Review of Batteries

• Define the following terms: • Primary Cell • Secondary Cell • Power Density • Memory Effect

Nickel-Cadmium

Advantages

• Can be recharged 1000 times or more • Low cost/cycle • Tough, stands up to abuse

Disadvantages

• Low energy density • Memory effect • Contains toxic metals

Popular Uses

• Two-way radios, power tools, medical equipment

Lithium-Ion

Advantages

• High energy density • No memory effect

Disadvantages

• More expensive than Ni-Cd • Not fully mature, technology is still evolving

Popular Uses

• Cell-phones, iPods, laptop computers

Lead-Acid

Advantages

• Mature technology, well understood • Cheap and easy to manufacture • No memory effect

Disadvantages

• Very low energy density; most applications require huge batteries • Limited number of full discharge cycles • Environmental concerns

Popular Uses

• Electric cars, golf carts, scooters

Reusable Alkaline

Advantages

• Cheap to manufacture • More economical than primary alkaline cells

Disadvantages

• Limited current, cannot be made on large scale • Limited cycle life (about 10 cycles); fully discharging shortens life

Popular Uses

• Personal CD players, radios, flashlights

Fuel Cells

Behind the hype

The Limit of Batteries

• A battery is a fancy type of galvanic cell. It changes chemicals into electricity.

• Eventually, all the chemical are reacted and the battery goes dead.

• If the battery is a secondary cell, you can recharge it, but this takes time and energy. Also, there is a limited number of times you can do this.

• Wouldn’t it be nice to be able to just open up a battery, and pour in some more chemicals, like refueling a car?

Fuel Cells: The Ultimate Battery

• A fuel cell is a type of galvanic cell that allows you to add fresh chemicals continuously. It will continue to run as long as you keep adding fuel.

Fuel Cell Comparisons

Energy Conversion Fuel Powered By Power Output Battery Fuel Cell Engine

Chemical> Electrical Chemical> Electrical Zinc or other metal Electrochemical Reaction H2, Methane, Propane, Methanol, etc.

Electrochemical reaction Chemical> Mechanical> Electrical Propane, Methane, Gasoline Combustion Reaction Low Variable High

Advantages of Fuel Cells

• Extremely versatile – can power everything from cell phones to buses • Can run on a variety of fuels • More environmentally friendly than combustion

Disadvantages of Fuel Cells

• Technology is still somewhat unreliable • Some types still produce greenhouse gas emissions • EXPENSIVE

The Promise of Hydrogen

• Many Fuel Cells are emission-free because they run on hydrogen O 2(g) H 2(g)

2 H +

Anode Electrolyte Cathode

The Promise of Hydrogen

• Many Fuel Cells are emission-free because they run on hydrogen H 2(g) H 2 O (l) Anode Electrolyte Cathode

Overall Reaction: H 2 + O 2 → H 2 O Question: Where does hydrogen come from?

Types of Fuel Cells

• Proton Exchange Membrane (PEM) • Solid Oxide Fuel Cells (SOFC) • Alkaline Fuel Cells (AFC) • Direct Methanol Fuel Cells (DMFC) • There are many more, but we won’t get into them here

Your Task

• You will work in groups of about 5 • Half of each group will argue “for” a particular type of fuel cell the other half will argue “against” • Each half-group will prepare an extremely short (60 s) presentation to convince the audience of their stance • The class will vote on who was most convincing