Electrochemistry and capacitive charging of porous electrodes in asymmetric multicomponent electrolytes

Biesheuvel, P.M.; Fu, Yeqing; Bazant, Martin Z.

doi:10.1134/s1023193512060031

Cited by 145 publications

(160 citation statements)

References 89 publications

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“…To this end, we extend non-linear theory for planar [48] and porous electrodes [49,51,54] developed for 1:1 salt solutions, to the case of solutions containing both NaCl and CaCl 2 . We will neglect effects of surface charge in the electrode of a chemical origin, related to how far the local pH deviates from the point of zero charge [54,57] and thus assume that the ionic charge in the diffuse part of the double layer is exactly compensated by electronic charge in the nearby conducting matrix (the carbon). We consider a one-dimensional geometry only (the depth direction x in Fig.…”

Section: Non-linear Theory -Porous Electrodesmentioning

confidence: 99%

Time-dependent ion selectivity in capacitive charging of porous electrodes

Zhao

Soestbergen

Rijnaarts

et al. 2012

Journal of Colloid and Interface Science

238

182

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In a combined experimental and theoretical study we show that capacitive charging of porous electrodes in multicomponent electrolytes may lead to the phenomenon of time-dependent ion selectivity of the electrical double layers (EDLs) in the electrodes. This effect is found in experiments on capacitive deionization of water containing NaCl/CaCl 2 mixtures, when the concentration of Na + ions in the water is 5 times higher than the Ca 2+ -ion concentration. In this experiment, after applying a voltage difference between two porous carbon electrodes, first the majority monovalent Na + cations are preferentially adsorbed in the EDLs, and later they are gradually replaced by the minority, divalent Ca 2+ cations. In a process where this ion adsorption step is followed by washing the electrode with freshwater under open-circuit conditions, and subsequent release of the ions while the cell is shortcircuited, a product stream is obtained which is significantly enriched in divalent ions. Repeating this process three times by taking the product concentrations of one run as the feed concentrations for the next, a final increase in the Ca 2+ /Na + -ratio of a factor of 300 is achieved. The phenomenon of timedependent ion selectivity of EDLs cannot be explained by linear response theory. Therefore, a nonlinear time-dependent analysis of capacitive charging is performed for both porous and flat electrodes. Both models attribute time-dependent ion selectivity to the interplay of the transport resistance for the ions in the aqueous solution outside the EDL, and the voltage-dependent ion adsorption capacity of the EDLs. Exact analytical expressions are presented for the excess ion adsorption in planar EDLs (Gouy-Chapman theory) for mixtures containing both monovalent and divalent cations.key-words: water desalination; porous electrode theory; capacitive (non-faradaic) electrochemical cells; electrostatic double layer theory.2

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Section: Non-linear Theory -Porous Electrodesmentioning

confidence: 99%

Time-dependent ion selectivity in capacitive charging of porous electrodes

Zhao

Soestbergen

Rijnaarts

et al. 2012

Journal of Colloid and Interface Science

238

182

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“…While our results do not strictly exclude the possibility that undetected differences in porosity at larger length scales may also impact electrochemical performance, nanoporous electrodes are known to have lower limiting current densities (i.e., the current density above which ion transport in the electrolyte is the limiting step) as compared to fully-dense electrodes. 56,57 In sum, our results plausibly suggest that differences in Li + transport within the FGS-TiO 2 as well as in the electrolyte have a significant impact on the high-rate, high-loading Li + storage performance of this material.…”

Section: Characterization Of Fgs-tiomentioning

confidence: 71%

High-Rate Li⁺Storage Capacity of Surfactant-Templated Graphene-TiO₂Nanocomposites

Hsieh

Punckt

Aksay

2015

J. Electrochem. Soc.

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Graphene-TiO 2 nanocomposites are a promising anode material for Li-ion batteries due to their good high-rate capacity, inherent safety, and mechanical and chemical robustness. However, despite a large number of scientific reports on the material, the mechanism of the enhanced high-rate Li + storage capacity that results from the addition of graphene to TiO 2 -typically attributed to improved electrical conductivity -is still not well understood. In this work, we focus on optimizing the processing of surfactant-templated graphene-TiO 2 hybrid nanocomposites. Towards this end, we examine the influence of various processing parameters, in particular the surfactant-mediated colloidal dispersion of graphene, on the material properties and electrochemical performance of grapheneTiO 2 . We investigate the influence of electrode mass loading on Li + storage capacity, focusing mainly on high-rate performance. Furthermore, we demonstrate an approach for estimating power loss during charge/discharge cycling, which offers a succinct method for characterizing the high-rate performance of Li-ion battery electrodes. Metal oxides have been studied extensively as anode materials for Li-ion batteries due to their comparably high Li-insertion/extraction potentials, 1,2 which make them inherently safe from Li-electroplating and dendrite formation, thus preventing membrane perforation and cell shorting even at high lithiation currents. Additionally, good mechanical and chemical stability during operation enables long cycling lifetimes.2-4 However, large oxide particles are restricted to slow charge/discharge rates (< C/5, meaning charge/discharge times > 5 h) because of low diffusion rates of Li +5-8 and poor electrical conductivity in oxides. Much work has therefore been done to address these limitations, with significant attention placed on titanium dioxide (TiO 2 ) 9-12 because it is abundant and chemically inert, and the availability of simple processes for producing nanostructured (i.e., nano-sized or nano-porous) TiO 2 make it attractive for large-scale use.Nanostructuring of TiO 2 improves Li + transport mainly by decreasing the length of Li + diffusion pathways through the oxide during lithiation/delithiation. 8,[13][14][15] In addition, the diffusivity of Li + in TiO 2 can be enhanced by using surfactant templates to orient the growth of the oxide. [16][17][18] To improve electron transport in TiO 2 electrodes, on the other hand, conductive coatings [19][20][21][22] at [SDS] just below the cmc, however, micelles will only be present on FGSs. 37 As such, the [SDS] used in the processing of FGS-TiO 2 will strongly influence where TiO 2 growth occurs and how intimately interconnected FGSs and TiO 2 will be, which will significantly affect the Li + storage performance of the nanocomposites. Furthermore, as the practical energy density of the system depends, in part, on the fraction of active mass present, 38 it is also necessary to investigate the effect of electrode mass loading, i.e., the amount of active material per unit ...

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“…Efforts toward developing pseudocapacitors have mostly focused on creating different electrode materials with most emphasis given to metal oxides, [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] and some effort going toward understanding charge/discharge behavior of these redox couple electrodes. [23][24][25][26][27] Devices in which the two electrodes exhibit the same capacitive behavior are known as symmetric capacitors.…”

Section: -7mentioning

confidence: 99%

“…z E-mail: staser@ohio.edu of the two electrodes is different, the device is known as an asymmetric capacitor. [8][9][10][11][12][13][14][15][16][17][18][30][31][32][33][34][35] In this paper, we will use the term "hybrid asymmetric capacitor" to indicate that one electrode behaves like a capacitor and the other electrode like a battery material (i.e., faradaic reactions).Srinivasan and Weidner developed analytical solutions for symmetric capacitors with porous electrodes to demonstrate the tradeoff between energy and power density upon varying the physical properties (i.e., the thickness) of the porous electrode.6 Lin, et al developed similar models based on finite difference solutions of the capacitor equations that showed that energy density increased with decreasing pore size, with little effect of pore size on power density.7 Recently, Kang, et al have developed equivalent circuit models for double-layer electrochemical capacitors using electrochemical impedance spectroscopy experiments. 36 They were able to correlate the resistance of the electrolyte with the capacitor performance during charge/discharge cycles.…”

mentioning

confidence: 99%

“…[4][5][6][7]28,29 If the capacitive behavior of the two electrodes is different, the device is known as an asymmetric capacitor. [8][9][10][11][12][13][14][15][16][17][18][30][31][32][33][34][35] In this paper, we will use the term "hybrid asymmetric capacitor" to indicate that one electrode behaves like a capacitor and the other electrode like a battery material (i.e., faradaic reactions).…”

mentioning

confidence: 99%

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Mathematical Modeling of Hybrid Asymmetric Electrochemical Capacitors

Weidner

2014

J. Electrochem. Soc.

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Electrochemical capacitors may be ideal energy storage devices for applications ranging from renewable energy storage to transportation. Electrochemical capacitors are characterized by high power density and cycle life, and can be classified based on the properties of their electrodes. Symmetric capacitors have two electrodes that exhibit the same behavior, while asymmetric capacitors have two electrodes that exhibit different behavior. A hybrid asymmetric capacitor is a device that has two electrodes that behave differently because of different processes occurring in them. In this paper, we present a mathematical model of hybrid asymmetric capacitors made up of a redox couple electrode and a double-layer electrode. We show that, because of the different behavior of each electrode, the hybrid asymmetric capacitor possesses higher energy and power density than the symmetric capacitor. Our model is generic and can be extended to any device so long as the properties of the electrodes are known. Electrochemical energy storage systems like electrochemical capacitors may be ideal to meet the needs of renewable energy storage and electric vehicles.1-3 Electrochemical capacitors are characterized by high power density and high cycle life. In the simplest terms, electrochemical capacitors store energy in the double layer at the interface of an electrically conductive material and the electrolyte. No faradaic reaction occurs. Double layer capacitance is low, usually between 10 and 40 μF cm −2 of electrode surface area. Therefore, high surface area materials are used (e.g., porous carbon electrodes) to significantly increase the capacitance of the device. 4 Because the voltage across a double layer is proportional to the charge stored, the voltage of a device decreases linearly with time during an entire constant-current discharge. In contrast, the voltage across a device where a faradaic reaction occurs across the electrode/electrolyte interface (i.e., a battery) is determined by the activity of the reactants and products. Therefore, its constant-current discharge curve is sigmoidal in shape, and hence the voltage is fairly constant over a significant portion of the discharge. Finally, pseudocapacitance is a term used to describe storage of charge via faradaic reactions where the activities of reactants and products are such that the discharge curve of a device more closely resembles a capacitor than it does a battery. Although pseudocapacitor response is much like a double-layer capacitor, they have considerably higher capacitance, and hence energy.Regardless of the type of device (i.e., double-layer capacitor or pseudocapacitor), the term "capacitor" is valid when the electrodes behave like a capacitor. Major efforts related to double-layer capacitors have focused on understanding the effect of electrode thickness and pore structure on the energy density and device capacity. 5-7Efforts toward developing pseudocapacitors have mostly focused on creating different electrode materials with most emphasis given to metal oxide...

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Electrochemistry and capacitive charging of porous electrodes in asymmetric multicomponent electrolytes

Cited by 145 publications

References 89 publications

Time-dependent ion selectivity in capacitive charging of porous electrodes

Time-dependent ion selectivity in capacitive charging of porous electrodes

High-Rate Li⁺Storage Capacity of Surfactant-Templated Graphene-TiO₂Nanocomposites

Mathematical Modeling of Hybrid Asymmetric Electrochemical Capacitors

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Electrochemistry and capacitive charging of porous electrodes in asymmetric multicomponent electrolytes

Cited by 145 publications

References 89 publications

Time-dependent ion selectivity in capacitive charging of porous electrodes

Time-dependent ion selectivity in capacitive charging of porous electrodes

High-Rate Li+Storage Capacity of Surfactant-Templated Graphene-TiO2Nanocomposites

Mathematical Modeling of Hybrid Asymmetric Electrochemical Capacitors

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Product

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High-Rate Li⁺Storage Capacity of Surfactant-Templated Graphene-TiO₂Nanocomposites