· 1980 1985 1990 1995 2000 2005 2010 2015 1 10 100 1000 10000 100000 number of IL publications / year year published Maier, Web of Science, ionic_liquid* in Topic, 16.5.2015 . The

1980 1985 1990 1995 2000 2005 2010 20151

10

100

1000

10000

100000

num

ber o

f IL

publ

icat

ions

/ ye

ar

year published

Maier, Web of Science, ionic_liquid* in Topic, 16.5.2015

The distillation and volatility of ionic liquids (Earle, Seddon, Rebelo et al., 2006)

Ionic liquids in vacuo; solution-phase X-ray photoelectron spectroscopy (Licence et al., 2005)

X-ray photoelectron spectroscopy and low energy ion scattering studies on 1-buthyl-3-methyl-imidazolium bis(trifluoromethane) sulfonimide (Caporali et al., 2006) Surface enrichment and depletion effects of ions dissolved in an ionic liquid: an X-ray photoelectron spectroscopy study (Maier et al., 2006)

Photoelectron Spectroscopy of IL-based Interfaces (Lovelock, Villar-Garcia, Maier, Steinrück, Licence, 2010)

Dissolution of cellose with ionic liquids (Rogers et al., 2002)

DIALKYLIMIDAZOLIUM CHLOROALUMINATE MELTS - A NEW CLASS OF ROOM-TEMPERATURE IONIC LIQUIDS FOR ELECTROCHEMISTRY, SPECTROSCOPY, AND SYNTHESIS (Wilkes et al., 1982)

AIR AND WATER STABLE 1-ETHYL-3-METHYL-IMIDAZOLIUM BASED IONIC LIQUIDS (Wilkes et al., 1992)

Hydrophobic, highly conductive ambient-temperature molten salts (Bonhote ,Grätzel et al., 1996)

Ionic liquids - New "solutions" for transition metal catalysis (Wasserscheid, 2000)

Ionic liquids for clean technology (Seddon, 1997)

BASIL –process (BASF, 2002) Biphasic acid scavenging utilizing ionic liquids: The first commercial process with ionic liquids (Maase, 2005)

Room-temperature ionic liquids. Solvents for synthesis and catalysis (Welton, 1999) Green processing using ionic liquids and CO2 (Brennecke et al., 1999)

Ionic Liquids meets Surface Science (2005) Ionic liquids in electrochemical devices and processes: managing interfacial electrochemistry (Macfarlane, 2007)

Ueber die Molekulargrosse und elektrische Leitfa higkeit einiger geschmolzenen Salze (Walden, 1914)

Ionic-liquid materials for the electrochemical challenges of the future (Armand, Endres, Macfarlane, 2009)

“..The vapour pressure of e.g. [C2C1Im][EtOSO3], is at room temperature

in the same order of magnitude as the vapour pressure of a piece of iron…”

Prof. Andreas Heintz, University Rostock,

private communication

Surface Science studies under UHV conditions are possible !!!!

• Consists entirely of ions ("molten salt") • Liquid below 100°C • Physico-chemical properties tunable by varying the molecular structure • Extremely low vapor pressure (<10-9 mbar at 300 K)

What is an ionic liquid?

Properties and applications of ionic liquids



E. Smith, P. Licence et al. (Nottingham), Chem.Comm., 2005, 5633.

self-synthesized IL (surface clean)

[C2C1Im] [EtOSO3]

(commercially: ECOENG 212)


J.M. Gottfried, F. Maier et al., Z. Phys. Chem., 2006, 220, 1439.



9 nm

– Si –

– Si – – Si – – Si – – Si – – Si –

Surface active species may strongly modify surface properties (surface tension, surface activity, …)

[C2C1Im] [EtOSO3]

(commercially: ECOENG 212)

SiOxRy-impurities of unknown origin (polysiloxane from glassware grease) contaminate the near-surface region (in-situ cleaning via sputtering possible)


J.M. Gottfried, F. Maier et al., Z. Phys. Chem., 2006, 220, 1439.

Why studying interfaces of ionic liquids?

multiphase catalysis with ionic liquids

+ -

+ -

+ -

+ -+ -

Reactants Products

Gas phase

Support material Solid catalyst

Reactants Products

Gas phase

Support material

OC RhPP

H

CO

SILP

SCILL

+ - Ionic liquid film

SILP/SCILL particle

Porous network

+ -

Immobilised catalyst Metal nanoparticle

SILP: Supported Ionic Liquid Phase - Riisager et al., Ind. Eng. Chem. Res. 44 (2005) 9853 SCILL: Solid Catalyst with Ionic Liquid Layer - Kernchen et al. , Chem. Eng. Technol. 8 (2007) 985


SCILL: Solid Catalyst with Ionic Liquid


Concept: From simple to complex systems

photoelectrons

Reactants Products

X-rays

Designed catalyst dissolved in a

designed ionic liquid

X-rays photoelectrons

Neat ionic liquid

Physical Chemistry II

group Prof. Dr. Hans-Peter Steinrück

SURFACE SCIENCE • Photoelectron spectroscopy

(ARXPS) • Surface properties • In-situ gas-phase reactions

Ionic Liquid Surface and Interface Science

Chemical Reaction Engineering

group Prof. Dr. Peter Wasserscheid

IONIC LIQUID CHEMISTRY • New IL structures,

quality assessment • Physico-chemical properties • Metal complexes in ILs,

IL catalysis

ILSS-project (2006-2012) IL-solid interfaces (2008-2017)

Prof. Dr. Peter Wasserscheid

C. Kolbeck I. Niedermaier B. May K. Lovelock A. Deyko T. Matsuda

T. Cremer F. Rietzler P. Schreiber B. Heller

Prof. Dr. Hans-Peter Steinrück

P. Schulz N. Taccardi N. Paape W. Wei M. Bahlmann J. Schwegler

Acknowledgements

Collaborations: P. Licence, R. Jones, B. Kirchner, A. Fröba, J. Libuda, S. Baldelli, J. Behm, J. Schatz, J. Lopes ...

Supported by: DFG (SPP 1191, CoE-EAM, STE 620/9-1), A.v.Humboldt- and Max-Buchner-Stiftung, Industry

2. „Bulk“, in-situ reactions

Surface and Interface Science of Ionic Liquids

��

1. Surface composition of ILs

3. IL - solid interfaces

e-

hν

X-ray gun

IL film Au

EB = hν - Ekin

X-ray photoelectron spectroscopy (XPS)

800 700 600 500 400 300 200 100 00

9000

S 2s S 2pC 1sN 1s

O 1s

F 1s

Inte

nsity

/ a.

u.

Binding Energy / eV

NS S

CF3 CF3

O

O

O

O

N N CH3

406 404 402 400 398 396

0

100

N 1s NIm

NTf2N

2 : 1 Element specific

Chemical shift

Quantitative analysis

Surface sensitive (IDmax ≈ 9nm)

ID

variation of surface sensitivity by varying electron detection angle

Angle-resolved XPS (ARXPS)

“bulk sensitive”

“surface sensitive”

0° emission 80° emission

Information depth 7-9 nm

Information depth 1-1.5 nm

X-rays e- e-

Key message 0° ⇒ 80°: Intensity of one species increases

enhancement of that species at surface region

~ ID(0°) ∙cosθ

N N

N S S

C F 3

O F 3 C

O

O O

297 294 291 288 285 2820

50

100

150

Binding Energy / eV

7 C“alkyl”

5 C“hetero”

2 CC-F

2 : 5 : 7

C1s

„bulk sensitive“ (0°)

[C8C1Im][Tf2N] non-functionalised ILs

Influence of chain length [CnC1Im]+

0°: alkyl / hetero = = 7/5 = 1.4

N N

N S S

C F 3

O F 3 C

O

O O

297 294 291 288 285 2820

50

100

150

200

0° 80°

Binding Energy / eV

C“alkyl”

C“hetero”

CC-F

„surface sensitive“ (80°)

C1s

[C8C1Im][Tf2N]


80°: alkyl / hetero = 2.2 more alkyl carbon

at surface on expense of ring and anion atoms

0°: alkyl / hetero = = 7/5 = 1.4

Lovelock et al. J Phys. Chem B, 2009, 113, 2854-2864. Maier et al., PCCP, 2010, 12, 1905-1915.

0 2 4 6 8 10 12 14 16 180

1

2

3

4

5

6

7(

I C 1s

(Cal

kyl)

/ IC

1s (C

hete

ro)

[CnC1Im][Tf2N]

0° 70° 80°

N S S

C F 3

O F 3 C

O

O O

N N Cn-1H2n-1

297 294 291 288 285 2820

50

100

150

200

0° 80°

Binding Energy / eV

Chetero

Calkyl

CC-F

[C8C1Im][Tf2N]

longer chains, more alkyl carbon at surface

7 : 5

11 : 5


• surface composed primarily of highly oriented alkyl chains

N

N

[NO3]-

Jiang et al. J. Phys. Chem. C 2008, 112, 1132-1139.


model for surface layer

Cation Anion Vm / nm3 σ / mN m-1

[C1C1Im]+ [Tf2N]- 0.400 36.3 [C4C1Im]+ [Tf2N]- 0.485 30.7 [C8C1Im]+ [Tf2N]- 0.603 29.5

• correlation with surface tension

Kolbeck, Lehmann, Paape et al., J. Phys. Chem. B, 2010, 114, 17025 (Fröba, Wasserscheid, Steinrück)

Influence of the anion ... ... on surface composition

B

F

FF

F

Cl- Br- I- P

F

F

F F

F FSF3C O

O

O

NS S

CF3

OF3C

O

OO NS S

C2F5

OC2F5

O

OO

P

F

C2F5

C2F5 F

C2F5 F

[TfO]- [PF6]- [BF4]-

[Tf2N]- [Pf2N]- [FAP]-

[C8C1Im]+ Co

Br

Br BrBr

2

[CoBr4]2-

Influence of the anion

from small (strongly coordinating) to large (weakly coordinating)

N N X

0.4 0.5 0.6 0.7

1.5

2.0

2.5

3.0

3.5[NO3]

-

[FAP]-

[Pf2N]-

[Tf2N]-

I-

[TfO]-[BF4]-

Cl-

[PF6]-

0° 80° Nominal

I C1s(C

alky

l) / I

C1s(C

hete

ro)

Ionic liquid molecular volume (using density) / nm3

Br-• more surface alkyl carbon

for smaller anions • increased packing density

of chains for smaller anions

N N X

Influence of the anion ... ... on surface composition

[C8C1Im]+

Kolbeck et al., J. Phys. Chem. B, 2009, 113, 8682-8688. Maier et al., PCCP, 2010, 12, 1905-1915. Lovelock et al., Chem. Soc. Rev., 2010, 110, 5158–5190.

Model for outer surface layer (interface vacuum / IL bulk)

Surface composition of non-functionalized ILs

non-

pola

r

(a

lkyl

cha

ins,

CF 3

)

pol

ar

(ioni

c he

adgr

oups

)

Cl- [Tf2N]-

N N X

Kolbeck et al., J. Phys. Chem. B, 2009, 113, 8682-8688. Maier et al., PCCP, 2010, 12, 1905-1915. Lovelock et al., Chem. Soc. Rev., 2010, 110, 5158–5190.

Surface composition of non-functionalized ILs

Kolbeck et al., ChemPhysChem 14 (2013) 3726

290 287 284 281

0

30000

Chetero

Binding Energy / eV

Inte

nsity

/ C

PS

[C8C1Im]Br Calkyl

290

[C8C1Im

Bi

300 K; 0° 300 K; 80° 400 K; 80° diff.(80°)

TEMPERATURE - Dependence

Surface enrichment less pronounced at higher temperature Due to entropic effects

Surface composition of functionalized ILs

N N

F F

F F

F F

FF

F

N NBr

N NI

N NCl

Cl

SO3

F

SO3

Halogen

N NN

Amine

Functionalisation of side chains Ether & Thioether

N NO

N N

Phenyl

C. Kolbeck et al., Chem. Eur. J. 20 (2014) 3954


• Surface enrichment of Cl and Calkyl

• Surface depletion of O, S and N

0° / 80°

Niedermaier et al. ChemPhysChem. 13 (2012) 1725 C. Kolbeck et al., Chem. Eur. J. 20 (2014) 3954


Surface orientation depends on interplay between ionic head group interaction

functional groups/alkyl chain interaction and

interaction between ionic head groups and functional groups

general conclusions

C. Kolbeck et al., Chem. Eur. J. 20 (2014) 3954 H.-P. Steinrück, Phys. Chem. Chem. Phys. 14 (2012) 5010


1) weak interactions between functional units and head groups: surface enrichment for long chains (n>4) non-, halogen-, alkoxysilane-, amine- ,thioether- functionalized ILs for functionalization of cation or anion. 2) significant interactions of functional group with head groups: inter-/intramolecular hydrogen bonding for ether groups quadrupole interactions for phenyl groups surface enrichment reduced or even suppressed

C. Kolbeck et al., Chem. Eur. J. 20 (2014) 3954

N

NH

OO

��



2. „Bulk“, in situ reactions • CO2 capture by amines


-O3S

NH2

N+

HO OH

O C O

R

HN

O

COH

R

HN

O

CO-

R+H3N

NH2

R

NH2

R

NH2

R

MEA (mono- ethanolamine)

HO

NH2

amine carbamic acid carbamate ammonium

CO2 : amine

1 : 2 1 : 1 RT

∆T

In-situ XPS: amine reaction with CO2

CO2

selective CO2

absorption by amines

CO2 postprocessing

CO2 stripping

amine recycling

Joan Brennecke (Notre Dame) B. Gurkan et al., J. Am. Chem. Soc. 2010, 132, 2116–2117

-

amine-functionalised

IL

-

- -

-

+

near-ambient pressure XPS: 0.9 mbar CO2 (atmosphere: ~0.4 mbar partial pressure)

J. Pantförder, Photoelektronenspektroskopie im „Pressure Gap“ – Aufbau einer neuen Apparatur für Messungen im Druckbereich von 10-10 bis 1 mbar, PhD thesis, 2004, Uni Erlangen-Nürnberg

In-situ XPS: amine reaction with CO2

Surface (in situ) vs. bulk (ex situ)

N+OH

OH

-O3SNH2

-O3SNH3

+

-O3S

HN

C

O-

O-O3S

HN

C

OH

O ?

CO2 : amine 1 : 2 1 : 1

at surface (1mbar): 0.6 CO2 per 1 IL (mainly 1:1 carbamic acid)

in bulk (1 mbar): no CO2

in bulk (1bar): 0.15 CO2 per IL (only 1:2 carbamate )

Niedermaier, Bahlmann, J. Am. Chem. Soc., 2014, 136, 436

CO2 1 mbar

CO2

Niedermaier, Bahlmann, J. Am. Chem. Soc., 2014, 136, 436

- O3S

H NC

OHO

- O3S

H NC

OHO

- O3S

H NC

OHO

- O3S

H NC

OHO

1:1

- O3S

H NC

OHO

1:2 -O3SNH3

+-O3S

HN

C

O-

O

Carbamic acid stabilised at surface (singly charged)

- O3S

NH

2

- O3S

NH

2

~0.15 mol

~0.45 mol


��



H2C

H2C

CH2

CH

CH

H2C

HC

CH C

H2

CH2

CH2

H2C

NPH

N+

N

C6H12

S

F

F

F

O

-O

O

2. in-situ reactions

• CO2 capture by amines

• IL-solid reaction LOHC dehydrogenation

Liquid organic hydrogen carrier (LOHC)

Brückner et al., ChemSusChem 2014, 7, 229

H12-NEC NEC

Liquid organic hydrogen carrier (LOHC)

Pt, Pd catalyzed

Ru catalyzed

Reversible hydrogenation (Ru) and dehydrogenation (Pt, Pd) of N-ethylcarbazole (NEC) and perhydro-N-ethylcarbazole (H12-NEC)

not observable in UHV (multilayer desorption > -30°C)

PerHydrogenated IL 1-[6-(N-dodecahydrocarbazole)hexyl]-3-methylimidazolium

trifluoromethanesulfonate

Synthesis of carbazole functionalized IL

NN

N+

F

F

F S

O

O

O-

NEC

DeHydrogenated IL 1-[6-(N-Carbazole)hexyl]-3-methylimidazolium

trifluoromethanesulfonate

N

H12-NEC

N+

NN

S O-

O

O

F

F

F

N

DH-IL

PH-IL

XP spectra of PH-IL and DH-IL (350 K)

HC

HC

HC C

C

CH

C

CHC

CH

CHCH

NDH

N+N

C6H12

S

F

F

F

O

-O

O

DH

-IL

406 404 402 400 398 396

PH-IL:DH-IL =1:1

DH-IL

In

tens

ity /

arb.

uni

ts

Binding Energy / eV

PH-IL

NIm

NDH

NPH

1.9 eV

3.2 eV

N 1s

H2C

H2C

CH2

CH

CH

H2C

HC

CH C

H2

CH2

CH2

H2C

NPH

N+

N

C6H12

S

F

F

F

O

-O

O

PH-IL

N 1s spectrum reflects hydrogenation state

of carbazole unit

e-

hν

X-ray gun

PH-IL film

Experimental: VG-ESCALAB 200 (Al Kα, ∆E = 0.9 eV)

Sample transfer system

Pressure <10-8 mbar (clean UHV conditions)

Equipped with QMS (PFEIFFER QMG220)

X-ray Photoelectron Spectroscopy (XPS) and Thermal Desorption Spectroscopy (TDS)

Heat

H2

QMS

ID ≤ 9 nm ~ 0.1 mm

Pt foil

Matsuda, Taccardi, Schwegler et al., ChemPhysChem, 2015, 16, 1873-1879

XPS of PH-IL on Pt

406 404 402 400 398 396

Inte

nsity

/ ar

b. u

nits

Binding Energy / eV

430K

440K

450K

460K

470K

475K

480K

485K

490K

495K

500K

520K

550K

DH-IL

420K

410K

400K

350K

Pt PH IL

Heat

~ 6K / h

NDH NPH

@ Pt-foil: 440 – 520 K

Nim

HC

HC

HC C

C

CH

C

CHC

CH

CHCH

NDH

N+N

C6H12

S

F

F

F

O

-O

O

DH

-IL

H2C

H2C

CH2

CH

CH

H2C

HC

CH C

H2

CH2

CH2

H2C

NPH

N+

N

C6H12

S

F

F

F

O

-O

O

PH-IL

XPS of PH-IL on Pt

406 404 402 400 398 396

Inte

nsity

/ ar

b. u

nits

Binding Energy / eV

430K

440K

450K

460K

470K

475K

480K

485K

490K

495K

500K

520K

550K

DH-IL

420K

410K

400K

350K

Pt PH IL

Heat

~ 6K / h

NDH NPH

@ Pt-foil: 440 – 520 K

or on Au Nim

406 404 402 400 398 396

Inte

nsity

/ ar

b. u

nits

Binding Energy / eV

NDH NPH

@ Au-foil: 500 – 550 K (decomp.)

350K

400K

450K

460K

470K

480K

490K

500K

510K

520K

530K

540K

550K

DH-IL

Au PH-IL

Heat

no catalyst (Au support): dehydrogenation & decomposition at T ≥ 510K

400 420 440 460 480 500 520 540 560 580 600

0.0

0.2

0.4

0.6

0.8

1.0 rPH

rDH

T / K

Inte

nsity

Rat

ios

0.0

2.0x10-9

4.0x10-9

6.0x10-9

8.0x10-9

1.0x10-8

PH-IL Q

MS

Inte

nsity

/ a.

u.

XPS of PH-IL on Pt

Pt PH IL

Relative intensity: rPH = NPH/(NPH + NDH), rDH = NDH/(NPH + NDH) Mean heating rate: 0.002 K/s (XPS), 0.04 - 0.14 K/s (TDS)

H2C

H2C

CH2

CH

CH

H2C

HC

CH C

H2

CH2

CH2

H2C

NPH

PH-IL

HC

HC

HC C

C

CH

C

CHC

CH

CHCH

NDH

DH

-IL

NDH

NPH

480 K

498 K

dehydrogenation liquid H12-NEC (supported Pt @ 500K)

Vacuum surface science meets heterogeneous catalysis: Dehydrogenation of a liquid organic hydrogen carrier in the liquid state

• LOHC linked to non-reactive IL-tag to reduce vapor pressure

• in situ reaction monitored (XPS, TDS) at equilibrium under UHV

• catalyzed dehydrogenation close to techn. conditions

• on Au dehydrogenation / decomposition at higher T (+30K)

T. Matsuda, N. Taccardi, J. Schwegler et al., ChemPhysChem, 2015, 16, 1873-1879

LOHC – IL: Summary

2. „Bulk“, in situ reactions

��




IL – solid interfaces studied by ARXPS

access to IL-solid interface: ultrathin IL layers required

substrate

e-

IL-Film 0-9 nm

• in-situ preparation in UHV: physical vapor deposition of IL (ion pairs)

• sub-monolayer dosing (typically ~0.3 ML IL / min at 400 – 450 K)

deposition of well-defined amount of clean IL on clean support

IL – solid interfaces studied by ARXPS

substrate

e-

IL-Film 0-9 nm

The distillation and volatility of ionic liquids (Earle, Seddon, Rebelo et al., 2006)

T. Cremer et al., ChemPhysChem, 2008, 9, 2185

< 0.5 ML

N N

NS S

O

OO

OFF

F

FF

F

N N

Au (111)

N N

NS

O O

CF3

S

OO

F3C

NS

O O

CF3

S

OO

F3C

~ 0.5 ML N NCF3

SN

O OS

O O

F3CN N

CF3

SN

O OS

O O

F3C

N N N N

CF3S

N

OOS

O O

F3C

CF3S

N

O OS

O O

F3C

N NCF3

SN

O OS

O O

F3CN N

CF3

SN

O OS

O O

F3C

N N N N

CF3S

N

OOS

O O

F3C

CF3S

N

O OS

O O

F3C

CF3

SNO OS

O O

F3C

N N

CF3

SNO OS

O O

F3CN N

> 0.5 ML • Subsequent IL multilayers • Restructuring at d = 0.5 ML

• Checkerboard-like structure

Cremer et al., Langmuir, 2011, 27, 3662

Interface [C8C1Im][Tf2N] / Au(111)

1.6

1.9

2.1

2.2

Calkyl / Chetero (nom. 1.4)

Interface [C4C1Pyr][Tf2N] „BMP-TFSA“ / Au(111)

Uhl, Cremer, Maier, Steinrück, Behm, PCCP, 2013, 15, 17295 U = -1.8 V, I = -0.060 nA, T = 102 K

STM: At 300 K highly mobile 2D liquid phase Disordered 2D amorphous phase next to well ordered 2D crystalline layer at T < 200 K XPS & STM: checkerboard-like structure cations and anions in contact with surface alkyl chains sticking out anion in cis-conformation (CF3 groups towards vacuum)

[C4C1Pyr][Tf2N] layer [1-butyl-1-methylpyrrolidinium-bis(trifluoromethylsulfonyl)imide

NS

OO

NS

OO

F

F F

F

FF

Interface [C4C1Pyr][Tf2N] „BMP-TFSA“ / Au(111)

Buchner, Uhl, Behm et al., ACS Nano, 2015, 7, 7773

Interface [C1C1Im][Tf2N] / Ni(111)

Enhancement of anion-related species for d < 1ML

404 402 400 398

404 402 400 398

294 291 288 285

294 291 288 285

Nanion

NcationN 1s

80°

Inte

nsity

/ ar

b. u

nits

Binding Energy / eV

Cadv

Ccation

Canion

d / ML

8

0.84

0.40

0.15

80°C 1s

Binding Energy / eV

Cremer et al., PCCP, 14 (2012) 5153

N NN

S S

O

OO

OFF

F

FF

F

Initially bilayer structure on Ni(111)

Rearrangement to checkerboard structure at higher film thickness

Ni(111)

NS S

O OOO

F3C CF3

NNNN

NS S

O OOO

F3C CF3

Ni(111)

NS S

O OOO

F3C CF3

NNNN

NS S

O OOO

F3C CF3

NS S

O OOO

F3C CF3

NN

NS S

O OOO

F3C CF3

NN

Interface [C1C1Im][Tf2N] / Ni(111)

Rearrangement from bilayer to checkerboard structure with coverage

Ni(111)

NS S

O OOO

F3C CF3

NNNN

NS S

O OOO

F3C CF3

Ni(111)

NS S

O OOO

F3C CF3

NNNN

NS S

O OOO

F3C CF3

NS S

O OOO

F3C CF3

NN

NS S

O OOO

F3C CF3

NN

Cremer et al., PCCP, 2012, 14, 5153

Reactions of ultrathin IL layers on solid surfaces

0.7 ML [C1C1Im][Tf2N] on Ni(111) + Heating:

• Cation + anion thermally desorbs as neutral ion pairs at ~400K

0.7 ML [C1C1Im][Tf2N] on NiO

+ Heating • Cation desorbs first, starting at 400K

• Anion + decomposition of NiO at T>500K

cation with OH – surface groups (volatile), [Tf2N]- at Ni2+ site still stable

294 291 288 285 282 404 402 400 398 396

Inte

nsity

/ ar

b. u

nits

Inte

nsity

/ ar

b. u

nits

c)b)

80°

400 K

Canion Chetero

Binding Energy / eV

C 1s

+0.7 ML+0.7 ML

80°NanionNcation

450 K

400 K

450 K

Binding Energy / eV

N 1s

Canion Ccation

296 292 288 284 404 402 400 398 396

In

tens

ity /

arb.

units

Inte

nsity

/ ar

b.un

its

CheteroCanion 700K

500K

450K

400K

80°

Binding Energy / eV

C 1s

+ 0.7 ML

+ 0.7 ML

Ncation Nanion

80°

Binding Energy / eV

N 1s

700K

500K

450K

400K

c)b)

Canion Ccation

Cremer et al., PCCP, 2012, 14, 5153

N SSO

F3C

OO

O

CF3N N

Ni(111)

0.7 ML [C1C1Im][Tf2N]

0 1 2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

I d /

I 0

d / ML

ϑλ cos)(

0

⋅−= kinEdd eII

For ideal layer-by-layer growth:

• Linear decay with monolayer breaks intersecting with exponential line

[C1C1Im][Tf2N] on Au(111): λ = 3 nm dML = 0.73 nm

Attenuation of substrate signal

ϑ = 0°

ϑ = 80°

IL growth behaviour: Au(111) vs Ni(111)

Initially: C&A at Au (checkerboard) C at Ni (sandwich)

Differences in growth for multilayers?

0 200 400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.00 1 2 3 4 5

I d / I 0

deposition time / s

d / ML

0 200 400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.00 1 2 3 4 5

I d / I 0

deposition time / s

d / ML

[C8C1Im][Tf2N] on Au(111)

0° 80°

• Perfect agreement between 0° and 80°

• Sectionwise decay not resolved (layer completed at 0.5 ML)

Layer-by-layer growth

[C1C1Im][Tf2N] on Ni(111)

80° 0°

• Sectionwise decay resolved within first monolayer

• 80° data deviates from calculated damping curve

Wetting layer followed by mixed growth (2D 3D)

min


0 200 400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.00 1 2 3 4 5

I d / I 0

deposition time / s

d / ML

0 200 400 600 800 1000 12000.0

0.2

0.4

0.6

0.8

1.00 1 2 3 4 5

I d / I 0

deposition time / s

d / ML

[C8C1Im][Tf2N] on Au(111)

0° 80°

Layer-by-layer growth


80° 0°

Wetting layer followed by mixed growth (2D 3D)

Au(111) Ni(111)

min


• in-situ preparation in UHV: physical vapor deposition of IL (ion pairs)

• sub-monolayer dosing (typically ~0.3 ML IL / min at 400 – 450 K)

deposition of well-defined amount of clean IL on clean support

Unstable ILs: alternative deposition methods

substrate

e-

IL-Film 0-9 nm

PVD requires thermally stable IL

For non-evaporable ILs (e.g. halide ILs) different in-situ method required electrospray deposition (ESID)

IL-ESID concept

Ionic liquid electrospray ionization deposition

(IL-ESID)

Coulomb

explosion

emitted charged droplets

Rayleigh limit

high voltage +/- 1 - 5 kV

ESI capillary

Taylor cone substrate

pumping stages

F. Rietzler et al., Langmuir, 2014, 30, 1063

Experimental Details Applied Voltages +1.5 kV Solvent MeOH (cIL = 10-3 M) Flow rate 500 µL/h Distance to sample: ~ 0.7 m Time for 1ML / 1cm2 : ~1h

0,0

0,2

0,4

0,6

0,8

1,0

0 2 4 6 8 10 12 14

I d/I 0

Coverage / Å

[C8C1Im]Cl

[C8C1Im][Tf2N]

0°

80°

Growth behaviour [C8C1Im]Cl on Au(111) 1st closed layer

Au(111) Au(111) [C8C1Im][Tf2N] [C8C1Im]Cl

θ < 1st closed layer

data agree with ideal 2D growth formation of a wetting layer

θ > 1st closed layer

80°data above ideal curve indication for 3D growth

IL-ESID: [C8C1Im]Cl / Au(111)


nominal IL coverage: ~ 50 ML on epitaxial Au(111)/mica ex-situ AFM measurements (ambient conditions)

[C8C1Im]Cl

Atomic force microscopy (AFM) measurements

IL-ESID: [C8C1Im]Cl / Au(111)


Influence of interionic interactions on growth mode stronger interionic interactions (particularly stronger hydrogen

bonding) between an imidazolium cation and Cl- compared to Tf2N- ,

Influence of IL / solid interface on growth mode

[C8C1Im]Cl-

non-polar outer surface of the wetting layer due to densely packed octyl chains

weak bonding of further deposited IL molecules to wetting layer

island nucleation

[C8C1Im][Tf2N] lower packing density of octyl chains

more open structure

prevention of early island nucleation

layer-by-layer growth

Au(111)

Au(111)

Discussion

Au(111)

Au(111)

[CnC1Im][Tf2N], [C4C1Pyr][Tf2N] on Au(111)


Summary: Surf. Sci. gives ”close look at the interface”

Au(111)

Ni(111)

Au(111)

N SS

O

F3C

O OO

CF3

N N

N N Cl

NSS

O

F3CO

OO

CF3

N N

[C8C1Im]Cl on Au(111)

[C1C1Im][Tf2N] on HOPG no wetting for macroscopic amounts

Role of carbon for IL film growth

15 mm

0°

80°

[C1C1Im][Tf2N] on HOPG onto 1ML graphene / Ni(111) no wetting for macroscopic amounts medium wetting, checkerboard ads.


0°

80°

0°

[C1C1Im][Tf2N] on HOPG onto 1ML graphene / Ni(111) no wetting for macroscopic amounts medium wetting, checkerboard ads.


0°

80°

0°

2. „Bulk“, in-situ reactions


��






80° emission


e-

photoelectrons

Reactants Products

X-rays

Designed catalyst dissolved in a

designed ionic liquid

How to measure ARXPS without tilting a liquid sample?




80° emission


e-

How to measure ARXPS without tilting a liquid sample? 2 analysers mounted in 0° and 80°

0° emission

80° emission

Information depth 7-9 nm

X-rays e-


Development of a new ARXPS system 2010-2014 together with Omicron dedicated for liquid systems

Dual Analyser System for Surface Analysis (DASSA)


Loadlock & Glove box

Preparation chamber

Analysis chamber 2 analysers (0° and 80°) two X-ray sources (XPS, imaging) ion gun (profiling, EIS) ) UV lamp (UPS)




Dual analyzer system for surface analysis dedicated for angle-resolved photoelectron spectroscopy at liquid surfaces and interfaces, I. Niedermaier, C. Kolbeck, H.-P. Steinrück, F. Maier, Rev. Sci. Instrum. 87, 045105 (2016) DOI: 10.1063/1.4942943

��


3. IL – solid interfaces

2. in-situ reactions H2C

H2C

CH2

CH

CH

H2C

HC

CH C

H2

CH2

CH2

H2C

NPH

N+

N

C6H12

S

F

F

F

O

-O

O

CO2

- O3S

H NC O

H

O

- O3S

NH2

(group J. Behm, university Ulm)


5 years ERC advanced grant:

Ionic Liquid Interface Dynamics (H.-P. Steinrück)

Near future

( Postdoc)

Prof. Dr. Peter Wasserscheid

C. Kolbeck I. Niedermaier B. May K. Lovelock A. Deyko T. Matsuda

T. Cremer F. Rietzler P. Schreiber B. Heller

Prof. Dr. Hans-Peter Steinrück

P. Schulz N. Taccardi N. Paape W. Wei M. Bahlmann J. Schwegler

Acknowledgements

Collaborations: P. Licence, R. Jones, B. Kirchner, A. Fröba, J. Libuda, S. Baldelli, J. Behm, J. Schatz, J. Lopes ...

Supported by: DFG (SPP 1191, CoE-EAM, STE 620/9-1), A.v.Humboldt- and Max-Buchner-Stiftung, Industry

· 1980 1985 1990 1995 2000 2005 2010 2015 1 10 100 1000 10000 100000 number of IL publications / year year published Maier, Web of Science, ionic_liquid* in Topic, 16.5.2015 . The

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