Search

The power density of a direct methanol fuel cell (DMFC) stack as a function of temperature, methanol concentration, oxygen flow rate, and methanol flow rate was studied using a response surface methodology (RSM) to maximize the power density. The operating variables investigated experimentally include temperature (50-75 °C), methanol concentration (0.5-2 M), methanol flow rate (15-30 ml min-1), and oxygen flow rate (900-1800 ml min-1). A new design of the central composite design (CCD) for a wide range of operating variables that optimize the power density was obtained using a quadratic model. The optimum conditions that yield the highest maximum power density of 86.45 mW cm-2 were provided using 3-cell stack at a fuel cell temperature of 75 °C with a methanol flow rate of 30 ml min-1, a methanol concentration of 0.5 M, and an oxygen flow rate of 1800 ml min-1. Results showed that the power density of DMFC increased with an increase in the temperature and methanol flow rate. The experimental data were in good agreement with the model predictions, demonstrating that the regression model was useful in optimizing maximum power density from the independent operating variables of the fuel cell stack.

A bipolar passive direct methanol fuel cell (DMFC) stack for portable applications is designed, fabricated and tested. Stainless steel sheet is chosen to fabricate the current collectors by using the traditional wire cutting and laser beam cutting techniques. A 3.5 μm Au layer is deposited on the current collectors using electroplating method to prevent electrochemical corrosion. A novel design of the current collectors is proposed, which makes internal and external electrical connections be seamlessly integrated so that the resistance loss can be reduced. The maximum power density of the passive stack is 18.7 mW cm −2 at 3 M methanol concentration. The effect of the passive DMFC stack placement mode is studied. The results indicate that the passive DMFC stack in mode B (vertical cathode air channels) exhibits better and more stable performance than its counterpart in mode A (parallel cathode air channels) in discharging of high currents. Finally, the bipolar passive DMFC stack proves its good performance in powering the experimental fan in 100 days while performance deterioration behaviour is also detected. [ABSTRACT FROM AUTHOR]

A “4-cell” modular passive DMFC (direct methanol fuel cell) stack, which can be freely combined and applied to various electronic devices, is designed, fabricated and tested. Two PCB (printed circuit board) based accessories are designed and fabricated for electrically connecting and mechanically assembling the “4-cell” modules. The maximum power density of the “4-cell” module is 27 mW cm −2 at 5 M methanol concentration. The steady-state performances of the modular stacks with different numbers of modules are tested. The extra power loss of the multiple module stacks due to inter-module electrical connections is predicted by mathematical fitting method. The fitting results indicate that the efficiencies of the multiple module stacks are all above 90% up to 10 modules. The dynamic performances of the modular stacks are also investigated for portable applications. The results show that the modular stacks exhibit good responsiveness and reproducibility at high loading current (>100 mA). Finally, the modular stacks are successfully applied to drive the experimental fan and charge the mobile phone. [ABSTRACT FROM AUTHOR]

A design configuration is presented for integrated series connection of micro direct methanol fuel cells in a planar array. The series path is oriented in a “flip-flop” configuration with electrical interconnections made by thin-film metal layers that coat the flow channels etched on the silicon substrate, presenting the unique advantage of small connection space and low connecting resistance. To overcome the disadvantage of “flip-flop” interconnection that reactant chambers must alternate between fuel and oxidant, an innovative reactant feeding configuration was designed, providing a uniform reactant feeder and reliable hermetic seals for a multitude of unit cavities per cell. The MEMS fabrication process was adopted to fabricate the silicon plates. The elements of reactant feeder were mechanically carved from PMMA and were assembled with the cells by agglutinant. Application of μDMFC stacks as portable power sources were demonstrated using small electric devices powered by this stack. [ABSTRACT FROM AUTHOR]

Abstract: Rational thermal management is essential for the steady and safe operation of direct methanol fuel cell (DMFC) stacks, even though experimental measurements of the thermal distribution inside DMFC stacks are difficult. Therefore, a double-phase mathematical model was developed for the thermal investigation of DMFC stacks and to further build guidelines for their manufacture and operation. The effects of various configurational and operational parameters on the thermal distribution of the stacks were systemically studied. Current density, the number of single cells in the stack, the fuel concentration, the reactant flow rates, and some configurational parameters of the bipolar plate were optimized using the model to obtain a relatively uniform temperature distribution within the stack. The current density can strongly influence the thermal properties of large-scale DMFC stacks. As an example, extremely uniform temperature distribution was obtained for a 10-cell stack fueled with low-concentration methanol. [Copyright &y& Elsevier]

Abstract: In this paper, a 6-cells direct methanol fuel cell (DMFC) stack with the volume of only 13.25 cm3 and the weight of 24.075 g is designed, fabricated and tested. First, the material characterization of the Au-coated Al current collector is investigated to exhibit superior characteristics in electric conductivity, weight and electrochemical corrosion resistance. And then the steady-state performance of the stack is tested, the maximum power output of the stack reaches 568.4 mW at room temperature. The dynamic performance and durability of the stack are also investigated in consideration of practical conditions. Results indicate that stack performance represents good responding and reproducible ability. Finally, the DMFC stack proves its good performance in powering experimental fan two times in 30 days successfully. [Copyright &y& Elsevier]