Transport and Interfacial Properties of Mixed Molten Carbonate/Hydroxide Electrolytes by Molecular Dynamics Simulations

Mondal, Anirban; Young, Jeffrey M.; Barckholtz, Timothy A.; Kiss, G.; Koziol, Lucas; Panagiotopoulos, Athanassios Z.

doi:10.1021/acs.jpcc.0c07295

Cited by 8 publications

(8 citation statements)

References 42 publications

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“…Nevertheless, the polarizable model BK3+AH/BK3 still slightly overestimates the effect of NaCl on solution viscosity. Interestingly, the tendency of full-charge, nonpolarizable models to overestimate the viscosity (and thus underestimate diffusivities and ionic conductivities) is also true for molten salts, as indicated for Li–K mixed carbonate melts in ref and for deep eutectic solvents in ref .…”

Section: Liquid-state Dynamic Propertiesmentioning

confidence: 87%

Dynamics of Aqueous Electrolyte Solutions: Challenges for Simulations

Panagiotopoulos

Yue

2023

J. Phys. Chem. B

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This Perspective article focuses on recent simulation work on the dynamics of aqueous electrolytes. It is well-established that full-charge, nonpolarizable models for water and ions generally predict solution dynamics that are too slow in comparison to experiments. Models with reduced (scaled) charges do better for solution diffusivities and viscosities but encounter issues describing other dynamic phenomena such as nucleation rates of crystals from solution. Polarizable models show promise, especially when appropriately parametrized, but may still miss important physical effects such as charge transfer. First-principles calculations are starting to emerge for these properties that are in principle able to capture polarization, charge transfer, and chemical transformations in solution. While direct ab initio simulations are still too slow for simulations of large systems over long time scales, machine-learning models trained on appropriate first-principles data show significant promise for accurate and transferable modeling of electrolyte solution dynamics.

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Section: Liquid-state Dynamic Propertiesmentioning

confidence: 87%

Dynamics of Aqueous Electrolyte Solutions: Challenges for Simulations

Panagiotopoulos

Yue

2023

J. Phys. Chem. B

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“…19,20 Details of the force field parameters and protocols are described elsewhere. 9,21,22 The equilibrated supercell from the classical MD trajectory was geometry optimized within the density functional theory (DFT) framework at the same level of theory as described below. The gradients on the wave functions and on the nuclear positions were optimized with convergence criteria of 10 −6 and 10 −3 au, respectively.…”

Section: ■ Simulation Detailsmentioning

confidence: 99%

“…The temperature was set to 923.15 K, the experimentally measured melting point of the eutectic mixture, [Li 0.6 K 0.4 ] 3 CO 3 OH . To obtain a pre-equilibrated configuration at 923.15 K, we first performed classical MD simulations in the NPT ensemble at P = 1 bar using the GROMACS simulation program. , Details of the force field parameters and protocols are described elsewhere. ,, …”

Section: Simulation Detailsmentioning

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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“…As hydroxides have a higher conductivity compared to the corresponding carbonate (Janz and Tomkins, 1983;Mondal et al, 2020) (e.g., Li 2 CO 3 vs. LiOH), the ohmic resistance is expected to decrease with increasing hydroxide concentration in the electrolyte melt. Thus, as the carbonate/hydroxide equilibrium shifts, R Ω should decrease with decreasing CO 2 /H 2 O ratios in the cathode gas.…”

Section: Internal Resistance Alterationmentioning

confidence: 99%

Experimental and Modeling Investigation of CO3=/OH– Equilibrium Effects on Molten Carbonate Fuel Cell Performance in Carbon Capture Applications

et al. 2021

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Molten Carbonate Fuel Cells (MCFCs) are used today commercially for power production. More recently they have also been considered for carbon capture from industrial and power generation CO2 sources. In this newer application context, our recent studies have shown that at low CO2/H2O cathode gas ratios, water supplements CO2 in the electrochemical process to generate power but not capture CO2. We now report the direct Raman observation of the underlying carbonate-hydroxide equilibrium in an alkali carbonate eutectic near MCFC operating conditions. Our improved electrochemical model built on the experimental equilibrium data adjusts the internal resistance terms and has improved the representation of the MCFC performance. This fundamentally improved model now also includes the temperature dependence of cell performance. It has been validated on experimental data collected in single cell tests. The average error in the simulated voltage is less than 4% even when extreme operating conditions of low CO2 concentration and high current density data are included. With the improvements, this electrochemical model is suitable for simulating industrial cells and stacks employed in a wide variety of carbon capture applications.

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Transport and Interfacial Properties of Mixed Molten Carbonate/Hydroxide Electrolytes by Molecular Dynamics Simulations

Cited by 8 publications

References 42 publications

Dynamics of Aqueous Electrolyte Solutions: Challenges for Simulations

Dynamics of Aqueous Electrolyte Solutions: Challenges for Simulations

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

Experimental and Modeling Investigation of CO3=/OH– Equilibrium Effects on Molten Carbonate Fuel Cell Performance in Carbon Capture Applications

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