The Role of Carbon Dioxide Layer Prepared by a Porous Carbon Plate in a Passive DMFC as a Mass Transport Barrier

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The effect of CO2 discharge from the CO2 gas layer formed between the anode surface and a porous carbon plate, PCP, was investigated to in order to clarify the role of the PCP and the CO2 gas layer on the performance and mass transfer in a passive DMFC using different types of PCPs with different pore structures. The relation between the gas discharge through or not through the PCP and the DMFC performance as well as the effect of the gas pressure in the layer were investigated using PCPs with a small pore size, i.e., 1 μm average diameter, PCPS, and that with a large pore size, a 42 μm average diameter, PCPY. The formation of the CO2 gas layer was essential for significantly limiting the methanol transport to the anode surface where the gaseous methanol diluted in the CO2 gas contacted with it. The resistance of the methanol transport across the PCP was affected by the pore structure of the PCP, i.e., the pore size and the bubble point pressure. The discharging of bubbles through the large pore size PCP of 42 μm accelerated the methanol transport through the PCP in contrast to the small diameter PCP.