Magnetic field influences on electrochemical processes

TU Dresden Institut für Physikalische Chemie und Elektrochemie

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Magnetic field influences on electrochemical processes

Silvio Köhler, Andreas Bund, Holger H. Kühnlein, Adriana Ispas, Waldfried Plieth

SFB 609, C5 Magnetic Field Control of Metal Deposition


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Motivation and Aimto find out

How does a magnetic field influence the several parts of an electrochemical reaction?

to describeexplaining of phenomena and creation of an

experimental basis for numerical simulations

to tailorcombinations of electric and magnetic fields for deposition of functionalized layers with defined properties and improving the mass transport in micro and nano structures, respectively


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Electrochemical Reactions

Influence on electron transfer kinetics ?

Influence on mass transportMHD effect

Gradient effects

Influence on surface diffusion/crystallization ?


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unstirred

Copper dissolution in microstructures

RE

AE

Va

GE

BRE

AE

VIa

GE

B

stirred

MHD-effectB E

Lorentz-Force FL +natural convection Fconv

))((

)(

.., ByvqF

BvqF

convLconv

L

Magnetic field on


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Copper dissolution in microstructures

RE

AE

IIIa

GE

BRE

AE

IVa

GE

B

unstirred stirred

02 2/ cBF mgrad

MHD-effectB E

Paramagneticgradient Force Fgrad


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Charge transfer reaction

0,0 0,2 0,4 0,6 0,8 1,00,8

1,0

1,2

1,4

i 0 / (

mA

cm

-2)

B / T

[Fe(H2O)

6]2+/ [Fe(H

2O)

6]3+

[Ir(Cl)6]2-/ [Ir(Cl)

6]3-

0,0

0,4

0,8

1,2 0,01M

0,00,40,81,21,6

0,008M

0,01M[Fe(CN)6]3-/ [Fe(CN)

6]4-

0,0 0,2 0,4 0,6 0,8 1,00,450,500,550,600,65

tran

sfer

coe

ffici

ent

B / T

0,450,500,550,600,65

[Ir(Cl)6]2-/ [Ir(Cl)

6]3-

0,450,500,550,600,65

[Fe(CN)6]3-/ [Fe(CN)

6]4-

[Fe(H2O)

6]2+/ [Fe(H

2O)

6]3+

Butler- Volmer- Equation:

TR

Fz

TR

Fz

ka

DD

eeiiii 1

0

(i: current density; i0: exchange current density; D : overvoltage ; z: number of electrons; :

transfer coefficient; F: Faraday´s constant; R: universal gas constant; T: absolute temperature)


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Electrochemical Quartz Crystal Microbalance (EQCM)

Counterelectrode

ReferenceElectrode Hg/ Hg2Cl2

Cell

Quartz

Potentiostat

RE

CE

WE

Network analyser

Working electrode

N S

Computer


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Experimental Technique (EQCM)

w0wLayer 1

w

f R,Layer 2

f R,Layer 1 fR,0

Layer 2

9,997 9,998 9,999 10,000

0

20

40

60

80

100

Quartz withRigid Layer

UnloadedQuartz

Quartz withDamping Layer

Re

al P

art

of

Ad

mitt

an

ce /

mS

f / MHZ

2* w

iΔff

Mass Damping

Complex frequency shift

in situ measurements of the mass changes at electrode surfaces during electrodepositionits functionality is based on the converse piezoelectric effect

quartz

gold electrodes

film

shear motion

mCf SB

Sauerbrey equation:

CSB: Sauerbrey constant


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curr

en

t d

en

sity

polarization

E2 E

1

02 H+ + 2e- H2

Ni2+ + 2e- Ni

B>0 B=0

Small Current Density (E1)iNi(B)iNi(B=0)iH2(B)>iH2(B=0) Current efficiency decreases

High Current Density (E2)iNi(B)>iNi(B=0)iH2(B)>iH2(B=0) Current efficiencynot affected by B

Deposition of NickelGalvanostatic deposition


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B= 0 mT, i=-50 mA cm2

i(H2)=-12.9 mA cm-2

Small damping change

B= 740 mT, i=-50 mA cm2

i(H2)=-7.8 mA cm-2

Large damping change

y x

L

0

L

0yxa dxdyyx,f

LL

1R

0 200 400 600 800

-2

0

2

4

6

8

Ra

(B)/

Ra

(B=

0mT

)

B / mT

itotal

= -50 mA.cm-2

itotal

= -0.5 mA.cm-2

Ra mean roughness

Lx, Ly dimension of the surface

f(x,y) relative surface to the central plane

Morphology and RoughnessAtomic Force Microscopy


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Deposition of Polypyrrole (PPy)

0 50 100 150 200 250

0.00

-0.00

-0.00

-0.00

curr

ent d

ensi

ty i

in m

A/c

m²

time in s

0T 0,7T

A- =

perchlorate ClO4-

A- =

p-toluenesulfonate TsO-

delocalized π-bondsdoping with anions (A-)Electrical conductivity

0 50 100 150 200 250

0

10000

20000

30000

40000

50000

dam

ping

in H

z

time in s

0T 0,7T

rough layers

0 50 100 150 200 250-400

-200

0

200

400

600

dam

ping

in H

z

time in s

0T0,7T

smooth layers

MFD-effectat PPy|ClO4

-

orientation-effect at

PPy|TsO-


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Ion ExchangeCyclovoltammetry 10mV/s 5 cycles at B= 0T in

monomer free solution

Exchange of anionsNo visible differences in Exchange behavior.

Exchange of cationsExchange suppressed in the case of magnetopolymerized Polypyrrole

-0,8 -0,6 -0,4 -0,2 0,0 0,2 0,4

-0,400

-0,200

0,000

0,200

curr

ent d

ensi

ty in

mA

/cm

²potential vs SCE in V

0T 0,7T

last cycle

-1,0 -0,8 -0,6 -0,4 -0,2 0,0 0,2 0,4-0,136

-0,090

-0,045

0,000

0,045

0,090

0,136

last cycle

curr

ent d

ensi

ty in

mA

/cm

²

potential vs SCE in V

0T 0,5T


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Conclusions

Influence on mass transport by Lorentz-Force (MHD-effect) and paramagnetic-gradient- Force

No influence on charge transfer kinetic

Magnetic field induces changes in surface roughness (nickel deposition)

MHD- (Polypyrrole|Perchlorate-Anions) and orientation effect (Polypyrrole|p-toluenesulfonate-Anions) at conducting polymers


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Outlook

Investigation of mass transport in microstructures including diamagnetic ions (Zn2+, Ag+)model system for numerical simulations

Deposition of alloys with different magnetic properties (NiFe)

Investigation of the magnetic field influences on the conductivity and dopand exchange kinetic of conducting polymers (Polypyrrole in combination with several anions)


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Acknowledgements

The authors are grateful to SFB 609 (Institution of German Research) for the financial support and Sino-German Scientific Center for the invitation

to the workshop.

Thank you for your attention!

Magnetic field influences on electrochemical processes

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