# 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