensive materials. We show in this review that ion-exchange membranes may be interesting alternatives for thermoelectric energy conversion, giving Seebeck coefficients around 1 mV/K. Laboratory cells with Ag|AgCl electrodes can be used to find the transported entropies of the ions in the membrane without making assumptions. Non-equilibrium thermodynamics can be used to compute the Seebeck coefficient of this and other cells, in particular the popular cell with calomel electrodes. We review experimental results in the literature on cells with ion-exchange membranes, document the relatively large Seebeck coefficient, and explain with the help of theory its variation with electrode materials and electrolyte concentration and composition. The impact of the membrane heterogeneity and water content on the transported entropies is documented, and it is concluded that this and other properties should be further investigated, to better understand how all transport properties can serve the purpose of thermoelectric energy conversion.

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“…The Seebeck coefficient is defined as ε = ∆φ ∆T j=0 [4] where ∆T = T s,c − T s,a . In the following we shall give expressions for all contributions to ∆φ , see (21,22) for more details.…”

Section: −1mentioning

confidence: 99%

“…The excess entropy production of the electrode surfaces refers to Li(s) intercalated in CoO 2 in contact with the electrolyte. Following Kjelstrup and Bedeaux (22) we obtain:…”

Section: Electrode Surface Contributionsmentioning

confidence: 99%

Single Electrode Entropy Change for LiCoO₂Electrodes

Richter

¹

,

Gunnarshaug

²

,

Burheim

³

et al. 2017

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Heat effects are known to be crucial for the performance of the Libattery. In addition to the irreversible effects (e.g. Joule heat), reversible heat effects may play a role. These effects, i.e. the Soret and Seebeck effects, are however scarcely investigated. We report the initial and stationary state thermoelectric potentials of a pouch cell having electrodes where Li is intercalated in CoO 2 . The electrolyte consists of 1.0 M lithium hexafluoro phosphate dissolved in a mixture of equal volumes of ethylene carbonate and diethyl carbonate. The two identical electrodes were thermostatted at different temperatures, the average being always 298 K and the potential was measured over several days. We observe two time-dependent phenomena with characteristic times of 4.5 and 21.3 hours. We explain them by thermal diffusion of salt and esters. The Seebeck coefficient varies from -2.8 mV/K in the initial state to 1.5 mV/K in the state characterized by partial Soret equilibrium. The time-variation of the signal is used to compute Seebeck coefficients, the contributions to the heats of transfer, and the reversible heat effect at the LiCoO 2 -and carbon electrodes. The electrode heat effects in a Li-battery is surprisingly asymmetric, given the small entropy of the total reaction. The LiCoO 2 electrode heat varies from 51 to -46 kJ/mol, while the carbon electrode will vary from -73 to 56 kJ/mol. Uncertainties in computations are within 15%. This may explain why the reaction entropy depends largely on the state of charge. It may also be important for thermal modeling of the battery.

show abstract

“…The Seebeck coefficient is defined as ε = ∆φ ∆T j=0 [4] where ∆T = T s,c − T s,a . In the following we shall give expressions for all contributions to ∆φ , see (21,22) for more details.…”

Section: The Thermoelectric Cellmentioning

confidence: 99%

Single Electrode Entropy Change for LiCoO₂ Electrodes

Richter,

Gunnarshaug,

Burheim

et al. 2017

Meet. Abstr.

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0

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Heat effects are known to be crucial for the performance of the Libattery. In addition to the irreversible effects (e.g. Joule heat), reversible heat effects may play a role. These effects, i.e. the Soret and Seebeck effects, are however scarcely investigated. We report the initial and stationary state thermoelectric potentials of a pouch cell having electrodes where Li is intercalated in CoO 2 . The electrolyte consists of 1.0 M lithium hexafluoro phosphate dissolved in a mixture of equal volumes of ethylene carbonate and diethyl carbonate. The two identical electrodes were thermostatted at different temperatures, the average being always 298 K and the potential was measured over several days. We observe two time-dependent phenomena with characteristic times of 4.5 and 21.3 hours. We explain them by thermal diffusion of salt and esters. The Seebeck coefficient varies from -2.8 mV/K in the initial state to 1.5 mV/K in the state characterized by partial Soret equilibrium. The time-variation of the signal is used to compute Seebeck coefficients, the contributions to the heats of transfer, and the reversible heat effect at the LiCoO 2 -and carbon electrodes. The electrode heat effects in a Li-battery is surprisingly asymmetric, given the small entropy of the total reaction. The LiCoO 2 electrode heat varies from 51 to -46 kJ/mol, while the carbon electrode will vary from -73 to 56 kJ/mol. Uncertainties in computations are within 15%. This may explain why the reaction entropy depends largely on the state of charge. It may also be important for thermal modeling of the battery.

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Thermodynamics of Electrochemical Systems

Cited by 7 publications

References 76 publications

Perspectives on Thermoelectric Energy Conversion in Ion-Exchange Membranes

Perspectives on Thermoelectric Energy Conversion in Ion-Exchange Membranes

Single Electrode Entropy Change for LiCoO₂Electrodes

Single Electrode Entropy Change for LiCoO₂ Electrodes

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Thermodynamics of Electrochemical Systems

Cited by 7 publications

References 76 publications

Perspectives on Thermoelectric Energy Conversion in Ion-Exchange Membranes

Perspectives on Thermoelectric Energy Conversion in Ion-Exchange Membranes

Single Electrode Entropy Change for LiCoO2Electrodes

Single Electrode Entropy Change for LiCoO2 Electrodes

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Product

Resources

About

Single Electrode Entropy Change for LiCoO₂Electrodes

Single Electrode Entropy Change for LiCoO₂ Electrodes