Unfortunately however, splitting the oxygen molecule is more difficult, and this causes significant electric losses. Splitting of the hydrogen molecule is relatively easy by using a platinum catalyst. Finally, the membrane must be resistant to the reducing environment at the cathode as well as the harsh oxidative environment at the anode. The membrane must also not allow either gas to pass to the other side of the cell, a problem known as gas crossover. To function, the membrane must conduct hydrogen ions (protons) but not electrons as this would in effect ' short circuit' the fuel cell. The potentials in each case are given with respect to the standard hydrogen electrode. The reversible reaction is expressed in the equation and shows the reincorporation of the hydrogen protons and electrons together with the oxygen molecule and the formation of one water molecule. This oxidation half-cell reaction or hydrogen oxidation reaction (HOR) is represented by:

At the anode side it is catalytically split into protons and electrons. Operating temperatures above 100 ☌ are desired so the water byproduct becomes steam and water management becomes less critical in cell design.Ī proton exchange membrane fuel cell transforms the chemical energy liberated during the electrochemical reaction of hydrogen and oxygen to electrical energy, as opposed to the direct combustion of hydrogen and oxygen gases to produce thermal energy.Ī stream of hydrogen is delivered to the anode side of the MEA.

Importantly, the membrane must not be electrically conductive so the half reactions do not mix. The pivotal part of the cell is the triple phase boundary (TPB) where the electrolyte, catalyst, and reactants mix and thus where the cell reactions actually occur. An ink of catalyst, carbon, and electrode are sprayed or painted onto the solid electrolyte and carbon paper is hot pressed on either side to protect the inside of the cell and also act as electrodes. PEMFCs are built out of membrane electrode assemblies (MEA) which include the electrodes, electrolyte, catalyst, and gas diffusion layers.

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