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
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)
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
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)
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
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
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)
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
The Landscape of a Cell
Glycoprotein
Glycolipid
Oligosaccharides
(taken from Bertozzi’s)
Glycoprotein
The Landscape of a Cell
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>