Papers by Keyword: Passive DMFC

Abstract: In this work, a transparent passive DMFC was constructed to investigate the transients in open circuit voltage (OCV) and the cell temperature difference, which changed as a consequence of the methanol crossover phenomenon, including anode temperature difference (ATD), cathode temperature difference (CTD) and methanol solution temperature difference (MTD). Experiments were carried out in a passive DMFC with an active membrane area of 9 cm2, at ambient temperature and pressure. Results showed that the OCV of the passive DMFC became relatively stable as the cell temperature difference rose to a relatively stable value about 30 min later. At the middle and high current densities (>2.21 mA cm^-2), the performance increased continuously with increasing the waiting time, but became stable when the waiting time was longer than 30 min. The experimental results indicated that the performance of the passive DMFC could be more objectively characterized by collecting polarization data simultaneously when the cell temperature rises to a relatively stable value. Without the temperature measuring equipment, a waiting time about 30 min would be a good choice for collecting polarization data.

Abstract: In this work, a transparent passive DMFC was constructed to investigate the CO₂ bubble behavior in perforated current-collector (PECC) and parallel current-collector (PACC) by using a digital camera. Experiments were carried out in a passive DMFC with active membrane area of 9 cm², working at ambient temperature and pressure. Results showed that small discrete bubbles appeared in PECC at low current densities; while the PECC was predominated by big bubbles at high current densities, which led to deterioration of methanol mass transfer. On the contrary, the PACC was more efficient to remove CO₂ bubbles than the PECC did. Therefore, it gained a better performance at high current densities.

Abstract: In this work, the effect of the current-collector structure on the performance of a passive direct methanol fuel cell (DMFC) was investigated. Parallel current-collector (PACC) and other two kinds of perforated current collectors (PECC) were designed, fabricated and tested. The studies were conducted in a passive DMFC with active membrane area of 9 cm², working at ambient temperature and pressure. Two kinds of methanol solution of 2 M and 4 M were used. Results showed that the PACC as anode current-collector has a positive effect on cell voltage and power. For the cathode current-collector structure, the methanol concentration of 2 M for PECC-2 (higher open ratio 50.27 %) increased performance of DMFC. But the methanol concentration of 4 M led to an enhancement of fuel cell performance that used PACC or PECC-2 as cathode current-collector.

Abstract: The supply of water to the anode from the cathode through the electrolyte membrane is a critical factor for the operation of vapor feed DMFC at high methanol concentrations. A comparative study in a passive vapor feed DMFC employing a PCP on the anode surface had been carried out with and without a hydrophobic cathode filter. Compact and a noncompact cells were fabricated and used. The noncompact cell could be operated with high methanol concentrations of even 100 wt%, while the compact one could not be operated with 90 wt% methanol. This was related to the deficiency of water at the anode surface in the compact cell design, where heat dissipation was not enhanced. For the supply of water to the anode surface, the employment of a hydrophobic filter on the cathode surface was necessary, especially for the compact cell.

Abstract: In this study, to control the methanol crossover occurring in a direct methanol fuel cell, DMFC, a perforated metal sheet of which the pore diameter and the porosity (open ratio) were regularly controlled was used in a passive DMFC, and the influence of the open ratio and the pore diameter on the power generation characteristics, and also on the methanol crossover of the passive DMFC were investigated on the basis of the power generation experiment at several different methanol concentrations. It was found that the pore diameter of the metal sheet did not affect the power generation characteristics and the methanol crossover in this experiment. On the other hand, the open ratio of the metal sheet significantly influenced the power generation characteristics, and the methanol transport was increased by decreasing open ratio of the metal sheets. It was found that a high concentration of methanol can be used at low open ratios below 3%. However, when the open ratio was higher than 3%, it hardly affected the current density and the mass transport. This means that the open ratio is not an important factor for the methanol transport or the electrode reaction in the range over 3%.