KİM 683

Electroanalytical

Chemistry

Impedance ?

Who won the Nobel Prize in Chemistry in 2019?

Conversion and storage of energy

Solar cells, DSSC, Photoelectrochemical Cells etc

315M421 Kuantum Parçacık Duyarlı Güneş Hücreleri İçin Yeni Nesil

Nanokompozit Elektrotlar

111T488 Nanoboyutlu metal oksit fotoaktif elektrotların elektrokimyasal sentezi ve

fotoakım performanslarının belirlenmesi (1001)

Electroplating

Electrochemical synthesis of some industrial

materials eg. Al, Cl2, Na,..

Organic compounds: adiponitrile

Electroanalytical chemistry (e.g. the analysis of chemicals in blood to

determine the development of a certain diseases)

Obtaining thermodynamic data about a reaction

Waste water purification and recycling

Corrosion protection and so on ………………….

Why electrochemistry?

• Clean and green (not always true!)

• Often no or few byproducts

• Electrons the cheapest redox “reagents”

What is a redox reaction?

Oxidation is the addition of oxygen to a substance and

Reduction is the removal of oxygen from a substance.

oxygen removed

reduction

oxygen added

oxidation

Reduction and oxidation always take place together.

Why is this type of reaction called a redox reaction?

redox = reduction and oxidation

Which substances are oxidized and reduced in this reaction?

lead oxide + carbon lead

carbon monoxide+

Redox and electronsMagnesium burns in oxygen

to form magnesium oxide.

A redox reaction can also

be explained in terms of the

gain or loss of electrons.

What happens to the atoms and electrons in this reaction?

It is obvious that the

magnesium has been

oxidized, but what has

happened to the oxygen?

magnesium + oxygen magnesium oxide

2Mg(s) O2(g) 2MgO(s)+

Oxidation and electron loss

When magnesium burns in oxygen to form magnesium oxide, what happens to

magnesium and its electrons?

Oxidation is the loss of electrons.

oxidized

(electrons lost)

⚫ The magnesium has been oxidized.

⚫ The Mg atom has lost 2 electrons to form a Mg2+ ion.

Mg Mg2+ O2-O+

Reduction and electron gain

When magnesium burns in oxygen to form magnesium oxide,

what happens to oxygen and its electrons?

Reduction is the gain of electrons.

reduced

(electrons gained)

Mg Mg2+ O2-O+

⚫ The oxygen has been reduced.

⚫ The O atom has gained 2 electrons to form a O2- ion.

An electrochemical system is not homogeneous but is heterogeneous.

Conductionoccurs via

migration ofelectrons .Solid state

Physics : energyband theory.

Material transport occursvia migration, diffusionand convection

Electronically conducting phase : metal, semiconductor,Conducting polymer material etc.

Ionically conductingmedium : electrolytesolution, molten salt,solid electrolyte,polymericelectrolyte, etc.

Electrode/Electrolyte İnterface

Representation of reduction and oxidation process of a species

A (molecule) in solution

Reduction

Oxidation

a) Potentials for possible reductions at a platinum electrode, initially at ~ 1 V vs.

NHE in a solution of 0.01 M each of Fe3+, Sn4+, and Ni2+ in 1M HCl (b) Potentials for

possible oxidation reactions at a gold electrode, initially at ~0.1V vs. NHE in a

solution of 0.01 M each of Sn2+ and Fe2+ in 1M HI.

Potentials for possible reductions at a mercury electrode in 0.01 M Cr3+ and Zn2+ in

1M HCl. The arrows indicate the directions of potential change discussed in the

text.

Current is always in

the opposite

directions from

electron flow.

The flow of

positive charge.

Electrochemical Cells

Galvanic

Electrolytic

Electrochemical processes are oxidation-reduction

reactions in which:

• The energy released by a spontaneous reaction

is converted to electricity or

• Electrical energy is used to cause a

nonspontaneous reaction to occur

A galvanic electrochemical cell at open circuit.

A galvanic cell doing work.

Zn(s) | Zn2+(aq) ¦¦ Cu2+(aq) | Cu(s)

Daniel Cell

ZnSO4 solution CuSO4 solution

Zn2+

Cu2+SO42–

SO42–

Zincanode

Coppercathode

ZnSO4 solution CuSO4 solution

Zn2+

Cu2+

Salt bridge

e– e–

Cl– K+

Voltmeter

CottonplugsSO4

2–

SO42–

Salt bridge provides electrical neutrality by providing

negative anions to equal the positive cations being

created at the Zn anode during oxidation. And cations

ions (K+) to replace Cu2+ being used up at reduction.

Zincanode

Coppercathode

ZnSO4 solution CuSO4 solution

Zn2+

Cu2+

Salt bridge

Zn

e– e–

Cl– K+

Voltmeter

CottonplugsSO4

2–

SO42–

Zincanode

Coppercathode

ZnSO4 solution CuSO4 solution

Zn2+

Cu2+

Salt bridge

Zn is oxidizedto Zn2+ at anode.

Zn(s) Zn2+(aq) + 2e–

Zn Zn2+

2e–

e– e–

Cl– K+

Voltmeter

CottonplugsSO4

2–

SO42–

Zincanode

Coppercathode

ZnSO4 solution CuSO4 solution

Zn2+

Cu2+

Salt bridge

Cu

Zn is oxidizedto Zn2+ at anode.

Zn(s) Zn2+(aq) + 2e–

Zn Zn2+

2e–

e– e–

Cl– K+

Voltmeter

CottonplugsSO4

2–

SO42–

Zincanode

Coppercathode

ZnSO4 solution CuSO4 solution

Zn2+

Cu2+

Salt bridge

2e–

Cu2+

Cu

Zn is oxidizedto Zn2+ at anode.

Zn(s) Zn2+(aq) + 2e–

Zn Zn2+

2e–

e– e–

Cl– K+

Voltmeter

CottonplugsSO4

2–

SO42–

Zincanode

Coppercathode

ZnSO4 solution CuSO4 solution

Zn2+

Cu2+

Salt bridge

2e–

Cu2+

Cu

2e– + Cu2+(aq) Cu(s)

Cu2+ is reducedto Cu at cathode.

Zn is oxidizedto Zn2+ at anode.

Zn(s) Zn2+(aq) + 2e–

Zn Zn2+

2e–

e– e–

Cl– K+

Voltmeter

CottonplugsSO4

2–

SO42–

Zincanode

Coppercathode

ZnSO4 solution CuSO4 solution

Zn2+

Cu2+

Salt bridge

Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)

Net reaction

2e–

Cu2+

Cu

2e– + Cu2+(aq) Cu(s)

Cu2+ is reducedto Cu at cathode.

Zn is oxidizedto Zn2+ at anode.

Zn(s) Zn2+(aq) + 2e–

Zn Zn2+

2e–

e– e–

Cl– K+

Voltmeter

CottonplugsSO4

2–

SO42–

Galvanic Cells

spontaneous

redox reaction

anode

oxidation

cathode

reduction

Zincanode

Coppercathode

ZnSO4 solution CuSO4 solution

Zn2+ SO42–

Cu2+

Salt bridge

Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s)

Net reaction

2e–

Cu2+

Cu

2e– + Cu2+(aq) Cu(s)

Cu2+ is reducedto Cu at cathode.

Zn is oxidizedto Zn2+ at anode.

Zn(s) Zn2+(aq) + 2e–

Zn Zn2+

2e–

e– e–

Cl– K+

Voltmeter

CottonplugsSO4

2–

Galvanic Cell

Flow of e- Flow of current

Cell notation

Zn(s) Zn2+(aq) Cu2+(aq) Cu(s)

phase difference phase differenceIndicated by solid vertical line Indicated by solid vertical line

anode components cathode components

salt bridge

An electrolytic cell.

Electrolytic Cells

• Electrolytic Cell – a cell in which a nonspontaneous redox reaction is forced to occur; a combination of two electrodes, an electrolyte and an external power source.

– Electrolysis – the process of supplying electrical energy to force a nonspontaneous redox reaction to occur

– The external power source acts as an “electron pump”; the electric energy is used to do work on the electrons to cause an electron transfer

Electrons are pulled from the anode and pushed to

the cathode by the battery or power supply

Comparing Electrochemical Cells:

Voltaic and Electrolytic

It is best to think of “positive” and “negative” for electrodes as labels, not charges.