Development and operation analysis of proton conducting electrolyte for direct methanol fuel cell

Abstract

In this study, the IV polarization at the steady state and the dynamic behavior of DMFC and the effect of operating parameter were interpreted by a pseudo-RHE (reversible hydrogen electrode) and the cell potential could be separated into the anode and cathode potentials. According to the diagnosis of IV polarization, the second and subsequent slopes in the anode Tafel plot showed the sharp increase when the mass transfer resistance of methanol to active site was dominant. For the cathode polarization, the deviation of Tafel slope of cathode from that of PEMFC at higher temperature above the methanol boiling point and with a high concentration of methanol solution means the effect of electro-osmotic $O_2$ affected the anode performance, especially the open circuit potential of the anode, by mixed potential and incomplete oxidation. From the dynamic response of each electrode, their mass transfer and charging of double layer characteristics was investigated in detail. The anode and cathode of liquid-fed DMFC showed the slower response than vapor-fed DMFC or PEMFC, which was affected by the mass and heat transfer and methanol oxidation, respectively. The anode and cathode showed the peak overpotential and relaxed to the steady state mainly because of the cleaning of catalyst surface and the alleviation of mixed potential, respectively. The changes of Tafel slope can be correlated with the changes of dynamic response. In addition, the interaction of cathode and anode also existed in the dynamic response. According to this analysis, it is confirmed again that the methanol crossover was the significant key factor to determine the performance of DMFC. In order to solve this problem, this study focused on the polymer electrolyte membranes. At first, using TEOS and organic silane agent, we could prepare Nafion/ORMOSIL hybrid membranes in order to reduce the methanol crossover of NafionTM and to modulate the methanol properties with the type and amount of ORMOSIL. As ...