Effect Of Hydrophobic Treatment On The Mass Transfer Characteristics Of PEMFC Gas Diffusion Layer

The proton exchange membrane fuel cell has been initially entered into the commercialization stage,but how to further reduce its production cost and improve its performance is still the focus of the current research.Exploring the characteristics of water vapor transmission within the fuel cell and finding an effective water management strategy,and then solving its internal water balance problem is still the key to prolong the cell life and improve the cell performance.Diffusion layer as the core components of fuel cells,bear the gas diffusion and water discharge function,in the fuel cell water management plays a pivotal role.This paper focuses on the management of fuel cell water and the diffusion layer as the research object.The main work includes three parts.The first part uses the hydrophobic agent PTFE to hydrophobize the ordinary hydrophilic diffusion layer to produce stripes with different width and PTFE content hybrid gas diffusion layer;The second part aims to the fuel cell water management,the above-mentioned hybrid diffusion layer is applied to the PEMFC cathode with more water content,and the effects of the hybrid gas diffusion layer both on the fuel cell performance and the cathode water distribution are studied experimentally.In the third part,the water distribution and water content of the diffusion layer were observed by visualization experiments,X-ray scanning,and neutron imaging technique respectively.First,the current research results show that the hydrophobic treatment of the gas diffusion layer does have an effect on the performance of the fuel cell,but most of the research is using hydrophobic agent to treat the whole GDL or to carry out partial hydrophobic treatment with microporous layer.The above two methods can not directly observe the water distribution changes caused by hydrophilicity and hydrophobicity.On the other hand,treating the diffusion layer with microporous layer by hydrophobic agent is easy to cause PTFE particles to plug the micro-pore layer,so that the performance of fuel cell was degraded.In this paper,a set of experimental devices has been designed to make a hybrid diffusion layer which does not contain a microporous layer but with the hydrophilic and hydrophobic areas.Then the hybrid diffusion layer is applied to the cathode of the fuel cell.Secondly,the fuel cell with a hybrid diffusion layer is tested by using the test platform.The results show that under the same working conditions,the fuel cells with a hybrid gas diffusion layer in the cathode exhibit better power generation performance.At the same time,the internal resistance of the cell was measured and the internal resistance of the fuel cell using the hybrid diffusion layer was found to be less.In addition,the fuel cell was in-situ visualized by using X-ray scanning equipment,the results show that the liquid water in the cathode of fuel cell withmixed diffusion layer is no longer evenly distributed,mainly concentrated in hydrophilic area.Finally,under the condition of natural evaporation,the changes of water distribution and water content were studied in order to further study the hybrid diffusion layer at vacuum soaking.The visualization and quantitative analysis of the neutron imaging technique are presented in this paper.The visualization and quantitative analysis by using the neutron imaging technique are presented in this paper.The study found that with the evaporation process,water evaporation in the hydrophobic area is faster,indicating that the same water content,hydrophobic area is more conducive to liquid water discharge;secondly,the results show that the water movement in the porous medium of the fuel cell is still affected by the gravity,which is very important to the study of the fuel cell water management problem.