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 BatteryFuel CellEngine Energy Conversion Chemical> Electrical Chemical> Electrical Chemical> Mechanical> Electrical FuelZinc or other metal H2, Methane, Propane, Methanol, etc. Propane, Methane, Gasoline Powered ByElectrochemical Reaction Electrochemical reaction Combustion Reaction Power OutputLowVariableHigh

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 H 2(g) AnodeCathode Electrolyte 2 H + O 2(g) 2 e -

The Promise of Hydrogen Many Fuel Cells are emission-free because they run on hydrogen H 2(g) AnodeCathode Electrolyte H 2 O (l)

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