Effect of accelerated ageing on the performance of high voltage carbon/carbon electrochemical capacitors in salt aqueous electrolyte

Ratajczak, Paula; Jurewicz, K.; Skowron, Piotr; Abbas, Qamar; Béguin, François

doi:10.1016/j.electacta.2014.02.140

Cited by 126 publications

(115 citation statements)

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“…In our previous reports, we demonstrated that oxidation of the positive AC electrode and corrosion of the positive current collector are essentially the cause of performance deterioration during floating of AC/AC capacitors in 1 mol L −1 Li 2 SO 4 at 1.6 V. 11 According to the Nernst equation, the thermodynamic limits for di-oxygen and di-hydrogen evolution at the positive and negative electrodes, and consequently the possible performance degradation, are pH dependent and given by the equations E ox = 1.23 − 0.059 pH and E red = −0.059 pH vs SHE, respectively. In other words, the operating potential ranges of positive and negative electrodes in aqueous based capacitor systems are controlled by the electrolyte pH.…”

Section: Resultsmentioning

confidence: 99%

“…Besides, when shifting from gold to stainless steel current collectors in order to develop low cost AC/AC capacitors in 1 mol L −1 Li 2 SO 4 , constant capacitance and low cell resistance have been observed during potentiostatic floating at cell potential of 1.5 V, while capacitance drops and resistance increases continuously if the floating potential is raised to 1.6 V. 10,11 The increase in resistance has been attributed to i) oxidation of the positive AC electrode owing to irreversible oxygen production and/or ii) generation and accumulation of stainless steel corrosion products (as the positive electrode potential is higher than the water oxidation limit) at the current collector/electrode interface, both impeding the cell performance. In order to overcome this issue, 0.1 mol L −1 Na 2 MoO 4 has been used as additive to 1 mol L −1 Li 2 SO 4 , allowing the operating potential of the positive electrode to be shifted below the thermodynamic water oxidation limit.…”

mentioning

confidence: 99%

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Strategies to Improve the Performance of Carbon/Carbon Capacitors in Salt Aqueous Electrolytes

Abbas

Ratajczak

Babuchowska

et al. 2015

J. Electrochem. Soc.

107

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Strategies are presented to enhance operating potential and cycle life of AC/AC capacitors using salt aqueous electrolytes. Li 2 SO 4 (pH = 6.5) allows 99% efficiency to be exhibited at 1.6 V cell potential with low self-discharge, while in BeSO 4 (pH = 2.1) efficiency is low (81%). Li 2 SO 4 performs better due to high di-hydrogen over-potential at the negative electrode and related pH increase in AC porosity. When stainless steel current collectors are used in Li 2 SO 4 , the cell resistance suddenly increases after 12 hours floating at 1.6 V, due to corrosion of the positive collector. With nickel negative and stainless steel positive collectors, the electrode potentials are shifted by −105 mV at cell potential of 1.6 V, allowing stable cell parameters (capacitance, resistance) and reduction of corrosion products formation on positive steel collector after 120 hours floating. Phenanthrenequinone was grafted on activated carbon to get an additional faradaic contribution in buffer solutions (pH = 4.0 or 7.2). The three-electrode cell CVs show that the redox peaks of the phenanthrenequinone graft shift toward negative values when pH increases from 4 to 7. Electrical double-layer capacitors (EDLCs) based on activated carbons (AC) and traditional aqueous electrolytes, such as H 2 SO 4 and KOH, operate at low cell potential (up to ∼0.8 V), limiting their capability at industrial level. [1][2][3][4] In order to improve the energy (E = 1 2 CU 2 ), both capacitance (C) and cell potential (U) determined by the stability window of the electrolyte have to be optimized. In this context, it has been recently demonstrated that symmetric capacitors based on AC electrodes and salt aqueous electrolyte (0.5 mol L −1 Na 2 SO 4 ) exhibit excellent cyclability under galvanostatic charge/discharge up to 1.6 V. 5,6 . While using 1 mol L −1 Li 2 SO 4 and gold current collectors, excellent cycle life has been shown up to ∼1.9 V using galvanostatic charge/discharge. 7,8 Such high cell potential value is caused by a high over-potential for di-hydrogen evolution as a consequence of water reduction and OH − ions generation in the porosity of the negative AC electrode. 5,7 According to the Nernst equation (E red = −0.059 pH), the pH increase associated to OH − ions causes locally a shift of redox potential to lower values. Based on this fact, it has been recently demonstrated that the di-hydrogen evolution over-potential is higher in almost neutral electrolyte solutions (pH = 4-8) than in acidic ones, resulting in larger operating cell potential of asymmetric capacitors in the former media.9 From the foregoing, it makes sense to study in more details the influence of aqueous electrolyte pH on the electrochemical performance of AC/AC capacitors beyond only the cell potential.Besides, when shifting from gold to stainless steel current collectors in order to develop low cost AC/AC capacitors in 1 mol L −1 Li 2 SO 4 , constant capacitance and low cell resistance have been observed during potentiostatic floating at cell potential of 1.5 V, whil...

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Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Strategies to Improve the Performance of Carbon/Carbon Capacitors in Salt Aqueous Electrolytes

Abbas

Ratajczak

Babuchowska

et al. 2015

J. Electrochem. Soc.

107

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“…[31]. Hence, the more significant leakage current and SD of the EC at higher Ui might be attributed to faradaic reactions related with water electrolysis when the cell potential exceeds the thermodynamic value of 1.23 V, namely: (i) overcharging and corrosion of the positive stainless steel collector [7,8]; (ii) reaction of the formed oxygen within the electrolyte solution or creation of functionalities on the surface of activated carbon, leading even to pore blockage during floating [7,32]; iii) other side faradaic reactions due to some impurities [21,22]. Recently, Abbas et al [9] have measured the potential range of electrodes vs cell potential of a carbon/carbon symmetric EC with AC-PTFE electrodes of same composition in neutral aqueous electrolyte, and have proved that the potential of the AC-PTFE positive electrode exceeds the thermodynamic limit of water oxidation at cell potential of 1.4 V. Hence, oxygen evolution and carbon oxidation [7] are likely important causes of the enhanced SD and leakage current at Ui > 1.4 V in our experiments; it will be further proved by analysis of the SD profiles, demonstrating activation controlled mechanism at Ui > 1.4 V. 3) reveals that the cell potential drop is higher by ca.…”

Section: Self-discharge Dependence With Initial Cell Potentialmentioning

confidence: 99%

“…The maximum cell potential of ECs using neutral aqueous electrolyte is essentially limited by the positive electrode which potential may exceed the electrochemical stability limit of water oxidation, leading to irreversible reactions, such as electrolyte decomposition, formation of oxygenated functional groups on the carbon surface and corrosion of the underlying stainless steel collector [7,8].…”

Section: H2so4mentioning

confidence: 99%

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Self-discharge of AC/AC electrochemical capacitors in salt aqueous electrolyte

García‐Cruz

Ratajczak

Iniesta

et al. 2016

Electrochimica Acta

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Please cite this article as: L.García-Cruz, P.Ratajczak, J.Iniesta, V.Montiel, F.Béguin, Self-discharge of AC/AC electrochemical capacitors in salt aqueous electrolyte, Electrochimica Acta http://dx.doi.org/10. 1016/j.electacta.2016.03.159 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. AbstractThe self-discharge (SD) of electrochemical capacitors based on activated carbon electrodes (AC/AC capacitors) in aqueous lithium sulfate was examined after applying a three-hour cell potential hold at Ui values from 1.0 to 1.6 V. The leakage current measured during the potentiostatic period as well as the amplitude of self-discharge increased with Ui; the cell potential drop was approximately doubled by 10°C increase of temperature. The potential decay of both negative and positive electrodes was explored separately, by introducing a reference electrode and it was found that the negative electrode contributes essentially to the capacitor self-discharge. A diffusion controlled mechanism was found at Ui ≤ 1.4 V and Ui ≤ 1.2 V for the positive and negative electrodes, respectively. At higher Ui of 1.6 V, both electrodes display an activation controlled mechanism due to water oxidation and subsequent carbon oxidation at the positive electrode and water or oxygen reduction at the negative electrode.

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Supercapacitors Based on Carbon or Pseudocapacitive Materials

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Effect of accelerated ageing on the performance of high voltage carbon/carbon electrochemical capacitors in salt aqueous electrolyte

Cited by 126 publications

References 24 publications

Strategies to Improve the Performance of Carbon/Carbon Capacitors in Salt Aqueous Electrolytes

Strategies to Improve the Performance of Carbon/Carbon Capacitors in Salt Aqueous Electrolytes

Self-discharge of AC/AC electrochemical capacitors in salt aqueous electrolyte

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