FUEL CELL TODAY
Opening doors to fuel cell commercialisation
Proton Exchange Membrane (PEM) Fuel Cells
Gemma Crawley, Fuel Cell Today – March 2006 Introduction This is the first of six articles designed to focus on each of the fuel cell technology types in turn. The reviews will provide a brief overview of the technical aspects of each system, the developmental milestones achieved, an estimate of the number of units currently in operation and a review of the key companies involved in the development, manufacture and commercialisation of each fuel cell type. Looking forward, the reports will also aim to provide details of any goals set by fuel cell companies for each system. The articles start by looking at PEMFC technology and will eventually cover SOFC, DMFC, AFC, MCFC, and PAFC over the course of the next year.
Technological Overview The Proton Exchange Membrane (PEM) fuel cell uses a thin, permeable polymeric membrane as the electrolyte. The membrane is very small and light and in order to catalyse the reaction, platinum electrodes are used on either side of the membrane. Within the PEM fuel cell unit, hydrogen molecules are supplied at the anode and split in to hydrogen protons and electrons. The protons pass across the polymeric membrane to the cathode while the electrons are pushed round an external circuit in order to produce electricity. Oxygen (in the form of air) is supplied to the cathode and combines with the hydrogen ions to produce water.
In-depth PEM Schematic (Courtesy of Johnson Matthey Fuel Cells)
Compared to other electrolytes (which require temperatures up to 1,0000C to operate effectively) PEMFCs operate at very low temperatures of about 800C allowing rapid start-up. The efficiency of a PEM unit usually reaches between 40 to 60 per cent and the output of the system can be varied to meet shifting demand patterns. Typical electric power is up to 250 kW. In addition, PEM fuel cells are often compact...