Studies Of Novel Electrode Structure For Direct Methanol Fuel Cell

A novel double catalytic layer anode and a novel double catalytic layercathode for direct methanol fuel cells (DMFC) was developed and a betterperformance was obtained compared with that of single layer electrode.A double catalytic layer anode is composed of an outer catalyst layer with 45wt% Pt-Ru/C and an inner catalyst layer with Pt-Ru black. In the double catalyticlayer anode, there existed a catalyst concentration gradient and porosity gradient,resulting in good mass transfer, proton and electron conductivity. With the samePt-Ru content, the double catalytic layer anode showed lower methanolpermeation current and higher power density compared with that of single layeranode. Noble metal loadings and Nafion content in double catalytic layers werealso evaluated from the current–voltage curves of single cells.A double catalytic layer cathode is composed of an outer catalyst layer with40 wt% Pt/C and an inner catalyst layer with Pt black. With the purpose ofdeveloping an cathode possessing predominant specialty both in the proton andelectron conductivities, noble metal loadings in double catalytic layers wereoptimized from the current–voltage curves of single cells. To enhance the oxygentransport properties when air is used as the feed stream, pore former such as(NH4)2CO3 was used to increase the porosity in the active layer of the cathode.The results showed that the cell performance was improved consequently.A stability test of a direct methanol fuel cell at a low current density of100mA/cm2 was carried out. In the process of life test, the performance fell downslowly. The voltage loss can be recovered after the long time operation to a greatextent when the cell was restarted, or when membrane electrode assembly waswashed by water or was electro-oxidized. It indicated that the structure of the cellis invariable during the lifetest. The decay in cell performance was not due to theagglomeration of the metal particles. The accumulation of the reactant, variousreaction intermediates or products on the surface of the electrocatalyst or in theactive layer of the electrode might be a major cause for performance decay.