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Green Hydrogen

The combination of high energy and zero direct emissions offered by green hydrogen opens the door to decarbonising energy-intensive processes that are hard or expensive to electrify (bp Hydrogen explainer). These include heavy industries (such as cement and steelmaking) which currently rely on combustion of fossil fuels which create intense heat) or heavy transport (such as trucks, ships and even aircraft).

Green hydrogen is produced by water electrolysis using power provided by renewable sources such as wind or solar farms. Two main technologies to deliver this process are available today: Alkaline and Proton Exchange Membrane (PEM).

The general principle of both technologies is similar: electricity is used to split water molecules into hydrogen and oxygen. The cathode splits water molecules by reduction into hydrogen and oxide ions. The oxide ions are transported through the electrolyte to the anode, where they are oxidized into oxygen. This is effectively the reverse of the process employed in the power generating unit of hydrogen fuel cell vehicles, which consume hydrogen (stored in the vehicle) and oxygen (from the atmosphere) to produce electricity.

The processes differ in that Alkaline electrolysis uses a liquid electrolyte whereas PEM has a solid polymer. The operating pressure and temperature of the processes may differ too.

The end result is effectively the same, with the key outputs produced by either process being high purity hydrogen and oxygen and heat.