Chemistry for Fuel Cells Alternative Energy and Fuel Cells Hocking Technical College July 23, 2007

What is Chemistry? Chemistry is the study of matter and its transformations. Chemistry is the study of matter and its transformations. Matter can simply be defined as “stuff” – anything that has mass and occupies space. Matter can simply be defined as “stuff” – anything that has mass and occupies space. –Some matter can be seen and felt. –Some matter is difficult to detect, but it still exists.

In order to define fuel cell technology, some basic chemistry and physics must be understood. In order to define fuel cell technology, some basic chemistry and physics must be understood. A fuel cell produces electricity by means of a chemical reaction. 2H 2 + O 2 2 H 2 O

All chemical compounds are made up of 2 or more elements, from a pool of about 100 different elements, combined together in what is called a chemical bond. All chemical compounds are made up of 2 or more elements, from a pool of about 100 different elements, combined together in what is called a chemical bond. H 2 – element H 2 – element O 2 – element O 2 – element H 2 O– chemical compound H 2 O– chemical compound

Periodic Table of the Elements A chart that organizes elements into columns and rows

The nature of the chemical bond must be understood to describe how a fuel cell works.

Each element is made up of atoms which are unique to that element. All atoms of a given element are essentially the same All atoms of a given element are essentially the same All atoms of other elements are very different from the atoms of the given element. All atoms of other elements are very different from the atoms of the given element.

Atoms are made up of a nucleus and electrons surrounding the nucleus. Electrons 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 atom Very small compared to the size of the atom Does not take part in chemical reactions Does not take part in chemical reactions Contains protons (positively charged particles) Contains protons (positively charged particles) Number of protons determines which element Number of protons determines which element Contains neutrons (particles not charged) Contains neutrons (particles not charged) ProtonNeutron

Subatomic Particles SubatomicParticleElectricalChargeRelative Mass (amu) Location in Atom Proton 11111 In nucleus Neutron01 Electron 11111/1837Outsidenucleus

Atomic Number Each element has its own atomic number (no. of protons). That’s what makes the element unique. Each element has its own atomic number (no. of protons). That’s what makes the element unique. Atoms are uncharged (neutral). Atoms are uncharged (neutral). Therefore, # protons = # electrons Therefore, # protons = # electrons Law of Electrical Neutrality Law of Electrical Neutrality

The Electrons Some of the electrons are on the edge of the atom. Some of the electrons are on the edge of the atom. Very small mass compared to the proton and neutron. Very small mass compared to the proton and neutron. Take part in a chemical reaction. Take part in a chemical reaction. The carrier of current in electricity. The carrier of current in electricity.

Organization of Electrons Electrons are found in energy levels (shells). Electrons are found in energy levels (shells). Valence electrons Valence electrons –Electrons in outer shell –Involved in formation of compounds Core electrons Core electrons –Not found in outer energy levels

Valence electrons (VE) Valenceelectronsdeterminechemicalproperties. No. of VE equals Group No. Group # IAIIAVAVIIIA # VE 1258 ExampleHMgNNe ExampleNaCaPAr

Oxygen atom has 8 electrons Nucleus Oxygen Atom

6 valence electrons (in outer shell) 2 core electrons inside Valence Electrons Core Electrons Oxygen Atom

Hydrogen has 1 electron Nucleus Hydrogen Atom

1 valence electron and no core electrons Valence Electron No Core Electrons Hydrogen Atom

Chemical Bonding Occurs when the electrons of two or more different atoms interact and form a compound containing the atoms. Occurs when the electrons of two or more different atoms interact and form a compound containing the atoms. The Valence Electrons form the bond and can be completely removed from one atom and added to another to form the bond (ionic). The Valence Electrons form the bond and can be completely removed from one atom and added to another to form the bond (ionic). The Valence Electrons form the bond and can be shared between the atoms to form the bond (covalent bond). The Valence Electrons form the bond and can be shared between the atoms to form the bond (covalent bond).

Noble Gas Theory G. N. Lewis discovered that atoms lose, gain, or share electrons to attain a noble G. N. Lewis discovered that atoms lose, gain, or share electrons to attain a noble gas arrangement. What does this mean? What does this mean? –Noble gases have a full outer shell of 8 electrons (except He which has 2 in a full outer shell) – great stability!

An Ion Is Formed When An Atom Loses One Or More Electrons This will form a positively charged ion. This will form a positively charged ion. Cu Cu e - Zn Zn e -

An Ion Is Formed When An Atom Gains One Or More Electrons This will form a negatively charged ion. This will form a negatively charged ion. Cl + e - Cl - O + 2e - O -2

Ionic Compound Formed when one atom pulls electrons from another atom to obtain the octet of electrons Formed when one atom pulls electrons from another atom to obtain the octet of electrons Cu Cu e - O + 2e - O -2 Cu + O Cu +2 O -2 Ionic Compound

Ions may be replaced by another atom changing to an ion. Zinc metal put into a solution of copper (+2) ions (CuCl 2 ) will lose 2 electrons to the copper (+2) and become zinc (+2) ions. The copper (+2) ions will gain the electrons from the zinc metal to become copper metal. Cu +2 Cl Zn Cu + Zn +2 Cl 2 -1

Ion Replacement can be Predicted by the Electromotive Series Na e -1 Na(s) –2.71 v Zn e -1 Zn(s) –.76 v Fe e -1 Fe(s) –.44 v Cd e -1 Cd(s) –.40 v Pb e -1 Pb(s) –.126 v 2 H e -1 H 2 (g) v Cu e -1 Cu(s) v Fe e -1 Fe v Ag e -1 Ag(s) v O2 (g) + 4 H e -1 2 H 2 O(l) v

Cu Zn battery uses this reaction by separating the two solutions by an electrolytic bridge. Electrons do not cross the electrolyte on the bridge. Electrons do not cross the electrolyte on the bridge. Ions cross the electrolyte bridge. Ions cross the electrolyte bridge. Electrons move through the wire since they cannot cross the bridge. Electrons move through the wire since they cannot cross the bridge.

The Cu Zn cell is shown below Cu +2 Cu metal 2e - V Zn +2 Zn metal 1.10 volts Na 2 SO 4 salt bridge Cu +2 + Zn Cu + Zn +2

In the Laboratory, we use a will use a Porous Cup Cu +2 SO 4 -2 Porous Cup Beaker Zn +2 SO 4 -2 Zinc Strip(anode) Copper Strip(cathode) Voltmeter +- Wire

Covalent Compound Formed when neither atom reacting can pull the electron from the other atom Formed when neither atom reacting can pull the electron from the other atom The atoms involved form a molecule and share the electrons to obtain the “octet of electrons” The atoms involved form a molecule and share the electrons to obtain the “octet of electrons” 2H 2 + O 2 2H 2 O

The reaction of hydrogen and oxygen In this reaction the oxygen and hydrogen share their electrons. In this reaction the oxygen and hydrogen share their electrons. Hydrogen and oxygen react to form water. Hydrogen and oxygen react to form water. This reaction can occur by burning the hydrogen in oxygen. This reaction can occur by burning the hydrogen in oxygen. Energy is given off during the reaction. Energy is given off during the reaction.

When oxygen bonds with another atom it needs 2 extra electrons added to the outer shell to have 8 electrons in the outer shell. (inert gas Neon) When oxygen bonds with another atom it needs 2 extra electrons added to the outer shell to have 8 electrons in the outer shell. (inert gas Neon) When hydrogen bonds with another atom it needs 1 extra electron added to the outer shell to have 2 electrons in the outer shell. (inert gas Helium) When hydrogen bonds with another atom it needs 1 extra electron added to the outer shell to have 2 electrons in the outer shell. (inert gas Helium) Formation of water

Valence Electrons are shared in the formation of water. Shared Electrons Hydrogen Atom Oxygen Atom

A fuel Cell works in the same way as the battery Hydrogen and oxygen are separated by an electrolyte that will not conduct electrons across it. Hydrogen and oxygen are separated by an electrolyte that will not conduct electrons across it. The electrons pass from one side to the other by means of a wire. The electrons pass from one side to the other by means of a wire. Hydrogen and oxygen react to form water. Hydrogen and oxygen react to form water.

Fuel Cell Operates as a Battery ElectrolyteH2H2 H2H2 O2O2 Catalyst Anode Cathode

Hydrogen and Oxygen are separated by an electrolyte H2H2 Electrolyte H2H2 O2O2 Catalyst Anode Cathode

A catalyst helps the hydrogen and electrons separate. H+H+ H+H+ e-e- e-e- Electrolyte H+H+ H+H+ e-e- e-e- O O Catalyst Anode Cathode

Hydrogen ions travel across the electrolyte. Electrons travel through the wire. Electrolyte H+H+ H+H+ H+H+ H+H+ e-e- e-e- e-e- e-e- O O Anode Cathode

The hydrogen ions, atomic oxygen, and electrons combine at the cathode. Electrolyte H+H+ H+H+ e-e- e-e- H+H+ H+H+ e-e- e-e- O O Anode Cathode

The hydrogen ions, atomic oxygen, and electrons combine at the cathode. Electrolyte H+H+ H+H+ e-e- e-e- H+H+ H+H+ e-e- e-e- O O Anode Cathode

The reaction is completed as water is formed at the cathode. Electrolyte O H H O H H Water Anode Cathode

The Fuel Cell Produces a Voltage and Heat The maximum voltage of the cell is volts. The maximum voltage of the cell is volts. Since some of the energy is given off as heat, this maximum voltage is not realized. Since some of the energy is given off as heat, this maximum voltage is not realized.