# Electrochemical Techniques - University of California ...chen. based techniques (Ch. 10):...

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Electrochemical Techniques

CHEM 269

Course Content This course is designed to introduce the basics (thermodynamics

and kinetics) and applications (experimental techniques) of electrochemistry to students in varied fields, including analytical, physical and materials chemistry. The major course content will include Part I Fundamentals

Overview of electrode processes (Ch. 1)

Potentials and thermodynamics (Ch. 2)

Electron transfer kinetics (Ch. 3)

Mass transfer: convection, migration and diffusion (Ch. 4)

Double-layer structures and surface adsorption (Ch. 13)

Part II Techniques and Applications Potential step techniques (Ch. 5): chronoamperometry

Potential sweep methods (Ch. 6): linear sweep, cyclic voltammetry

Controlled current microelectrode (Ch. 8): chronopotentiometry

Hydrodynamic techniques (Ch. 9): RDE, RRE, RRDE

Impedance based techniques (Ch. 10): electrochemical impedance spectroscopy, AC voltammetry

Grade: 1 mid-term (30%); 1 final (50%); homework (20%)

Chronoamperometry (CA)

E

t

E1 E2

E3

E4

0

x

Co

Co*

t

x

Co

Co*

E

t

i

E2

E3

E4

0 t

i

E

iLIM,c

Sampled-current

voltammetry

Chronoamperometry

Current-Potential Characteristics

Large-amplitude potential step

Totally mass-transfer controlled

Electrode surface concentration ~ zero

Current is independent of potential

Small-amplitude potential changes

i =iof

Reversible electrode processes

Totally irreversible ET (Tafel region) R

Oo

C

C

nF

RTEE ln

''1

,0,0

oo EERT

nF

R

EERT

nF

Oo etCetCnFAki

Electrode Reactions

Mass-transfer control

Kinetic control

Obulk Osurf

Oads

Rads

Rsurf Rbulk

Osurf

Rsurf

ele

ctro

de

Double layer

mass transfer

chemical electron transfer

Mass Transfer Issues

)()(

)()(

xvCx

xCD

RT

Fz

x

CDxJ jjj

jxjjj

In a one-dimension system,

In a three-dimension system,

)()()()( rvCrCDRT

FzrCDrJ jjj

jjjj

diffusion migration convection

diffusion current

migration current

convection current

Potential Step under Diffusion Control

Planar electrode: O + ne R

Ficks Law 2

2 ),(),(

x

txCD

t

txC OO

O

CO(x,0) = CO*

CO(0,t) = 0

LimCO(x,t) = CO* x

xD

s

OO

OesAs

CsxC

)(),(*

xD

s

OO

Oes

CsxC 1),(

*

Laplacian transformation

0),0( sCO

0

)()}({ dttFetFL st

Cottrell Equation

Frederick Gardner Cottrell (1877 - 1948) was born in Oakland, California. He received a B.S. in chemistry from the University of California at Berkeley in 1896 and a Ph.D. from the University of Leipzig in 1902.

Although best known to electrochemists for the "Cottrell equation" his primary source of fame was as the inventor of electrostatic precipitators for removal of suspended particles from gases. These devices are still widely used for abatement of pollution by smoke from power plants and dust from cement kilns and other industrial sources.

Cottrell played a part in the development of a process for the separation of helium from natural gas. He was also instrumental in establishing the synthetic ammonia industry in the United States during attempts to perfect a process for formation of nitric oxide at high temperatures.

0

),(),0(

)(

x

OOO

x

txCDtJ

nFA

ti

0

),()(

x

OO

x

sxCD

nFA

si

21

21

21 *

)(t

CnFADti

OO

Reverse LT

*)(O

O Cs

D

nFA

si

CO(0,t) = 0

Depletion Layer Thickness

*

)(o

o

o Ct

DnFAi

tDt OO )(

x

Co

Co*

t

tDO =

30 mm

1 mm

30 nm

at t =

1 s

1 ms

1 ms

Concentration Profile

xD

s

OO

Oes

CsxC 1),(

*

tD

xerfC

tD

xerfcCtxC

oO

oOO

221),( **

In mathematics, the error function (also called the Gauss error function) is a

special function (non-elementary) which occurs in probability, statistics, materials

science, and partial differential equations. It is defined as:

Sampled Current Voltammetry

Linear diffusion at a planar electrode

Reversible electrode reaction

Stepped to an arbitrary potential

),0(

),0(ln

tC

tC

nF

RTEE

R

Oo oR

O EEnftC

tC exp

),0(

),0(

2

2 ),(),(

x

txCD

t

txC OO

O

2

2 ),(),(

x

txCD

t

txC RR

R

CO(x,0) = CO*

LimCO(x,t) = CO* x

CR(x,0) = CR* = 0

LimCR(x,t) = CR* = 0 x

Flux Balance

xD

s

OO

OesAs

CsxC

)(),(*

xD

s

RResBsxC

)(),(

0]),(

[]),(

[ 00

xx

x

txCD

x

txCD RR

OO

Incoming flux Outgoing flux

0)()( sBD

ssA

D

s

RO

)()()( sAsAD

DsB

O

R

xD

s

RResAsxC

)(),(

I-E at any Potential

oR

O EEnftC

tC exp

),0(

),0(

xD

s

s

C

RRO esxC

1),(

*

11),(

*

xD

s

s

C

O

R

Oe

sxC

),0(

),0(

sC

sC

R

O

)()(*

sAsAs

CO

1)(

*

s

CO

sA

0

),(

x

OO

x

txCnFADi

1)(

21

21

21 *

t

CnFADti

OO

Shape of I-E Curve

11)(

21

21

21 *

dOO i

t

CnFADti

At very negative potentials, 0, and i(t) id

)(

)(lnln'

ti

tii

nF

RT

D

D

nF

RTEE d

O

Ro

y

E E1/2

Slope n

E1/2 Wave-shape analysis

CA Reverse Technique

E

t

Ei Er

Ef

0 t

1)(

21

21

21 *

t

CnFADti

OOf

21

21

21

)1(

11

"1

1

'1

1)(

*

tt

CnFADti

OOr

t

or EEnf exp" of EEnf exp'

tt

CnFADti

OOr

11)(

21

21 *

t

r

f

r

f

f

r

t

t

t

t

i

i

t

when =0 and =

rf

r

ti

i t

11tr tf = t

Semi-Infinite Spherical Diffusion

r

trC

rr

trCD

t

trC OOO

O ),(2),(),(

2

2

oOO rt

CnFADti11

)(2

12

12

1 *

21

21

21 *

)(t

CnFADti

OO

CO(r,0) = CO*

CO(r0,t) = 0

LimCO(r,t) = CO* r

boundary

conditions

oOO rt

CnFADti11

)(2

12

12

1 *

Cottrell equation

Ultramicroelectrode

Radius < 25 mm, smaller than the diffusion layer

Response to a large amplitude potential step

First term: short time (effect of double-layer charging

Second term: steady state

oOO rt

CnFADti11

)(2

12

12

1 *

**

4 OoOo

OOss CrnFD

r

CnFADi

t

i

iss planar

electrode

spherical

electrode

21

21

21 *

)(t

CnFADti

OO

oOO rt

CnFADti11

)(2

12

12

1 *

Amperometric glucose sensor based on platinumiridium

nanomaterials

Peter Holt-Hindle, Samantha Nigro, Matt Asmussen and Aicheng Chen

Electrochemistry Communications, 10 (2008) 1438-1441

This communication reports on a novel amperometric glucose sensor based on nanoporous PtIr catalysts. PtIr nanostructures with different contents of iridium were directly grown on Ti substrates using a one-step facile hydrothermal method and were characterized using scanning electron microscopy and energy dispersive X-ray spectroscopy. Our electrochemical study has shown that the nanoporous PtIr(38%) electrode exhibits very strong and sensitive amperometric responses to glucose even in the presence of a high concentration of Cl and other common interfering species such as ascorbic acid, acetamidophenol and uric acid, promising for nonenzymatic glucose detection.

(a) Chronoamperometric responses of S0, S1, S2 and

S3 measured at 0.1 V in 0.1 M PBS (pH 7.4) +0.15 M

NaCl with successive additions of 1 mM glucose (0

20 mM). (b) The corresponding calibration plots.

(a) S0: PtIr(0%), (b) S1: PtIr(22%), (c) S2: PtIr(38%). (d) EDX

spectra of samples S0 and S2. Insert: the enlarged portion of the

EDX spectrum of samples S0 and S2 between 9.0 and 12.0 keV.

Interference Study

Chronoamperometric curves of S0 and S2 recorded in 0.1 M PBS

+0.15 M NaCl with successive additions of 0.2 mM UA, 0.1 mM AP,

0.1 mM AA and 1 mM Glucose at 60 second

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