Transcript Electrolysis

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 Hydrogencause 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