The Power of ElectrochemistryThe Power of Electrochemistry

2005년도 첨단화학의 이해 강의자료

전기화학: 물질과 전기 사이의 작용으로 일어나는 현상을 다루는 분야

전지의 작용 및 전기분해

물 속 또는 혈액 속에 들어 있는 산소의 농도, 포도당(glucose)의 농도 측정 센서

금속의 부식 과정 조사 및 부식 방지 기술

한 금속 위에 새로운 금속을 입히는 도금

불순한 물질을 순수하게 정제하는 기술

전류를 통하여 한 물질이 다른 물질로 변하게 하는 반응 (NaOH, Cl2 생산 등)

신경이 감각을 전달하고 근육을 수축시키는 메커니즘 및 생체대사 과정 이해

건전지, 연료전지 및 태양전지 연구

Introduction to ElectrochemistryIntroduction to Electrochemistry

A redox reaction: transfer of electrons from one species to another

Oxidation: loss of electronsReduction: gain of electrons

Fe3+ + V2+ -->Fe2+ + V3+

electron

Fe3+: Fe2+ 로 환원, V2+를 V3+로 산화시킴: 산화제 (oxidant)V2+: V3+로 산화, Fe3+를 Fe2+로 환원시킴: 환원제 (reductant)

When electrons form a redox reaction flow through an electric circuit

Current ∝ the rate of the electrochemical reaction

Voltage ∝ the free energy change for the electrochemical reaction

Chemistry and ElectricityChemistry and Electricity

Basic ConceptsBasic Concepts

Galvanic cell

Anode reaction : oxidation

Cathode reaction: reduction

Zn Zn2+ + 2e-

Cu2+ + 2e- Cu

High input impedance

Cell potentialCell potential : a measure of difference in electron energy between the two electrodes

OpenOpen--circuit potential (zerocircuit potential (zero--current potential)current potential): can be calculated from thermodynamic data, ie.

standard cell potentials of the half-cell reactions.

Zn + Cu2+ Zn2+ + Cu

Digital voltmeter

KClKCl

Salt bridge Zn Zn Cu Cu

A

B

Anode Anode Cathode Cathode

Zn2+

SO42-Zn2+

Zn

2e-

Zn2+

Cl-

Cu2+

SO42-

SO42-

K+

Cu2+

Cu

2e-

e-

e-

(-) (+)

Fig. 1 Electrochemical cell consisting of a zinc electrode in 0.1 M ZnSO4, a copper electrode in 0.1 MCuSO4, and a salt bridge. Galvanic cell. (From Heineman book)

Electrochemical cellsElectrochemical cells

Galvanic Cell: 전하의 이동Galvanic Cell: Galvanic Cell: 전하의전하의 이동이동

electron

Cu Cu2+ + 2e Ag+ + e Ag(s)

Electrolytic cell

Power Supply

KClKCl

Salt bridge Zn Zn Cu Cu

Anode Anode Cathode Cathode

Zn2+

SO42-Zn2+

Zn

2e-

Cu2+

Cl-

Cu2+

SO42-

SO42-

Cu2+

Cu

2e-

e-

(-) (+)

e-

K+

(-) (+)

Anode reaction : oxidation

Cathode reaction: reduction

Zn2+ + 2e- Zn

Cu Cu2+ + 2e-

Cu + Zn2+ Cu2+ + Zn

Fig. 2 Electrochemical cell consisting of a zinc electrode in 0.1 M ZnSO4, a copper electrode in 0.1 MCuSO4, and a salt bridge. Electrolytic cell.

Electrochemical cellsElectrochemical cells

Fig. 3 Definition of the atandard electrode potential for M2+(aq) + 2e- M(s).

Table 22.1 Standard Electrode Potentials

+1.359+1.229+1.087+1.065+-.799+0.771+0.536+0.337+0.268+0.222+0.0100.000-0.151-0.350-0.403-0.763

Cl2(g) + 2e- 2Cl-

O2(g) + 4H+ +4e- 2H2OBr2(aq) + 2e- 2Br-

Br2(l) + 2e- 2Br-

Ag+ + e- Ag(s)Fe3+ + e- Fe2+

I3- + 2e- 3I-

Cu2+ + 2e- Cu(s)Hg2Cl2(s) + 2e- 2Hg(l) + 2Cl-

AgCl(s) + e- Ag(s) + Cl-

Ag(S2O3)23- + e- Ag(s) + 2S2O3

2-

2H+ + 2e- H2(g)AgI(s) + e- Ag(s) + I-

PbSO4(s) + 2e- Pb(S) + SO42-

Cd2+ + 2e- Cd(s)Zn2+ + 2e- Zn(s)

E0 at 25 ℃, VReaction

A quantitative description of the relative driving force for a half-cell reaction.

A relative quantity vs standard hydrogen electron assigned to zero volt. E0(SHE)=0

SHE SHE

Reduction 자발적

Oxidation 자발적

Standard Electrode PotentialStandard Electrode Potential

Le Chatelier’s principle: increasing reactant concentrations drives the reacting to the right

The net driving force of the reaction is expressed by the Nernst equation

The Nernst equation tells us

the potential of a cell whose reagents are not all unit activity

Nernst Equation (activities of all species = 1)NernstNernst Equation Equation (activities of all species = 1)

Nernst Equation for a Half-ReactionNernstNernst Equation for a HalfEquation for a Half--ReactionReaction

aA + ne- bB

------- (14.13)aA

bBo

AA

nFRTEE ln−=

ΔG = ΔGo + RT lnQ (Q; reaction quotient)

-nFE = -nFEo + RT lnQ (양변을 nF 로 나누어 준다)

E = Eo –(RT/nF) lnQ

R: gas constant = 8.314 J/KmolT: temperature (K)

미래의미래의 에너지의에너지의 자원은자원은??

전기자동차

우주 / 군사휴대기기

저공해

고효율

저소음충전편리성

Battery: a collection of several electrochemical cells

(chemical energy electrical energy)1차 전지: 일회용 전지 (primary cell or battery)

2차 전지: 재충전 가능 전지 (secondary battery)

Volta 전지Volta 전지

- 1800년: 아연과 은판을 교대로 쌓고 그사이에 염 용액으로 포화된 종이판을 끼워 놓음

-쌓은 판이 많을 때: 충격을 느낄 수 있는 전위차 발생

- 일련의 갈바니 전지가 직렬로 연결된 상태

Zn Zn2+ + 2e : +0.76V

2Ag+ + 2e 2Ag : +0.8V

Zn + 2Ag+ Zn2+ + Ag : + 1.56V

BatteryBattery

Daniel CellDaniel Cell

John Daniel; English chemist who invented it in 1836.

르크랑세 건전지르크랑세 건전지

• 매년 전세계적으로 사용되는 건전지: 50억개 이상

• 아연전극과 MnO2가 혼합된 흑연 전극사용 (전해질: NH4Cl, ZnCl2)

건전지건전지 (1(1차차 전지전지))

산화전극 ( - , 음극)

Zn(s) Zn2+(aq) + 2e-

환원전극 ( +, 양극)

2MnO2(s) + 2NH4+(aq) + 2e- Mn2O3(s) + 2NH3(aq) + H2O(l)

1.5 V 건전지: 시간이 지남에 따라 농도가 변하여 전지의 전압이 변하는 단점이 있음

양극: MnO2 + 탄소 환원전극

음극: Zn 산화전극

전체 반응

Zn(s) + 2MnO2(s) + 2NH4+(aq) Zn2+(aq) + Mn2O3(s) + 2NH3(aq) + H2O(l)

니켈-카드늄 전지 (nickel-cadmium cell)니켈-카드늄 전지 (nickel-cadmium cell)

재충전재충전 전지전지 (2(2차차 전지전지))

방전과정(화학에너지 전기에너지: 갈바니전지):

Cd(s) + 2OH- Cd(OH)2(s) + 2e-

2NiO(OH)(s) + 2H2O + 2e- 2Ni(OH)2(s) + 2OH-

(전체반응)

Cd(s) + 2NiO(OH)(s) + 2H2O(l) Cd(OH)2(s) + Ni(OH)2(s)

1.4V 의 일정한 전압제공

충전과정 (전기에너지 화학반응: 전해전지)

:

외부전원에 의해 위의 역반응이 일어난다

납산 축전지(lead-acid storage battery납산 축전지(lead-acid storage battery

자동차용자동차용 Battery (2Battery (2차전지차전지))

2.0 V 전지 6개 직렬 연결: 12V 제공

(산화전극) Pb(s) + SO42-(aq) PbSO4(s) + 2e-

(환원전극) PbO2(s) + SO42- + 4H3O+ + 2e- PbSO4(s) + 6H2O

(전체반응)

Pb(s) + PbO2(s) + 2SO42- + 4H3O+ 2PbSO4(s) + 6H2O

방전 후 전해질의 농도가 감소하므로 전해질의 농도측정으로

배터리의 충전상태 알 수 있음

충전과정: 자동차의 발전기로 위의 역반응을 일으킴

Li Battery (2Li Battery (2차차 전지전지))

(-) 극: LixC6 xLi+ + 6C + xe- (3.045V) (금속 리튬 혹은 탄소에 삽입된 L

(+) 극: MnO2 + xLi+ + xe- LixMnO2 (층간 삽입반응: intercalation )

방전

충전

방전

충전

층상물질 (CoO2, MnO2, V2O5 등)

전해질: Li염 + 유기용매 (폭발 위험)(Li: 물과 격렬히 반응)

Li-polymer batteryLi-polymer battery

전해질이 유기용매가 아닌 고분자 물질(polyethylene oxide, polyacrylonitrile 등)과 리툼염의 혼합체

• 차세대 환경 친화적 에너지 공급원 (배기가스가 물!!)• 충전이 필요 없는 값싼 연료(H2, O2)를 사용 에너지 발생

2H2 + O2 2H2O + ∆E연료 Energy

H + O H2O

연료전지연료전지 (Fuel Cell)(Fuel Cell)

PEM Fuel CellPEM Fuel Cell

(oxidation electrode) 2 H2(g) 4H+ + 4 e-

(reduction electrode) O2(g) + 4H+ + 4e- 2H2O

(overall reaction) 2 H2(g) + O2 2 H2O 1.229V voltage generation

PEM (proton exchange membrane) : allows protons to travel between the two electrodes while keeping the gases apart

carbon carbon nanonano support support

Platinum (Pt) particlesPlatinum (Pt) particles▲노트북 에너지

▲차세대 자동차

촉매

2H2 + O2

2H2O

∆E

촉매 사용

Fuel Cell Fuel Cell 촉매촉매 -- Pt based materials Pt based materials

Direct Methanol Fuel Cell (DMFC)Direct Methanol Fuel Cell (DMFC)

To avoid the problems of transport and storage of hydrogen,

One uses methanol as the fuel (DMFC)

Fuel CellFuel Cell

Photosynthesis at green leaves of plants:- Use of sunlight to reduce CO2 to carbohydrates

- Animals and plants: use of carbohydrate to get energy

(carbohydrate back to CO2)

Solar Cell:If solar energy could be used with 10% efficiency,

3% of the sunlight falling on the earth’s deserts provides all the energy used in the world in 1980.

Harnessing Solar EnergyHarnessing Solar Energy

Battery & fuel cell: chemical sources electrical energy

Solar cell (photovoltaic cell) : solar energy electrical energy

Solar CellSolar Cell

Michael Grätzel at the Swiss Federal Institute of Technology

Ru(II) + hν Ru(II)* (*denotes excited state)

Ru(II)* Ru(III) + e- (injected into TiO2)

e- flows through the circuit from tin oxide electrode to Pt electrode

(at Pt electrode): I3- + 2e- 3I-

3I- + 2Ru(III) I3- + 2Ru(II)

Making organic chemicals

2 CH2=CHCN + 2H2O + 2e-

NCCH2CH2CH2CN + 2 OH-

Production of hexanedinitrileProduction of hexanedinitrile

Hexanedinitrile is one of the starting materials for the manufacture of nylon

Sharpless reactionSharpless reaction

One of the first chemical methods for introducing chiral centers into molecules

Electrochemical oxidation of alkenes to diols

Electrochemical Extraction of Al

Al (liquid)

Graphite electrode (+)

Al2O3 in Na3AlF6 (liquid)

(-)

B.P of Al2O3 ; 2050 oC

B.P. of Al; 950 oC (operation temp of cell: 950 oC)

Hall-Héroult ProcessHall-Héroult Process

The system operates with several pairs of electrodes which are covered with appropriate ion exchange membranes and placed in the ground

Can be applied to

1. Cations (Cu2+, Cd2+, Fe2+, Zn2+, etc)

2. Anions (nitrates from agricultural fertilizers, cyanide, radioactive isotopes, etc)

3. Neutral toxic organic compounds

Cleaning Up Polluted SoilCleaning Up Polluted Soil

General concept

Spectrophotometric experiment

λ

I

Excitation System Response

Electrochemical experiment

t

E

Lamp Monochromator Optical cellwith sample Phototube

λ

A

Power supply

i

t

i

Introduction to Introduction to ElectroanalyticalElectroanalytical ChemistryChemistry

ElectroanalyticalElectroanalytical techniquestechniques

전위차법(potentiometry): 전압(potential) 측정

• pH electrode, ion-selective electrode

전압전류법(voltammetry): 전압을 조절한 후 전류(current)측정

• 전류 vs 전압 (voltammetry): 시간에 따라 일정속도로 전압변화

(e.g. cyclic voltammetry)

• 전류 vs 시간 (amperometry): 전압 일정

Measurement of the difference in potential between the two electrodes of a galvaniccell under the condition of zero current are described by the term potentiometryEquilibrium MethodAccurate measurements of (a) activities or concentration (b) free-energy change and equilibrium constants of many solution reactions

The indicator electrode is chosen so that its half-cell potential responds tothe activity of a particular species in solution whose activity or concentrationis to be measured

Sample or Sample or standard standard

pH/mV meter

Magnetic

Stirring bar

Magnetic Stirrer

ReferenceReferenceElectrode Electrode

Indicator Indicator Electrode Electrode EEcellcell = = EEindind –– EErefref

Fig. 28.1 Schematic diagram of apparatus for potentiometry.

PotentiometryPotentiometry

antibiotic

IonophoresIonophores (neutral carriers) for ISE(neutral carriers) for ISE

Ion-selective or gas-permeable membrane

Biocatalyst layer

Semi-permeable membrane

2NH2NH44++ + CO+ CO33

22--Urea Urea P P ss

ssFig. 4 Schematic diagram of biocatalytic electrode.

Enzyme (Enzyme (ureaseurease) )

NH4+ - selective ISE

BUN (Blood Urea Nitrogen) Biosensor: BUN (Blood Urea Nitrogen) Biosensor: potentiometricpotentiometric

Glucose + O2 Gluconolactone + H2O2

Glucose Oxidase

2e-

Mred

Mox

FAD

FADH2 Gluconolactone

Glucose

Glucose OxidaseGlucose Oxidase

A.E.G. Cass, et. al., Anal. Chem., 1984, 56, 667-671

Glucose Biosensor : amperometric

H2O2 O2 + 2H+ + 2e-

+0.6 V 일정: 전류 측정 (glucose 농도에 비례)

i-STAT Co. (Princeton, NJ)

Cartridge label

Sample entry well gasket

Fluid channel

Cartridge cover

Sample entry well

Tape gasket

Biosensor chips

Calibrant pouch

Puncturing barb

Cartridge base

Air bladder

Sodium, Potassium, Chloride, Ionized Calcium, pH and PCO2by ion-selective electrode potentiometry.

Urea is first hydrolyzed to ammonium ions in a reaction catalyzedby the enzyme urease. The ammonium ions are measured by anion-selective electrode.

Glucose is measured amperometrically.

PO2 is measured amperometrically.

Hematocrit is determined conductometrically.

HCO3, TCO2 , BE, sO2, Anion Gap and Hemoglobin.

“Chem 7” test:

Na+, K+, Cl-, total CO2,

glucose, urea, creatinine

Biochip TechnologyBiochip Technology (Multi(Multi--biosensor)biosensor)

Microscopic and Spectroscopic methods

To study electrochemical surface/electrolyte interface

These are used to obtain information about the topographyand the local electronic properties on a surface.

Scanner: piezoelectric tube for x,y,z-position scan

Probe: electron tunneling forceController: feedback and

processing electronics

Basic set-up

STM (scanning tunneling microscopy)STM (scanning tunneling microscopy)

Constant height modeConstant height modeConstant current modeConstant current mode

STM (scanning tunneling microscopy)STM (scanning tunneling microscopy)

Fig. 21.23 STM scan of iodine atoms in a 3-nm arrayadsorbed on platinum. Note the missingiodine atom in the bottom center of theimage.

Start Start

Finish Finish

FastFast--scan direction scan direction

Slow

Slow

-- sca

n di

rect

ion

sc

an d

irec

tion

STM (scanning tunneling microscopy)STM (scanning tunneling microscopy)

Figure 1.2.Van der Waals force versus tip-to-sample separation. Atomic force microscopes

can be designed to operate in either of the two regimes indicated by heavy lines.

Figure Schematic of optical-deflection technique for detecting cantilever deflection. This method is also called beam-bounce detection.

LennardLennard--Jones potentialJones potentialu = A/ru = A/r1212 -- B/rB/r66

Force detection via Force detection via cantilever deflection cantilever deflection

Very flexible Very flexible

PSPD detectorPSPD detector

Atomic Force Microscopy (AFM)Atomic Force Microscopy (AFM)

Figure 21.22. Micrograph of (a) an SiO2 cantilever and tip and (b) a SiO2 tip.

Atomic Force Microscopy (AFM)Atomic Force Microscopy (AFM)

PlatinizedPlatinized Glassy Carbon ElectrodeGlassy Carbon Electrode

Figure 11.Figure 11. Surface images (a) SEM image, (b) 2D AFM image, (c) 3D AFM image .

Plantization under cyclic voltammetric scanPlantization under cyclic voltammetric scan

Platinization Conditions:• 0.2 mM K2PtCl6 in 0.1 M HCl• 0.6 V ~ - 0.5V vs Ag/AgCl (3M NaCl)• scan rate = 100 mV/S, 50 scans

0

SteadySteady--state current state current iiTT,,∞∞ = 4nFCDr (r : tip radius) = 4nFCDr (r : tip radius)

iiTT> > iiTT,,∞∞

iiTT< < iiTT,,∞∞

The imaging signal in SECM arises because the faradaic current flow resulting from the e- transfer rxn at the tip is perturbed by the surface of substrate

Scanning Electrochemical Microscopy (SECM)

Detecting a Single Molecule

Tip: Pt or C microwires or fibers (0.2 ~ 50 µm diameter sealed in glass)

By Scanning electrochemical microscopy (SECM)

For AT-cut QCM, vq = 3,340m/sec and ρq = 2,650kg/m3

∆f = - 2.3 ´ 106 fo2 ∆m / A : Sauerbrey’s equation

if fo = 9 MHz, ∆f = 1 Hz 1 ng/cm2

Mass Measurement using Mass Measurement using QCM(quartzQCM(quartz crystal microbalance)crystal microbalance)

• Identification of complex genetic disease and pathogen analysisDrug discovery and expression information of genes over time, between tissues, and disease states

AGAGCATATATGCA

TATGCC

TATGCT

TATGCGATACGAGA

Hybridization

TATGCA

TATGCC

TATGCT

TATGCG

Probe DNA

Sample DNA

HybridizationDetection byFlorescence

Applications

R. J. Lipshultz, et. al., Nature, Genetics, 1999, 21, 20-24

DNA Chip: ordered array of a variety of immobilized DNA molecules

Y. Okahata, et. Al. J. Am. Chem. Soc., 1992, 114, 8299-8300

The Landscape of a Cell

Glycoprotein

Glycolipid

Oligosaccharides

(taken from Bertozzi’s)

Glycoprotein

The Landscape of a Cell

Cell Surface Recognition by Glycoconjugates

BacteriumCell

VirusToxinHormone

Cell

Blocking Bacterial Attachment for Combating Infections

(taken from Scientific American)

JACS, 2003, 125, 9292-9293

SEM Image of SEM Image of Electropolymerized 3-Thiopheneacetic Acid on Au ElectrodeAu Electrode

Experimental ConditionsExperimental Conditions • CV : -1000 ~ 1350 mV vs Ag/AgCl(3M NaCl), 50 mV/s , 34 cycle• Au electrode area: 0.196 cm2

• 50 mM 3TA in 200 mM LiClO4• 25 mL aqueous solution

S

OHO

S

OOH

S

OHO

S

OOH

S

OOH

S

OHO

EQCM Monitoring during EQCM Monitoring during Electropolymerization

Experimental ConditionsExperimental Conditions • CV : -1000 ~ 1350 mV vs Ag/AgCl(3M NaCl), 50 mV/s , 34 cycle• Au electrode area: 0.196 cm2

• 50 mM 3TA in 200 mM LiClO4• 25 mL aqueous solution

∆F = - 1000Hz 1000 ng (1 ㎍) increased

<Frequency Change> < Mass Change>