Ruthenium Oxide-Carbon Composite Electrodes for Electrochemical Capacitors

Zheng, Jim P.

doi:10.1149/1.1390837

Cited by 242 publications

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“…A good kinetic reversibility is an important factor for ideal capacitor behaviour. It can also be seen that for the four nanomaterials, the redox current increases with increasing scan rate which indicates good rate ability [20][21][22][23]. [24] demonstrated that the specific capacitance decreases with increasing charging rate; similar to the result shown in Figure 6(b).The decrease in specific capacitance with increasing charging rate is due to the limited transfer of ions to the pores, leading to inaccessible pore portions of the electrode layer at high charging rates.…”

Section: Resultssupporting

confidence: 67%

Study of ternary metal oxides as supercapacitor electrodes

Bhujun¹,

Anandan²,

Tan³

2014

Energy and Sustainability V

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Supercapacitors are energy storage devices that make use of ion adsorption (electrochemical double layer capacitors) or fast surface redox reactions (pseudocapacitors). They complement batteries in electrical energy storage. Recent advances in charge storage mechanisms and the development of advanced nanostructured materials has yielded notable improvement in the performance of supercapacitors. The structural and electrochemical properties of the mixed metallic oxides Al x Cu y Co z Fe 2 O 4 (where x + y + z = 1) nanomaterials, which crystallise in a cubic spinel AFe 2 O 4 structure are investigated systematically with a gradual substitution of Al by transition metals. The crystal structure information studied by X-ray diffraction (XRD) depicts the formation of single phase spinel structure, while electron-dispersive X-ray spectroscopy (EDX) reveals the stoichiometric relations of Al, Cu and Co.

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Section: Resultssupporting

confidence: 67%

Study of ternary metal oxides as supercapacitor electrodes

Bhujun¹,

Anandan²,

Tan³

2014

Energy and Sustainability V

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“…18 A porosity of 1 corresponds to a fully flooded electrolyte. Figure 11 illustrates the potential drop in the solution phase while changing the porosity of the electrode.…”

Section: Scmentioning

confidence: 99%

“…This is in accordance with previous experimental data. 18,19 In reality, the porosity of the electrode varies even at the same carbon/RuO 2 ratio according to the particle size of RuO 2 and also in the way RuO 2 and carbon are mixed ͑physical or chemical mixture͒. It has been shown that large particles of RuO 2 deposited chemically block the pores of the carbon, which cannot be expected to reduce the solution potential drop.…”

Section: Scmentioning

confidence: 99%

A Mathematical Model of Oxide/Carbon Composite Electrode for Supercapacitors

Kim

Popov

2003

J. Electrochem. Soc.

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A pseudo two-dimensional model is developed for the general application of supercapacitors consisting of an oxide/carbon composite electrode. The model takes into account the diffusion of protons in the oxide particle by employing the method of superposition. RuO 2 /carbon system is modeled as a specific example. From the simulation data, it is found that the oxide particle size and proton diffusion coefficient have an enormous effect on the performance at high discharge rate due to the limitation of proton transport into RuO 2 particles. With increasing carbon ratio, the porosity of electrode increases, which causes the potential drop in solution phase to decrease. However, excess of carbon lowers the total capacitance because the pseudocapacitance from RuO 2 decreases. Finally, the present model successfully provides a methodology to optimize cell configurations and operating conditions. © presented an analytical solution of the double-layer capacitor under constant current mode, which was used to investigate the relative importance of ionic and electronic resistance in the design of supercapacitors. Farahmandi 5 also presented an analytic solution of the model for double-layer capacitors to study the effects of both ionic and solid-phase conductivities on the behavior of an electrochemical capacitor.Few models have been developed for pseudocapacitance. Lin et al.6 reported a supercapacitor model, which considers the faradaic reaction occurring on RuO 2 . It was modified to include both doublelayer capacitance and pseudocapacitance using the packing theory and the concentrated solution theory.7 This model explained the effect of the particle size of the oxide and of the cell current density on the charge/discharge behavior. However, this model did not analyze the difference in capacitance exhibited by crystalline and amorphous RuO 2 . It is well known in literature 8,9 that proton transfer rates within ruthenium oxide particle determines the capacitance of the electrode. An amorphous structure allows the proton to diffuse faster inside the oxide particle as compared to crystalline RuO 2 . The proton transfer rate and the capacitance obtained are related closely and strongly depend on the degree of crystallinity of the Ru oxide. The model by Lin et al. 6 does not consider proton diffusion and hence cannot distinguish between different forms of ruthenium oxide. As a result, this model has limitations when applied to the real system. To overcome this problem, in this paper we consider the proton diffusion in oxide particles using the procedure presented by Doyle et al. 10 The present model successfully provides a theoretical simulation of the charge or discharge behavior of a hybrid supercapacitor as a function of cell parameters such as the porosity of electrode, the particle size of oxide, the concentration of electrolyte, and the ratio between oxide and carbon.The objective of this study is to develop a general full cell model for supercapacitors which considers the diffusion of protons within the oxide partic...

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“…Low power density combined with its high cost make pure RuO 2 •xH 2 O unsuitable for commercial electrochemical capacitor applications. To improve power density, high rate performance, and cost, recent electrochemical capacitor research has focused on developing nanostructured RuO 2 •xH 2 O-carbon composite materials. [1][2][3] These materials have a high DL capacitance originating from high surface area of porous activated carbon, plus pseudocapacitance derived from the redox reactions of RuO 2 dispersed over the carbon surface.…”

mentioning

confidence: 99%

Modeling the Effects of Electrode Composition and Pore Structure on the Performance of Electrochemical Capacitors

Cheng

Popov

Ploehn

2002

J. Electrochem. Soc.

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This work presents a mathematical model for charge/discharge of electrochemical capacitors that explicitly accounts for particlepacking effects in a composite electrochemical capacitor consisting of hydrous RuO 2 nanoparticles dispersed within porous activated carbon. The model is also used to investigate the effect of nonuniform distributions of salt in the electrolyte phase of the electrode in the context of dilute solution theory. We use the model to compare the performance of capacitors with electrodes made from different activated carbons and to investigate the effects of varying carbon content and discharge current density. Even at low discharge current density, concentration polarization in the electrodes results in underutilization of the electrodes' charge-storage capability, and thus decreased performance. Among various types of activated carbons, those with large micropore surface areas and low meso-and macropore surface areas are preferred because they give high double-layer capacitance and favor efficient packing of RuO 2 nanoparticles, thus maximizing faradaic pseudocapacitance. Increasing the electrode carbon content decreases the delivered charge and energy density, but the reductions are not severe at moderate carbon content and high discharge current. This suggests the possibility of optimizing the carbon content to minimize cost while achieving acceptable discharge performance. Electrochemical capacitors are urgently needed as components in many advanced power systems requiring high power density, high energy density, and high cycleability.1-6 Energy storage mechanisms in an electrochemical capacitor include separation of charge at the interface between a solid electrode and a liquid electrolyte, leading to double-layer ͑DL͒ capacitance, and faradaic redox reactions occurring at or near a solid electrode surface, known as pseudocapacitance. Charge storage in DL capacitance is essentially electrostatic in nature, and so DL charge/discharge processes are usually highly reversible. Pseudocapacitance, originating from faradaic redox reactions of oxides like RuO 2 , IrO 2 , or Co 3 O 4 at or near the electrode surface, involves interfacial reaction as well as mass transfer of ionic charge across the double layer. 6 Capacitors employing both DL and pseudocapacitance generally perform better than those featuring just one kind of capacitance. Activated carbon has been frequently used because its porous structure and large internal surface area result in electrodes with high specific energy and specific power densities. 6 The pore structure of activated carbon is a significant element in determining electrochemical capacitor performance. Shi 7 argued that pores of different sizes ͑micro-, meso-, and macropores͒ play different roles in contributing to DL capacitance. Macropores make a small contribution to the total specific surface area and thus contribute little to the DL capacitance. At the other extreme, micropores are responsible for most of the specific surface area, but the smallest pores may not...

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Ruthenium Oxide-Carbon Composite Electrodes for Electrochemical Capacitors

Cited by 242 publications

References 0 publications

Study of ternary metal oxides as supercapacitor electrodes

Study of ternary metal oxides as supercapacitor electrodes

A Mathematical Model of Oxide/Carbon Composite Electrode for Supercapacitors

Modeling the Effects of Electrode Composition and Pore Structure on the Performance of Electrochemical Capacitors

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