Electrolysis

1
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

2
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.

3
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

4
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

5
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.

6
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

7
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

8
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, dont do that!

9
Air pollution

• If its in the air, its in your body
• Components of the Earths 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.

10
Profile of the Earths atmosphere