Sandia LabNews

How a polymer electrolyte membrane — or PEM — fuel cell works

A hydrogen-fueled polymer electrolyte membrane (PEM) fuel cell uses hydrogen and oxygen to generate electricity by an electrochemical process in which electrons are produced in the anodic hydrogen-oxidation reaction and consumed in the cathodic oxygen-reduction reaction. A single fuel cell consists of the MEA (membrane electrode assembly), the anode and cathode GDLs (gas diffusion layers), and GFCs (gas flow channels).

The MEA is the heart of the fuel cell, which is fabricated by sandwiching the polymer electrolyte membrane (e.g., Nafion) between two electrodes. They are composed of conductive carbon support, catalytic platinum particles, and polymer electrolyte binder. Carbon papers or woven carbon cloths are typically used as GDLs. The GFCs are usually etched out of graphite or metal materials. To achieve the desired voltages, single cells are connected in series to produce a fuel cell stack.

In an operating PEM fuel cell, humidified hydrogen is fed to the anode GFCs whereas humidified air is forced through the cathode GFCs. Hydrogen and oxygen are then transported through the respective GDLs. Electrons produced in the anode are conducted through the electrical load to the cathode where they are consumed; protons from the hydrogen oxidation reaction are transported through the membrane. This movement of electrons is an electrical current that can be used to power an automobile or a home. Water and heat are generated in the cathodic oxygen-reduction reaction. The waste heat generated is mostly attributed to the efficiency loss (more specifically, loss due to various over-potentials) in converting chemical energy to electricity.