Chapter 8 (CIC) and Chapter 20 (CTCS)

• Read in CTCS Chapter 20.7,8

• Problems in CTCS: 20.63, 65, 67, 69, 71, 73

Battery

• Electrochemical Cell– May have several

wired together in series or parallel

• Primary – one use once EMF = 0

• Secondary – rechargeable *Stanitski, D.L.; Eubanks, L.P.; Middlecamp, C.H.;

Stratton, W.J. Chemistry in Context: Applying Chemistry to Society, 3rd Edition, McGraw-Hill, Boston, MA, 2000, pg 316.

Common BatteriesType Voltage Recharge?

Dry Cell 1.5 N

Alkaline 1.54 N

Mercury 1.3 N

Lithium ion 2.8 N

Lead 2.0 Y

Ni-cad/Ni-MH 1.46 Y

Comments

Lasts longer than dry-cell

Small, long lasting, disposal problems

Reliable, long living (10 yrs), lightweight

Corrosive, heavy, long lasting

Cd is toxic/H now replacing Cd

Lead Acid BatteryPbO2(s) + HSO4

-(aq) + 3H+(aq) + 2e- PbSO4(aq) + 2H2O(l)

Pb(s) + HSO4-(aq) PbSO4(aq) + H+(aq) + 2e-

PbO2(s) + Pb(s) + 2HSO4-(aq)+2H+(aq)PbSO4(aq)+2H2O(l)

• So, E is independent of Pb or PbO2 concentrations• What is the voltage on each cell? There are a total

of 6 cells in a standard car battery

2 2+4

1K =

HSO H

Battery Technology Needs Improvement (Quickly)

• California will require 10% of all cars sold in ’03 to be ZEV– Automakers fined $5K for each vehicle over 90%

– No CO2, CO, SOx, NOx, O3, particulate matter

• Currently, Pb-storage electric cars travel 90 mi and recharging is needed every 3 hrs– Batteries need replacement after 25-50 K mi– Need 220 V chargers ($2K)– Car costs ~$34K

• All cars by 2007 in LA basin to be converted to “clean” power

• Energy has to come from somewhere! (power plants – 40% efficient)– Release CO2, CO, SOx, NOx, O3, particulate matter

• Calculations show an increase in SO2, NOx, but a 50% decrease in CO2

• Costs are $2.50/100 mi for electric and $6.50/100 mi for gasoline

• Ni-H battery allows– 15 min recharge time– 175 mi before recharge needed – Batteries last the lifetime of the car

• CA (and NY and MA) may want to consider a compromise for 2007 using the hybrid cars currently available

• Hybrid car uses a Ni-H battery and consumes 50% gas (thereby releasing 50% CO2)

• Gets 66 mpg

• Charges batteries by transferring Kinetic Energy of the car from the brakes through a generator

• Currently being sold for ~$18-20K (little profit here)

Photovoltaics• Ultimately move toward Solar cells• Currently used on satellites, Hwy signs, street

lights, etc.• Sunlight must move e- to create electricity• Remember that visible light makes e- jump!• In Si, 1.8 x 10-19 J/photon are required to release

an e- from a bond– λ = 1100 nm (visible light is 350 – 700 nm)

• Si must be 99.999% pure • Source is SiO2

• Efficiencies are 10 – 20%

Si Semiconductor

n-type

Doped Semiconductors

p-type

*Stanitski, D.L.; Eubanks, L.P.; Middlecamp, C.H.; Stratton, W.J. Chemistry in Context: Applying Chemistry to Society, 3rd Edition, McGraw-Hill, Boston, MA, 2000, pg 323-4.

Doped Semiconductors

• Introduction of 1 ppm Ga gives only 7 e- around it yielding a “positive hole”

• Introduction of 1 ppm As gives 9 e- around it yielding a “negative hole”

• These holes will increase conductivity

• This allows light of longer wavelengths to move e-

Costs

• In 1974, photovoltaics cost $3/kw-hr• By 1998 the cost was $0.28/kw-hr• This compares to a cost of about $0.07/kw-

hr for fossil fuels• If no gains were made on semiconductors,

the US could get all electrical needs by a photovoltaic generating station the size of NJ (85 mi2)

Corrosion

• M + O2 MxOy

Fe Fe2+ + 2e- E = -0.44 V

O2 + 4H+ + 4e- 2H2O E = 1.23 V

2Fe + O2 + 4H+ 2Fe2+ + 2H2O E = 0.79 V

• Fe2+ will ultimately be converted to Fe3+

Fe2+ Fe3+ + e- E = -0.771 V

• Acid rain should help promote corrosion

Cures for Corrosion• Cover with paint

– If you get a scratch in paint, it will still rust

• Cover with Zn (what is the Eº?)– If coating is scratched, the Zn still gets oxidized

• Alloyed with 18% Cr – If you get a scratch in surface, the underlayer will

still rust

• You can use a sacrificial anode (Mg) for buried pipes (Mg Mg2+ + 2e-)– Simply done by attaching (conductively) a piece of

Mg metal to your metal of interest