Studies On Structure And Performance Of Passive Direct Methanol Fuel Cells

Passive direct methanol fuel cell (DMFC) has potential applications in powering portable electronic devices such as mobile phone and PDA because of its simple design. Improvement of MEA performance, simplification of stack structure and realization of neat methanol feed, which can improve the system energy density effectively, are important for miniaturization of the passive DMFCs.In this dissertation, the performance of passive DMFC was improved to 20mW/cm2 by employing high metal loading catalyst and optimizing preparation method of MEA. Sintered stainless steel fiber felt was used as the anode backing layer in passive DMFC. It was found that the performance was further improved to 24mW/cm2 due to its hydrophilicity and good electric conductivity.Printed-circuit board (PCB) was adopted as the monopolar plate in passive DMFC and the strip structure was improved. Thus current collection, series connection and clamping could be realized on one plate, which simplified the stack structure to a certain extent. Two passive DMFC stacks with 12 cells and 40 cells were designed and fabricated to power a mobile phone and a laptop computer respectively. A replenishment device which could realize fuel self-circulation was designed and prepared by employing the difference of solution density caused by CO2.The passive DMFC feed with neat methanol was realized successfully by employing pervaporation membrane which was used to control the methanoldiffusion to the anode. The effects of carbon loadings of the cathode gas diffusion layers and the thickness of Nafion membrane were investigated on the performance and stability of neat methanol feed passive DMFC. Simultaneously, Water losses and methanol efficiencies were quantitatively calculated. The results indicated that the water loss was reduced from 3.31molH2O/molCH3OH to 2.28molH2O/CH3OH, Faradic efficiency and energy conversion efficiency were improved from 32.6% and 9.3% to 36.3% and 14.7% respectively by increasing carbon loadings from 4mg/cm2 to 8mg/cm2. However the water loss, Faradic efficiency and energy conversion efficiency were improved from 2.28molH2O/molCH3OH , 36.3% and 14.7% to 2.86 molH2O/molCH3OH , 58.4% and 17.8% respectively by increasing the thickness of Nafion membrane from 87.5μm to 175μm .