Week 3 - Hydrogen Flashcards
Hydrogen
- Most abundant element in the universe
- 10th most abundant element in Earth’s crust
- Abundant, but bound in a chemical compound e.g. H2O, hydrocarbons
Challenge with Hydrogen
Production - must first be dissociated from chemical compound (this requires energy)
Clean hydrogen (‘renewable hydrogen’ or ‘green hydrogen’)
Produced by electrolysis of water with renewable electricity. No GHG emitted during the process.
Grey Hydrogen
Produced from natural gas by steam-methane reforming. Emissions of about 9.3kg CO2 per kg of hydrogen.
Blue Hydrogen
Same production process as with grey hydrogen, but the CO2 is captured and stored permanently.
Turquoise Hydrogen
Produced by pyrolysis of natural gas, with pure carbon as a side product that can be sold on the market.
Pyrolysis is the heating of an organic material in the absence of oxygen.
Electrolysis
Water splitting in electrolyser using electricity.
Converts electrical energy into chemical energy
Photoelectrochemical cells (PEC)
Hydrogen production using sunlight and photoelectrochemical materials (semiconductors).
Conversion of solar energy into chemical energy
Semiconductor is immersed in aqueous electrolyte
Solar thermochemical hydrogen production
Driving chemical reactions at elevated temperatures using solar energy
Photobiological water splitting
Microbes absorb sunlight and produce hydrogen
Hydrogen storage
Stored in liquid and gaseous state
Concerns regarding safety, cost, weight, volume and capacity
Hydrogen in transport
Combustion of H2 with oxygen is highly exothermic (energy release)
Combusts without carbon emissions
Produces NOx emissions
Extra tank needed - increases costs compared to normal ICE
Same working principle as ICE:
Intake - Compression - Ignition - Exhaust
Fuel Cells
Reverse mechanism of electrolysis
Produces water from hydrogen and oxygen
Converts chemical energy into electrical energy
Hydrogen flow rate required for current production in fuel cell:
0.037605 kgH2/hr.kA
