MASS TRANSPORT AND METHANOL CROSSOVER ASPECTS OF MATERIALS FOR DIRECT METHANOL FUEL CELLS

摘要

A study of a small scale Liquid Feed Direct Methanol Fuel Cell (LFDMFC), based on solid polymer electrolyte membrane, is reported. The performance of a variety of flow cell designs based on a parallel flow channel, a spot design of flow bed and a series of stainless steel mesh are compared. The study was supported from a flow visualisation study analysing the effect of flow bed design on cell gas management and performance. The performance of the direct methanol fuel cell (DMFC) using membrane electrode assemblies (MEA) based on radiation grafted proton exchange membranes is also reported. The performance of the DMFC, with these low cost membranes, is as good as or superior to that of cells based on Nafion~(~R) under identical operating conditions. The use of stainless steel as material for flow beds is shown to be a viable alternative to the use of graphite and alternative structures using mesh can enhance performance. An improvement in the performance of the direct methanol fuel cell has also been achieved by performing a dynamic feeding strategy of the methanol feed to the cell. The membrane electrode assemblies used in the work were based on Nafion~(~R) bonded carbon supported catalyst; platinum/ruthenium (2 mg cm~(-2)) for the anode and platinum (1 mg cm~(-2)) for the cathode. All experiments were performed in cells with a cross section area of 9 cm~2. The cells were either made with either graphite, stainless steel or stainless steel mesh flow beds. The membranes used in the MEA were either Nafion~R 117 or radiation grafted ETFE-styrene copolymer.