Water effect on oxygen reduction in molten (Li + K)CO3 eutectic

Nishina, Tatsuo; Ohuchi, Shinji; Yamada, Kazutoyo; Uchida, Isamu

doi:10.1016/0022-0728(96)04514-7

Cited by 22 publications

(14 citation statements)

References 25 publications

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“…Consequently, the high-temperature ionic melt contains additional species in the electrolyte besides the dominant carbonate ions , due to chemical reactions between carbonate and dissolved species. One component that may be present in significant concentrations is hydroxide ions. − Hydroxide can affect the carbon capture efficiency of fuel cells as well as cause electrolyte loss. , Our recent computational study of chemical reaction equilibria based on classical force fields revealed that substantial fractions of hydroxide ions can be present in alkali carbonate eutectic mixtures, provided that the partial pressure ratio of CO 2 /H 2 O over the molten salt is low, meaning that more water is present than CO 2 , which is the case in carbon capture applications. These findings are consistent with recent experiments by Rosen et al that suggest a net consumption of water at the cathode, caused by water reacting with oxygen to produce hydroxide ions (eq ) when operating at low CO 2 gas-phase concentration and high current density.…”

Section: Introductionmentioning

confidence: 99%

First-Principles Modeling of Transport Mechanisms in Carbonate–Hydroxide Electrolytes

et al. 2021

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We performed ab initio molecular dynamics simulations of a molten [Li 0.6 K 0.4 ] 3 CO 3 OH electrolyte containing dissolved CO 2 and confirmed the presence of pyrocarbonate, bicarbonate, and water along with the constituent ions and molecular CO 2 . Our calculations indicate kinetics-driven formation of pyrocarbonate whereas bicarbonate and water are thermodynamically favored. Our results also demonstrate the presence of water at higher concentrations (double or more) than that of CO 2 , which reinforces the conclusions in our earlier work [AIChE J. 2020, e16988] based on chemical reaction equilibrium simulations. Structural analysis indicates a larger distortion in water geometry, due to its higher polarizability compared to the nonpolar CO 2 , explaining the higher reactivity and smaller average lifetime of H 2 O in the melt. The computed lifetime distributions of the reaction products reveal that the bicarbonate ion lives the shortest among all the species present in the system. It initiates a sequence of successive proton exchange events; such sequences of exchanges along a hydrogen-bonded network gives the Grotthuss mechanism for proton transport in liquid water. The estimated proton diffusion, based on a random walk model, is about 30 times faster than the hydroxide diffusion obtained from classical molecular dynamics simulations. We believe that the presence of proton transfer events in the system has a large impact on the overall ion dynamics and electrical conductivity of the medium.

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Section: Introductionmentioning

confidence: 99%

First-Principles Modeling of Transport Mechanisms in Carbonate–Hydroxide Electrolytes

et al. 2021

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“…While this process still contributes to power generation, it does not contribute to CO 2 capture from the cathode feed and thus reduces the carbon capture efficiency of the cell. Previous studies have emphasized the role of hydroxide ions as an intermediate reactant and as the principal water‐derived species in molten carbonates 14,15 . Hydroxide ions have also been implicated in cell degradation through the evaporation of alkali hydroxide species 16 .…”

Section: Introductionmentioning

confidence: 99%

“…Previous studies have emphasized the role of hydroxide ions as an intermediate reactant and as the principal water-derived species in molten carbonates. 14,15 Hydroxide ions have also been implicated in cell degradation through the evaporation of alkali hydroxide species. 16 Although the cathode reactions may be kinetically limited, understanding the carbonatehydroxide reaction equilibrium in molten carbonates is an appropriate first step towards understanding the overall process.…”

Section: Introductionmentioning

confidence: 99%

Predicting chemical reaction equilibria in molten carbonate fuel cells via molecular simulations

et al. 2020

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It has been recently suggested that hydroxide ions can be formed in the electrolyte of molten carbonate fuel cells when water vapor is present. The hydroxide can replace carbonate in transporting electrons across the electrolyte, thereby reducing the CO 2 separation efficiency of the fuel cell although still producing electricity. In 3 ð1Þ Anode : H 2 + CO 2− 3 ! H 2 O + CO 2 + 2e − ð2Þ However, recent experiments have revealed a parallel oxygen reduction mechanism when operating at low CO 2 gas-phase Jeffrey M. Young and Anirban Mondal contributed equally to this work.

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“…The mechanism of this reaction has been extensively investigated in the literature (Appleby and Nicholson, 1974, 1977Selman, 1990, 1992;Moutiers et al, 1991Moutiers et al, , 1992Nishina et al, 1994Nishina et al, , 1996Cassir et al, 1997), with 3 main paths being proposed, the Superoxide Path (SOP), the Peroxide Path (POP), and possibly the Peroximonocarbonate Path (POCP). SOP:…”

Section: Role In Cathode Mechanismmentioning

confidence: 99%

“…In most cases, CO 2 diffusion dominates the reaction process (Arato et al, 2016). Some research groups observed, either experimentally (Nishina et al, 1996;Audasso et al, 2017) or by modeling (Arato et al, 2016), a water effect on the cathode reaction: presence of water vapor decreased the apparent diffusion resistance of CO 2 and increased apparent mass transfer. This behavior was to be expected, as it has previously been explained that water reacts as an oxide ion acceptor, linked to its conjugated oxobase OH − by reaction 1, and can be later reobtained through reaction 9 reversed.…”

Section: Role In Cathode Mechanismmentioning

confidence: 99%

Significance of Molten Hydroxides With or Without Molten Carbonates in High-Temperature Electrochemical Devices

et al. 2021

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Due to their low melting point and high conductivity molten hydroxides are interesting electrolytes, or additive to other molten electrolytes for high-temperature electrochemical devices. There is nowadays a revival of such reactive media, first of all for their significant role in the electrode mechanisms in molten carbonate fuel cells (MCFCs) and the reverse co-electrolysis of water and carbon dioxide process, but also in different applications, among which direct carbon fuel cells (DCFCs), hybrid carbonate/oxide fuel cells. This overview shows the properties and interest of molten hydroxides and their use in relevant energy devices, pointing out their direct use as electrolytic media or as key species in complex kinetic processes. A thorough understanding of their behavior should allow improving and optimizing significantly fuel cells, electrolyzers, and probably also CO2 capture and valorization.

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Water effect on oxygen reduction in molten (Li + K)CO3 eutectic

Cited by 22 publications

References 25 publications

First-Principles Modeling of Transport Mechanisms in Carbonate–Hydroxide Electrolytes

First-Principles Modeling of Transport Mechanisms in Carbonate–Hydroxide Electrolytes

Predicting chemical reaction equilibria in molten carbonate fuel cells via molecular simulations

Significance of Molten Hydroxides With or Without Molten Carbonates in High-Temperature Electrochemical Devices

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