The membrane
- Provides ionic conduction (protons) while blocking electrons
- Needs hydration to stay conductive
- Degrades chemically (radicals/oxidation) and mechanically (stress cycles)
Catalyst layers
- Enable the core reactions to occur efficiently
- Performance depends on catalyst type, loading, distribution, and support materials
- Sensitive to contamination (fuel cells especially)
Gas diffusion / porous transport layers
- Move reactants and remove products (water in fuel cells; gas bubbles in electrolysers)
- Provide electrical conduction and structural support
- Strongly affect mass transport losses at high current density
Interface engineering
A lot of “real” performance comes down to interfaces: how well layers contact, how water moves, and how gases are distributed without creating local starvation or flooding.