chemistry for fuel cells
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Chemistry for Fuel CellsChemistry for Fuel Cells
Alternative Energy and Fuel Alternative Energy and Fuel CellsCells
Hocking Technical CollegeHocking Technical College
July 23, 2007July 23, 2007
What is Chemistry?What is Chemistry?
Chemistry is the study of matter and Chemistry is the study of matter and its transformations.its transformations.
Matter can simply be defined as Matter can simply be defined as “stuff” – anything that has mass and “stuff” – anything that has mass and occupies space. occupies space.
– Some matter can be seen and felt. Some matter can be seen and felt.
– Some matter is difficult to detect, but it Some matter is difficult to detect, but it still exists.still exists.
In order to define fuel In order to define fuel cell technology, some cell technology, some basic chemistry and basic chemistry and
physics must be physics must be understood.understood.
A fuel cell produces electricity A fuel cell produces electricity
by means of a chemical by means of a chemical reaction.reaction.
2H2 + O2 2 H2O
All chemical compounds are All chemical compounds are made up of 2 or more elements, made up of 2 or more elements,
from a pool of about 100 from a pool of about 100 different elements, combined different elements, combined together in what is called a together in what is called a
chemical bond.chemical bond. HH22– element– element
OO22– element– element
HH22O– chemical compoundO– chemical compound
Periodic Table of the Periodic Table of the ElementsElements
A chart that A chart that
organizesorganizes
elements intoelements into
columns columns
and rowsand rows
The nature of the The nature of the chemical bond must chemical bond must be understood to be understood to describe how a fuel describe how a fuel cell works.cell works.
Each element is made Each element is made up of atoms which are up of atoms which are
unique to that unique to that element. element.
All atoms of a given element are All atoms of a given element are essentially the sameessentially the same
All atoms of other elements are All atoms of other elements are very different from the atoms of very different from the atoms of the given element. the given element.
Atoms are made up of a Atoms are made up of a nucleus and electronsnucleus and electrons
surrounding the nucleus.surrounding the nucleus.
Electrons
Nucleus
The nucleus The nucleus In the very center of the atom In the very center of the atom Very small compared to the size of the Very small compared to the size of the
atom atom Does not take part in chemical reactions Does not take part in chemical reactions Contains protons (positively charged Contains protons (positively charged
particles)particles) Number of protons determines which Number of protons determines which
elementelement Contains neutrons (particles not charged)Contains neutrons (particles not charged)
Proton Neutron
Subatomic ParticlesSubatomic Particles
SubatomSubatomicic
ParticleParticle
ElectricalElectrical
ChargeChargeRelativeRelative
Mass Mass (amu)(amu)
Location Location in Atomin Atom
ProtonProton 11 1 1 In nucleusIn nucleus
NeutronNeutron 00 11 In nucleusIn nucleus
ElectronElectron 11 1/18371/1837 OutsideOutside
nucleusnucleus
Atomic NumberAtomic Number
Each element has its own atomic Each element has its own atomic number (no. of protons). That’s what number (no. of protons). That’s what makes the element unique.makes the element unique.
Atoms are uncharged (neutral).Atoms are uncharged (neutral).
Therefore, Therefore, # protons = # electrons# protons = # electrons
Law of Electrical NeutralityLaw of Electrical Neutrality
The ElectronsThe Electrons
Some of the electrons are on the Some of the electrons are on the edge of the atom.edge of the atom.
Very small mass compared to the Very small mass compared to the proton and neutron.proton and neutron.
Take part in a chemical reaction.Take part in a chemical reaction. The carrier of current in The carrier of current in
electricity.electricity.
Organization of ElectronsOrganization of Electrons
Electrons are found in energy levels (shells).Electrons are found in energy levels (shells).
Valence electronsValence electrons
– Electrons in outer shell Electrons in outer shell
– Involved in formation of compoundsInvolved in formation of compounds
Core electrons Core electrons
– Not found in outer energy levelsNot found in outer energy levels
Valence electrons (VE)Valence electrons (VE)
Valence Valence electronselectronsdeterminedeterminechemical chemical properties.properties.
No. of VE No. of VE equals equals Group NoGroup No..
Group Group ##
IAIA IIAIIA VAVA VIIIAVIIIA
# VE# VE 11 22 55 88
ExamplExamplee
HH MgMg NN NeNe
ExamplExamplee
NaNa CaCa PP ArAr
6 valence electrons (in outer 6 valence electrons (in outer shell)shell)
2 core electrons inside2 core electrons inside
Valence Electrons Valence Electrons
Core Electrons
Oxygen Atom
1 valence electron and 1 valence electron and no core electronsno core electrons
Valence Electron
No Core Electrons
Hydrogen Atom
Chemical BondingChemical Bonding
Occurs when the electrons of two or more Occurs when the electrons of two or more different atoms interact and form a different atoms interact and form a compound containing the atoms.compound containing the atoms.
The Valence Electrons form the bond and The Valence Electrons form the bond and can be completely removed from one can be completely removed from one atom and added to another to form the atom and added to another to form the bond (ionic).bond (ionic).
The Valence Electrons form the bond and The Valence Electrons form the bond and can be shared between the atoms to form can be shared between the atoms to form the bond (covalent bond). the bond (covalent bond).
Noble Gas TheoryNoble Gas Theory
G. N. Lewis discovered that atoms lose, G. N. Lewis discovered that atoms lose, gain, or share electrons to attain a gain, or share electrons to attain a noblenoble
gas arrangement.gas arrangement.
What does this mean?What does this mean?
– Noble gases have a full outer shell of Noble gases have a full outer shell of
8 electrons (except He which has 2 in a full 8 electrons (except He which has 2 in a full outer shell) – great stability!outer shell) – great stability!
An Ion Is Formed When An Ion Is Formed When An Atom Loses One Or An Atom Loses One Or
More ElectronsMore Electrons This will form a positively charged This will form a positively charged
ion.ion.
Cu Cu+2 + 2e-
Zn Zn+2 + 2e-
An Ion Is Formed When An Ion Is Formed When An Atom Gains One Or An Atom Gains One Or
More ElectronsMore Electrons This will form a negatively charged This will form a negatively charged
ion.ion.Cl + e- Cl-
O + 2e- O-2
Ionic CompoundIonic Compound
Formed when one atom pulls Formed when one atom pulls electrons from another atom to electrons from another atom to
obtain the octet of electronsobtain the octet of electrons
Cu Cu+2 + 2e-
O + 2e- O-2
Cu + O Cu+2O-2
Ionic Compound
Ions may be replaced by Ions may be replaced by another atom changing another atom changing
to an ion.to an ion.Zinc metal put into a solution of copper Zinc metal put into a solution of copper
(+2) ions (CuCl(+2) ions (CuCl22) will lose 2 electrons to ) will lose 2 electrons to the copper (+2) and become zinc (+2) the copper (+2) and become zinc (+2) ions.ions.
The copper (+2) ions will gain the The copper (+2) ions will gain the electrons from the zinc metal to electrons from the zinc metal to become copper metal.become copper metal.Cu+2Cl2
-1 + Zn Cu + Zn+2Cl2-1
Ion Replacement can be Ion Replacement can be Predicted by the Predicted by the
Electromotive SeriesElectromotive Series
Na+1 + 1 e-1 Na(s) –2.71 vZn+2 + 2 e-1 Zn(s) –.76 vFe+2 + 2 e-1 Fe(s) –.44 vCd+2 + 2 e-1 Cd(s) –.40 vPb+2 + 2 e-1 Pb(s) –.126 v2 H+1 + 2 e-1 H 2 (g) 0.000 vCu+2 + 2 e-1 Cu(s) +.337 vFe+3 + 1 e-1 Fe+2 +.771 vAg+1 + 1 e-1 Ag(s) +.799 vO2 (g) + 4 H +1 + 4 e-1 2 H 2 O(l) +1.229 v
Cu Zn battery uses this Cu Zn battery uses this reaction by separating the two reaction by separating the two
solutions by an electrolytic solutions by an electrolytic bridge.bridge.
Electrons do not cross the Electrons do not cross the electrolyte on the bridge.electrolyte on the bridge.
Ions cross the electrolyte bridge.Ions cross the electrolyte bridge.
Electrons move through the wire Electrons move through the wire since they cannot cross the bridge.since they cannot cross the bridge.
The Cu Zn cell is The Cu Zn cell is shown belowshown below
Cu+2
Cu metal
2e-
V
Zn+2
Zn metal1.10 volts
Na2SO4 salt bridge
Cu+2 + Zn Cu + Zn+2
In the Laboratory, we In the Laboratory, we use a will use a Porous use a will use a Porous
CupCup
Cu+2
SO4-2
Porous Cup
Beaker
Zn+2
SO4-2
Zinc Strip(anode)
Copper Strip(cathode)
Voltmeter+ -
Wire
Covalent CompoundCovalent Compound
Formed when neither atom Formed when neither atom reacting can pull the electron reacting can pull the electron from the other atomfrom the other atom
The atoms involved form a The atoms involved form a molecule and share the electrons molecule and share the electrons to obtain the “octet of electrons”to obtain the “octet of electrons”
2H2 + O2 2H2O
The reaction of The reaction of hydrogen and oxygenhydrogen and oxygen
In this reaction the oxygen and In this reaction the oxygen and hydrogen share their electrons.hydrogen share their electrons.
Hydrogen and oxygen react to Hydrogen and oxygen react to form water.form water.
This reaction can occur by burning This reaction can occur by burning the hydrogen in oxygen.the hydrogen in oxygen.
Energy is given off during the Energy is given off during the reaction.reaction.
When oxygen bonds with another When oxygen bonds with another atom it needs 2 extra electrons added atom it needs 2 extra electrons added to the outer shell to have 8 electrons to the outer shell to have 8 electrons in the outer shell. (inert gas Neon)in the outer shell. (inert gas Neon)
When hydrogen bonds with another When hydrogen bonds with another atom it needs 1 extra electron added atom it needs 1 extra electron added to the outer shell to have 2 electrons to the outer shell to have 2 electrons in the outer shell. (inert gas Helium)in the outer shell. (inert gas Helium)
Formation of waterFormation of water
Valence Electrons are Valence Electrons are shared in the formation shared in the formation
of water.of water.
Shared Electrons
Hydrogen Atom
Hydrogen Atom
Oxygen Atom
A fuel Cell works in the A fuel Cell works in the same way as the same way as the
batterybattery
Hydrogen and oxygen are Hydrogen and oxygen are separated by an electrolyte that separated by an electrolyte that will not conduct electrons across it.will not conduct electrons across it.
The electrons pass from one side The electrons pass from one side to the other by means of a wire.to the other by means of a wire.
Hydrogen and oxygen react to Hydrogen and oxygen react to form water.form water.
Fuel Cell Operates as a Fuel Cell Operates as a BatteryBattery
ElectrolyteH2
H2
O2
Catalyst Catalyst
Anode Cathode
Hydrogen and Oxygen Hydrogen and Oxygen are separated by an are separated by an electrolyteelectrolyte
H2
Electrolyte
H2
O2
CatalystCatalyst
Anode Cathode
A catalyst helps the A catalyst helps the hydrogen and electrons hydrogen and electrons
separate.separate.
H+
H+
e-
e-
Electrolyte
H+
H+
e-
e-OO
CatalystCatalyst
Anode Cathode
Hydrogen ions travel Hydrogen ions travel across the electrolyte. across the electrolyte.
Electrons travel through Electrons travel through the wire.the wire.
Electrolyte
H+
H+
H+
H+
e-e-
e-
e-
O
O
Anode Cathode
The hydrogen ions, The hydrogen ions, atomic oxygen, and atomic oxygen, and
electrons combine at the electrons combine at the cathode.cathode.
Electrolyte
H+
H+
e-
e-
H+
H+e-
e-
O
O
Anode Cathode
The hydrogen ions, The hydrogen ions, atomic oxygen, and atomic oxygen, and
electrons combine at the electrons combine at the cathode.cathode.
Electrolyte
H+
H+
e-
e-
H+
H+e-
e-
O
O
Anode Cathode
The reaction is The reaction is completed as water is completed as water is formed at the cathode.formed at the cathode.
Electrolyte
OHH
OHH
Water
Water
Anode Cathode
The Fuel Cell Produces The Fuel Cell Produces a Voltage and Heata Voltage and Heat
The maximum voltage of the cell The maximum voltage of the cell is 1.229 volts.is 1.229 volts.
Since some of the energy is given Since some of the energy is given off as heat, this maximum voltage off as heat, this maximum voltage is not realized.is not realized.
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