Alternative Fuels

1 Alternative Fuels

See also ``Chemistry in Context'' textbook, Chapter 8

Batteries
- Alkaline
- Lithium Metal
- Nickel-Metal Hydride

Solar Cells

Fuel Cells
- Hydrogen-Oxygen
- Aluminum-Air
- Miniature Methanol

2 Batteries

Cathode
- Reduction (gain of electrons) occurs here

Anode
- Oxidation (loss of electrons) occurs here

Electrolyte
- Allows charge to flow
- Doesn't allow anode and cathode reactions to ``short circuit''

External Connection
- Completes circuit, Supplies ``power''

3 Alkaline Cell Batteries

Cathode
- 2 MnO ₂ + H ₂ O + 2 e ^- ® Mn ₂ O ₃ + 2 OH ^-

Anode
- Zn + 2 OH ^- ® Zn(OH) ₂ + 2 e ^-

Electrolyte
- KOH _(aq)

4 Alkaline Cell Cutaway

5 Lithium Metal Batteries

Benefits
- Highest energy density
- Lowest weight

Disadvantages
- Lithium reacts violently with water
- Usually discharges slower

6 Lithium Metal Overview

7 Lithium Metal Chemistry

Cathode
- MnO ₂ + Li ⁺ + e ^- ® LiMnO ₂

Anode
- Li ® Li ⁺ + e ^-

Electrolyte
- Often propylene carbonate/dimethoxyethane
- MUST avoid water

8 Lithium-Metal Cutaway

9 Nickel/Cadmium Batteries

Benefits
- Good under high-drain applications
- Long life
- Rechargable

Disadvantages
- Lower power density
- Memory effect

10 Nickel/Cadmium Chemistry

Cathode
- NiO ₂ + 2H ₂ O + 2 e ^- ® Ni(OH) ₂ + 2 OH ^-

Anode
- Cd + 2 OH ^- ® Cd(OH) ₂ + 2 e ^-

Electrolyte
- KOH _(aq)

11 Nickel/Metal-Hydride Batteries

Benefits
- Excellent under high-drain applications
- High energy density
- Rechargable
- Little ``memory effects''

Disadvantages
- Cost
- Shorter life than Ni/Cd

12 Nickel/Metal-Hydride Chemistry

Cathode
- Ni(O)(OH) + H ₂ O + e ^- ® Ni(OH) ₂ + OH ^-

Anode
- Metal (M) is complex alloy (such as LaNi ₅ )
- MH + OH ^- ® M + H ₂ O + e ^-

Electrolyte
- KOH _(aq)

13 Battery Limitations

Batteries provide energy, but where does energy come from?

Processing of electrode materials typically requires more energy than battery supplies.

Electric Cars may be less polluting, but energy needed to charge them.

14 Solar Energy

Energy in Sunlight converted to electricity

Practical on small scale. (Calculators, small lights, ...)

Cells still too expensive and inefficient on larger scale

15 Fuel Cells

Direct conversion of ``fuel'' into electricity.

Advantages
- Less polluting
- More efficient (maybe)
- Dream is to use H ₂ from water as fuel

Disadvantages
- Still requires fuel
- Still releases CO ₂
- Technology not there yet

16 H ₂ /O ₂ Fuel Cells

Cathode

O ₂ + 4 H ⁺ + e ^- ® 2 H ₂ O

Anode

2 H ₂ ® 4 H ⁺ + 4 e ^-

Net Reaction

2 H ₂ + O ₂ ® 2 H ₂ O

17 Methanol Fuel Cells

Cathode

3 O ₂ + 12 H ⁺ + 12 e ^- ® 6 H ₂ O

Anode

2 CH ₃ OH + 2 H ₂ O ® 2 CO ₂ + 12 H ⁺ + 12 e ^-

Net Reaction

2 CH ₃ OH + 3 O ₂ ® 4 H ₂ O +

18 Aluminum-Air Fuel Cells

Still being developed.

Uses oxidation of aluminum as fuel.

Lycos Environmental News - Aug 23, 2000

Aluminum-Power, Inc.

19 Miniature Fuel Cells

Being developed as a replacement for batteries

Advantages
- Could last much longer
- Replace fuel instead of recharge
- Fuel might come from renewable sources

Disadvantages
- Will require liquid (or gaseous) fuel
- Might still release CO ₂
- Technology not there yet

20 Miniature Fuel Cells References

MIT Technology Review

ABC News (Sep. 9, 1999)

ABC News (1999)

Scientific American (July 2001)

Energy Related Devices - Hockaday's company

Manhattan Scientifics' site - Developing Hockaday's fuel cell

Motorola's prototype

21 Schematic

Hockaday's fuel cell

22 Prototype

Prototype methanol fuel cell in a phone

23 Prototype

Prototype methanol fuel cell in a calculator

24 Prototype

Motorola's fuel cell powering a Palm

File translated from T_EX by T_TH, version 3.02.
On 14 Mar 2002, 10:40.