Direct Methanol Fuel Cell Membrane Electrode Electrochemical And Ui Performance

Direct methanol fuel cell (DMFC) is viewed as a promising power sources for various mobile and portable devices due to its advantages of environment friendly, high-energy efficiency, simplicity and easy transportation and storage of the fuel. The cell performance largely depends on the properties of membrane electrode assembly (MEA) which is essential part of DMFC. The analysis of dynamic behavior and interior mechanism of MEA has great significance in optimizing the electrode structure and operating parameters, which have tremendous influence to improve performance and stability of DMFC.The electrochemical impedance spectrum (EIS) of DMFC in working states was investigated. The effect of discharging current and working temperature to the system resistance, the charge transfer resistance of electrochemical reaction, low-inductance and low-frequency resistance had been analysed through the equivalent circuit. The internal dynamic mechanism of DMFC was investigated through the constant phase element (CPE) Q, and the result showed that there existed a transition process from ideal capacitance to the charge transfer with the discharging current increasing.The performance of discharge, crossover and proton conduction of Nafion membrane had been studied by current-voltage polarization curve and AC impedance spectroscopy. The thickness of Nafion membrane, the preconditioning process of anode gas diffusion layer (GDL), the types and the loading composition of carbons were optimized. The result showed that the performance of MEA was affected by the proton conductivity, the methanol permeation rate, the transport of CO₂ and H₂O. Nafion 117 membrane was found to be the ideal electrolysis for the low methanol permeation rate, and the performance of BP2000 was suitable carbon for anode GDL. The optimized loading compositions of carbon and PTFE in the supporting layer were reported to be lmg/cm² and 5wt%, respectively. These values were rationalized on the basis of the transport of methanol and CO₂ and proton conductivity.The effects of cell temperature, methanol concentration, anode flow rate, and air flow rate on the performances of the DMFC had been studied. The results showed that all operating parameters had significant effects on the DMFC cell performances. The study revealed that the detrimental effects of methanol crossover can be alleviated by decreasing the methanol concentration. Optimized conditions were 1mol/L methanol, and flow rate at 4mL/min. The cell performance had been improved with increasing the flow rate of cathode air. For improving the electrochemical reaction kinetics and reducing the resistance of cell, the cell performance had been remarkably improved with the temperature increasing. The stability of membrane electrode was monitored by the AC impedance spectroscopy. The results showed that the cell performance had been improved due to the electrode activised at initial discharging. But then, the cell showed a rapid decay in performance after continuous operation. The EIS results showed that the ohm resistance increasing with discharging time increasing was the principal reasons which lead to the degradation of the single cell during its long-term operation.