Compare the Four Technologies
One overall reaction. Different electrolytes, ions and pathways.
Follow the ion
What stays the same?
Oxidation occurs at the anode; reduction occurs at the cathode. Electrons follow the external electrical circuit. Hydrogen forms at the cathode and oxygen at the anode.
Ideally, H₂:O₂ = 2:1 by amount of substance and by gas volume at the same temperature and pressure.
What changes?
| Technology | Ionic medium | Ion | Direction | Operation |
|---|---|---|---|---|
| PEMWE | Proton-conducting polymer membrane | H⁺ | Anode → cathode | Typically low-temperature |
| AWE | Liquid alkaline electrolyte + separator | OH⁻ | Cathode → anode | Typically low-temperature |
| AEMWE | Anion-exchange membrane | OH⁻ | Cathode → anode | Typically low-temperature |
| SOEC | Solid ceramic electrolyte | O²⁻ | Cathode → anode | High-temperature operation |
AWE and AEMWE share the OH⁻ charge carrier and alkaline half-reactions; their electrolyte structures differ. SOEC uses steam and a high-temperature ceramic electrolyte.
Match the charge carriers
Which way does the ion move?
Symbols used here
H⁺: proton. OH⁻: hydroxide ion. O²⁻: oxide ion. e⁻: electron. DC: direct current. Electrolyte: the ion-conducting medium. Anode / cathode: oxidation / reduction electrode.
These illustrations show conceptual transport directions. They are not to scale and do not compare actual transport rates.