Hydrogen - a singular atom
Hydrogen produced from renewable sources has the potential to be a source of green energy, and an alternative energy carrier to electricity.
Hydrogen atoms were fleetingly formed during the Big Bang but it wasn't until the recombination 370,000 years later that conditions became favourable for electrons to remain in orbit around atomic nuclei.
Covalent and hydrogen bonds
Hydrogen bonds explain cohesion (why water molecules 'bead'), and the relatively high boiling point of water - energy is needed to break apart the hydrogen bonds.
The polarity of water makes it a good solvent. When salt Na+Cl- is added to water, it dissolves; positive sodium ions - charged atoms are called ions - are attracted to the slightly negative hydrogen end of the water molecule, and positive chlorine ions are attracted to the oxygen end, thereby breaking apart, or dissolving, the bonds between the sodium and chlorine atoms.
Why are the sodium and chlorine atoms in salt charged? The sodium and chlorine atoms in salt are bound together by an ionic bond (video). Ionic bonds occur where an electron, or electrons, are transferred from one atom to another, in this case from a sodium atom to a chlorine atom. Since the two atoms now have opposite charges they attract. Na becomes Na+ and Cl becomes Cl-.
Hydrogen bonds can also form between molecules of different species, for example in DNA, where they hold together the two (polynucleotide) chains. The hydrogen bonds are strong enough to keep the double helix together, but not so strong as to prevent the chains separating when they need to be replicated.
Production
95% of hydrogen is produced by natural gas reforming in two ways.
The methane in natural gas reacts with steam under high pressure in the presence of a catalyst to produce hydrogen, carbon monoxide and carbon dioxide.
The carbon monoxide and steam are then reacted using a catalyst to produce carbon dioxide and more hydrogen in the "water-gas shift reaction".
In a final step, the "pressure-swing adsorption" reaction, carbon dioxide and other impurities are removed from the gas stream, to leave pure hydrogen.
The methane and other hydrocarbons in natural gas react with a limited amount of oxygen to partially oxidise the hydrocarbons. The carbon monoxide produced is once again reacted with water in the "water-gas shift reaction".
Electrolysis
Electrolysis is a process whereby electricity is used to split water into hydrogen and oxygen. The process varies depending on the electrolyte selected. Oxygen gas forms at the anode, hydrogen gas at the cathode.
Electrolysis can produce hydrogen with no greenhouse gas emissions, if the original source of the energy used is renewable. The process is currently 70% to 80% efficient; for every 40kWh of energy produced 50kWh to 55kWh of electricity is required. 95% efficiency has been claimed but not proven in production.
Transporting hydrogen
Hydrogen gas has a low energy density by volume at ambient temperatures even compared to natural gas. It is therefore either compressed or liquified (molecular hydrogen has high energy density by mass) for transportation by road or rail.
Hydrogen fuel cells
Current production and use
A fraction of hydrogen is currently produced from low carbon energy; the latest figure for the EU is 0.1%. Global production of hydrogen from electrolysis is less than 0.1%.
Hydrogen use today is dominated by industry, namely: oil refining, ammonia production, methanol production and steel production.
Potential
Hydrogen as a fuel is attractive because at the point of use it emits no greenhouse gases, and it can be used for long term storage at potentially lower cost than electricity. There are, however, drawbacks.
Drawbacks
'Green' hydrogen, produced only using renewable energy, and transported through 'hydrogen ready' pipelines is a seductive idea but if the path to that goal is overly long or impossible, we will be saddled with the cost of maintaining CCS infrastructure, and safeguarding sequestered CO2 indefinitely, whilst still emitting greenhouse gases.
Greasing the wheels of failure
Talk of 'blue' hydrogen and carbon capture and storage means burning gas with no guarantee of a transition towards 'green' hydrogen.
A mixed future
One positive example of combining wind power and hydrogen storage is the Surf 'n' Turf community project on the Orkney Islands north of Scotland where the abundance of energy makes conversion to hydrogen and back viable.
How much do your remember?
References
- A crash-course on hydrogen
- University of Nottingham | Periodic Videos - Hydrogen
- BBC In Our Time | The Proton
- Dr. Edward Murphy, University of Virginia | The Origin of the Elements
- Bozeman Science | Water: A Polar Molecule
- Khan Academy | Hydrogen bonding in water
- Khan Academy | Hydrogen bonding
- Fuel Cells & Hydrogen Observatory
- The hydrogen hype | Food and Water Action Europe
- International Energy Agency | The future of hydrogen
- Does the world need hydrogen to solve climate change?