外文翻譯--粘接劑對碳碳水系對稱電容器性能的影響（英文）

1、A5148 Journal of The Electrochemical Society, 162 (5) A5148-A5157 (2015)JES FOCUS ISSUE ON ELECTROCHEMICAL CAPACITORS: FUNDAMENTALS TO APPLICATIONSStrategies to Improve the Performance of Carbon/Carbon Capacitors in Salt

2、 Aqueous ElectrolytesQ. Abbas,a P. Ratajczak,a,? P. Babuchowska,a A. Le Comte,b,c,d D. B´ elanger,c,??T. Brousse,b,d,?? and F. B´ eguina,??,zaInstitute of Chemistry and Technical Electrochemistry, Poznan Univer

3、sity of Technology, 60-965 Poznan, Poland bInstitut des Mat´ eriaux Jean Rouxel (IMN), Universit´ e de Nantes, CNRS, BP32229, 44322 Nantes Cedex 3, France cD´ epartement Chimie, Universit´ e du Qu

4、0; ebec ` a Montr´ eal, Succursale Centre-Ville, Montr´ eal, Qu´ ebec H3C 3P8, Canada dR´ eseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459, FranceStrategies are presented to enh

5、ance operating potential and cycle life of AC/AC capacitors using salt aqueous electrolytes. Li2SO4 (pH = 6.5) allows 99% efficiency to be exhibited at 1.6 V cell potential with low self-discharge, while in BeSO4 (pH = 2

6、.1) efficiency is low (81%). Li2SO4 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 Li2SO4, the

7、 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

8、 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 grafte

9、d 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

10、 when pH increases from 4 to 7.2. The grafted carbon displays a capacitance value of 194 F g?1 at pH = 4.0 as compared to 82 F g?1 for the as-received carbon. © The Author(s) 2015. Published by ECS. This is an open

11、access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the or

12、iginal work is properly cited. [DOI: 10.1149/2.0241505jes] All rights reserved.Manuscript submitted December 18, 2014; revised manuscript received February 6, 2015. Published February 26, 2015. This paper is part of the

13、JES Focus Issue on Electrochemical Capacitors: Fundamentals to Applications.Electrical double-layer capacitors (EDLCs) based on activated car- bons (AC) and traditional aqueous electrolytes, such as H2SO4 and KOH, operat

14、e at low cell potential (up to ～0.8 V), limiting their capa- bility at industrial level.1–4 In order to improve the energy (E = 12 CU2), both capacitance (C) and cell potential (U) determined by the stability window of t

15、he 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 Na2SO4) exhibit excellent cyclability und

16、er galvanostatic charge/discharge up to 1.6 V.5,6. While using 1 mol L?1 Li2SO4 and gold current collectors, ex- cellent cycle life has been shown up to ～1.9 V using galvanostatic charge/discharge.7,8 Such high cell pote

17、ntial 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 (Ered

18、 = ?0.059 pH), the pH increase associated to OH? ions causes locally a shift of re- dox potential to lower values. Based on this fact, it has been recently demonstrated that the di-hydrogen evolution over-potential is hi

19、gher 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

20、 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 d

21、evelop low cost AC/AC capacitors in 1 mol L?1 Li2SO4, constant capacitance and low cell resistance have been observed during potentiostatic floating at cell potential of 1.5 V, while capacitance drops and resistance incr

22、eases 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) generat

23、ion and accumu- lation 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

24、. In order to overcome this issue, 0.1 mol L?1 Na2MoO4 has been used?Electrochemical Society Student Member. ??Electrochemical Society Active Member. zE-mail: francois.beguin@put.poznan.plas additive to 1 mol L?1 Li2SO4,

25、 allowing the operating potential of the positive electrode to be shifted below the thermodynamic water oxidation limit. As a consequence, sodium molybdate prevents from corrosion of the positive current collector, enabl

26、ing constant low cell resistance and high capacitance during potentiostatic floating at 1.6 V for 120 hours.12 Active material coatings on metallic foil have been further employed in order to eliminate the possible depos

27、ition of a resistive layer at the active material/current collector interface when self-standing AC electrodes are used in physical contact with the current collectors. Accelerated ageing by floating has been applied to

28、verify the long term stability of the cells prepared with this strategy.13Upon floating AC/AC cells in 1 mol L?1 Li2SO4 for 120 hours at 1.6 V, the cell resistance increased by 136% with self-standing electrodes and only

29、 by 93% when coated electrodes were used.14 Another tactics could be to replace stainless steel by nickel current collectors. Indeed, due to its good stability and easy availability, nickel is a widely used electrode mat

30、erial for e.g., water electrolysis15 and was also found in this study as a proper collector to improve the performance of carbon/carbon capacitors in 1 mol L?1 Li2SO4. Various strategies based on pseudo-capacitive or far

31、adaic con- tributions have been reported to enhance the capacitance of car- bon/carbon capacitors in aqueous media. Such contributions were obtained by i) adding electrochemically active species such as quinones16 and al

32、kali metal iodides17–19 in the electrolyte, ii) us- ing carbon electrode materials undergoing redox reactions result- ing from naturally occurring surface functionalities, hydrogen stor- age and chemically/electrochemica

33、lly grafted active molecules such as quinone derivatives.20–26 The later modification is generally real- ized by electrochemical27,28 or chemical29–31 reduction of diazonium cations. The pH of the applied electrolyte has

34、 a significant influ- ence on the possible redox mechanisms involving proton and elec- tron transfer,31–33 and consequently on the capacitance properties of quinone-modified carbons. Surface functionalization enables an

35、in- crease of the specific capacitance of the modified electrode even by a factor of two compared to the pristine carbon electrode in acid and basic aqueous electrolytes. For example, the attachment of an- thraquinone gr

36、oups to the surface of the Black Pearl 2000 carbon enhanced the capacitance from 100 F g?1 for the unmodified carbon to 195 F g?1 for grafted carbon in 0.1 mol L?1 H2SO4.34 However,) unless CC License in place (see abstr

37、act). ecsdl.org/site/terms_useaddress. Redistribution subject to ECS terms of use (see 118.120.152.182 Downloaded on 2015-06-27 to IP A5150 Journal of The Electrochemical Society, 162 (5) A5148-A5157 (2015)Figure 1. T

38、hree-electrode cyclic voltammograms (2 mV s?1) of AC obtained by stepwise decrease of the negative cutoff potential (a) in 1 mol L?1 Li2SO4 solution with pH = 6.5; (b) in 1 mol L?1 BeSO4 solution with pH = 2.1. The verti

39、cal dashed lines represent the theoretical water reduction potential at the considered pH.glass mat separator (AGM, Bernard Dumas, thickness = 0.52 mm) between two coated electrodes and cylindrical current collectors, ei

40、- ther from stainless steel or nickel. Before being closed, the assembled system was soaked under vacuum with 1 mol L?1 Li2SO4 electrolytic solution. The electrochemical performance of the two-electrode (without and with

41、 reference) and three-electrode cells was determined with a VMP3 (Biologic, France) multichannel potentiostat/galvanostat. The gravimetric capacitance C (F g?1 of as-received as well as DLC Supra 30-PQ activated carbons

42、in one electrode) was estimated from gal- vanostatic discharge at 0.2 A g?1 and cyclic voltammetry at scan rates of 2 mV s?1 and 5 mV s?1. Accelerated ageing of the cells was realized as reported in Ref. 9 by a successio

43、n of two-hour po- tentiostatic floating periods, each followed by five galvanostatic (1 A g?1 referred to the active mass of one electrode) cycles the cell potential hold during floating and the maximum cell potential du

44、ring galvanostatic cycling were fixed at the same value. The capacitance and cell resistance were estimated from the fifth discharge to monitor the state of health (SOH) after each floating period. The test sequences wer

45、e repeated 60 times, for a total floating time of 120 h. A digital pressure sensor Keller 35X Ei was connected to the capacitors in 1 mol L?1 Li2SO4 or BeSO4 to monitor gas evolution.Results and DiscussionEffect of elect

46、rolyte pH on the performance of AC/AC cells.— In this section, self-standing electrodes made from as-received DLC Supra 30 (further named AC) and stainless steel (grade 316L) current collectors were used. In our previous

47、 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?

48、1 Li2SO4 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

49、pH dependent and given by the equations Eox = 1.23 ? 0.059 pH and Ered = ?0.059 pH vs SHE, respectively. In other words, the operating potential ranges of positive and negative electrodes in aqueous based capacitor syste

50、ms are controlled by the electrolyte pH. For this reason, we have determined the electrochemical performance of the activated carbon DLC Supra 30 (AC) in cells using the various sulfate salt solutions listed in Table I.

51、Fig. 1 shows the three-electrode cyclic voltammograms (CV) of AC in 1 mol L?1 Li2SO4 and 1 mol L?1 BeSO4. When the scans are realized at potential higher than the water reduction limit (?0.383 V vs SHE in Li2SO4 and ?0.1

52、24 V vs SHE in BeSO4), the CVs demon- strate only electrical double-layer charging in both electrolytes. By contrast, upon polarization toward potentials lower than the reductionlimit at the considered pH, the performanc

53、e of AC differs significantly in the two electrolytes. A negative current leap related with nascent hydrogen formation and chemisorption in the AC electrode38 starts to appear at potential lower than the limit, and it ra

54、pidly gives rise to important oscillations related with di-hydrogen bubbling in case of the cell in BeSO4, while such clearly visible oscillations are almost not observed with Li2SO4. Since the pH of bulk 1 mol L?1 Li2SO

55、4 is close to neutrality (pH = 6.5), a low amount of OH? anions pro- duced due to water reduction provokes a sudden pH increase inside the AC porosity to much higher values (after polarization of the cell, the pH measure

56、d on electrode surface is higher than 10), and it re- sults in higher over-potential for di-hydrogen evolution. During CV experiments in 1 mol L?1 Li2SO4, the onset of oscillations attributed to di-hydrogen evolution sta

57、rts at about ?0.8 V vs SHE. Hence, the negative AC electrode in 1 mol L?1 Li2SO4 is capable of i) storing hydrogen produced through water reduction and ii) operating safely up to low potential owing to high local pH in t

58、he pores of AC. By contrast, in the acidic 1 mol L?1 BeSO4 solution (pH = 2.1), the pH within the AC porosity is almost not changed by the produced OH?during water reduction. Consequently, di-hydrogen evolution starts at

59、 ?0.3 V vs SHE, very close to the thermodynamic reduction potential of water (Fig. 1b), and drives the negative AC electrode to perform in narrow potential range.9 The difference of over-potential for AC in the two elect

60、rolytes is even better seen during the anodic scan, where hydrogen stored in the AC porosity during the negative scan is oxi- dized, giving rise to a desorption peak. As it can be seen on Fig. 1, the polarization potenti

61、al difference between the desorption peak and the thermodynamic water reduction potential is ～0.78 V and ～0.42 V in Li2SO4 and BeSO4, respectively. Hence, the desorption activation energy is higher in Li2SO4 than in BeSO

62、4 medium.38The potential extrema of the positive and negative electrodes of AC/AC capacitors in 1 mol L?1 Li2SO4 and 1 mol L?1 BeSO4 with Hg/Hg2SO4 reference have been determined by galvanostatic cycling for cell potenti

63、als ranging from 0.8 V to 1.6 V (Fig. 2). The positive electrode of the capacitors in 1 mol L?1 Li2SO4 and in 1 mol L?1BeSO4 operates below the water oxidation limit (marked by the upper dashed line) up to cell potential

64、s of 1.4 V and 1.5 V, respectively. The potential range of the negative AC electrode itself is controlled by the lower dashed-line representing the practical di-hydrogen evo- lution determined from the previous three-ele

65、ctrode cell experiments. Consequently, in Li2SO4 electrolytes, the negative electrode works without any di-hydrogen production in all the considered cell poten- tial range, while in case of BeSO4 the limit seems to be re

66、ached for a cell potential of 1.3 V. Hence, AC/AC capacitors in salt aqueous electrolytes can operate safely up to 1.6 V only when pH is close to neutrality. In order to better evaluate the effect of different hydrogen e

67、volu- tion over-potential in the two electrolytes, a pressure sensor has been) unless CC License in place (see abstract). ecsdl.org/site/terms_useaddress. Redistribution subject to ECS terms of use (see 118.120.152.18