Electrolysers

Equipment that uses electricity to split compounds: water into hydrogen, brine into chlorine, alumina into aluminium.

Conversion and use · Conversion devices · No. 103

• Conversion and use

The world can build 58 GW of electrolysers a year but made under 5 GW in 2025, leaving factories about 91% idle.

Chart: Illustration: Electrolysers

Where it comes from

Chart: Map of where it comes from

Direct current drives reactions uphill: water into hydrogen and oxygen, brine into chlorine, alumina into aluminium; Faraday's law sets the charge needed.

Three things to know

1. Chinese electrolysers installed in China cost USD 500 to 1,100 per kW in 2025, against USD 1,900 to 2,500 for those made elsewhere.
2. PEM electrolysers need iridium, of which only about 7.5 tonnes are mined a year; 1 GW needs about a tenth of that (calculated).
3. Aluminium smelters use 14.1 MWh per tonne, about 2.3 times the theoretical minimum (calculated).

The journey

1. 1 Grid powerAC electricity, ideally cheap and clean
2. 2 RectifierConverts it to DC for the stack
3. 3 StackCurrent splits water, brine or alumina
4. 4 ProductsHydrogen, chlorine, caustic soda, aluminium
5. 5 UsersRefining, ammonia, methanol, steel, chemicals

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