Proton-exchange fuel cell Guide, Meaning , Facts, Information and Description
Proton-exchange fuel cells, also known as Polymer Electrolyte (Membrane) Fuel Cells ("PEM" or "PEMFC") are low temperature fuel cells which are being developed for transport applications as well as for stationary applications. In this fuel cell, hydrogen is split at the membrane surface in protons, that travel through the membrane, and electrons, that travel through our external electric circuit, and provide electric power. The hydrogen ions travel through the water that is entrained in the membrane to the other side, where they are combined with oxygen to form water.Unfortunately, while the splitting of the hydrogen molecule is relatively easy, splitting the stronger oxygen molecule is more difficult, and this causes significant losses. Another significant source of losses is the electrical resistance of the membrane itself, which is therefore made as thin as possible.
The PEMFC is a prime candidate for vehicle and other mobile applications of all sizes down to mobile phones, because of its compactness. However, the water-entraining membrane is crucial to performance: too much water will flood the membrane, too little will dry it; in both cases, power output will drop. Water management is a very difficult subject in PEM systems. Furthermore, the platinum catalyst on the membrane is easily poisoned by carbon monoxide.
PEM systems that use reformed methanol were proposed, as in Daimler Chrysler Necar 5; reforming methanol, i.e. making it react to obtain hydrogen, is however a very complicated process, that requires also purification from the carbon monoxide the reaction produces. A platinum-ruthenium catalyst is necessary as some carbon monoxide will unavoidably reach the membrane. The level should not exceed 10 parts per million. Furthermore, the start-up times of such a reformer reactor are of about half an hour. Efficiencies of PEMs are in the range of 40-50%.
Manufacturers of PEMs include Dupont, 3M Corporation, and Ballard Power Systems.
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