Molecular Simulation Of Proton Transfer In HT-PEM Fuel Cell And Experiments On Its Performance

As PEM fuel cell can transform chemical energy stored in fuel into electric energy directly,it has higher energy conversion efficiency.Meanwhile,due to its advantages of low pollution,low noise,flexibility,it is widely used in the car industry,communications,power stations and other fields.As working temperature of high temperature proton exchange membrane(HT-PEM)fuel cell can reach 120-200?,it has lower demands for water and heat managements.Therefore,it has a wide application prospect.Core component of HT-PEM fuel cell is HT-PEM,in which proton exchange plays an important role in fuel cell performance.In this thesis,the author referred to a lot of related literatures about fuel cell at home and abroad,summarized the development history,classification,characteristics and applications of fuel cell.This thesis introduced key components of the PEM fuel cell,and mainly expounded related theory of thermodynamics and dynamics.In addition,the efficiency and working principle of the fuel cell were recounted in the thesis.On the basis of theoretical researches,a fuel cell test system 'was established.At the same time,the structure,functions,testing technology and operation process of the fuel cell test device were discussed.In the experiment,the ab-PBI membrane HT-PEM fuel cell monomer was assembled.By the fuel cell test device,the volt-ampere characteristic curve and ac impedance spectra were achieved.The influence of cell temperature,CO2 content,reaction gas flow and other operating parameters on the performance of HT-PEM fuel cell were tested.According to the ac impedance spectroscopy,the equivalent elements of fuel cell were obtained by the equivalent circuit analysis.Temperature and CO2 content in fuel on the the ohmic impedance and faraday impedance were analyzed.The results showed that:CO2 in fuel could significantly reduce cell current density,increase the faraday impedance of high temperature proton exchange membrane fuel cell,reduce electrochemical reaction rate of the anode of fuel cell;when CO2 content in fuel increased,more and more active positions of catalyst were occupied with reaction product derived from CO2 and Pt,which would lead to fuel cell performance degradation;the rise of cell temperature could improve Pt catalyst activity,accelerate reaction product derived from CO2 and Pt on catalyst surface,quicken electrochemical reaction rate of electrodes and enhance HT-PEM fuel cell performance.In the simulation,based on the basic theories of molecular dynamics,NVT ensemble was used to establish and optimize molecular model of proton transfer in ab-PBI membrane doped with phosphoric acid by coupling kinetic energy,potential energy,radial distribution function and diffusion coefficient equation.Electric conductivity,radial distribution function,diffusion coefficient,displacement,structure factors and other parameters were obtained.Temperature,external electric intensity and H3PO4 doping level on the proton transfer in ab-PBI membrane and diffusion were analyzed.The results showed that:the main proton transfer form in ab-PBI membrane was combining and separating H2PO4-,proton transfer in ab-PBI membrane could be easy by raising temperature,H3PO4 doping level and electric intensity.