Statistical Mechanics of ‘Unwanted Electroactuation’ in Nanoporous Supercapacitors

Rochester, Christopher; Pruessner, Gunnar; Kornyshev, Alexei A.

doi:10.1016/j.electacta.2015.04.064

Cited by 14 publications

(27 citation statements)

References 33 publications

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“…The hysteresis loop between adsorption and desorption along with a sharp fall at a relatively high pressure suggests the slit geometry of major mesopores [30], which appears to be in good agreement with the electron microscopy images (Fig. 1b, c complex pore shape, interaction between carbon atoms, solvent molecules and ions, and the electrosorption-induced electrode swelling [32][33][34]. Therefore, the device performance cannot be simply evaluated by the BET surface area.…”

Section: Resultssupporting

confidence: 70%

Graphene supercapacitor with both high power and energy density

et al. 2017

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Supercapacitors, based on fast ion transportation, are specialized to provide high power, long stability, and efficient energy storage using highly porous electrode materials. However, their low energy density excludes them from many potential applications that require both high energy density and high power density performances. Using a scalable nanoporous graphene synthesis method involving an annealing process in hydrogen, here we show supercapacitors with highly porous graphene electrodes capable of achieving not only a high power density of 41 kW kg and a Coulombic efficiency of 97.5%, but also a high energy density of 148.75 Wh kg. A high specific gravimetric and volumetric capacitance (306.03 F g and 64.27 F cm) are demonstrated. The devices can retain almost 100% capacitance after 7000 charging/discharging cycles at a current density of 8 A g. The superior performance of supercapacitors is attributed to their ideal pore size, pore uniformity, and good ion accessibility of the synthesized graphene.

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Section: Resultssupporting

confidence: 70%

Graphene supercapacitor with both high power and energy density

et al. 2017

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“…The most common model for micropores is the random distribution of opposite charges in a micropore − in which the exciting co-ions leave the micropore upon charging. Forse et al stated that NMR is the only technique, which can detect the pre-existence of co-ions in the micropores, but the cited experimental data were based on a carbon sample with an average pore size of 0.9 nm.…”

Section: Available Models For Microporesmentioning

confidence: 99%

Surface Diffusion and Adsorption in Supercapacitors

Eftekhari¹

2018

ACS Sustainable Chem. Eng.

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The prospect of double layer capacitors relies on the high specific surface area provided by microporosity of carbon. Since there is not enough space within narrow micropores for forming a double layer, recent theoretical/computational studies have aimed at explaining the mechanism in micropores. The problem is that the available models suggest substantial differences in the mechanism of energy storage by microporous and other types of carbon, but the electrochemical behaviors are similar to a significant degree. Here, a conceptual model is proposed empirically, which is in full agreement with the experimental data reported in the literature, to reasonably explain a universal mechanism of all carbon-based capacitors including microporous, mesoporous, graphene, etc. It is described that none of the available models for double layer charging from Helmholtz to Graham is valid for carbon-based capacitors, as no double layer is formed within the micropores, as well as the partial contribution of double layer charging in larger pores or on graphene sheets. The mechanism of charge accumulation in supercapacitors is based on the adsorption of electroactive species over active sites of the carbon nanomaterial, and the surface diffusion of the adsorbed species collects the charge over the high surface area of carbon. The rate-determining step is usually controlled by the availability of active sites, which defines the rate capability of supercapacitors. This explains why the rate capability of double layer capacitors is much lower than the theoretical expectations, and why the alignment of graphene sheets results in fast performance in the so-called kilohertz supercapacitors. Any factors, such as narrow pores and irregularities, slowing down the subsequent surface diffusion cause the deviation from ideal capacitive behavior. The present paper attempts to highlight two points: surface diffusion might be a critical step in the mechanism of supercapacitors (probably a rate-determining step) and if narrow micropores exhibit capacitive behavior without forming a double layer, larger pores may do the same since no sudden change in the capacitive behavior with response to the pore size is observed (to represent a crucial change in the mechanism).

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“…Equation ( 28)), D = 0. The other constants, B and C, can be determined by the continuity of the potential across r = a (26), and the quantum capacitance condition (27). These conditions yield…”

mentioning

confidence: 99%

“…Quantum Capacitance Modifies Interionic Interactions in Semiconducting Nanopores r = a (26), and the quantum capacitance condition (27). These conditions yield…”

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confidence: 99%

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Quantum capacitance modifies interionic interactions in semiconducting nanopores

Lee¹,

Vella²,

Goriely³

2016

EPL

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-Nanopores made with low dimensional semiconducting materials, such as carbon nanotubes and graphene slit pores, are used in supercapacitors. In theories and simulations of their operation, it is often assumed that such pores screen ion-ion interactions like metallic pores, i.e. that screening leads to an exponential decay of the interaction potential with ion separation. By introducing a quantum capacitance that accounts for the density of states in the material, we show that ion-ion interactions in carbon nanotubes and graphene slit pores actually decay algebraically with ion separation. This result suggests a new avenue of capacitance optimization based on tuning the electronic structure of a pore: a marked enhancement in capacitance might be achieved by developing nanopores made with metallic materials or bulk semimetallic materials.Introduction. -Confinement of ions in nanostructures underpins the physics of many new electrochemical devices, ranging from supercapacitors [1] to field effect transistors [2]. These nanostructures are usually porous semiconducting materials such as carbon nanotubes or graphene slit pores. Early experiments have shown that electrodes made with porous carbide-derived-carbon deliver large volumetric capacitance as the pore-size (which can be precisely controlled) approaches the ion size [3][4][5]. This increase in capacitance cannot be rationalised by surface area enhancement alone, leading to the general hypothesis that the electronic structure of the electrodes significantly modifies the Coulomb interaction between ions [6,7].

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Statistical Mechanics of ‘Unwanted Electroactuation’ in Nanoporous Supercapacitors

Cited by 14 publications

References 33 publications

Graphene supercapacitor with both high power and energy density

Graphene supercapacitor with both high power and energy density

Surface Diffusion and Adsorption in Supercapacitors

Quantum capacitance modifies interionic interactions in semiconducting nanopores

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