In situ NMR and electrochemical quartz crystal microbalance techniques reveal the structure of the electrical double layer in supercapacitors

Griffin, John M.; Forse, Alexander C.; Tsai, Wan‐Yu; Taberna, Pierre‐Louis; Simon, Patrice; Grey, Clare P.

doi:10.1038/nmat4318

Cited by 337 publications

(299 citation statements)

References 32 publications

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“…We previously showed that charging in the positive electrode takes place by swapping of anions and cations (counter-ion -co-ion exchange mechanism, X = 0), while charging in the negative electrode occurs by counter-ion adsorption (X = +1, see Figure 3c inset). 5 As a result, for positive polarisations the total in-pore ion population shows only minor changes with voltage, while for negative polarisation a marked increase is observed (Figure 3c). This increase of in-pore ion population correlates with the reduction of D in-pore for both ions: i.e., it appears that increasing ion-ion interactions lead to a reduction of D in-pore with 7 voltage for negative polarisations.…”

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confidence: 85%

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Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

et al. 2017

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Ionic transport inside porous carbon electrodes underpins the storage of energy in supercapacitors and the rate at which they can charge and discharge, yet few studies have elucidated the materials properties that influence ion dynamics. Here we use in situ pulsed field gradient NMR spectroscopy to measure ionic diffusion in supercapacitors directly. We find that confinement in the nanoporous electrode structures decreases the effective self-diffusion coefficients of ions by over two orders of magnitude compared to neat electrolyte, and in-pore diffusion is modulated by changes in ion populations at the electrode-electrolyte interface during charging.Electrolyte concentration and carbon pore size distributions also affect in-pore diffusion and the movement of ions in and out of the nanopores. In light of our findings we propose that controlling the charging mechanism may allow the tuning of the energy and power performances of supercapacitors for a range of different applications.As renewable energy and green technologies such as electric vehicles become prevalent, we must develop new ways to store and release energy on a range of timescales. Rechargeable batteries are ideal for timescales of minutes or hours (electric cars, portable electronic devices, grid storage etc.), while supercapacitors are more promising for second or sub-second timescales and are increasingly being used for transport applications where rapid charging and discharging are required. The superior power handling and cycle lifetime of supercapacitors comes at the expense of energy density, with recent materials-driven research aiming to address this issue by fine-tuning the nanoporous structure of the carbon electrodes, 1,2 and by using ionic liquid electrolytes that are stable at higher voltages. 3,4 Both approaches have afforded some increases in energy density, though not without sacrificing power density. The delicate balance between energy and power density must be understood if supercapacitors are to be used in a wide range of applications.Fundamental studies based on spectroscopic, 5-14 and theoretical, 15-18 methods have recently revealed the complex nature of charging in supercapacitors. Prior to charging, the electrode pores contain a large number of electrolyte ions, 15,19,20 and as a result charge storage is generally more complex than simple counter-ion adsorption (counter-ions are defined as having charge opposite to the electrode in which they are located). [5][6][7]15 A range of different charging mechanisms can operate

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confidence: 85%

“…Prior to charging, the electrode pores contain a large number of electrolyte ions, 15,19,20 and as a result charge storage is generally more complex than simple counter-ion adsorption (counter-ions are defined as having charge opposite to the electrode in which they are located). [5][6][7]15 A range of different charging mechanisms can operate …”

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confidence: 99%

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

et al. 2017

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“…The electrode materials, which is a key component of ECs [15], generally fall into three categories: (1) porous carbons with high specific surface area (e.g., metal-organic frameworks-derived nanoporous carbon [16,17], carbidederived carbon [18], carbon nanotubes [19], graphene [20]), (2) intrinsically conductive polymers (ICPs, e.g., polyaniline [21][22][23], polypyrrole [24,25], poly(DNTD) [26,27]), and (3) transition metal oxides/hydroxides (e.g., RuO 2 [28], MnO 2 [29], MoS 2 [30], Ni(OH) 2 [31], Co(OH) 2 [32]). Generally, porous carbons serve as electrode materials of electric doublelayer capacitors (EDLCs) to store energy via an electrostatic charge accumulation [33], while the ICPs and transition metal oxides/hydroxides serve as electrode materials of pseudocapacitors to store energy via redox reactions [34]. Actually, ICPs and their composites have received ever increasing attention because of their low cost, environmental friendliness, good redox reversibility, and high pseudocapacitance values [35,36].…”

Section: Electronic Supplementary Materialsmentioning

confidence: 99%

Significantly enhanced energy density of magnetite/polypyrrole nanocomposite capacitors at high rates by low magnetic fields

Wei

Guo

et al. 2017

Adv Compos Hybrid Mater

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One great challenge existing in electrochemical capacitors (ECs) is to achieve high energy densities at high rates. Currently, most research efforts are focused on development of new electrode materials or modification of the microstructure of traditional electrode materials. Herein, we propose a new strategy for significant enhancement of the energy density of ECs at high rates, in which an external magnetic field is exerted. Results indicate that exertion of a magnetic field can increase the energy density of nanocomposite capacitors significantly. In particular, the energy densities of the magnetite/ polypyrrole nanocomposite capacitors containing different content magnetite nanoparticles achieve an increase of more than 10 times at a high current density of 10 A/g, compared to the counterparts without a magnetic field. The possible mechanism is that the magnetic field induces electrolyte ion movement enhancement and charge transfer resistance reduction, which remarkably cause the increase of capacitance and energy density. This work provides an innovative strategy to significantly enhance the rate capabilities of current ECs by a simple physical process rather than chemical process.

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“…The accessibility of the micropores of the as-prepared carbons to electrolytes was investigated using NMR spectroscopy, which is achieved by analysising the perturbation of NMR spectra of the electrolyte induced by the adsorbents. When the electrolytes are confined in a nanopore, the NMR peak for a nucleus shifts to a higher position due to the diamagnetic shielding effect of the sp 2 hybridized carbon networks [21]. Such effect is only appreciable when the pores are small enough (i.e.…”

Section: Figurementioning

confidence: 99%

“…Such effect is only appreciable when the pores are small enough (i.e. micropores) and thus the NMR technique can be used to probe the infiltration of ions into small pores [21][22][23][24]. Both HA-800 and CNF-800 were impregnated with an acetonitrile solution of EMIImBF4 and 11 B NMR spectra were acquired for the electrolyte-loaded carbons after evaporating the solvent and the results are shown in Figure 4.…”

Section: Figurementioning

confidence: 99%

The enhancement of electrochemical capacitance of biomass-carbon by pyrolysis of extracted nanofibers

Deng

Zhong

Wang

et al. 2017

Electrochimica Acta

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The enhancement of electrochemical capacitance of biomass-carbon by pyrolysis of extracted nanofibers, Electrochimica Acta http://dx.doi.org/10. 1016/j.electacta.2017.01.099 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. extracted from an inexpensive natural fungus using a hydrothermal method and were converted to porous carbon nanofibers (CNFs) by potassium hydroxide activation.The porous carbons were assembled into symmetric supercapacitors using both potassium hydroxide and an ionic liquid (IL) as electrolytes. Solid state nuclear magnetic resonance characterization showed that the micropores of the as-prepared carbons are accessible to the IL electrolyte when uncharged and thus high capacitance is expected. It is found in both electrolytes the electrochemical capacitances of CNFs are significantly higher than those of the porous carbon derived directly from the crude fungus. Furthermore, the CNFs delivered an extraordinary energy density of 92.3 Wh kg -1 in the IL electrolyte, making it a promising candidate for electrode materials for supercapacitors.

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In situ NMR and electrochemical quartz crystal microbalance techniques reveal the structure of the electrical double layer in supercapacitors

Cited by 337 publications

References 32 publications

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

Direct observation of ion dynamics in supercapacitor electrodes using in situ diffusion NMR spectroscopy

Significantly enhanced energy density of magnetite/polypyrrole nanocomposite capacitors at high rates by low magnetic fields

The enhancement of electrochemical capacitance of biomass-carbon by pyrolysis of extracted nanofibers

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