Experimental Study Of Internal Transport Phenomena In A Direct Methanol Fuel Cell And Designing And Testing A Passive Stack

Because of its simple, high energy density and fuel easy storage, direct methanol fuel cell was suited for portable devices such as computer or mobile phone compared to other fuel cell system. That is to say, DMFC has a broad application prospects in the field of micro and small mobile power.From the perspective of thermal physics, experimental study on the direct methanol fuel cell has been carried out by changing the operating parameters of cell, such as the anode methanol flow rate, fuel cell temperature, cathode back pressure and methanol concentration. The results showed that: the performance of the fuel cell increased with the increasing anode methanol flow rate first and then decreased. There is an optimal value of the methanol flow rate to make the fuel cell performance best. The fuel cell performance increased with temperature. The excessive air preheating temperature made the cathode dehydration, thus reducing the fuel cell performance. There is an optimal concentration of methanol to make the best fuel cell performance best. In addition, improving the cathode back-pressure air can inhibit the negative impact of methanol permeation.The relationship between operating conditions and the gas-liquid two-phase flow of an anode multi-channel serpentine flow has been studied by using visualization method. The results show that: The visualization study found that a continuous bubble generation yielded on some specific points, while in others there is no point bubbles observed. The phenomenon of the bubble's appearance, grown up and separation will always occur at each point. At low current density conditions, CO2 bubbles generated by the electrochemical action dissolved in methanol solution, so that the bubble flow can't be observed in the channel. With the current density increased, the gradual emergence of bubbles within the flow channel flow appeared, and gradually formed a column in the flow channel, blocked channel at the exit. When the methanol flow rate is very small, CO2 bubbles show long plunger-like. With the methanol flow rate increased, the short length of the plunger block foam into foam and gradually disappeared. At the same current density, increasing the battery temperature, on the one hand, it reduced the CO2 gas solubility in solution, on the other hand, increased the molar volume of CO2 gas and reduced the surface tension of the bubble, so that the bubble more likely to gather to form long plunger-like fluid in the flow channel, which severely reduced the contact area between the methanol solution and the effective diffusion layer, thereby enhanced the concentration polarization of the battery, reduced battery performance.A bipolar-plate passive direct methanol fuel cell stack was designed and produced which consists of 6 cells with 2.5×2.5cm~2 active area each. The open circuit voltage, V-I curve of the fuel cell stack and 100mA continuous discharge have been tested under different methanol concentration. In this study, the optimum performance is achieved by using methanol at a concentration of 4M. The maximum current density is 4.6mA/cm~2, the highest power density is 6.13mW/cm~2 and the whole cell stack power is 0.23W.