Fuel cells

• An electrochemical conversion device• Chemical reactions cause electrons (current)

to flow• Requires a fuel, an oxidant and an electrolyte (

a substance that contains free ions and acts as a conductor)

• Typical type of fuel cell is called a proton exchange membrane fuel cell (PEMFC)

Hydrogen Fuel Cells

• Clean-only emission is water• Expensive to produce• Highly efficient-in an automobile, efficiencies

of converting fuel energy to mechanical energy of 60% could be achieved, almost double the current efficiencies

• Hydrogen itself has issues as a fuel source

Issues with Hydrogen

• Abundant in nature, but not a freely available fuel

• Must be unbound from compounds• Currently obtained via steam reforming– Steam and a nickel catalyst react, producing H– Need steam at very high temperatures, 1600F

• In the future, H is anticipated to be produced by the electrolysis of water, requiring large amount of water and electricity

Electrolysis• Pass an electrical current through water and

obtain H• Pass a direct current from a battery or other DC

power supply through a cup of water (salt water solution increases the reaction intensity making it easier to observe).

• Using platinum electrodes, hydrogen gas will be seen to bubble up at the cathode, and oxygen will bubble at the anode.

• Choice of the electrode is critical, you do not want a metal that will react with oxygen

Issues with Hydrogen

• Storage-occurs in gas form at room temperature, hard to contain

• As a liquid, it can be stored, but needs temperatures of -253 C.– As a liquid, its energy density increases 1000 times– In principle, could replace gasoline as a liquid fuel, but

not practical at this time• One solution is to store it as a metallic hydride

(the negative ion of Hydrogen in a compound with another element) at room T.

Issues with H

• Highly explosive– Forms a volatile mixture with air

• A mixture of 4-75% of H in air is explosive, compared with natural gas which is only explosive in a range of 5-15% concentration in air

• Ignition energy is small, needing only 2 x 10-5 J (basically a spark of static electricity can ignite H)

• Only good news is its low density means if there is a H leak, it disperses quickly

Hydrogen• Hindenburg disaster• Hindenburg was a

German passenger airship (zeppelins) built for transatlantic air flight.

• Filled with Hydrogen• Something caused

ignition of the Hydrogen-cause is debatable

• 36 fatalities out of 79 people onboard

Alchohol• Use methanol or ethanol as a fuel– Already gone over ethanol

• Methanol is already in use at Indy 500 race– Proven that no significant loss of performance is

experienced (though they are in the process of switching to ethanol)

• About ½ the energy content of gasoline• Produces only CO2 and water– Some nitrogen oxides produced in the engine

• Can be manufactured from re-newable sources (biomass for example)

• Technologies exist now.

Disadvantages

• Very dangerous– Burns with no visible flame-needs a colorant

added– Fumes are toxic

• CO2 is a greenhouse gas• Currently made mostly from natural gas-a

non-renewable fossil fuel• Possibly more corrosive than ethanol to

engine parts

Use in liquid fuel cells• Another use is as a input to a

liquid feed fuel cell• In these cells, Methanol

replaces hydrogen• Methanol has a much higher

energy density and is easier to store than H

• Current methanol fuel cells produce power too low for vehicles, but can be used in cell phones, laptops etc

• Advantage is that they store lots of power in a small space, which they over a long period of time

Environmental effects of energy production

• All of our energy producing mechanisms have some effect on the environment– Production of waste products pollutes air, water

and ground– Disruptions to local ecosystems

• Our job is to understand and mitigate these effects to the best of our ability

• Philosophy : If it hurts (the environment) when you do that, don’t do that!

Air pollution• If its in the air, its in your body• Components of the Earth’s Atmosphere:– Nitrogen 78.08%– Oxygen 20.95%– Argon 0.93%– Also small amounts of Neon, Helium, Krypton,& Hydrogen

• In addition, there are compounds whose concentrations vary with height: water vapor, carbon dioxide, methane, carbon monoxide, ozone, ammonia

• These are naturally occurring concentrations, any additional influx or destruction of these compounds via human beings alters the system.

Profile of the Earth’s atmosphere