Thermophysical properties of room temperature ionic liquids with oligomeric formate and hydrogen sulfate

Thermophysical

properties

of

room

temperature

ionic

liquids

with

oligomeric

formate

and

hydrogen

sulfate

Tzi-Yi

Wu

a,b

,

I.-Wen

Sun

a

,

Ming-Wei

Lin

a

,

Bor-Kuan

Chen

b

,

Chung-Wen

Kuo

c

,

H.

Paul

Wang

d

,

Yu-Yuan

Chen

a

_,

_Shyh-Gang

_Su

a,

_*

a

DepartmentofChemistry,NationalChengKungUniversity,Tainan701,Taiwan

b

DepartmentofMaterialsEngineering,KunShanUniversity,Tainan710,Taiwan

c

DepartmentofChemicalandMaterialsEngineering,NationalKaohsiungUniversityofAppliedSciences,Kaohsiung807,Taiwan

d_{DepartmentofEnvironmentalEngineering,NationalChengKungUniversity,Tainan701,Taiwan}

1.

Introduction

Reducing

the

amount

of

volatile

organic

compounds

in

chemical

and

industrial

processes

is

challenging.

Room-tempera-ture

ionic

liquids

(RTILs)

have

been

used

as

solvents

in

many

academic

and

industrial

research

areas

due

to

their

unique

properties,

such

as

a

wide

liquid

range,

negligible

vapor

pressure,

good

thermal

stability,

excellent

solvent

power

for

organic,

inorganic,

and

polymeric

compounds,

suitable

viscosity,

and

non-flammability

[1]

.

Owing

to

their

nonvolatile

nature

and

favorable

solvation

properties,

RTILs

have

been

suggested

as

green

and

benign

replacements

for

traditional

volatile

organic

solvents,

and

are

expected

by

both

industrial

and

scientific

communities

to

have

a

broad

range

of

applications,

including

as

electrolytes

in

lithium

or

lithium-ion

batteries

[2,3]

,

solar

cells

[4–7]

,

electrode-position

[8–10]

,

reaction

media

in

nanoscience

[11,12]

,

electro-analysis

[13]

,

and

physical

chemistry

[14–28]

.

ILs

can

be

tuned

by

varying

the

combination

of

cations

and

anions

[29]

.

When

designing

industrial

processes

and

products

that

involve

ILs,

it

is

necessary

to

determine

their

thermophysical

properties

including

viscosity,

density,

and

conductivity.

A

thermophysical

study

of

compounds

enables

an

understanding

of

their

properties

that

depend

on

fundamental

factors

such

as

ionic

structure

and

intermolecular

interactions.

Such

information

allows

the

design

of

RTILs

with

the

desired

properties.

The

application

of

RTILs

is

limited

by

their

relatively

high

viscosity.

Therefore,

if

the

relationships

between

the

viscosity

and

the

molecular

structure

of

RTILs

are

quantitatively

determined,

the

design

of

low-viscosity

RTILs

will

become

possible.

ILs

can

be

divided

into

two

distinct

groups:

aprotic

ILs

and

protic

ILs.

Protic

ionic

liquids

(PILs)

have

received

increasing

attention

as

a

protic

solvent.

They

are

easily

produced

via

the

combination

of

a

Brønsted

acid

and

a

Brønsted

base

[30]

.

As

the

ions

of

PILs

can

both

accept

and

donate

protons,

PILs

have

characteristics

of

an

amphoteric

solvent.

PILs

are

expected

to

be

candidates

for

fuel

cell

electrolytes

due

to

their

excess

of

electrochemically

available

protons

[31]

.

A

number

of

studies

have

shown

that

the

formation

of

dimeric

anions

is

possible

in

the

IL

system

and

that

they

may

be

weaker

bases

than

monomeric

anions

due

to

solvation

by

an

additional

acid

molecule.

For

example,

the

HF

2

anion

has

been

extensively

studied

by

Hagiwara

et

al.

[32]

.

The

formation

of

dimeric

anions

occurs

strongly

at

a

2:1

composition,

which

exhibits

the

highest

conductivity

and

which

is

thought

to

be

of

potential

use

in

fuel

cell

applications.

In

the

present

study,

we

report

two

series

of

ionic

liquids

that

use

pyrrolidinium

as

cations,

and

oligomeric

formate

JournaloftheTaiwanInstituteofChemicalEngineers43(2012)58–66

ARTICLE INFO

Articlehistory:

Received26February2011 Receivedinrevisedform9May2011 Accepted5June2011

Availableonline4August2011

Keywords: Ionicliquid Thermophysicalproperties Density Viscosity Conductivity Waldenrule ABSTRACT

Brønstedacidroomtemperatureionicliquids(RTILs)comprisedofoligomericformate(orhydrogen sulfate)anionsandpyrrolidinium-basedcationsareprepared.Itisfoundthationidentitygreatlyaffects thethermophysicalproperties.AllRTILsstudiedhereareliquidandhaveahighionicconductivity(upto 55.4mS/cm)and alowviscosity (downto 6.42mPas) atroom temperature. Theincorporation of oligomericanionsinILssignificantlyincreasesthedensityandconductivity,anddecreasestheviscosity. Thecorrelationbetweenionic conductivityandviscosity isbased ontheclassicalWalden rule; a relativelylargedeviation oftheplotsfromtheidealWaldenlineisobservedforformate-basedILs synthesizedusingequimolaramountsofacidandbase,whereasthedeviationdecreasessignificantly whentheformate-basedILscontainoligomericanions.TheStokes–EinsteinplotofDT1_vs.

_h

1_for

ferrocenceinILsshowsthathydrodynamicradiusofdiffusingspeciesisindependentoftemperature. ß2011TaiwanInstituteofChemicalEngineers.PublishedbyElsevierB.V.Allrightsreserved.

*Correspondingauthor.Tel.:+88662757575x65330. E-mailaddress:z7902010@email.ncku.edu.tw(S.-G.Su).

Contents

lists

available

at

ScienceDirect

Journal

of

the

Taiwan

Institute

of

Chemical

Engineers

j o u

r

n a l

h

o

m e p

a g e :

w

w w . e l s

e v i e r

. c o

m / l o

c

a t e / j t i c

e

1876-1070/$–seefrontmatterß2011TaiwanInstituteofChemicalEngineers.PublishedbyElsevierB.V.Allrightsreserved.

and

hydrogen

sulfate

as

anions.

Their

thermophysical

properties,

such

as

viscosity,

density,

conductivity,

and

diffusion

coefficient

of

ferrocene,

are

evaluated

and

studied

in

detail.

The

conductivity

and

viscosity

data

are

plotted

under

Walden’s

rule,

where

ion

association

plays

a

major

role.

It

is

expected

that

the

incorporation

of

oligomeric

formate

(hydrogen

sulfate)

containing

ILs

into

the

ionic

liquid

family

may

facilitate

the

use

of

ionic

liquids

and

open

up

a

new

field

of

ionic

liquid

chemistry.

2.

Experimental

2.1.

Materials

and

measurement

All

starting

materials

were

purchased

from

Aldrich,

Alfa

Aesar,

TCI,

or

Acros

and

used

as

received.

Solvents

were

freshly

distilled

prior

to

use.

The

conductivity

(

s

)

of

the

ILs

was

systematically

measured

with

a

conductivity

meter

(LF

340)

and

a

standard

conductivity

cell

(TetraCon

325,

Wissenschaftlich-Technische

Werksta¨tten

GmbH,

Germany).

The

cell

constant

was

determined

by

calibration

after

each

sample

measurement

using

an

aqueous

0.01

M

KCl

solution.

The

densities

of

the

ILs

were

measured

gravimetrically

with

a

1

ml

volumetric

flask.

Values

for

the

densities

are

given

as

0.0001

g/ml.

The

dynamic

viscosities

(

h

)

of

the

ILs

were

measured

using

a

calibrated

modified

Ostwald

viscometer

(Cannon-Fenske

glass

capillary

viscometers,

CFRU,

9721-A50)

with

inner

diameters

of

1.2



2%

mm.

The

viscometer

was

placed

in

a

thermostatic

water

bath

(TV-4000,

TAMSON)

whose

temperature

was

regulated

to

within

0.01

K.

The

flow

time

was

measured

using

a

stop

watch

with

a

time

resolution

of

0.01

s.

For

each

IL,

the

experimental

viscosity

was

obtained

by

averaging

three

to

five

flow

time

measurements.

The

melting

point

of

each

IL

was

analyzed

using

a

differential

scanning

calorimeter

(DSC,

Perkin–Elmer

Pyris

1)

in

the

temperature

range

of

140

8C

to

a

predetermined

temperature.

The

sample

was

sealed

in

an

aluminum

pan,

and

then

heated

at

a

scan

rate

of

10

8C/min

under

a

flow

of

nitrogen.

The

thermal

data

were

collected

during

heating

in

the

second

heating–cooling

scan.

The

thermal

stabilities

were

measured

with

thermogravimetric

analysis

(TGA)

(Perkin–Elmer,

7

series

thermal

analysis

system).

The

sample

was

heated

at

10

8C/min

from

room

temperature

to

800

8C

under

nitrogen.

The

water

content

of

the

dried

ILs

was

measured

with

a

moisture

titrator

(Metrohm

73KF

coulometer)

using

the

Karl–Fischer

method;

the

content

was

less

than

300

ppm.

The

cyclic

voltammetry

was

performed

using

an

electrochemical

workstation

(CH

instruments

Inc.,

CHI,

model

750A).

The

working

electrode

was

a

glassy

carbon

electrode,

the

counter

electrode

was

a

Pt

wire,

and

the

quasi-reference

electrode

was

a

Pt

wire.

All

electrochemical

experiments

were

performed

under

a

dry

argon

atmosphere

to

remove

oxygen

and

air

humidity.

2.2.

Synthetic

procedure

of

cyclic

amine-based

Brønsted

acid

ionic

liquids

Amine

compounds

were

placed

in

a

three-necked

glass

flask

equipped

with

a

reflux

condenser

and

a

dropping

funnel.

The

flask

was

mounted

in

an

ice

bath.

Formic

acid

was

added

dropwise

to

the

flask

under

stirring

with

a

magnetic

bar

at

room

temperature

(25



3

8C).

Stirring

was

continued

for

24

h

at

ambient

temperature

in

order

to

obtain

a

final

viscous

liquid.

The

produced

ILs

were

washed

repeatedly

with

diethyl

ether

to

remove

unreacted

materials.

The

same

general

process

was

used

for

the

synthesis

of

all

ILs.

The

product

was

then

dried

at

80

8C

for

12

h

in

a

vacuum

oven

(0.5

mmHg)

containing

phosphorus

pentoxide

(P

2

O

5

)

to

remove

any

excess

water.

The

synthetic

reactions

were

carried

out

without

any

solvent.

The

structure

of

each

protic

IL

was

identified

using

nuclear

magnetic

resonance

(NMR)

spectroscopy.

The

ionic

liquid

samples

were

kept

sealed

in

vials

using

thick

layers

of

paraffin

and

stored

in

an

argon

atmosphere

glovebox

(VAC,

O

2

<

1

ppm,

H

2

O

<

1

ppm)

before

use.

2.2.1.

[MePyr][HCOO]

Feed

ratio

of

N-methylpyrrolidine:formic

acid

=

1:1.

Yield:

76%.

1

_H

_NMR

₍₄₀₀

_MHz,

_DMSO-d

6

,

ppm):

9.92

(br,

1H,

N–H),

8.30

(s,

1H,

HCOO–),

3.08

(m,

4H,

N–CH

2

–),

2.67

(s,

3H,

N–CH

3

),

1.90–1.85

(m,

4H,

N–CH

2

–CH

2

).

1

H

NMR

(400

MHz,

D

2

O,

ppm):

8.18

(s,

1H,

HCOO–),

3.47–3.31

(t,

2H,

N–CH

2

–CH

2

),

2.88–2.80

(t,

2H,

N–CH

2

–

CH

2

),

2.71

(s,

3H,

N–CH

3

),

1.95–1.79

(m,

4H,

N–CH

2

–CH

2

).

2.2.2.

[MePyr][2HCOO]

Feed

ratio

of

N-methylpyrrolidine:formic

acid

=

1:2.

Yield:

72%.

1

_H

_NMR

₍₄₀₀

_MHz,

_D

2

O,

ppm):

8.21

(s,

1H,

HCOO–),

3.50

(t,

2H,

N–

CH

2

–CH

2

),

2.91

(t,

2H,

N–CH

2

–CH

2

),

2.77

(s,

3H,

N–CH

3

),

2.04–1.93

(m,

2H,

N–CH

2

–CH

2

),

1.91–1.83

(m,

4H,

N–CH

2

–CH

2

).

2.2.3.

[MePyr][4HCOO]

Feed

ratio

of

N-methylpyrrolidine:formic

acid

=

1:4.

Yield:

75%.

1

_H

_NMR

₍₄₀₀

_MHz,

_D

2

O,

ppm):

8.19

(s,

1H,

HCOO–),

3.50

(t,

2H,

N–

CH

2

–),

2.91

(t,

2H,

N–CH

2

–),

2.78

(s,

3H,

N–CH

3

),

2.05–2.00

(m,

2H,

N–CH

2

–CH

2

),

1.91–1.85

(m,

4H,

N–CH

2

–CH

2

).

2.2.4.

[MePyr][HSO

4

]

Feed

ratio

of

N-methylpyrrolidine:sulfuric

acid

=

1:1.

Yield:

92%.

1

_H

_NMR

₍₄₀₀

_MHz,

_DMSO-d

6

,

ppm):

7.51

(br,

1H,

N–H),

3.16

(m,

4H,

N–CH

2

–),

2.73

(s,

3H,

N–CH

3

),

1.86

(m,

4H,

N–CH

2

–CH

2

).

1

H

NMR

(400

MHz,

D

2

O,

ppm):

8.68

(br,

1H,

N–H),

3.36

(t,

2H,

N–CH

2

–

CH

2

),

2.76

(t,

2H,

N–CH

2

–CH

2

),

2.62

(s,

3H,

N–CH

3

),

1.85–1.73

(m,

4H,

N–CH

2

–CH

2

).

2.2.5.

[MePyr][2HSO

4

]

Feed

ratio

of

N-methylpyrrolidine:sulfuric

acid

=

1:2.

Yield:

87%.

1

H

NMR

(400

MHz,

D

2

O,

ppm):

3.38

(t,

2H,

N–CH

2

–CH

2

),

2.79

(t,

2H,

N–CH

2

–CH

2

),

2.66

(s,

3H,

N–CH

3

),

1.89

(m,

2H,

N–CH

2

–CH

2

–

),

1.77–1.76

(m,

3H,

N–CH

2

–CH

2

–

and

HSO

4

).

2.2.6.

[MePyr][4HSO

4

]

Feed

ratio

of

N-methylpyrrolidine:sulfuric

acid

=

1:4.

Yield:

83%.

1

_H

_NMR

₍₄₀₀

_MHz,

_D

2

O,

ppm):

3.33

(t,

2H,

N–CH

2

–CH

2

),

2.73

(t,

2H,

N–CH

2

–CH

2

),

2.60

(s,

3H,

N–CH

3

),

1.83

(m,

2H,

N–CH

2

–CH

2

–

),

1.73–1.68

(m,

3H,

N–CH

2

–CH

2

–

and

HSO

4

).

O

H

O

H

O

H

O

O

H

O

H

O

H

O

H

O

H

O

N

H

3

C

H

N

H

3

C

H

(a)

(b)

Fig.1.Possibleformationof(a)dimericand(b)higher-orderoligomericformicacid. T.-Y.Wuetal./JournaloftheTaiwanInstituteofChemicalEngineers43(2012)58–66 59

3.7.

Stokes–Einstein

relationship

The

classical

Stokes–Einstein

equation

[53]

relates

the

viscosity

of

an

incompressible

medium

to

the

diffusion

coefficient,

D,

of

a

spherical

particle

with

a

hydrodynamic

radius,

a

,

moving

through

the

medium

D

¼

kBT

6

pha

(9)

where

k

B

is

the

Boltzmann

constant,

T

is

the

temperature,

and

h

is

the

viscosity

of

the

solution.

The

Stokes–Einstein

product,

D

h

/T,

where

D

is

derived

from

electrochemical

mass

transport

data,

is

often

used

to

make

temperature-independent

comparisons

of

the

relative

value

of

a

.

Fig.

9

shows

a

graph

of

DT

1

_vs.

_h

1

_resulting

from

experiments

conducted

in

[MePyr][HCOO]

at

temperatures

ranging

from

303

to

333

K.

The

results

clearly

demonstrate

the

applicability

of

the

relationship

between

D

and

h

1

_for

_the

diffusion

of

ferrocenium

in

[MePyr][HCOO],

and

they

indicate

that

a

is

independent

of

the

viscosity

of

the

IL

and

temperature.

4.

Conclusions

Brønsted

acid

ionic

liquids

containing

oligomeric

formate

and

hydrogen

sulfate

anions

were

synthesized.

The

density,

viscosity,

ionic

conductivity,

and

diffusion

coefficient

of

ferrocene

in

the

ionic

liquids

were

characterized

as

a

function

of

temperature

over

the

range

from

303

to

353

K.

Brønsted

acid

ILs

contains

oligomeric

anions

have

lower

viscosity,

higher

density,

and

higher

conductiv-ity

compared

to

those

of

ILs

prepared

using

equimolar

amounts

of

acid

and

base.

The

temperature-dependent

electrolyte

viscosity

is

correlated

with

molar

conductivity

via

an

empirical

Walden’s

rule.

The

a

values

of

ILs

calculated

from

the

slopes

of

the

Walden

plots

were

compared

to

those

calculated

from

the

ratio

of

activation

energies

for

viscosity

and

molar

conductivity

(E

a,L

/E

a,h

).

The

diffusion

coefficients

of

ferrocene

in

ILs

were

calculated

from

the

cyclic

voltammetry.

The

hydrodynamic

radius

of

the

diffusing

species

calculated

from

the

diffusion

coefficients

using

the

traditional

Stokes–Einstein

equation

was

found

to

be

independent

of

the

viscosity

of

the

IL

and

temperature.

Acknowledgements

The

authors

would

like

to

thank

the

National

Science

Council

of

the

Republic

of

China

for

financially

supporting

this

project.

The

authors

also

gratefully

acknowledge

the

contributions

of

Chao-anx

Lai,

Department

of

chemistry,

National

Cheng

Kung

University,

for

helping

with

the

laboratory

work.

References

[1]RogersRD,SeddonKR.Ionicliquids:industrialapplicationsforgreen chemis-try.Washington,DC:AmericanChemicalSociety;2003.

[2]LewandowskiA,S´widerska-MocekA,AcznikI.Synthesisandcharacterization ofhighlystableopticallypassiveCeO2–ZrO2counterelectrode.Electrochim

Acta2010;55:1990.

[3]SunXG,DaiS.Electrochemicalinvestigationsofionicliquidswithvinylene carbonateforapplicationsinrechargeablelithiumionbatteries.Electrochim Acta2010;55:4618.

[4]WuTY,TsaoMH,ChenFL,SuS-G,ChangCW,WangHP,etal.Synthesisand characterizationoforganicdyescontainingvariousdonorsandacceptors.IntJ MolSci2010;11:329.

[5]TsaoMH,WuTY,WangHP,SunIW,SuSG,LinYC,etal.Anefficientmetalfree sensitizerfordye-sensitizedsolarcells.MaterLett2011;65:583.

[6]WuTY,TsaoMH,ChenFL,SuS-G,ChangCW,WangHP,etal.Synthesisand characterizationofthreeorganicdyeswithvariousdonorsandrhodaninering acceptorforuseindye-sensitizedsolarcells.JIranChemSoc2010;7:707. [7]WuTY,TsaoMH,SuSG,WangHP,LinYC,ChenFL,etal.Synthesis,

characteri-zationandphotovoltaicpropertiesofdi-anchoringorganicdyes.JBrazChem Soc2011;22:780.

[8]ChenPY,DengMJ,ZhuangDX.Electrochemicalcodepositionofcopperand manganesefromroom-temperatureN-butyl-N-methylpyrrolidinium bis(tri-fluoromethylsulfonyl)imideionicliquid.ElectrochimActa2009;54:6935. [9]TsaiMC,ZhuangDX,ChenPY.Electrodepositionofmacroporoussilverfilms

from ionic liquids and assessment of thesefilms in the electrocatalytic reductionofnitrate.ElectrochimActa2010;55:1019.

[10]ElAbedinSZ,GiridharP,SchwabP,EndresF.Electrodepositionof nanocrystal-linealuminiumfromachloroaluminateionicliquid.ElectrochemCommun 2010;12:1084.

[11]YangJM,GouSP,SunIW.Single-steplarge-scaleandtemplate-free electro-chemicalgrowthofNi–Znalloyfilamentarraysfromazincchloridebased ionicliquid.ChemCommun2010;46:2686.

[12]HsiehYT,LeongTI,HuangCC,YehCS,SunIW.Directtemplate-free electro-chemicalgrowthofhexagonalCuSntubesfromanionicliquid.Chem Com-mum2010;46:484.

[13]BarnesEO,O’MahonyAM,AldousL,HardacreC,ComptonRG.The electro-chemical oxidationof catecholand dopamineonplatinumin 1-ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide ([C2mim][NTf2]) and

1-butyl-3-methylimidazoliumtetrafluoroborate([C4mim][BF4]):Adsorption

effectsinionicliquidvoltammetry.JElectroanalChem2010;646:11. [14]LeBideauJ,ViauL,ViouxA.Ionogels,ionicliquidbasedhybridmaterials.Chem

SocRev2011;40:907.

[15]XieZL,TaubertA.Thermomorphicbehavioroftheionicliquids[C4mim][FeCl4]

and[C12mim][FeCl4].ChemPhysChem2011;12:364.

[16]Lazzu´sJA.

r

–T–Ppredictionforionicliquidsusingneuralnetworks.JTaiwan InstChemEngrs2009;40:213.

[17]WuTY,WangHC,SuS-G,GungST,LinMW,LinCB.Characterizationofionic conductivity,viscosity,density,andself-diffusioncoefficientforbinary mix-turesofpolyethyleneglycol(orpolyethyleneimine)organicsolventwithroom temperature ionic liquidBMIBF4 (or BMIPF6). JTaiwan Inst ChemEngrs

2010;41:315.

[18]TienCP,TengH.Efficientiontransportinactivatedcarboncapacitors assem-bledwithgelledpolymerelectrolytesbasedonpoly(ethyleneoxide)cured withpoly(propyleneoxide)diamines.JTaiwanInstChemEngrs2009;40:452. [19]WuTY,SuSG,GungST,LinMW,LinYC,LaiCA,etal.Ionicliquidscontainingan alkylsulfategroupaspotentialelectrolytes.ElectrochimActa2010;55:4475. [20]SorianoAN,DomaBT,LiMH.Carbondioxidesolubilityinsomeionicliquidsat

moderatepressures.JTaiwanInstChemEngrs2009;40:387.

[21]SorianoAN,AgapitoAM,Lagumbay LJLI,CaparangaAR,LiMH.Asimple approachtopredictmolarheatcapacityofionicliquidsusinggroup-additivity method.JTaiwanInstChemEngrs2010;41:307.

[22]WuTY,WangHC,SuSG,GungST,LinMW,LinCB.Aggregationinfluenceof polyethyleneglycolorganicsolventswithionicliquidsBMIBF4andBMIPF6.J

ChinChemSoc2010;57:44.

[23]SorianoAN,DomaBT,LiMH.Densityandrefractiveindexmeasurementsof 1-ethyl-3-methylimidazolium-basedionicliquids.JTaiwanInstChemEngrs 2010;41:115.

[24]SorianoAN,AgapitoAM, LagumbayLJLI, CaparangaAR,LiMH.Diffusion coefficientsofaqueousionicliquidsolutionsatinfinitedilutiondetermined from electrolytic conductivity measurements. J Taiwan Inst Chem Engrs 2011;42:258.

[25]WongC-L,SorianoAN,LiMH.Infinitedilutiondiffusioncoefficientsof [Bmim]-basedionicliquidsinwateranditsmolarconductivities.JTaiwanInstChem Engrs2009;40:77.

[26]WuTY,SuSG,WangHP,LinYC,GungST,LinMW,etal.Electrochemicalstudies andselfdiffusioncoefficientsincyclicammoniumbasedionicliquidswith allylsubstituents.ElectrochimActa2011;56:3209.

[27]Wang M-H, SorianoAN, Caparanga AR, Li MH. Binarymutual diffusion coefficientofaqueoussolutionsofpropyleneglycolanddipropyleneglycol. JTaiwanInstChemEngrs2010;41:279.

η

-1

_{/ cP}

-1 0.20 0.15 0.10 0.05 0.00

10

10

D T

-1 0 20 40 60 80 100 120 140

Fig.9.Stokes–EinsteinplotofDT1

vs.1/viscosity(

h

1

)forFcin[MePyr][HCOO].

[28]Yu Y-H,SorianoAN,Li MH.Heatcapacityandelectrical conductivityof aqueousmixturesof[Bmim][BF4]and[Bmim][PF6].JTaiwanInstChemEngrs

2009;40:205.

[29]WuTY,SuSG,WangHP,SunIW.Glycine-basedionicliquidsaspotential electrolyteforelectrochemicalstudiesoforganometallicandorganicredox couples.ElectrochemCommun2011;13:237.

[30]AngellCA,ByrneN,BelieresJP.Paralleldevelopmentsinaproticandprotic ionic liquids: physical chemistry and applications. Acc Chem Res 2007;40:1228.

[31]Nakamoto H,WatanabeM.Bronstedacid–base ionicliquidsfor fuelcell electrolytes.ChemCommun2007;24:2539.

[32]HagiwaraR,NakamoriY,MatsumotoK,ItoY.Theeffectoftheanionfractionon thephysicochemicalpropertiesofEMIm(HF)nF(n=1.0–2.6).JPhysChemB

2005;109:5445.

[33]JohanssonKM,IzgorodinaEI,ForsythM,MacFarlaneDR,SeddonKR.Protic ionicliquidsbasedonthedimericandoligomericanions:[(AcO)xHx1].Phys

ChemChemPhys2008;10:2972.

[34]CasesAM,MariglianoACG,BonattiCM,So´limoHN.Density,viscosity,and refractiveindexofformamide,threecarboxylicacids,andformamide+ car-boxylicacidbinarymixtures.JChemEngData2001;46:712.

[35]Wasserscheid P,WeltonT,editors.Ionic liquidsinsynthesis. Weinheim: Wiley-VCH;2008.

[36]FangS,YangL,WangJ,LiM,TachibanaK,KamijimaK.Ionicliquidsbasedon functionalizedguanidiniumcationsandTFSIanionaspotentialelectrolytes. ElectrochimActa2009;54:4269.

[37]WuTY,SuSG,GungST,LinMW,LinYC,Ou-YangWC,etal.Synthesisand characterizationofproticionicliquidscontainingcyclicaminecationsand tetrafluoroborateanion.JIranChemSoc2011;8:149.

[38]MokhtaraniB,SharifiA,MortahebHR,MirzaeiM,MafiM,SadeghianF. Densityandviscosityof1-butyl-3-methylimidazoliumnitratewithethanol, 1-propanol, or 1-butanol at several temperatures. J Chem Thermodyn 2009;41:1432.

[39]Ste˛pniakI, AndrzejewskaE.Highlyconductive ionicliquidbasedternary polymerelectrolytesobtainedbyinsituphotopolymerisation.Electrochim Acta2009;54:5660.

[40]NakamotoH,NodaA,HayamizuK,HayashiS,HamaguchiH,WatanabeM. Proton-conductingpropertiesofaBrønstedacid–baseionicliquidandionic

meltsconsistingofbis(trifluoromethanesulfonyl)imideandbenzimidazolefor fuelcellelectrolytes.JPhysChemC2007;111:1541.

[41]VideaM,AngellCA.Glassformation,ionicconductivity,andconductivity/ viscositydecoupling,inLiAlCl4+LiClO4andLiAlCl4+LiAlCl3imidesolutions.J

PhysChemB1999;103:4185.

[42]ZhuQ,SongY,ZhuX,WangX.Ionicliquid-basedelectrolytesforcapacitor applications.JElectroanalChem2007;601:229.

[43]OhnoH,YoshizawaM.Ionconductivecharacteristicsofionicliquidsprepared byneutralizationofalkylimidazoles.SolidStateIonics2002;154–155:303. [44]Mayrand-ProvencherL,RochefortD.Originandeffectofimpuritiesinprotic

ionicliquidsbasedon2-methylpyridineandtrifluoroaceticacidfor applica-tionsinelectrochemistry.ElectrochimActa2009;54:7422.

[45]AppetecchiGB,MontaninoM,ZaneD,CarewskaM,AlessandriniF,PasseriniS. Effectofthealkylgrouponthesynthesisandtheelectrochemicalpropertiesof N-alkyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquids.ElectrochimActa2009;54:1325.

[46]ChangJK,LeeMT,TsaiWT,DengMJ,ChengHF,SunIW.Pseudocapacitive mechanismofmanganeseoxidein1-ethyl-3-methylimidazoliumthiocyanate ionicliquidelectrolytestudiedusingX-rayphotoelectronspectroscopy. Lang-muir2009;25:11955.

[47]XuW,AngellCA.Solvent-freeelectrolyteswithaqueoussolution-like con-ductivities.Science2003;302:422.

[48]NittaK,NohiraT,HagiwaraR,MajimaM,InazawaS.Physicochemical proper-tiesofZnCl2–NaCl–KCleutecticmelt.ElectrochimActa2009;54:4898.

[49]AnoutiM,Caillon-CaravanierM,DridiY,GalianoH,LemordantD.Synthesis andcharacterizationofnewpyrrolidiniumbasedproticionicliquids.Good andsuperionicliquids.JPhysChemB2008;112:13335.

[50]FraserKJ,IzgorodinaEI,ForsythM,ScottJL,MacFarlaneDR.Liquids interme-diatebetween‘‘molecular’’and‘‘ionic’’liquids:Liquidionpairs?Chem Com-mun2007;3817.

[51]MacFarlaneDR,ForsythM,IzgorodinEI,AbbottAP,AnnataG,FraserK.Onthe conceptofionicityinionicliquids.PhysChemChemPhys2009;11:4962. [52]BardAJ,FaulknerLR.Electrochemicalmethods—fundamentalsand

applica-tions.NewYork:Wiley;1980.

[53]WuTY,SunIW,GungST,LinMW,ChenBK,WangHP,etal.Effectsofcations andanionsontransportpropertiesintetrafluoroborate-basedionicliquids.J TaiwanInstChemEng2011;42:513.

T.-Y.Wuetal./JournaloftheTaiwanInstituteofChemicalEngineers43(2012)58–66 66