Energy Materials

• To measure energy, we only really care about \(\Delta H\), since only exothermic energies matter
  • While \(\Delta G\) will tell us about sponteneity, endothermic reactions which would give us \(−\Delta H\) would pe positive \(\Delta G\)
• A Watt is a unit of power, \(W=\frac{E}{T}=\frac{j}{s}\)

Energy Consumption

• The vast majority of our energy consumption is from fossil fuels:
  • 33% coal
    • Amorphous carbon
  • 25% natural gas
    • Primarily methane and ethane
  • 36% oil
    • Fractionally distilled into grades of fuel
• Renewable sources are as follows
  • 2% Hydroelectricity
  • 3% biomass
  • 1% wind and solar

• The end of oil isn’t the end of oil, since we can liquefy coal

  • \(\ce{C_{(s)} + H2_{(g)} -> C_x H_{y(l)}}\)
  • We can also produce natural gas from coal in a similar process
  • \(\ce{C_{(s)} + O2_{(g)} + H2O_{(l)} -> H2_{(g)} + 3CO_{(g)} + CH4_{(g)}}\)
  • This can be tweaked with more water to produce more H_2
    • \(\ce{CO_{(g)} + H2O_{(l)} -> CO2_{(g)} + H2_{(g)}}\)

Future Consumption

• We currently need 14 TW
  • 16 TW by 2050
• If we were to fully use the resources of the planet, this is how much energy we’d produce:
  • 4.6 TW (1.6 TW feasible) - Hydroelectric
  • 8 TW - nuclear (one new plant every 1.5 days forever)
  • 2 TW - tidal
  • 12 TW - geothermal (highly dependent on loacation)
  • 5-7 TW - biomass (if all cultivatable land, not used for food, were used to grow fuel)
  • 2-4 TW - wind
• Solar would produce 120000 TW over the globe
  • 800 TW feasibly
  • Is currently only 0.1% of the energy market

Energy Density

• Is a measure of energy per unit mass
  • 0.512 \(MJ\cdot kg^{-1}\) (300 bar, 12°C) - Compressed air
  • 0.001 \(MJ\cdot kg^{-1}\) (100m dam height) - Pumped Water
  • Batteries:
    • 0.54-0.72 \(MJ\cdot kg^{-1}\) - Li ion
    • 0.14-0.22 \(MJ\cdot kg^{-1}\) - NiCd
    • 0.14-0.17 \(MJ\cdot kg^{-1}\) - Pb/\(\ce{H+}\)
  • Capacitors:
    • 0.0206 \(MJ\cdot kg^{-1}\) - Ultracapacitor
    • 0.01 \(MJ\cdot kg^{-1}\) - Supercapacitor
  • Chemical bonds: (not currently efficient extraction)
    • 143 \(MJ\cdot kg^{-1}\) - \(\ce{H2}\) (700 bar)
    • 44 \(MJ\cdot kg^{-1}\) - liquid fuels

Solar Energy Capture

“Fundamentally, a solar cell turns light into current”

• Currently available - pn junction type
  • Amorphous silica (a-Si)
  • Cadmium Telluride (CdTe)
  • Organic photovoltaic cells (OPCs)
  • Copper Indium Gallium Selenide (CIS/CIGS)
• Future types?
  • Photosynthetic - solar to chemical fuels
    • Leaf mimicking - dye sensitised solar cells
    • Biological photosynthesis

Solar Fuels

• A fuel produced by solar means
• Typically through artificial photosynthesis or some other thermochemical reaction
• The holy grail of energy conversion is to reduce \(\ce{CO2}\) to organic compounds
• Could be used as an alternative to fossil fuels
• \(\ce{H2, CH4, CH3CH2OH}\)

Water splitting

• The general term for the reduction of water to
• Easiest way is to electrolyse water in hydrogen and oxygen
• In photosynthesis, water splitting donates electrons into the electron transport chain
• Hydrogen is a commodity chemical, so this is a valuable process