Molecular Simulation Of The Proton Transfer In PEM And Performance Experiments Of PEM Fuel Cell

By the PEM fuel cell,the chemical energy can be directly converted into electricity.Therefore,its efficiency is much higher than traditional power systems.At the same time,due to its advantages of electrochemical product without pollution,high power density,easy to carry,it is widely used in aerospace,the car industry,communications,submarines,power stations and other fields.However,in the working process of proton exchange membrane fuel cell,proton transfer needs water.For this reason,water management of proton exchange membrane fuel cell directly has very important impact on the fuel cell performance.During the working process of the proton exchange membrane fuel cell,with the change of the cell temperature and humidification temperature,the water content of proton exchange membrane will change,which can affect the cell performance and proton transfer.In this paper,refered to a lot of related literatures about fuel cell at home and abroad,summarized the development history,classification and characteristics of fuel cell and its application.This paper introduced the working principle of the PEM fuel cell,key components,and mainly expounded related theory of thermodynamics and dynamics.In addition,the efficiency of the fuel cell and the calculation of the reaction gas flow were introduced in the paper.According to research content,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 introduced.In the experiment,the PEM fuel cell flow field plate was the processed and the PEM fuel cell monomer was assembled.By the fuel cell test device,the influence of cell temperature,humidification temperature and reaction gas flow and other operating parameters on the performance of PEM fuel cell was tested.The volt-ampere characteristic curve and ac impedance spectra were achieved.According to the ac impedance spectroscopy,analyzed the equivalent impedance of the PEM fuel cell,the law of the influence of the cell temperature,humidification temperature and gas flow and other parameters on the the ohmic impedance and faraday impedance was acquired.The results show that:when the humidification temperature is lower than the celltemperature,elevating the humidification temperature will make the moisture content of proton exchange membrane increase,which make the cell performance improved;when the humidification temperature is higher than the cell temperature,elevating humidification temperature,too much water will remain in the fuel cell,which leads the cell performance to decline.Proton transfer impedance in the proton exchange membrane has important influence on the performance of the PEM fuel cell.In this paper,based on the basic theory of molecular mechanics and molecular dynamics,a three dimensional periodic cell model was established,which contains Nafion117 chain,water molecules and hydronium ion.In the entire process of model building and calculation,COMPASS force field was applied,the truncation radius method and the Ewald method were used to calculate the molecular inter-atomic forces.In the process of molecular dynamics calculation,Verlet algorithm was used to solve the Newton's equations of motion,the Andersen hot bath method was used to control the temperature.According to the result of model calculation,analyzed the radial distribution function and diffusion coefficient.In this paper,the effects of temperature,water content,the electric field intensity on the microscopic structure of the proton exchange membrane and proton transfer was studied.Simulation results show that:in the membrane,hydrated proton H5O2+ is mainly structure during the process of proton transfer;in the process of proton transfer,the break and formation of hydrogen bonds between water molecules occur;when the temperature,the water content and the electric field intensity increased,hydrated proton transfer in the membrane Nafion117 becomes easier.