Pretty Porous

Scale 3

Scale 3: The individual fuel cell and its porous layers

These processes take place on different scales.
Credits: University of Stuttgart / SFB 1313

The research on the PEM (polymer electrolyte membrane) fuel cell serves as an example. It consists of nine porous and non-porous layers and materials with different properties.

A single fuell cell is very thin, less than 2 cm thick and about 30 cm long.

If the PEM fuel cell is opened, the nine different layers become visible.

The nine different layers of the PEM fuel cell
Credits: University of Stuttgart / SFB 1313 / Cynthia Michalkowski

Enumeration of the 9 layers of the PEM fuel cell

1) Anode side: Gas channels – Channel structure (not porous). Material: metal or ceramics

2) Anode side: GDL = Gas Diffusion Layer (porous). Material: coated carbon fiber

3) Anode side: MPL = Membrane Polymer Layer (porous). Material: coated carbon particles/grains

4) Anode side: CL = Catalyst Layer (nano-porous). Very fine scale, but the transport processes are the same as in a porous medium. Material: carbon particle and Ionomer chains with platinum as catalyze

5) PEM = Polymer Electrolyte Membrane (more or less porous). The transport is chemical rather than comparable to a porous medium. Material: Nafion

6) Cathode side: CL – see anode side

7) Cathode side: MPL – see anode side

8) Cathode side: GDL  – see anode side

9) Cathode side: Gas channel. Classical channel structure (not porous), but can also be expanded metal or similar material that can be interpreted as a porous medium. Material: metal or ceramics.

Hydrogen (H2) and oxygen (O2) (from the air) pass through the porous layers of the fuel cell and finally react to water (H2O) that is transported out of the cell. A “transport” of hydrogen and oxygen through the porous layers of the fuel cell takes place.

Reaction equation of water:  2 H2 + O2 ⇌ 2 H2O

This reaction and the interaction of the various systems in the vehicle generate electrical energy, which ultimately drives the vehicle.