Fuel Cells - Green Power - Martin's Marine Engineering Page

The FlowFields / CurrentCollectorse -AnodecurrentcollectorPhotographs of stainless steelflow fields/current collectorsMicrograph of a milled carbon-fibercomposite flow-field. Height, widthand spacing of channels = 0.8mm(0.032 inch)Hydrogenflow fieldAir (oxygen)flow fieldWater and airCathodecurrentcollectore -Pressed against the outer surface of each backinglayer is a piece of hardware, called a plate, whichoften serves the dual role of flow field and currentcollector. In a single fuel cell, these two plates are thelast of the components making up the cell. The platesare made of a light-weight, strong, gas-impermeable,electron-conducting material; graphite or metals arecommonly used although composite plates are nowbeing developed.The first task served by each plate is to provide a gas“flow field.” The side of the plate next to the backinglayer contains channels machined into the plate. Thechannels are used to carry the reactant gas from thepoint at which it enters the fuel cell to the point atwhich the gas exits. The pattern of the flow field in theplate as well as the width and depth of the channels havea large impact on the effectiveness of the distribution ofthe reactant gases evenly across the active area of themembrane/electrode assembly. Flow field design alsoaffects water supply to the membrane and water removalfrom the cathode.The second purpose served by each plate is that ofcurrent collector. Electrons produced by the oxidationof hydrogen must be conducted through the anode,through the backing layer and through the plate beforethey can exit the cell, travel through an external circuitand re-enter the cell at the cathode plate.With the addition of the flow fields and current collectors,the polymer electrolyte membrane fuel cell is nowcomplete. Only a load-containing external circuit, suchas an electric motor, is required for electric current toflow, the power having been generated by passinghydrogen and air on either side of what looks like apiece of food wrap painted black.AnodebackingHydrogenoutletMEACathodebackingA single polymer electrolyte membrane fuel cell.This document, and more, is available for download at Martin's Marine Engineering Page - www.dieselduck.net