PEM Electrolysis (PEM)

In plain terms

A PEM electrolyzer uses a thin solid polymer membrane instead of a liquid electrolyte. Water is split at the anode; protons cross the membrane and recombine as hydrogen at the cathode. The membrane is a tight gas barrier, so stacks run at high current density and can deliver hydrogen at pressure.

The acidic environment forces the use of precious-metal catalysts: iridium on the anode, platinum on the cathode. Iridium makes up most of that load and is a key supply-chain risk.

PEM's strength is speed. The Clean Hydrogen JU gives a state-of-the-art hot-idle ramp of 2 s and a cold start of 30 s (2020 baseline, SRIA 2022), which suits direct coupling to solar and wind.

Typical range

DOE targets 51 kWh/kg system use and 0.5 mg/cm² PGM by 2026; the Clean Hydrogen JU targets 48 kWh/kg by 2030.

Why it moves LCOH

PEM costs more per kilowatt: DOE puts uninstalled system cost at $1,000/kW (2022 status), against $500/kW for alkaline. It recovers part of that gap on variable renewables, because fast ramps let it absorb more of each solar or wind hour and raise the electrolyzer capacity factor. Which effect wins depends on the site's power profile, not on the technology alone.

Common mistake