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

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

  • 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