Electrolyser
An electrochemical device that uses electric current to split water into hydrogen and oxygen; the core equipment of green hydrogen production.
An electrolyser stack consists of cells, each with an anode, cathode and electrolyte or membrane. The thermoneutral cell voltage is 1.48 V; commercial cells operate at 1.7–2.2 V, and the excess is lost as heat.
Four technologies compete:
- Alkaline (AEL): KOH electrolyte, nickel electrodes; mature, cheapest (especially Chinese units), 50–55 kWh/kg system, slower to ramp.
- PEM: proton exchange membrane with platinum and iridium catalysts; compact, fast response to variable power, 52–58 kWh/kg system; iridium supply is a constraint.
- Solid oxide (SOEC): operates at 700–850°C, using heat to cut electricity demand to about 38–42 kWh/kg; suited to sites with waste heat or nuclear steam; lower durability so far.
- AEM: anion exchange membrane; early commercial stage, aims to combine alkaline materials with PEM-like performance.
Stacks degrade at roughly 0.5–1.5% efficiency per year and need replacement after 60,000–90,000 operating hours. Installed system costs outside China were about USD 1,700–2,500/kW in 2024 including balance of plant, compression and water treatment. China held more than half of global manufacturing capacity and installed electrolysis. See green hydrogen.
Related terms
All terms →- Green hydrogen
Hydrogen produced by splitting water in an electrolyser powered by renewable electricity, with near-zero direct CO2 emissions.
- Fuel cell
An electrochemical device that converts the chemical energy of hydrogen or another fuel directly into electricity and heat, without combustion.
- E-fuels (power-to-X)
Synthetic fuels made from electrolytic hydrogen, sometimes combined with captured CO2 or nitrogen, such as e-methane, e-methanol, e-kerosene and e-ammonia.
- Capacity factor
The ratio of the energy a power plant actually produces over a period to the energy it would produce running at full nameplate capacity for the whole period.
- Curtailment
Deliberate reduction of a generator’s output below what it could produce, usually wind or solar, because of grid, market or system constraints.