Water Crossover Reduction in DMFC Utilizing Hydrophobic Anode MPL
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Reducing the water crossover from anode to cathode is an important goal for direct methanol fuel cell (DMFC) technology, especially if highly concentrated methanol fuel is to be used. A well-documented way to reduce this water loss to the cathode side is by using a hydrophobic cathode microporous layer (MPL). Recently, however, it has been demonstrated that in addition to a cathode MPL, the use of a hydrophobic anode MPL further reduces the water loss to the cathode. In this work, we use a two-phase transport model that accounts for capillary induced liquid flow in porous media to explain physically how a hydrophobic anode MPL acts to control the net water transport from anode to cathode. Additionally, we perform a case study and show that a thicker, more hydrophobic anode MPL with lower permeability is most effective in controlling the net water transport from anode to cathode.Keywords:
Water Transport
Reducing the water crossover from anode to cathode is an important goal for direct methanol fuel cell (DMFC) technology, especially if highly concentrated methanol fuel is to be used. A well-documented way to reduce this water loss to the cathode side is by using a hydrophobic cathode microporous layer (MPL). Recently, however, it has been demonstrated that in addition to a cathode MPL, the use of a hydrophobic anode MPL further reduces the water loss to the cathode. In this work, we use a two-phase transport model that accounts for capillary induced liquid flow in porous media to explain physically how a hydrophobic anode MPL acts to control the net water transport from anode to cathode. Additionally, we perform a case study and show that a thicker, more hydrophobic anode MPL with lower permeability is most effective in controlling the net water transport from anode to cathode.
Water Transport
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Methanol fuel
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A simple electrochemical impedance spectroscopy (EIS) measurement method to characterize the influence of microstructure on the direct methanol fuel cell (DMFC) is proposed in this paper. The membrane electrode assembly (MEA) with and without the anodic micro porous layer (MPL) are evaluated respectively by EIS. The interaction of anode and cathode are on-line measured during the discharge regime of DMFC. By the separation of anode and cathode EIS, the effects of anodic MPL on the anode and cathode reaction are systematically discussed and analyzed in an operating DMFC. Moreover, the functions of anodic microstructure on the full cell impedance that correspond with the practical cell performance are interpreted reasonably.
Membrane electrode assembly
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Limiting current
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Microscale mass transfer structure in the anode catalyst layer (CL) can significantly alter the performance of a direct methanol fuel cell (DMFC) because it changes both the oxidation rate and crossover flux of methanol. The microscale mass transfer structure can be modified by changing the loading of the pore former (PF). An empirical model was developed for the microstructural design and optimization of anode CL by incorporating the PF into the anode CL. The optimal loading of PF is 100 g/m 2 according to the calculated results. Experimental results confirmed the accuracy of the calculations, and the passive DMFC performs 37% better by incorporating the optimal loading of PF into the anode CL as compared to the conventional anode CL. The validity of the proposed empirical model can also be proven by comparing the calculated polarization results with the previously reported experimental data. © 2012 American Institute of Chemical Engineers AIChE J, 59: 780–786, 2013
Microscale chemistry
Methanol fuel
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The anode catalyst of direct methanol fuel cell(DMFC)is one of the key materials for DMFC.The electrochemical activity of the catalysts affects the performance and cost of the fuel cell.The electro oxidation mechanism of DMFC anode catalyst was introduced;exiting questions and developing direction were discussed,which had excellent referenced value for studying anode catalysts of DMFC.
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The stability of a direct methanol fuel cell (DMFC) was investigated by two single DMFCs with different anode structure membrane electrode assembly (MEA) under discharging at the constant current model for more than 4000 h. One of the MEAs with a catalyst coating membrane (CCM) anode electrode loads 5.5 mg cm–2 anode catalyst of Ru black loading, and the other with a gas diffusion layer coating (GDE) anode electrode loads 5.5 mg cm–2 of 60% PtRu/C. During the stability testing, DMFC with a CCM anode structure with a noble metal loading (5.5 mg cm–2) showed a 22% performance loss and that of GDE anode structure with a lower noble metal loading (3.3 mg cm–2) was 17%. Polarization curves, electrochemical measurements, and EDX (energy dispersive X-ray spectroscopy) were performed to analyze the difference of catalyst activity, internal resistance, and Ru loss between two DMFCs.
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Methanol fuel
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In order to overcome the disadvantages of low mass transport efficiency of oxygen to the cathode and poor performance of passive micro direct methanol fuel cells (DMFC), the structures of the cathode current collector for the passive micro DMFC have been studied. The passive micro DMFC employing the cathode current collector with the planar perforated-plate structure has been fabricated. The effect of the anode methanol concentration and the opening area ratio of the cathode on the performance has been investigated. Owing to the influence of contact resistance and oxygen mass transport, the passive micro DMFC exhibits the optimal performance when opening ratio is 50%. Furthermore, the new parallel channels structure of the cathode current collector has been proposed, and the corresponding passive micro DMFC has also been fabricated by utilizing micro precision processing technology. The test results indicate that the mass transfer of oxygen and performance stability have been improved based on the cathode current collector with the parallel channels structure compared to the conventional planar structure. Moreover, a maximum output power density of 9.7 mW/cm 2 is achieved. The above studies might be helpful for the developing and application of portable micro power systems.
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Methanol fuel
Power density
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