PEM vs AEM Electrolyzers: What Is the Difference?
A PEM electrolyzer carries protons through an acidic membrane and needs precious-metal catalysts such as iridium and platinum. An AEM electrolyzer carries hydroxide ions through an alkaline membrane, which allows cheaper catalysts, but the technology is younger and its membranes are less durable.
PEM, AEM and alkaline electrolysis compared
| PEM | AEM | Liquid alkaline | |
|---|---|---|---|
| Ion carried | Proton (H⁺) | Hydroxide (OH⁻) | Hydroxide (OH⁻) |
| Separator | Proton exchange membrane | Anion exchange membrane | Porous diaphragm |
| Feed | Pure water | Pure water or dilute alkali | Concentrated KOH |
| Typical catalysts | Iridium and platinum | Nickel-based and other non-noble metals possible | Nickel-based |
| Maturity | Commercial | Developing | Most established |
| Main challenge | Cost of precious metals | Membrane durability | Lower current density |
Which one should a lab study?
- Choose PEM to work with an established device and materials such as PFSA membranes.
- Choose AEM to explore cheaper catalysts and newer membranes, where much of the open research lies.
- In either case, test at device level with a zero-gap cell once the catalyst works in a three-electrode cell.
What you need to test each
For PEM work: a PFSA proton exchange membrane, a PFSA ionomer for the catalyst layer, and hardware with corrosion-resistant parts such as titanium on the anode side.
For AEM work: an anion exchange membrane, a matching anion ionomer, and hardware that suits alkaline conditions, often with nickel on the anode side.
Frequently asked questions
Why does a PEM electrolyzer need iridium?
Its anode runs at high potential in an acidic environment, and iridium oxide is the catalyst that survives those conditions while staying active.
Can an AEM electrolyzer run on pure water?
It can, but many systems feed dilute KOH because this gives better performance and durability today.