Catalyst

All electrochemical reactions in a fuel cell consist of two separate reactions: an oxidation half-reaction at the anode and a reduction half-reaction at the cathode. Normally, the two half-reactions would occur very slowly at the low operating temperature of the PEM fuel cell. So each of the electrodes is coated on one side with a catalyst layer that speeds up the reaction of oxygen and hydrogen. It is usually made of platinum powder very thinly coated onto carbon paper or cloth.

The catalyst is rough and porous so that the maximum surface area of the platinum can be exposed to the hydrogen or oxygen. The platinum-coated side of the catalyst faces the PEM. Platinum-group metals are critical to catalyzing reactions in the fuel cell, but they are very expensive. DOE's goal is to reduce the use of platinum in fuel cell cathodes by at least a factor of 20 or eliminate it altogether to decrease the cost of fuel cells to consumers.