synthesis and characterization of modified silicas and ...a d´epass ´e les buts du programme....

Defence R&D Canada – Atlantic

DEFENCE DÉFENSE&

Synthesis and Characterization of Modified

Silicas and Carbons for Use as Electrodes in

Electrochemical SupercapacitorsSecond Annual Report

Peter G. Pickup, Karunakaran Kalinathan, Xiaorong Liu and Derrick DesRochesMemorial University of Newfoundland

Memorial University of NewfoundlandDepartment of ChemistrySt. John’s, NL A1B 3X7

Project Manager: Peter G. Pickup, 709-737-8657

Contract Number: W7707-063350

Contract Scientific Authority: Colin G. Cameron, 902-427-1367

The scientific or technical validity of this Contract Report is entirely the responsibility of the contractorand the contents do not necessarily have the approval or endorsement of Defence R&D Canada.

Contract Report

DRDC Atlantic CR 2008-090

July 2008

Copy No. _____

Defence Research andDevelopment Canada

Recherche et développementpour la défense Canada

This page intentionally left blank.

Synthesis and Characterization of Modified

Silicas and Carbons for Use as Electrodes in

Electrochemical SupercapacitorsSecond Annual Report

PeterG.Pickup

M em orialUniversity

Karunakaran Kalinathan


Xiaorong Liu


DerrickDesRoches


Prepared by:

M em orialUniversityofNewfoundland

Departm entofChem istry

St.John’s,NL A1B 3X7

ProjectM anager:PeterG.Pickup 709-737-8657

ContractNum ber:W 7707-063350

ContractScientificAuthority:Colin G.Cam eron 902-427-1367

The scientific ortechnicalvalidity ofthis ContractReportis entirely the responsibility ofthe contractor

and the contentsdo notnecessarilyhave the approvalorendorsem entofDefence R&D Canada.


ContractReport

DRDC AtlanticCR 2008-090

July2008

Approved by

Colin G. Cameron

Scientific Authority

Approved for release by

James L. Kennedy

Chair/Document Review Panel

c© Her Majesty the Queen in Right of Canada as represented by the Minister of National

Defence, 2008

c© Sa Majesté la Reine (en droit du Canada), telle que représentée par le ministre de la

Défense nationale, 2008

Original signed by Colin G. Cameron

Original signed by Ron Kuwahara for

Abstract

By using 0.001′′ Nafion (NRE-211) and 0.003′′ carbon paper, the equivalent series resis-

tance of our ruthenium oxide supercapacitors has been decreased to 0.10 Ohm. This has

increased the maximum power over full discharge to > 50 kW/kg. We have also determined

the usable voltage range and found that the device can be efficiently charged to 1.4 V. This

increases the power and energy density further. The low temperature performance of the

supercapacitors appears to be significantly better than literature results.

Work on improving the specific capacitance of ruthenium oxide has focussed on variation

of the annealing temperature and preparing composites with Spectrcarb 2225 carbon fabric.

Ruthenium oxide samples annealed at temperatures below the optimum of 110◦C exhibit

a broad peak in their current-voltage response that is characteristic of redox behaviour.

This offers the potential for enhanced specific capacitances, energy densities, and power

densities, although these have not yet been realized. However, the specific capacitance of

the ruthenium oxide annealed at 110◦C has been increased to > 1000 F/g by dispersion

on carbon fabric. Further work will be focused on similar composites with ruthenium

oxide annealed at lower temperatures. Manganese oxide dispersed on carbon fabric has

also yielded potentially useful capacitive behaviour, although there is a rapid initial loss of

capacitance. It is not yet clear how large the sustainable specific capacitance will be.

Black Pearl 2000 electrodes with high loadings have been prepared by using a cold rolling

process. Poly(tetrafluoroethylene) (PTFE) was used as a binder, and we have supplemented

this with Nafion and our sulphonated ormosil. It has been found that the ormosil provides

no benefit over the use of Nafion + PTFE, which is the best binder system that we have

found.

Carbon black has been modified with anthraquinone (AQ) to improve its energy and power

density as a negative electrode material. Improved energy density has been demonstrated

by cyclic voltammetry and at constant current. The measured peak specific capacitance

due to the AQ was ∼ 9000 F/g. The theoretical average specific capacitance of AQ over a

0.5 V discharge (as for one side of a 1 V supercapacitor) is 1856 F/g. A survey of other

redox species that would be useful for enhancing the capacitance of carbon black has been

undertaken. Polymers have been used to increase the loadings of several redox species.

Résumé

En utilisant 0.001′′ Nafion (NRE-211) et 0.003′′ papier carbone, la résistance en séries a été

diminuée jusqu’à 0.10 Ohm. Ceci a augmenté la puissance maximale de décharge complète

au-delà de 50 kW/kg. De plus on a déterminé la gamme utile de voltage et on a trouvé que

le dispositif peut être chargé efficacement à 1.4 V, augmentant davantage les densités de

DRDC AtlanticCR 2008-090 i

puissance et d’énergie. La performance de nos condensateurs à basse température semble

être meilleure que celles des travaux déjà publiés.

Afin d’améliorer la capacitance spécifique de l’oxyde de ruthenium, on a visé la varia-

tion du température de recuit et les composites du tissu carbone Spectracarb 2225. Les

échantillons d’oxyde de ruthenium recuit aux températures en dessous de l’optimum de

110◦C démontrent une amplitude maximum de courant qui indique une comportement re-

dox. Ceci offre la possibilité d’augmenter la capacitance spécifique et les densités d’énergie

et de puissance, mais on ne les a pas encore réalisées. Néanmoins on a augmenté la capa-

citance spécifique de l’oxyde de ruthenium au-delà de 1000 F/g en le dispersant sur du

tissu carbone. Dans le futur, on examinera des composites similaires avec de l’oxyde de

ruthenium ayant été recuit à des températures plus basses. L’oxyde de manganese dispersé

sur du tissu carbone a aussi démontré un comportement capacitive utile, malgré une perte

rapide de capacitance, et il n’est pas clair si la capacitance spécifique serait soutenable.

On a préparé des électrodes de Black Pearls 2000 de chargement élevée par un processus de

laminage à froid. Le liant était du poly(tetrafluoroethylene) (PTFE) avec du Nafion et notre

ormosil sulfoné. On a découvert que l’ormosil ne fournit aucun avantage sur Nafion+PTFE,

notre meilleur système de liage.

Le carbone noir a été modifié avec de l’anthraquinone (AQ) pour améliorer son énergie et

sa puissance comme matériau d’électrode négatif. Une densité d’énergie augmentée a été

démontrée par voltamétrie cyclique et à courant constant. La capacitance maximum attri-

buable à AQ était d’environ 9000 F/g. La capacitance spécifique moyen théorique d’AQ sur

une décharge de 0.5 V (tel qu’une moitié d’un supercondensateur de 1 V) est 1856 F/g. Un

sondage d’autres matériaux redox a eu lieu. Des polymères ont été utilisés pour augmenter

le chargement de plusieurs espèces redox.

ii DRDC AtlanticCR 2008-090

Executive summary

Synthesis and Characterization of Modified Silicas and

Carbons for Use as Electrodes in Electrochemical

Supercapacitors

PeterG.Pickup, Karunakaran Kalinathan, Xiaorong Liu, DerrickDesRoches;

DRDC AtlanticCR 2008-090;Defence R&D Canada – Atlantic; July2008.

Background: This Technology Investment Fund (TIF) program aims to develop improved

supercapacitor technology through the design of better electrode materials. This will ulti-

mately yield devices with elevated power and energy densities and/or performance custom-

tailored to the needs of the Canadian military. The present work represents one branch of

the program, where supercapacitor electrodes are being developed from modified carbons

and ruthenium oxides dispersed on high surface area carbon cloth.

Principal Results: The Equivalent Series Resistance (ESR) of the ruthenium oxide su-

percapacitors has been decreased to 0.10 Ω. This has increased the maximum power over

full discharge to >50 kW/kg. Maximum usable energy density has been measured beyond

30 Wh/kg. The cell voltage has been increased to 1.4 V, and the effect of temperature (−40

to +40 ◦C) on performance has been documented. Specific capacitances of over 1000 F/ghave been achieved for ruthenium oxide by dispersion on carbon fabric. Dispersion of

manganese oxide on carbon fabric has also been investigated with potentially useful ca-

pacitive behaviour being obtained. Carbon black has been modified with anthraquinone to

improve its energy and power density as a negative electrode material. Improved energy

density has been demonstrated at constant current. Several redox polymers have also been

used to enhance the capacitance of carbon black.

Significance: Progress in this arm of the project is very encouraging. The project target

was a device capable of 10 kW/kg and 10 Wh/kg. While they have not yet been tested in a

free-standing device (which will lead to lesser overall performance due to the added mass

of packaging), the performance of these materials has far surpassed the project goals.

Future Work: In the final year of the program, work will continue in optimizing the ma-

terials. Asymmetric devices will be explored further in order to extend the energy density.

Prototype devices, probably in coin cell assemblies, will be demonstrated.

DRDC AtlanticCR 2008-090 iii

Sommaire

Synthesis and Characterization of Modified Silicas and

Carbons for Use as Electrodes in Electrochemical

Supercapacitors

PeterG.Pickup, Karunakaran Kalinathan, Xiaorong Liu, DerrickDesRoches;

DRDC AtlanticCR 2008-090;R & D pourla défense Canada – Atlantique; juillet

2008.

Contexte : Ce programme de fonds d’investissement technologique vise à développer de

meilleurs technologies de supercondensateur par concevoir de meilleurs matériaux d’élec-

trode. Ceci donnera enfin des supercondensateurs à densités de puissance et d’energie

élevées, et des dispositifs personnalisés pour les forces canadiennes. Le présent œuvre

représente une partie du programme, où on développe des électrodes basées sur les car-

bones modifiés et des oxydes de ruthenium dispersés sur du tissu carbone à haute surface.

Résultats principaux : On a diminué la résistance en séries des supercondensateurs en

oxyde de ruthenium jusqu’à 0.10 Ω, augmentant la puissance maximum au-delà de 50 kW/kg.

On a mesuré une densité d’énergie de plus de 30 Wh/kg. On a augmenté la tension du

dispositif à 1.4 V, et on a décrit les effets de la température sur le fonctionnement. Des ca-

pacitances spécifiques de plus de 1000 F/g ont été réalisées par la dispersion de l’oxyde de

ruthenium sur du tissu carbone. La dispersion de l’oxyde de Mn a été examinée aussi, don-

nant une capacitance possiblement utile. On a modifié du noir de charbon avec de l’anthra-

quinone pour améliorer ses densités d’énergie et puissance comme matériau d’électrode

négatif. Plusieurs polymères redox ont été utilisés pour augmenter la capacitance du noir

de charbon.

Portée : Les progrès de cette partie du projet sont encourageants. Le but du projet est de

réaliser un dispositif qui pourrait contenir 10 Wh/kg d’énergie et soutenir une décharge de

10 kW/kg. Tandis qu’ils n’ont pas encore été testés dans un dispositif (ceci mènera à une

performance diminuée à cause du poids de l’emballage), la performance de ces matériaux

a dépassé les buts du programme.

Recherches futures : Pendant la dernière année du programme, on continuera à optimiser

les matériaux. Des dispositifs asymétriques seront examinés davantage pour augmenter

l’énergie. Les appareils prototypes seront démontrés, probablement utilisant le coffrage

des piles au lithium.

iv DRDC AtlanticCR 2008-090

Table of contents

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

Résumé . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

Executive summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii

Sommaire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv

Table of contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

List of figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

List of tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

1 Ru Oxide Supercapacitors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Voltammetric and Impedance Studies of Ru Oxide as a Function of

Annealing Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2.1 Cyclic voltammetry . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2.2 Impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.3 Potential Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.4 The Effect of the Separator on Performance . . . . . . . . . . . . . . . . . 6


1.4.2 Impedance spectroscopy . . . . . . . . . . . . . . . . . . . . . . 6

1.4.3 Constant current discharge . . . . . . . . . . . . . . . . . . . . . 7

1.5 The Effect of Operating Temperature on Performance . . . . . . . . . . . 10

1.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2 Ru Oxide and Carbon Composites . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.1 Ru/Ru Oxide on Carbon Blacks . . . . . . . . . . . . . . . . . . . . . . . 13

2.2 Deposition of Ru Oxide on Spectracarb Carbon Fabric . . . . . . . . . . . 14

DRDC AtlanticCR 2008-090 v

2.2.1 Composite synthesis . . . . . . . . . . . . . . . . . . . . . . . . 15

2.2.2 Electrodes and supercapacitors . . . . . . . . . . . . . . . . . . . 15

2.2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.2.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3 Mn Oxide and Carbon Composites . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.1 Preparation of the Mn Oxide/Carbon Fabric Composite . . . . . . . . . . 18

3.2 Electrodes and Supercapacitors . . . . . . . . . . . . . . . . . . . . . . . 18

3.3 Cyclic Voltammetry of Supercapacitors . . . . . . . . . . . . . . . . . . . 19

4 Carbon Black Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.1 Use of a Sulphonated Ormosil Binder . . . . . . . . . . . . . . . . . . . . 20

4.2 Experimental Carbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

5 Modification of Carbon Black with Redox Groups . . . . . . . . . . . . . . . . . 21

5.1 Covalent Attachment of Anthraquinone to Carbon Fabric . . . . . . . . . 22

5.1.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22


5.2 Anthraquinone Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . 22

5.2.1 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22


5.3 Fluorenone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

5.4 Azure A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

6 Supercapacitor with an Anthraquinone Modified Carbon Fabric Electrode . . . . 25

Symbols and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Distribution list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

vi DRDC AtlanticCR 2008-090

List of figures

Figure 1: Specific capacitance vs annealing temperature for various Ru oxide

samples. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 2: Cyclic voltammograms of a supercapacitor with Ru oxide (1.75+1.80

mg on CFP) annealed at 50 ◦C (1 M H2SO4 electrolyte, Nafion

NRE211 separator, Ti plate current collector). . . . . . . . . . . . . . . . 3

Figure 3: Impedance of a single Ru oxide electrode (1.80 mg on CFP) annealed

at 50 ◦C (1 M H2SO4 electrolyte, Nafion NRE211 separator, Ag/AgCl

reference, Ru oxide counter). . . . . . . . . . . . . . . . . . . . . . . . 4

Figure 4: Specific capacitances, electronic resistances and time constants

obtained from the impedance data shown in Figure 3. . . . . . . . . . . . 4

Figure 5: Cyclic voltammograms at 20 mV/s for a Ru oxide supercapacitor with a

1 M H2SO4 electrolyte. . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Figure 6: Cyclic voltammograms at 20 mV/s for Ru oxide supercapacitors with

various separators and a 1 M H2SO4 electrolyte. . . . . . . . . . . . . . 6

Figure 7: (a) Nyquist plots and (b) capacitance plots of ruthenium oxide

supercapacitors with various separators. . . . . . . . . . . . . . . . . . . 8

Figure 8: Constant current (1 mA) charging and discharging of a Ru oxide

supercapacitor with 10.72 mg of ruthenium oxide and a Nafion

NRE-211 separator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 9: Constant current (1 A) charging and discharging of a Ru oxide

supercapacitor with 10.72 mg of ruthenium oxide and a Nafion

NRE-211 separator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Figure 10: Ragone plots for 1 V Ru oxide supercapacitors with a 1 M H2SO4electrolyte. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 11: Variable temperature Nyquist plots for a supercapacitor with 9.2 mg of

ruthenium oxide, 5 M H2SO4 as electrolyte, and a Nafion NRE-211

separator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Figure 12: ESR and Ri as functions of operating temperature. . . . . . . . . . . . . 12

Figure 13: Specific capacitance as a function of temperature. . . . . . . . . . . . . . 12

DRDC AtlanticCR 2008-090 vii

Figure 14: Cyclic voltammograms at 20 mV/s for Spectracarb (CC) and Ru

oxide/CC composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Figure 15: Specific capacitances of RuO2/CC composite . . . . . . . . . . . . . . . 17

Figure 16: Specific capacitances for Ru oxide, CC and Ru oxide + CC in

supercapacitors at different scan speeds . . . . . . . . . . . . . . . . . . 18

Figure 17: SEM image of Mn oxide/CC . . . . . . . . . . . . . . . . . . . . . . . . 19

Figure 18: Cyclic voltammograms(first cycle at 2 mV/s) of Spectracarb (CC) and

Mn oxide/CC composite supercapacitors. Panel B shows the calculated

component of the specific capacitance due to the Mn oxide. . . . . . . . 20

Figure 19: Cyclic voltammograms (2 mV/s) of Spectracarb (CC) and Mn

oxide/CC composite supercapacitors . . . . . . . . . . . . . . . . . . . 20

Figure 20: CV of an AQ modified Spectracarb electrode. . . . . . . . . . . . . . . . 23

Figure 21: CVs at 50 mV/s in 0.1 M H2SO4(aq) (1 M for the final CV) of BP2000

on carbon fibre paper following deposition of increasing amounts of

poly(1,2-diaminoanthraquinone). . . . . . . . . . . . . . . . . . . . . . 24

Figure 22: CV at 100 mV/s of fluorenone modified Norit carbon on carbon fibre

paper in acetonitrile containing 1 M Et4NBF4 . . . . . . . . . . . . . . . 24

Figure 23: Cyclic voltammetry at 50 mV/s of poly-Azure A modified Black Pearls

2000 on carbon fibre paper in 1 M H2SO4. . . . . . . . . . . . . . . . . 25

Figure 24: Cyclic voltammetry (2-electrode mode) at 10 mV/s of a supercapacitor

with an unmodified Spectracarb working electrode and an AQ modified

Spectracarb counter electrode. . . . . . . . . . . . . . . . . . . . . . . . 26

Figure 25: Discharge curves at 1 A for a supercapacitor with an unmodified

Spectracarb working electrode and an AQ modified Spectracarb

counter electrode (modified negative) and for the same device under

reverse polarity (modified positive). . . . . . . . . . . . . . . . . . . . . 27

viii DRDC AtlanticCR 2008-090

List of tables

Table 1: Characteristics of Ru oxide supercapacitors with various separators. . . . 7

Table 2: Summary of specific capacitance data for Ru/Ru oxide/C composites. . . 13

Table 3: Specific capacitances (CS) of Ru oxide/CC composites . . . . . . . . . . 16

DRDC AtlanticCR 2008-090 ix


x DRDC AtlanticCR 2008-090

1 Ru Oxide Supercapacitors

Since ruthenium oxide appears to be the best electrode material for meeting the target speci-

fications of the contract we have focused our effort in year 2 on improving the performance

of Ru oxide in supercapacitors. Variations in the synthesis method have been explored,

with a particular emphasis on understanding the influence of the annealing temperature.

The influence of the separator, potential window, and temperature has also been explored

for the best material.

1.1 Experimental

The hydrous ruthenium oxide power was prepared as described in our first annual report [1]

and in reference [2], except that the drying (annealing) temperature was varied. Electro-

chemical experiments were performed in the sandwich cell (supercapacitor) [2]. In this

cell an electrolyte separator (Nafion or Celgard 3400 impregnated with H2SO4(aq)) is sand-

wiched between two similar electrodes consisting of the Ru oxide with 5% Nafion as a

binder spread on carbon fibre paper. Ti plate current collectors are used, and the whole cell

is immersed in a H2SO4(aq) solution containing a reference electrode.

1.2 Voltammetric and Impedance Studies of Ru Oxide

as a Function of Annealing Temperature

Literature reports [3, 4] suggest that a specific capacitance of 2000 F/g or more is theo-

retically possible, and experimental values as high as 1580 F/g have been claimed for the

Ru oxide component of composites with 90% carbon. However, the best reported specific

capacitance of Ru oxide alone is only 977 F/g [2]. In order to understand the factors that

limit its capacitance, we have conducted an impedance study aimed at resolving the ionic,

electronic, and contact resistances of samples annealed at various temperatures.

The specific capacitance of Ru oxide is reported to go through a peak as the annealing tem-

perature is increased [5], and we have obtained similar results as shown in Figure 1. The

low specific capacitances obtained at low temperatures are thought to be due to insuffi-

cient cross-linking of the Ru oxide structure, which causes its electronic conductivity to be

low [6]. At higher temperatures, the structure becomes too crystalline and Ru sites within

the crystalline regions become electrochemically inactive due to lack of connectivity with

the electrolyte (i.e., insufficient proton conductivity) [6]. We have probed these effects by

impedance spectroscopy, and aim to access higher specific capacitances by simultaneously

optimizing both ionic and electronic conductivity.

DRDC AtlanticCR 2008-090 1

0 50 100 150 200 250100

150

200

250

300

350

400

450

500

550

600

650

700

750

800

850

Csp(F

/g)

Annealing Temperature (C)

RuO2 1mA discharge

RuO2CV(5mV/s)

47.23% RuO2/C 1mA discharge

47.23% RuO2/C CV(5mV/s)

Figure 1: Specific capacitance vs annealing temperature for various Ru oxide samples.

1.2.1 Cyclic voltammetry

Figure 2 shows cyclic voltammograms for a supercapacitor with Ru oxide annealed at

50 ◦C. Unlike those for Ru oxide annealed at 110 ◦C or higher, which have a more ideal

capacitive response (see first annual report [1] for example), the single electrode CVs show

clear peaks that are characteristic of normal redox behaviour. They are broader than for

an ideal Nernstian process because of interactions between sites. In supercapacitor mode,

the response approximates capacitive behaviour because the simultaneous changing of the

potential of both electrodes doubles the peak width (only half of the potential change is

applied to each electrode). The best single electrode specific capacitance derived from the

supercapacitor mode experiments was 545 F/g at 40 mV/s, and a value of 668 F/g was

obtained by constant current discharge at 1 mA. Thus, the redox capacitance of this type of

Ru oxide appears to be promising for supercapacitor applications.

Although the specific capacitances obtained in these experiments are not quite as good

as those that we have obtained with Ru oxide annealed at 110 ◦C, the attraction of the

lower annealing temperature is that it should be possible to obtain high capacitances. The

redox wave seen in the single electrode experiments in Figure 2 must correspond to at least

one electron per Ru site. Assuming a formula of RuO2 ·H2O (151 g/mol), this yields a

specific capacitance of 799 F/g averaged over the 0.8 V range that the peak covers. The

peak capacitance should be much higher, and there should be additional capacitance from

the second process seen at higher potentials. We therefore believe that the best specific

2 DRDC AtlanticCR 2008-090

-1200 -800 -400 0 400 800 1200-40

-30

-20

-10

0

10

20

30

40

curr

ent

(mA

)

potential (mV)

20 mV/s supercapacitor mode 524F/g

50 mV/s supercapacitor mode 545 F/g

5 mV/s single electrode mode 429 F/g

20 mV/s single electrode mode 485 F/g

Figure 2: Cyclic voltammograms of a supercapacitor with Ru oxide (1.75+1.80 mg on

CFP) annealed at 50 ◦C (1 M H2SO4 electrolyte, Nafion NRE211 separator, Ti plate current

collector).

capacitance for Ru oxide will be obtained by accessing the full redox activity of Ru oxide

annealed at low temperatures, which should maximize the fraction of electrochemically

active redox sites. To do this, we need to understand why the charge for the Ru redox

process at 0.5 V is not fully accessible, and so we have begun to explore this by impedance

spectroscopy.

1.2.2 Impedance

Figure 3 shows the real component of the capacitance vs frequency for the 1.8 mg electrode

at different potentials vs. Ag/AgCl. The key observation here is that the capacitance con-

tinues to increase at the lowest frequency used (20 mHz) at all potentials, indicating that

there is indeed additional capacitance that we are not able to access. The highest capaci-

tances obtained (at 0.4 and 0.5 V; see Figure 4) were around 600 F/g, which is much lower

than the expected value for a one-electron process (>1500 F/g). Strangely, the impedance

at these potentials did not show any large resistances, although a large resistance that we

tentatively assign as an electronic resistance was observed at lower potentials (Figure 4).

Further work is clearly needed to provide an understanding of these results.


0.01 0.1 1 10 100 1000

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Cre

(F

)

Frequency (Hz)

0 V

0.1 V

0.2 V 0.3 V

0.4 V

0.5 V

0.6 V 0.7 V

0.8 V

0.9 V 1.0 V

Figure 3: Impedance of a single Ru oxide electrode (1.80 mg on CFP) annealed at 50 ◦C

(1 M H2SO4 electrolyte, Nafion NRE211 separator, Ag/AgCl reference, Ru oxide counter).

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.00.0 0.2 0.4 0.6 0.8 1.0

0

100

200

300

400

500

600

700

RC

or

Re

DC potential (V)

Re (ohms)

RC (s)

Csp

(F

/g)

DC potential (V)

Figure 4: Specific capacitances, electronic resistances and time constants obtained from

the impedance data shown in Figure 3.


-1600 -1200 -800 -400 0 400 800 1200 1600-500

-400

-300

-200

-100

0

100

200

300

400

500

Csp(F

/g)

Potential (mV)

0-1.4v

-1.5v-1.5v

-1.6v-1.6v

Figure 5: Cyclic voltammograms at 20 mV/s for a Ru oxide supercapacitor with a 1 M

H2SO4 electrolyte.

1.3 Potential Range

Figure 5 shows that the specific capacitance obtained increases with increasing potential

window for our best Ru oxide, which was annealed at 110 ◦C. With higher potential lim-

its, more ruthenium oxide is involved in the redox processes, and the average change in

oxidation state of the Ru is increased. However, as the limit is increased beyond 1.4 V (or

−1.4 V, since this is a symmetric device), an increasing amount of irreversible charge is

passed. For the cycling to 1.4 V and back to 0 V, 93% of the charge passed on the forward

(charging) scan was recovered on the reverse scan, while this fell to 83% for cycling to

1.5 V and 53% for cycling to 1.6 V.

The practical limit for use of the supercapacitor is difficult to estimate because many factors

are involved, including the efficiency required, tolerance of self discharge, and the nature

and effects of substances produced by overcharge (e.g., gases). We have conducted some

constant current discharge experiments from potentials as high as 1.4 V, but have observed

gas evolution. Exclusion of oxygen and control of the initial oxidation state of the two Ru

oxide electrodes are required for further evaluation of the maximum sustainable voltage.

This will be pursued in year 3 of the project.


0 200 400 600 800 1000-50

-40

-30

-20

-10

0

10

20

30

40

50

Cu

rre

nt

(mA

)

Potential (mV)

Nafion N-115

Celgard 3400

Nafion NRE-211

Nafion N-112

Figure 6: Cyclic voltammograms at 20 mV/s for Ru oxide supercapacitors with various

separators and a 1 M H2SO4 electrolyte.

1.4 The Effect of the Separator on Performance

The performances of ruthenium oxide (annealed at 110 ◦C) supercapacitors with Nafion R©

N-115, N-112, NRE-211 and Celgard 3400 (Celgard Inc.) separators were characterized

by constant current discharging, impedance spectroscopy and cyclic voltammetry.


Figure 6 shows cyclic voltammograms of ruthenium oxide supercapacitors with different

separators. The Nafion membranes gave high quality capacitive behaviour over the 0 to

1 V range used here, while the Celgard separator gave a significantly inferior performance.

Table 1 lists the average specific capacitances obtained from these results. The Nafion 115

membrane gave the highest specific capacitance of 165 F/g (662 F/g for each electrode)

while the Celgard 3400 supercapacitor has the lowest specific capacitance 126 (501) F/g.

The reasons for these differences are unclear.

1.4.2 Impedance spectroscopy

Figure 7a shows complex plane impedance (Nyquist) plots for supercapacitors with dif-

ferent separators. High frequency resistances, which correspond to the Effective Series


Table 1: Characteristics of Ru oxide supercapacitors with various separators.

Mass RuOx Separator Thickness ESR Ri Cs (F/g) Cs (F/g)

(mg) µm Ω Ω by impedance by CV

10.34 Nafion N-115 127 0.30 0.66 141(563) 165(662)

10.24 Celgard 3400 25 0.26 0.39 125(499) 126(501)

10.94 Nafion NRE-211 25 0.16 0.18 138(552) 161(642)

10.23 Nafion N-112 51 0.21 0.21 135(540) 157(629)

Values in parenthesis correspond to a single electrode

Resistance (ESR) of the supercapacitor, are listed in Table 1. The ESR includes the mem-

brane resistance, lead, clip and Ti plate resistances, the electronic resistances of the Ru

oxide and CFP layers, and assorted contact resistances. ESR increased with increasing of

thickness of the Nafion film, and the lowest ESR of 0.16 Ω was obtained with a 25 mi-

cron Nafion NRE-211 separator. Although the thickness of the Celgard 3400 film is the

same as that of Nafion NRE-211, its ESR was greater. In our prototype ruthenium oxide

supercapacitors, Nafion NRE-211 is the best choice.

The Nyquist plots in Figure 7a all have the expected shape for porous electrodes, consisting

of a ∼ 45◦ intermediate region and a ∼ 90◦ low frequency region. The sum of the ionic

resistances of the two capacitive layers (Ri) corresponds to three times the length of the

45◦ region on the real axis, i.e., Ri = 3(Rlow −Rhigh). Values from the data in Figure 7a arepresented in Table 1.

Table 1 shows that the lowest ionic resistance for the Ru oxide layers (Ri) was 0.18 Ω,

obtained for Nafion NRE-211. Curiously, the Ru oxide ionic resistance appears to increase

with increasing thickness of the Nafion separator. Closer inspection of the data as capaci-

tance plots (Figure 7b) indicates that increases in both bulk and interfacial resistances are

involved, since for Nafion 115 and Celgard the initial slopes of these plots are low due to

an interfacial resistance, and the maximum slopes are lower than for Nafion NRE-211 be-

cause of decreased bulk conductivity. The Ru oxide resistance with the Celgard separator

was intermediate between the values for Nafion 112 and Nafion 115. Thus Ri follows the

same trend as the ESR. Limited series capacitances, obtained at 5 mHz from the impedance

data are listed in Table 1. Although the Nafion N-115 supercapacitor had the highest ESR

and Ru oxide resistance, it yielded the highest specific capacitance. Celgard 3400 gave the

lowest specific capacitance.

1.4.3 Constant current discharge

Figures 8 and 9 show constant current charge/discharge data at 1 mA and 1 A, respec-

tively, for a supercapacitor with a Nafion NRE-211 separator. The supercapacitor was fully

charged or discharged (at 1 V or 0 V) before each charging/discharging segment.


0 1 2 3 4 5

0

-1

-2

-3

-4

-5

Zim

(o

hm

s)

Zre (ohms)

Nafion N-115

Celgard 3400 Nafion NRE-211

Nafion N-112

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

0.0 0.5 1.0 1.5 2.0 2.5

Cs (

F)

R (Ω)

Nafion N-115Celgard 3400

Nafion NRE-211Nafion N-112

Figure 7: (a) Nyquist plots and (b) capacitance plots of ruthenium oxide supercapacitors

with various separators.

0.0 4.0x103

8.0x103

1.2x104

1.6x104

2.0x104

0

200

400

600

800

1000

po

ten

tia

l (m

v)

t(s)

Figure 8: Constant current (1 mA) charging and discharging of a Ru oxide supercapacitor

with 10.72 mg of ruthenium oxide and a Nafion NRE-211 separator.


0 2 4 6 8 10 12 14 16 18 20 22 240

200

400

600

800

1000

1200

Po

ten

tia

l (m

V)

time (s)

charging or discharging at 1 A/cm2 of constant current density (196 A/g)

Figure 9: Constant current (1 A) charging and discharging of a Ru oxide supercapacitor

with 10.72 mg of ruthenium oxide and a Nafion NRE-211 separator.

At 1 mA (Figure 8), charging and discharging of the supercapacitor to a maximum volt-

age of 1 V was very reproducible, with no significant differences between the times (and

charges) for charging and discharging, nor between consecutive charging/discharging cy-

cles. The specific capacitance of the device was 196 F/g (784 F/g for each electrode).

At 1 A (Figure 9), both charging and discharging were accompanied by a large instanta-

neous jump in potential due the ESR of ∼ 160 mΩ (as determined by impedance spec-

troscopy and reported in Table 1).

Energy and power densities were calculated from constant current data over a range of

current densities to construct Ragone plots. Energy was calculated by integration of current

× voltage over the discharge time, while the average power was obtained by division of the

energy by the discharge time.

Ragone plots derived from results for cells with different separators are shown in Figure 10.

It can be seen that the usable energy and average power density depend significantly on the

separator employed. The highest energy density was obtained with a Nafion N-115 sep-

arator (31.2 Wh/kg at 1 mA/cm2), while the lowest energy density was obtained with the

Celgard separator (23.4 Wh/kg at 1 mA/cm2). The other Nafion separators gave interme-

diate energy densities. The combined effects of the lower ESR with Nafion NRE 211 and

better Ru oxide electrochemistry improve the average power density (34.3 kW /kg) by 20%

at 1 A/cm2 (183 A/g) relative to Celgard (28.5 kW/kg). Moreover, the energy density at


5 10 15 20 25 30 35

0.1

1

10

100

Ave

rag

e P

ow

er

De

nsity (

kW

/kg

)

Usable Energy Density (Wh/kg)

Celgard N-115

NRE-211

N-112

1mA

10 mA

0.1 A

1.0 A

Figure 10: Ragone plots for 1 V Ru oxide supercapacitors with a 1 M H2SO4 electrolyte.

this discharge rate was improved by 120%, from 6.4 Wh/kg to 14.2 Wh/kg.

By using 1 mil Nafion (NRE-211) and 3 mil carbon paper, the ESR of the cell has been

decreased to 0.10 Ω. This has increased the maximum power output over full discharge to

> 50 kW/kg, as shown in our Q5 report.

1.5 The Effect of Operating Temperature on

Performance

Variable temperature experiments were carried out by using a 33% H2SO4 electrolyte.

Dry ice was added to the electrolyte to obtain temperatures below ambient. Nyquist plots

obtained at selected operating temperatures are shown in Figure 11. ESR values and ionic

resistance (Ri = 3(Rlow−Rhigh)) for the Ru oxide layer obtained from these plots are shownin Figure 12 as a function of temperature. It can be seen that both increased with decreasing

temperature with the effect being much more pronounced for the Ru oxide resistance. The

specific capacitance of the Ru oxide, measured by constant current discharge at 10 mA,

dropped linearly from 770 F/g at 40◦C to 690 F/g at −40◦C (Figure 13).

There is little data in the literature for comparison with these results. Du Pasquier et al. [7]

have reported a 32% loss of energy density at 1000 W/kg, when a carbon supercapacitor

was operated at −20◦C. An energy loss of ∼ 50% at 500 W/kg at −40◦C was reported for


0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.00.2

0.0

-0.2

-0.4

-0.6

-0.8

-1.0

-1.2

-1.4

-1.6

-1.8

-2.0

-2.2

-2.4

-2.6

-2.8

-40 O

C

-25 O

C

-12 O

C

4 O

C

7 O

C

25 O

C

40 O

C

Zim

(o

hm

s)

Zre (ohms)

Figure 11: Variable temperature Nyquist plots for a supercapacitor with 9.2 mg of ruthe-

nium oxide, 5 M H2SO4 as electrolyte, and a Nafion NRE-211 separator.

a hybrid supercapacitor with activated carbon and Li4Ti5O12 electrodes [8]. Our loss of

only 15% at −41◦C and an average power density of 500 W/kg (5% at −18◦C) therefore

appears to be very encouraging. Both of these losses are calculated relative to +25◦C dataat 530 W/kg.

1.6 Conclusions

Our study of Ru oxide samples annealed at low temperatures suggests that it will be pos-

sible to achieve specific capacitances higher than the maximum of 977 F/g that we have

obtained to date. There appears to be additional capacitance that we currently cannot ac-

cess electrochemically. The use of a carbon fabric support, or conducting polymer binder

may facilitate the electrochemistry of Ru oxide annealed at low temperatures, and these ap-

proaches will be explored in Year 3. It should also be noted that the peak-shaped responses

seen for the low T materials should be useful in combination with the anthraquinone nega-

tive electrode that we have developed (Section 6). By using 1 mil Nafion (NRE-211), both

the ESR of the cell and electrode resistances have been decreased. These combine to im-

prove average power density at 1 V operation (34.3 kW/kg) by 20% at 1 A/cm2 (183 A/g)

relative to a commercial Celgard separator (28.5 kW/kg). A maximum power density of

> 50 kW/kg over full discharge has been obtained to date, for charging to 1 V. Higher

voltage operation (e.g. 1.2 V) of our Ru oxide supercapacitors provides higher energy and


-50 -40 -30 -20 -10 0 10 20 30 40 500

1

2

3

4

5

6

7

8

9

Re

sis

tan

ce

(o

hm

s)

Temperature (oC)

ESR

Ri

Figure 12: ESR and Ri as functions of operating temperature.

-50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50

680

690

700

710

720

730

740

750

760

770

780

Linear Regression for Experimental Data:

Y = A + B * X

A=730.90617±0.77778

B=1.05423±0.02883

R=0.99814SD=2.05294

Experimental Results

Linear Fit for Data

Csp

(F/g

)

Temperature (O

C)

Figure 13: Specific capacitance as a function of temperature.


Table 2: Summary of specific capacitance data for Ru/Ru oxide/C composites.

Carbon Analytical Mass % CS,total CS,Ru/RuOxSupport Ru/RuOx F/g F/g

Vulcan 9.6 56 ±5 360 ±95

23.5 138 ±3 508 ±31

29.9 179 ±8 541 ±33

53.4 177 ±45 310 ±85

81.1 216 ±3 260 ±4

Black 13.4 174 ±6 338 ±88

Pearls 25.7 217 ±3 412 ±36

38.9 262 ±20 438 ±55

56.7 344 ±25 493 ±44

power densities, but values and sustainability have not been fully quantified. Ru oxide su-

percapacitors can be operated at temperatures as low as −40◦C with a specific capacitance

loss of only ∼ 10%. However, the cell ESR and electrode resistances increase sharply,

indicating that power density drops sharply. Low temperature performance appears to be

very good relative to literature data.

2 Ru Oxide and Carbon Composites

2.1 Ru/Ru Oxide on Carbon Blacks

During the first year of the contact a series of Ru/Ru oxide and carbon black composites

were prepared, characterized, and evaluated. The results of this work were reported in our

first annual report and Aaron Rowe’s M.Sc. thesis. Subsequent work on these materials

in year 2 has led to a re-evaluation of their specific capacitances, as described in our Q7

report. The new values are summarized in Table 2.

The specific capacitance of the Vulcan composites increased linearly with %Ru/RuOx at

low loadings, indicating that the specific capacitance of the Ru/RuOx was independent

of loading on the carbon, but then leveled off at higher loadings. The average Ru/RuOx

specific capacitance is 470 F/g for the three samples with less than 50% Ru/RuOx. The

maximum value of 541±33 F/g for the Ru/RuOx component is ∼ 80% of the best specific

capacitance reported for hydrous RuO2, and could presumably be improved with complete

conversion of the Ru to Ru oxide. CS,Ru/RuOx values for the two Vulcan samples with

higher loadings (53.4 and 81.1%) were lower by much more than the standard deviations

for replicate measurements on individual samples, indicating statistically significant lower

utilization of the Ru. This is likely due to less complete conversion of Ru to Ru oxide,

presumably because of the larger average Ru particle sizes for these two samples.


For the Black Pearls (BP) composites, the specific capacitance increased linearly with

%Ru/RuOx with higher CS,total values than for the Vulcan composites. The latter is due

to the higher surface area of the BP support. Consistent with the linearity of the CS,total vs.

% Ru/RuOx plot, the calculated CS,Ru/RuOx values (Table 2) do not vary greatly between

samples, although they do appear to increase somewhat with Ru/RuOx loading. This is

presumably due to overestimation of the % Ru/RuOx at low loadings due to the effect of

residual water on the elemental analysis. The CS,Ru/RuOx value of 493± 44 F/g for the

56.7% sample would therefore appear to be the most reliable. Within experimental error,

this is not significantly different from the best value for the Vulcan samples.

Despite the uncertainties in the CS,Ru/RuOx values in Table 2, it is clear that the air oxidation

of Ru nanoparticles leads to a form of Ru oxide that is highly capacitive, and competitive

with state of the art Ru oxides for supercapacitor applications. In terms of total specific ca-

pacitance, the value of 344 F/g obtained for 57% Ru/RuOx on BP was the best (except for

488 F/g for a single experiment on a BP sample with a targeted loading of 79% Ru but un-

known Ru/RuOx loading), and this compares favourably with many specific capacitances

reported for other carbon-supported RuO2 supercapacitor materials.

The new capacitances reported in Table 2 are more consistent than those reported in our

first annual report, but also somewhat lower. The highest specific capacitance achieved was

488 F/g (previously reported as 574 F/g). The best specific capacitance for the Ru/RuOx

component is now 541 F/g (previously 711 F/g).

These specific capacitances are still high enough for the composites to be of significant

value for use in supercapacitors, but literature results suggest that better materials can be

prepared from Ru oxide (we deposited Ru particles, and then allowed them to oxidize

in air). However, superior results have only be achieved with low loadings of Ru oxide

(10%) on carbon. Our use of Ru particles, which can be deposited with high loadings,

high dispersions, and small particle size is one of the best methods for producing Ru oxide

composites with high specific capacitances.

2.2 Deposition of Ru Oxide on Spectracarb Carbon

Fabric

During the first 18 months of the contract it was established that Spectracarb 2225 carbon

cloth fabric (CC) produced much better performances in supercapacitors than any of the

other carbons that we have evaluated. It was therefore expected that deposition of Ru oxide

on CC would produce the best composites. Since the Ru oxide that we have prepared has

a higher specific capacitance than the Ru/Ru oxide in any of the Vulcan and Black Pearls

composites reported in Table 2, we have focused on the deposition of Ru oxide rather than

Ru particles.


2.2.1 Composite synthesis

Ruthenium oxide (∼ 0.5 g) annealed at 150◦C was dispersed in deionized water (100 ml)

by sonication for 30 min. Spectracarb 2225 (CC, typically ∼ 4×4 cm) that had been dried

(24 hours at 150◦C) and weighed was then immersed in the colloidal Ru oxide dispersion

for typically 30 min, then removed and dried at 150◦C for around 10 min. This proce-

dure was repeated until the desired loading of ruthenium oxide was achieved. Finally, the

composite was annealed for 1–2 h at 150◦C and weighed.

2.2.2 Electrodes and supercapacitors

Two identical 1 cm2 Ru oxide/CC electrodes were assembled into a supercapacitor with a

Nafion NRE211 (DuPont) separator and 1 M H2SO4(aq) electrolyte. Ti current collectors

were used with carbon fibre paper discs (TGP-H-090) between each Ru oxide/CC compos-

ite disc and the Ti. In some cases, Nafion solution (5%) was added to the electrodes, and

they were then dried at 150◦C before cell assembly.

2.2.3 Results

Cyclic voltammetry (Fig. 14) demonstrated that the addition of Ru oxide increased the ca-

pacitance of the CC discs. Capacitances were also measured by constant current discharge,

and the results are summarized in Table 3 with the voltammetric results, and plotted in

Fig. 15. It can be seen that the specific capacitances increased with Ru oxide loading,

while the specific capacitance of the Ru oxide component decreased. Some of the spe-

cific capacitances estimated for the Ru oxide component are higher than the best value of

978 F/g that we have obtained for Ru oxide alone. However, these high values are only seen

at low Ru oxide loadings, and the specific capacitances of the actual materials are not par-

ticularly high (248–259 F/g). In fact, in one case (CV with Nafion added) the unmodified

carbon produced a higher specific capacitance (273 F/g). The specific capacitance for each

material depended on the measurement method, and whether Nafion was added, in a com-

plex way. Constant current generally yields higher values than CV, but rapid self-discharge

can reverse this. Nafion increases capacitance but also increases resistance.

It is clear from examination of the data in Table 3 that there is considerable uncertainty

in the specific capacitance of the carbon fabric, and this creates uncertainty in the specific

capacitances calculated for the Ru oxide component. At low Ru oxide loadings the values

in Table 3 are so uncertain that they could be meaningless. Replicate experiments were

therefore performed in order to estimate precision. Under a fixed set of conditions, relative

standard deviations of 3.5% and 2.2% were obtained for the CC and 10% Ru oxide on

CC, respectively. The specific capacitance of the Ru oxide component was estimated to be

790±79 F/g.


0 221 166

0 3.7 170 2739.09 280 870 248 1068

9.09 3.6 255 1105 326 85610.88 279 754 259 1021

18.99 278 521 255 635

19.71 264 439 294 81522.00 232 271 251 552

38.96 383 637 340 61359.16 427 569 402 565

-1200 -1000 -800 -600 -400 -200 0 200 400 600 800 1000 1200-180

-160

-140

-120

-100

-80

-60

-40

-20

0

20

40

60

80

100

120

140

160

180

Curr

ent(

mA

)

Potential(mV)

carbon cloth(CC)

9.09% RuO2/CC

19.71% RuO2/CC

38.96% RuO2/CC

59.16% RuO2/CC

Figure 14: Cyclic voltammograms at 20 mV/s for Spectracarb (CC) and Ru oxide/CC

composites

Table 3: Specific capacitances (CS) of Ru oxide/CC composites

Mass% Mass% @10 mA discharge @CV 20 mV/s

Ru Oxide Nafion CS,total (F/g) CS,Ru/RuOx (F/g) CS,total (F/g) CS,Ru/RuOx (F/g)

0 221 166

0 3.7 170 273

9.09 280 870 248 1068

9.09 3.6 255 1105 326 856

10.88 279 754 259 1021

18.99 278 521 255 635

19.71 264 439 294 815

22.00 232 271 251 552

38.96 383 637 340 613

59.16 427 569 402 565


0 9.09% 19.71% 38.96% 59.16%

150

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

1100

Csp(F

/g)

RuO2%

Discharge results (10mA)

Discharge results (10mA) (based on RuO2)

CV(20mV/s)

CV(20mV/s) based on RuO2

Figure 15: Specific capacitances of RuO2/CC composite

2.2.4 Conclusions

Further work is clearly needed to optimize the Ru oxide composites, and to understand

the decline in the specific capacitance of the Ru oxide component with increasing loading

seen in Fig. 15. However, it is clear from this initial work that deposition of Ru oxide on

Spectracarb carbon fabric is a promising approach. This is further illustrated in Fig. 16,

where specific capacitances from cyclic voltammetry are compared at different scan speed.

The decline for the composite is not as steep as for Ru oxide alone, indicating better relative

power.

3 Mn Oxide and Carbon Composites

Although Ru oxide provides outstanding performances in supercapacitors its utilization

will continue to be limited by the high cost of Ru. It is therefore important to investi-

gate the use of other metal oxides, and Mn oxide is currently receiving rapidly growing

attention [9–13]. However, since it has low conductivity, only very thin films and small

particles in composites provide useful specific capacitances. Our experience with com-

posites of Ru oxide with Spectracarb 2225 carbon fabric have therefore prompted us to

investigate whether Mn oxide could be effectively used in place of Ru oxide.


0 50 100 150 200 250 300 350 400 450100

200

300

400

500

600

700

800

900

1000

1100

1200

9.09% RuO2/CC composite

Carbon cloth

9.09% RuO2/CC composite(Csp based on RuO2)

RuO2 supercapacitor (5.51+5.50mg )

Csp(F

/g)

Scanning rate(mV/s)

Figure 16: Specific capacitances for Ru oxide, CC and Ru oxide + CC in supercapacitors

at different scan speeds

3.1 Preparation of the Mn Oxide/Carbon Fabric

Composite

The composite was synthesized by a method [13] based on self-sacrifice (oxidation) of

Spectracarb 2225 carbon fabric (CC) in KMnO4 solution, thus leading to a layer of MnO2coating its surface. A known mass of carbon fabric was immersed in KMnO4(aq) (0.025 g/mL)

for around 10 minutes and then washed with deionized water until the filtrate reached a pH

of 7. The composite was dried at ambient temperature in air. The loading of MnO2 ·xH2O

was estimated to be ∼ 22% by mass from the increase in mass. Fig. 17 shows an SEM

image of the composite. It can be seen that the MnO2 forms a thin deposit on the fibres of

the carbon fabric. Portions of the composite, cut from the large piece modified as described

above, were annealed at various temperatures in air. From the mass loss, which is assumed

to be due to loss of water, a stable MnO2 loading of 16.5% was estimated for the samples

annealed at 100 and 150◦C. An additional mass loss at 200◦C appears to be due to loss of

carbon.

3.2 Electrodes and Supercapacitors

Supercapacitors were prepared with two equivalent Mn oxide/CC electrodes (∼ 1 cm2

each), a Celgard separator and 2 M LiOH(aq) as the electrolyte (other electrolytes were


Figure 17: SEM image of Mn oxide/CC

evaluated, but LiOH was by far the best). Ti current collectors were used with carbon fibre

paper discs (TGP-H-090) between each Mn oxide/CC composite disc and the Ti.

3.3 Cyclic Voltammetry of Supercapacitors

Cyclic voltammograms (first cycle) of supercapacitors (2-electrode mode; plotted in single

electrode specific capacitance units) with the as prepared composite and following anneal-

ing at various temperatures are shown in Fig. 18A, together with a CV for a supercapacitor

with unmodified CC.

It can be seen from the voltammograms in Fig. 18A that the Mn oxide increases the specific

capacitance of the CC greatly, and introduces capacitance peaks in the 0.4 to 0.5 V (charg-

ing) and 0.2 to 0.1 V (discharging) regions. The Mn oxide contributions are more clearly

seen following subtraction of the current due to the CC, as shown in Fig.18B (this subtrac-

tion is not possible for the sample annealed at 200◦C because of its uncertain composition).

Annealing at 100 and 150◦C produced the best results.

Estimation of specific capacitances from the data in Fig. 18 is difficult because of the large

peak separations, which indicate a significant degree of irreversibility. It would also be of

little value because of a rapid decrease in the charge passed with cycling.

CVs for further cycling on the as prepared sample and composite annealed at 200◦C are


-1200 -800 -400 0 400 800 1200-600

-500

-400

-300

-200

-100

0

100

200

300

400

500

600

CC

MnO2/CC as prepared

MnO2/CC 50 °C

MnO2/CC 100 °C

MnO2/CC 150 °C

MnO2/CC 200 °C

Csp (

F/g

)

Potential (mV)

B)

-1200 -800 -400 0 400 800 1200-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

CC

MnO2/CC as prepared

MnO2/CC 50 °C

MnO2/CC 100 °C

MnO2/CC 150 °C

Csp (

F/g

)

Potential (mV)

substracting the contribution of CC

C)A B

B

Figure 18: Cyclic voltammograms(first cycle at 2 mV/s) of Spectracarb (CC) and Mn ox-

ide/CC composite supercapacitors. Panel B shows the calculated component of the specific

capacitance due to the Mn oxide.

-1200 -800 -400 0 400 800 1200

-10

-8

-6

-4

-2

0

2

4

6

8

10

Curr

ent (m

A)

Potential (mV)

1st cycle

2nd cycle

3rd cycle

4th cycle

5th cycle

22.36 % MnO2/CC

2M LiOH

-1200 -800 -400 0 400 800 1200-8

-6

-4

-2

0

2

4

6

8

1st cycle

2nd cycle

3rd cycle

4th cycle

5th cycle

Curr

ent (m

A)

Potential (mV)

22.36 % MnO2/CC at 200

0C annealed

2M LiOH

Figure 19: Cyclic voltammograms (2 mV/s) of Spectracarb (CC) and Mn oxide/CC com-

posite supercapacitors

shown in Fig. 19. It is clear from these results that annealing increases the stability of the

Mn oxide. However, further work is needed to determine whether high specific capaci-

tances can be sustained for a sufficiently large number of cycles. Results of longer term

testing, and for other Mn oxide/Spectracarb composites that have been prepared will be

reported in Year 3.

4 Carbon Black Electrodes

4.1 Use of a Sulphonated Ormosil Binder

Although the results in our first annual report indicated that our sulphonated ormosil binder

was not significantly better than Nafion as a binder, we continued to evaluate it in Q5 by

using Black Pearl 2000 electrodes with high loadings prepared by using a cold rolling

process. The results, reported briefly in our Q5 report, indicated that the ormosil provided


no benefit over the use of Nafion + PTFE, which was found to be the best binder system. It

was therefore decided that no further work would be performed with ormosil binders.

4.2 Experimental Carbons

Arnd Garsuch, a post-doctoral fellow at Dalhousie University, provided us with a number

of high surface area carbon samples that he prepared by a templating method. Initial re-

sults, outlined in our Q6 report, indicated that these materials might have advantages over

commercial carbon blacks. However, testing of addition samples gave inferior results. It

was therefore decided that commercial carbons were more suitable for our work, and we

have no plans for further evaluation of experimental carbons.

5 Modification of Carbon Black with Redox

Groups

The modification of carbons with redox groups for use in supercapacitors has been patented

by Cabot Corp. [14], and also suggested by Leitner et al., [15]. The addition of redox ca-

pacitance to high surface area carbons by immobilization of redox species has considerable

potential to increase energy and power densities, but the formal potentials of these species

should be carefully chosen to provide additional charge at the beginning of discharge of the

supercapacitor, when its voltage is high. Thus the negative electrode should be modified

with a redox species with a formal potential close to the cathodic limit of the carbon in the

electrolyte employed. For an aqueous acid electrolyte, this is ∼ −0.3 V vs. SCE. Con-

versely, the modifier on the positive electrode should have a potential close to the anodic

limit of ∼ +0.9 V. For nonaqueous supercapacitors, potentials of ∼ −1 V and ∼ +1 Vwould be suitable, with the minimum and maximum usable values being determined by the

stability of the reduced and oxidized products, respectively.

Anthraquinone has been shown to be effective by Cabot, and has a suitable potential for the

negative electrode in a supercapacitor with an aqueous acid electrolyte. However, there are

no reported examples that would be suitable for the positive electrode, and none suitable

for use in non-aqueous supercapacitors. A survey of redox species that would be useful

for enhancing the capacitance of carbon black has therefore been undertaken. We are

specifically looking for:

• molecules and complexes with suitable redox potentials that can be covalently at-

tached to carbon

• polymeric materials to increase the loading of the redox component

• oxidizable materials for the positive electrode


• materials for use in non-aqueous electrolytes

5.1 Covalent Attachment of Anthraquinone to Carbon

Fabric5.1.1 Experimental

AQ was attached to Spectracarb fabric [16] via diazonium chemistry as reported by Comp-

ton and coworkers [17]. FastRed Al salt (anthraquinone-1-diazonium chloride·0.5ZnCl2,

Acros, 10 ml, 50 mM) was mixed with a 10 ml solution of 50 wt.% hypophosphorous acid

(Aldrich) with sonication until the diazonium salt was fully dissolved. This solution was

then placed in an ice bath and two pieces (22.9 and 14.1 mg) of Spectracarb 2225 carbon

fabric (Engineered Fibers Technology) were added. After 30 min with occasional stirring

the Spectracarb discs were collected by filtration, washed well with de-ionized water and

then acetonitrile, air dried, and weighed. The masses of the two samples increased by 7.1%

and 9.8%. We have subsequently found that it is necessary to add acetone (approx. 50%)

to the reaction mixture to reproduce these loadings.

Prototype supercapacitors (2-electrode sandwich cells) were constructed by sandwiching

an electrolyte separator (Nafion 115) between an AQ modified Spectracarb electrode (∼ 1

cm2 ; 14.2 mg or 15.1 mg) and an unmodified Spectracarb electrode (∼ 1 cm2; 14.1 mg).

Ti plates in polycarbonate blocks were used to make electrical contact, and the whole

cell was immersed in 1 M saaq containing an Ag/AgCl reference electrode. Carbon fibre

paper discs (Toray TGP-H-090) were placed between each Spectracarb electrode and its Ti

current collector. Air was not excluded from the cell.


Fig. 20 shows a cyclic voltammogram of the AQ modified electrode. Redox peaks due

to the AQ can be seen at a formal potential of ∼ −0.11 V. These peaks are very stable

(actually increasing slightly with scanning in this experiment) and suitable for enhancing

the charge and power of the carbon as the negative electrode in a supercapacitor.

5.2 Anthraquinone Polymers5.2.1 Experimental

These experiments were performed in a conventional glass cell with working electrodes

consisting of carbon black supported on a strip of carbon fibre paper (Toray TGP-H-090).

1,2-diamino-anthraquinone (50 mM; Aldrich) in 1 M HCl(aq) was polymerized onto the

working electrode by cycling the potential between −0.5 and +0.9 V. The electrode wasthen rinsed with water and CVs were obtained in H2SO4(aq).


-500

-400

-300

-200

-100

0

100

200

300

400

500

600

-0.3 -0.1 0.1 0.3 0.5 0.7 0.9potential vs Ag/AgCl (V)

cu

rren

t/(s

can

rate

*mass)

(F/g

)

Figure 20: CV of an AQ modified Spectracarb electrode.


1,2-diamino-anthraquinone was electrochemically polymerized onto carbon fibre paper

and Black Pearls 2000 from solution in 1 M HCl. Increases in capacitance with peaks

at ∼ 0 to −0.1 V were observed (e.g., Fig. 21), however it was difficult to quantify specific

capacitances because of the small changes in the mass of the electrodes. This appears to be

a promising approach, but requires further work.

5.3 Fluorenone

O

fluorenone

Since anthraquinone modified carbon was found not to provide

useful additional capacitance over unmodified carbon in acetoni-

trile, the use of fluorenone was evaluated. Thus 2-amino-9-

fluorenone was attached to Norit (SX Ultra) carbon black by a di-

azonium coupling method. Cyclic voltammograms in acetonitrile

are shown in Fig. 22. Reversible electrochemistry of the immobi-

lized fluorenone is clearly seen by the peaks at a formal potential

of ∼ −1.2 V superimposed on the capacitance due to the Norit

carbon. Thus fluorenone appears to be a suitable redox species for

improving the energy and power densities of non-aqueous super-

capacitors. However, a species with a more negative potential would be more desirable, if

sufficiently stable.


-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

-0.5 0.0 0.5 1.0

potential vs Ag/AgCl (V)

cu

rren

t (A

)

Figure 21: CVs at 50 mV/s in 0.1 M H2SO4 (aq) (1 M for the final CV) of BP2000 on carbon

fibre paper following deposition of increasing amounts of poly(1,2-diaminoanthraquinone).

-0.02

-0.01

0.00

0.01

0.02

-2.0 -1.0 0.0 1.0 2.0


cu

rren

t (A

)

modified Norit

Norit SX Ultra

Figure 22: CV at 100 mV/s of fluorenone modified Norit carbon on carbon fibre paper in

acetonitrile containing 1 M Et4NBF4


-0.05

-0.04

-0.03

-0.02

-0.01

0.00

0.01

0.02

0.03

0.04

0.05

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4


cu

rre

nt

(A)

Figure 23: Cyclic voltammetry at 50 mV/s of poly-Azure A modified Black Pearls 2000

on carbon fibre paper in 1 M H2SO4.

5.4 Azure A

S

N

H2N N+

CH3

CH3

Cl-

Azure A

Azure A was polymerized from 1 M H2SO4(aq)onto Black Pearls 2000 on carbon fibre paper.

Voltammograms of the resulting electrode in 1 M

H2SO4(aq) containing no Azure A in solution are

shown in Fig. 23. The electrode has high capaci-

tance and large Faradaic capacitance peaks centred

at a formal potential of ∼ +0.3 V. This is not avery useful potential for an acid supercapacitor, but this type of electrode may be of use

under basic conditions or for non-aqueous supercapacitors. Other phenothiazines are being

investigated for acid and non-aqueous supercapacitors.

6 Supercapacitor with an Anthraquinone

Modified Carbon Fabric Electrode

A supercapacitor was assembled with an unmodified Spectracarb working electrode, a

Nafion 115 membrane, and an AQ modified Spectracarb counter electrode (see §5.1.1).

It was immersed in 1 M H2SO4(aq) containing a reference electrode. Details of the experi-


-200

-150

-100

-50

0

50

100

150

200

-1.0 -0.5 0.0 0.5 1.0

cell voltage (V)

cu

rre

nt/

(sc

an

ra

te *

ma

ss

) (F

/g)

Figure 24: Cyclic voltammetry (2-electrode mode) at 10 mV/s of a supercapacitor with

an unmodified Spectracarb working electrode and an AQ modified Spectracarb counter

electrode.

ments and results are provided in our J. Power Sources paper [16].

Fig. 24 shows a cyclic voltammogram of the supercapacitor. In this experiment the modi-

fied electrode was driven negative as the cell voltage was scanned positively. The capaci-

tance waves in the +0.3 to +1.0 V range are due to reduction and then reoxidation of theAQ groups. During discharge (negative scan from +1 to 0 V), these groups provide extraenergy and power. When the cell voltage is in the negative region in Fig. 24, the AQ groups

remain oxidized and do not contribute to the capacitance. The behaviour of the capacitor

is then as if both electrodes were unmodified.

In order to assess the benefits of using the modified electrode as the negative electrode of

the supercapacitor, relative to an “unmodified” electrode, constant current discharges were

run from 1 V, first with the modified electrode as the negative electrode and then as the

positive electrode (where it behaves as if unmodified). Results at 1 A discharge are shown

in Fig. 25. The benefit of the AQ groups is clearly impressive. Further results, analysis

and discussion are available in ref [16]. To put the role of the AQ into perspective it should

be noted that its mass in the electrode used here was only around 0.5 mg. Thus the peak

specific capacitance due to the AQ was approximately 9000 F/g. The theoretical average

specific capacitance of AQ over a 0.5 V discharge (as for one side of a 1 V supercapacitor)

is 1856 F/g, while the experimental value at 1 mV/s was 1470 F/g.


0

200

400

600

800

1000

1200

0 100 200 300 400 500 600

time (ms)

ce

ll v

olt

ag

e (

mV

)

modified -ve

modified +ve

Figure 25: Discharge curves at 1 A for a supercapacitor with an unmodified Spectracarb

working electrode and an AQ modified Spectracarb counter electrode (modified negative)

and for the same device under reverse polarity (modified positive).

Symbols and Abbreviations

CS specific capacitance

Ri ionic resistance

AQ anthraquinone

BP black pearls

CC carbon cloth

CFP carbon fibre paper

CV cyclic voltammetry or cyclic voltammogram

ESR equivalent series resistance

PTFE poly(tetrafluoroethylene), a.k.a. Teflon


References

[1] Pickup, Peter G., Rowe, Aaron, Liu, Xiaorong, and DesRoches, Derrick (2007),

Synthesis and Characterization of Modified Silicas and Carbons for Use as

Electrodes in Electrochemical Supercapacitors: First Annual Report, (CR 2007-120)

Defence R&D Canada – Atlantic.

[2] Liu, X. R. and Pickup, P. G. (2008), Ru oxide supercapacitors with high loadings

and high power and energy densities, J. Power Sources, 176, 410–416.

[3] Hu, C. C. and Chen, W. C. (2004), Effects of substrates on the capacitive

performance of RuOx center dot nH(2)O and activated carbon-RuOx electrodes for

supercapacitors, Electrochimica Acta, 49, 3469–3477.

[4] Hu, C. C., Chen, W. C., and Chang, K. H. (2004), How to achieve maximum

utilization of hydrous ruthenium oxide for supercapacitors, J. Electrochemical Soc.,

151, A281–A290.

[5] Foelske, A., Barbieri, O., Hahn, M., and Kotz, R. (2006), An X-ray photoelectron

spectroscopy study of hydrous ruthenium oxide powders with various water contents

for supercapacitors, Electrochemical Solid State Lett., 9, A268–A272.

[6] Sugimoto, W., Iwata, H., Yokoshima, K., Murakami, Y., and Takasu, Y. (2005),

Proton and electron conductivity in hydrous ruthenium oxides evaluated by

electrochemical impedance spectroscopy: The origin of large capacitance, J. Phys.

Chem. B, 109, 7330–7338.

[7] Pasquier, A. Du, Plitz, I., Menocal, S., and Amatucci, G. (2003), A comparative

study of Li-ion battery, supercapacitor and nonaqueous asymmetric hybrid devices

for automotive applications, J. Power Sources, 115, 171–178.

[8] Plitz, I., DuPasquier, A., Badway, F., Gural, J., Pereira, N., Gmitter, A., and

Amatucci, G. G. (2006), The design of alternative nonaqueous high power

chemistries, Appl. Phys. A-materials Science & Processing, 82, 615–626.

[9] Cottineau, T., Toupin, M., Delahaye, T., Brousse, T., and Belanger, D. (2006),

Nanostructured transition metal oxides for aqueous hybrid electrochemical

supercapacitors, Appl. Phys. A-materials Science & Processing, 82, 599–606.

[10] Xu, M. W., Zhao, D. D., Bao, S. J., and Li, H. L. (2007), Mesoporous amorphous

MnO2 as electrode material for supercapacitor, J. Solid State Electrochemistry, 11,

1101–1107.

[11] Khomenko, V., Raymundo-Pinero, E., and Beguin, F. (2006), Optimisation of an

asymmetric manganese oxide/activated carbon capacitor working at 2 V in aqueous

medium, J. Power Sources, 153, 183–190.


[12] Sharma, R. K., Oh, H. S., Shul, Y. G., and Kim, H. (2007), Carbon-supported,

nano-structured, manganese oxide composite electrode for electrochemical

supercapacitor, J. Power Sources, 173, 1024–1028.

[13] Fischer, A. E., Pettigrew, K. A., Rolison, D. R., Stroud, R. M., and Long, J. W.

(2007), Incorporation of homogeneous, nanoscale MnO2 within ultraporous carbon

structures via self-limiting electroless deposition: Implications for electrochemical

capacitors, Nano Lett., 7, 281–286.

[14] Yu, Y. and Adams, C.E. (2003). U.S. Patent 6,522,522.

[15] Leitner, K. W., Gollas, B., Winter, M., and Besenhard, J. O. (2004), Combination of

redox capacity and double layer capacitance in composite electrodes through

immobilization of an organic redox couple on carbon black, Electrochimica Acta,

50, 199–204.

[16] Kalinathan, K., DesRoches, D. P., Liu, X., and Pickup, P. G. (2008), J. Power

Sources. in press.

[17] Wildgoose, G. G., Pandurangappa, M., Lawrence, N. S., Jiang, L., Jones, T. G. J.,

and Compton, R. G. (2003), Anthraquinone-derivatised carbon powder: reagentless

voltammetric pH electrodes, Talanta, 60, 887–893.


Distribution list


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Total internal copies: 11

External distribution

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Department of Chemistry

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University of Manitoba

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McMaster University

1280 Main St. W

Hamilton, ON L8S 4M1


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Dept. de chimie

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Synthesis and Characterization ofM odified Silicas and Carbons forUse as Electrodes in

Electrochem icalSupercapacitors

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Pickup,P.G.;Kalinathan,K.;Liu,X.;DesRoches,D.

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Byusing 0.001′′ Nafion (NRE-211)and 0.003′′ carbon paper,the equivalentseriesresistance of

ourruthenium oxide supercapacitors has been decreased to 0.10 Ohm .This has increased the

m axim um poweroverfulldischarge to> 50 kW /kg.W e have also determ ined the usable voltage

range and found thatthe device can be efficiently charged to 1.4 V.This increases the power

and energydensityfurther.The low tem perature perform ance ofthe supercapacitorsappearsto

be significantlybetterthan literature results.

W ork on im proving the specific capacitance ofruthenium oxide has focussed on variation ofthe

annealing tem perature and preparing com posites with Spectrcarb 2225 carbon fabric. Ruthe-

nium oxide sam plesannealed attem peraturesbelow the optim um of110◦C exhibita broad peak

in theircurrent-voltage response thatis characteristic ofredox behaviour.This offers the poten-

tialforenhanced specific capacitances,energy densities,and powerdensities,although these

have notyetbeen realized.However,the specific capacitance ofthe ruthenium oxide annealed

at110◦C has been increased to > 1000 F/g by dispersion on carbon fabric. Furtherwork will

be focused on sim ilarcom posites with ruthenium oxide annealed atlowertem peratures. M an-

ganese oxide dispersed on carbon fabrichasalso yielded potentiallyusefulcapacitive behaviour,

although there is a rapid initialloss ofcapacitance.Itis notyetclearhow large the sustainable

specificcapacitance willbe.

Black Pearl2000 electrodes with high loadings have been prepared by using a cold rolling pro-

cess. Poly(tetrafluoroethylene)(PTFE)was used as a binder,and we have supplem ented this

with Nafion and oursulphonated orm osil.Ithas been found thatthe orm osilprovides no benefit

overthe use ofNafion + PTFE,which isthe bestbindersystem thatwe have found.

Carbon black has been m odified with anthraquinone (AQ)to im prove its energy and powerden-

sityasa negative electrode m aterial.Im proved energydensityhasbeen dem onstrated bycyclic

voltam m etry and atconstantcurrent. The m easured peak specific capacitance due to the AQ

was∼ 9000 F/g.The theoreticalaverage specific capacitance ofAQ overa 0.5 V discharge (as

forone side ofa 1 V supercapacitor)is 1856 F/g. A survey ofotherredox species thatwould

be usefulforenhancing the capacitance ofcarbon black has been undertaken.Polym ers have

been used to increase the loadingsofseveralredoxspecies.

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supercapacitor;ruthenium ;carbon

synthesis and characterization of modified silicas and ...a d´epass ´e les buts du programme....

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