November 14

Recap--

Hydrogen Fuel, Batteries and Fuel Cells

• just repackaged energy
• convenience, portability
• clean energy at point of use

• Hydrogen-- where do we get the energy to make it?
  • electricity from hydro, solar, nuclear = no CO₂
  • electricity from coal, gas, oil= no net CO₂reduction
  • could reduce CO, NOx, SO2
  • could keep CO, NOx, SOx in dense urban areas
• Primary Batteries
  • energy from Zn, Li
  • spend energy to reduce ores (oxides)
  • electricity without wires-- generally limited power
• Secondary (Rechargeable) Cells
  • some energy spent to make battery
  • but in use, energy comes from charging
    • tap into power lines (recharge computer battery)
    • tap into power from engine (automobile alternator)
• Fuel Cell
  • might consume methane or methanol
    • (CO₂ product)
  • might use H₂ (see above)
  • we can deliver the fuel;
    • get significant electricity without wires
• Solar panels--
  • direct conversion of sunlight into electricity

• Alternative Energy Source (not in chapter, here)
  • Ethanol, from fermentation
    • some used in car fuel, discussed earlier
    • Brazil-- alternative to gasoline, hard currency
  • Methane from Manure and Landfills
    • one of the products of bacterial fermentation
    • can construct manure tanks and collect the gas
    • landfills will produce some (marginal as fuel)
    • need to monitor and allow to escape
    • would collect, leak into cellars, etc.
    • provides risk of explosion otherwise

• Topic 1 -- Batteries (Actual examples, comparisons)
  • 1a. Discuss disposal, landfills, recycling batteries
  • 1b. electroplating (not a battery, but related ideas)
• Topic 2 -- Photocopiers and Laser Printers
  • (using photoconductivity) (not in text)
• Topic 3 -- Nuclear Fusion as an Energy Source
• Topic 4 -- How do we make tiny devices like computer chips? (not in text)

Batteries--

Primary

• (chemical ingredients in a sealed battery)
• Reaction produces electrical energy
• Cell is "dead" when reactants are consumed
• Disposable

Secondary

• reverse electrical flow regenerates components
• can run for 100's-1000's of cycles
• (some need added water)

Historical-- Oldest Primary Battery

• Volta--1800
• stacked disks of Zn/blotter/silver

• Almost all electrical experiments, devices, games
  • ran from batteries
  • from 1800 to 1900-1910
  • (weren't that many devices, of course)
  • (games-- parlor tricks were common)

Telegraph (and telephone)

• Telegraph-- developed 1845- in large operation by 1860
  • precedes development of light bulb
  • electrical systems followed light bulb invention
  • even in 1915, telegraph station often located far from power lines
  • needed reliable local electrical power
    • not a lot of power, just to signal
    • can't be delicate, technically demanding

Crow Foot Cell (Daniel's Cell, gravity cell)

• Zn ---oxidize--> Zn²⁺ (aq) +2e
• Cu²⁺(aq) + 2e ----reduced---> Cu
  • need to separate Zn from Cu²⁺
  • why? (they would react directly)
• Copper metal electrode used
  • will get more copper (ok)
  • won't react with Cu²⁺
  • immerse in a CuSO₄ solution

• On top, float a lower density ZnSO₄ solution
  • gravity/density prevents mixing
• Then insert a large Zn metal electrode
• Both electrodes shaped like metal "crow's foot")
• Connect a wire to both electrodes

1. Easy to prepare from salts, water, electrodes
2. Produces voltage like a flashlight battery (1.5V)
3. produces current larger than our D-cells
4. No gases, fumes, acids, toxic materials
5. Will last for weeks or few months of use
6. can add more Cu solution or replace a metal electrode
7. Not portable, but most telegraph shops didn't travel; military wasn't too pleased with this cell

Gradually replaced with "dry" cells

• anode (oxidized material) still Zinc
  • Zn ---> Zn²⁺ + 2e-
• other cathodes were used
  • favorite is 2MnO₂ +2e ---> Mn₂O₃
• need an inert electrical conductor
  • just to funnel electrons into the material
  • usually a carbon rod (cheap)
• need to keep material damp
• need ions for electrical conductivity
  • usually Ammonium Chloride (slightly acidic)
• could be sealed, used in any position
• developed ____
  • Noyes: Chemistry Text, 1914 doesn't find enough use to mention
  • widely used through 1985
  • gradually displaced by the alkaline cell

Alkaline cell, similar

• but inside is a paste or gel of KOH
• alkali = another name for a strong base
• Zn + 2OH^- ----> Zn(OH)₂ + 2 e
• slightly higher voltage,
• slightly better performance

• Cell begins to "die" when any of these occur
  • a. runs out of Zinc
  • b. runs out of MnO₂
  • c. runs out of KOH
• voltage begins to drop near the end

Other batteries have other chemistry, other electrodes

• Mercury / Zinc battery--
  • keeps steady voltage, then dies all at once
  • much better, but little or no warning of dead battery
  • Hg = serious problem with disposal
• Lithium Batteries
  • More active metals (Li, Na, K, Ca)
  • make good anodes
  • will get higher voltages, more energy
  • need to be well protected from air, water
  • Li Battery has been well developed
  • Li itself is relatively cheap
  • more expensive to make a safe case
  • Li ion is not a disposal problem
  • Li battery has 3V (twice that of dry cell)
  • enough to run watch, computer circuit from 1 cell
  • too expensive for flashlight, radio

Rechargable Batteries

• Automobile, Golfcarts : Acid Lead Cell
• Calculators, older Computer laptops: Nickel-Cadmium/Alkaline (NiCad)
• Computers: Metal Hydride Batteries,
• Lithium Ion (different from Li cells)
• Electric Drills, portable: mostly NiCad, high end uses metal Hydride

Old electric cars, circa 1890-1915

• reliable, efficient, common
• perhaps 50-100 manufacturers
  • batteries failed after being charged several hundred times
  • (may need to replace every year or two.)
• generally more expensive, but more reliable and safer than gasoline cars
  • it was the electric starter for gasoline engines (1915) that led to loss of popularity of electric cars

Lead Acid Battery

• standard battery doesn't like deep charging
  • in normal car use, use maybe 5-10% of power to start a car
  • then recharge the battery in next 5-10 min
  • electric car, might use 50-90% of the charge
  • then nearly complete recharging
• few batteries hold up well in that manner
• technology is improving, but marginal

Chemistry--

• One electrode is plate of lead,
  • filled with lead dioxide, PbO₂
• The Other electrode is simply Lead, Pb
  • The electrolyte is 5-10% sulfuric acid
• Overall reaction
  • Pb + PbO₂ + 2 H₂SO₄ --> 2 PbSO₄ + 2 H₂O
• Reversible reaction
  • usually small amount of H₂O converted to H₂ , O₂
  • vent, avoid flames
  • will need to add water
    • newer batteries reduce this, won't need water

Disposal and Environment

• disposable batteries-- large volume of material
• zinc is not toxic at modest levels
• alkali or weak acid, not very toxic
• such cells are ok in landfills
• not ok thrown in rivers, fields, etc.
• recycling sounds good but
• expensive to collect
• value of used zinc less than cost to recover it
  • recycling seldom pays in material recovered
  • Al is rare exception
  • recycling may pay in reduced disposal costs
• a few bad actors in disposable batteries
  • mercury-zinc (hearing aid batteries often)
  • Hg is quite toxic

• rechargeable batteries
  • tradeoff-- generally more toxic materials
  • but use only 1/100-1/1000 as many cells
• unfortunately Lead, Cadmium = major health problems
  • the acid is easily dealt with

landfill--

• hold in ground, usually with waterproof liner
• filled with trash
• covered
• assumed it stays there...
  • until decomposes (slow if dry)
  • forever (elements won't decompose)
  • until leached out by water (centuries)
  • until forgotten (often < 1 century)
  • won't accept rechargeable batteries

hazardous landfill

• similar, but much more tightly regulated
• better protected from ground water, rain
• more expensive to run and to use
• only safe place for rechargeables
• now, often cheaper to collect and recycle

Electroplating

• simple oxidation/ reduction
  • Cu²⁺ + 2e--------cathode, reduction----> Cu
  • Cu ------anode, oxidation ----> Cu²⁺ + 2e
  • net reaction looks like nothing
    • but Cu (anode) moves, covers cathode with Cu
  • Of course, we could cover any metal with any other
    • Ni, Gold, Silver plating
    • often very thick coats for added strength
    • often thin coats of expensive metals

--------

Nuclear Fusion as an energy Source

• Promising (since 1950's)
• No prospects for use in next 10-25-50 years

Cold Fusion Story

• Pons and Fleishman
• Muon role

Some references, Web links

A classroom discussion of batteries

telegrapher's batteries, 1908 publication

photograph of a crowsfoot battery

about batteries

A list of old electric cars 1890-present

Details on Potocopiers

details on laser printers

comparison: ink jet printers