Two water electrolysis technologies dominate today. Alkaline electrolysers are mature and use inexpensive materials, but rely on a porous separator in liquid electrolyte. PEM electrolysers are compact and respond quickly to variable power, but need platinum-group metal catalysts and expensive titanium components. AEM electrolysis sits between them.
How AEM works
Like alkaline electrolysis, AEM moves hydroxide ions (OH⁻) from cathode to anode. Unlike alkaline electrolysis, the ions travel through a dense, solid polymer membrane rather than a porous sheet soaked in concentrated KOH. The membrane conducts ions and blocks gases at the same time, so the electrodes can sit directly against it in a compact, zero-gap cell, much like PEM.
| Alkaline | AEM | PEM | |
|---|---|---|---|
| Ion carried | OH⁻ | OH⁻ | H⁺ |
| Electrolyte | Concentrated KOH | Dilute alkaline solution or pure water | Pure water |
| Separator | Porous separator | Dense anion-exchange membrane | Dense proton-exchange membrane |
| Typical catalysts | Nickel-based | Nickel- and iron-based possible | Platinum and iridium |
| Cell design | Mature, large stacks | Compact, zero-gap | Compact, zero-gap |
| Maturity | Commercial at scale | Emerging | Commercial |
General characteristics of each technology; individual designs vary.
Why the membrane is the make-or-break part
Everything that makes AEM attractive depends on the membrane. It has to conduct hydroxide ions quickly enough to support high current density, stay chemically stable in an alkaline environment at operating temperature, keep hydrogen and oxygen apart, and remain mechanically sound under compression and cycling. Membranes that are highly conductive tend to swell or degrade; membranes that are robust tend to conduct poorly. Resolving that trade-off is the central materials challenge of AEM electrolysis.
Where Greenprastha fits
Greenprastha's separators combine low resistance and high strength, usually a trade-off, using nanomaterial-modified composites developed at IIT Bombay. We are applying the same materials science to anion-exchange membranes, and to AEM stacks built around them. Both are in development, and we work with partners who want early access to membranes and test data.
Note. This overview describes the general characteristics of each electrolysis technology. Greenprastha's AEM membranes and stacks are in development; no performance figures are published for them.
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