AEM vs PEM vs SOEC

Uses a solid polymer membrane that carries protons (H⁺) from the anode to the cathode. PEM units are compact, run at high current density, and respond fast — they can ramp up and down quickly, which pairs well with variable solar and wind. The catch is that they rely on precious-metal catalysts such as platinum and iridium, which add cost and raise questions about material supply.

A newer approach that carries hydroxide ions (OH⁻) across a solid polymer membrane. AEM aims to combine PEM's compact, membrane-based design with cheaper materials — avoiding precious-metal catalysts in favor of more abundant metals like nickel. It's the least mature of the three commercially, with membrane durability and lifetime being the main areas still being proven at scale.

Runs hot, using a solid ceramic electrolyte and splitting steam rather than liquid water. At high temperature, some of the energy can come from heat instead of electricity, so SOEC can reach the highest electrical efficiency — especially when paired with an industrial waste-heat source. The trade-offs are slow start-up and material stress: the extreme heat and thermal cycling make long-term durability the central challenge.