Investigation On Water Diffusion Of Composite Proton Exchange Membrane In Fuel Cell

Fuel cell is a device converting the chemical energy of the fuel (like H2) to electrical energy through electrochemical reaction. The characteristics of fast start-up, high efficiency and low emission make it the promising candidate for the mobile and stationary power.Proton exchange membrane is the key component of PEMFC. It is believed that the fast degradation of the proton exchange membrane would lead to the early failure of the PEMFC. The proton conducts in the membrane by H2O/H+form the anode to negative, and the water is the carrier of the proton in the membrane. In the same kind of polymer membrane, the one with higher water content has quicker speed of proton, and higher membrane conductivity. Maintenance proton exchange membrane has sufficient water content is extremely important for PEMFC. Replaced the pure Nafion membrane with Nafion/PTFE composite membranes is very favorable to obtain a highly stable and physical durable proton exchange membrane. So the investigation of the water management in composite membrane is very important.In present, the study of water management research mainly adopts simulation based on model, the present paper has analyzed the water diffusion in membrane according to the Springer fuel cell model. Then the diffusion fluxes of water across the membranes were measured through steady state permeation, as a function of the dry nitrogen flow rate and temperature. The conclusions have been drawn as followed:(1)In this paper, the diffusion coefficient of water in composite membrane (Nafion/PTFE) was calculated based on the mass transfer model of porous media. During the study, we use the fractal model to calculate and the data was based on the diffusion coefficient of Nafion211.(2)The diffusion fluxes of water across the membranes were measured through steady state permeation, as a function of the dry nitrogen flow rate and temperature. The water diffusion coefficient of composite membrane is calculated according to the experimental data. Compared with the theory data, the experiment data vary by two orders of magnitude, so the springer model also exist certain error. (3)We discussed the possibility of the anode does not increase the wet. The performance of the single battery does not increase so much because the anode increases the humidity when the cathode100%humidification. The phenomenon is more obvious in the thin film, namely when the thin membrane to a certain extent, the diffusion of water through the proton exchange membrane is enough. Then the anode humidification does not need any more.