Platinum nanoparticles are widely used as the cathode material in hydrogen/oxygen fuel cells (like the polymer electrolyte fuel cell - PEFC) due to their efficiency in catalyzing the oxygen reduction reaction (ORR), the process that breaks the bonds of the oxygen molecules. Although platinum is still considered the state-of-the-art ORR catalyst, it does not exhibit good stability. Typically, catalyst performance degradation begins as soon as the catalyst is introduced into a fuel cell and continues until it is no longer active.
Platinum can lose its effectiveness either by clumping together or by becoming 'poisoned' by carbon monoxide, requiring high hydrogen purity or higher catalyst densities for the fuel cell to stay effective. This, together with the high cost of platinum is seen as one of the major showstoppers to producing mass market fuel cells for commercial applications.
Researchers have been searching for viable non-precious metal ORR catalysts - an effort that is by no means new but dates back to 1960s, and several different classes of non-precious metal catalysts have been investigated over the years.