Chemistry for Fuel Cells

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

2. What is Chemistry? • Chemistry is the study of matter and its transformations. • 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.

3. 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. 2H2 + O2 2 H2O

4. 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. • H2– element • O2– element • H2O– chemical compound

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

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

7. 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 other elements are very different from the atoms of the given element.

8. Electrons Nucleus Atoms are made up of a nucleus and electrons surrounding the nucleus.

9. The nucleus • In the very center of the atom • Very small compared to the size of the atom • Does not take part in chemical reactions • Contains protons (positively charged particles) • Number of protons determines which element • Contains neutrons (particles not charged) Proton Neutron

10. Subatomic Particles

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

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

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

14. Valence electrons (VE) Valence electrons determine chemical properties. No. of VE equals Group No.

15. Nucleus Oxygen atom has 8 electrons Oxygen Atom

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

17. Hydrogen has 1 electron Hydrogen Atom Nucleus

18. 1 valence electron and no core electrons Hydrogen Atom Valence Electron No Core Electrons

19. Chemical Bonding • 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 shared between the atoms to form the bond (covalent bond).

20. Noble Gas Theory • G. N. Lewis discovered that atoms lose, gain, or share electrons to attain a noble gas arrangement. • 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!

21. Cu Cu+2 + 2e- Zn Zn+2 + 2e- An Ion Is Formed When An Atom Loses One Or More Electrons • This will form a positively charged ion.

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

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

24. Ions may be replaced by another atom changing to an ion. Zinc metal put into a solution of copper (+2) ions (CuCl2) 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+2Cl2-1 + Zn Cu + Zn+2Cl2-1

25. Ion Replacement can be Predicted by the Electromotive Series Na+1 + 1 e-1 Na(s) –2.71 v Zn+2 + 2 e-1 Zn(s) –.76 v Fe+2 + 2 e-1 Fe(s) –.44 v Cd+2 + 2 e-1 Cd(s) –.40 v Pb+2 + 2 e-1 Pb(s) –.126 v 2 H+1 + 2 e-1H 2 (g) 0.000 v Cu+2 + 2 e-1 Cu(s) +.337 v Fe+3 + 1 e-1 Fe+2 +.771 v Ag+1 + 1 e-1 Ag(s) +.799 v O2 (g) + 4 H +1 + 4 e-1 2 H 2 O(l) +1.229 v

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

27. 2e- V 1.10 volts Zn metal Cu metal Na2SO4 salt bridge Cu+2 Zn+2 The Cu Zn cell is shown below Cu+2 +Zn Cu + Zn+2

28. Voltmeter + - Copper Strip(cathode) Wire Zinc Strip(anode) Porous Cup Cu+2 SO4-2 Beaker Zn+2 SO4-2 In the Laboratory, we use a will use a Porous Cup

29. 2H2 + O2 2H2O Covalent Compound • 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”

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

31. Formation of water • 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)

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

33. 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. • The electrons pass from one side to the other by means of a wire. • Hydrogen and oxygen react to form water.

34. Fuel Cell Operates as a Battery Catalyst Catalyst O2 H2 Electrolyte H2 Anode Cathode

35. Hydrogen and Oxygen are separated by an electrolyte Catalyst Catalyst Electrolyte H2 O2 H2 Anode Cathode

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

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

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

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

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

41. The Fuel Cell Produces a Voltage and Heat • The maximum voltage of the cell is 1.229 volts. • Since some of the energy is given off as heat, this maximum voltage is not realized.