Membrane electrode assembly

The bonded membrane and catalyst layers at the core of an electrolyser cell.

Abbreviated MEA. An ion-conducting membrane with catalyst layers applied to each face, sandwiched between porous transport layers. It is where the electrochemistry happens and, in PEM, where most of the material cost sits, because PEM catalysts depend on iridium and platinum.

The construction is not confined to PEM. Anion exchange membrane cells use the same bonded arrangement with a hydroxide-conducting membrane and largely platinum-group-free catalysts, and zero-gap alkaline cells press the electrodes directly against the diaphragm to the same end. What differs between them is the ion carried, the catalyst chemistry and the operating pH, not the idea of bonding the electrochemistry into one assembly.

Degradation mechanisms include catalyst dissolution and migration, membrane thinning through chemical attack, and mechanical damage from pressure and humidity cycling. Several of them accelerate under the transient operation typical of renewable coupling.

Because the assembly is bonded, these mechanisms are not individually serviceable. They present as a rising cell voltage or a rising crossover rate, which is why cell-level monitoring is the practical route to observing them at all.