Impurity Detection And Protonation Confirmation Of Proton Exchange Membrane With The Methodology Of Electrochemical Impedance Spectrum

Proton exchange membrane fuel cell (PEMFC) is a device converting the chemical energy of the fuel to electrical energy with the characteristics of low pollution,high energy efficiency of energy conversion, free from Carno circulatory restriction and fast start-up.The advantages of PEMFC make it very important to develop this new energy especially at the times of traditional fossil energy running out.Various of impurities may be pulse into during the operation in complex ernviroment and preparation of the parts of PEMFC.It has been studied that impurities such as Ni2+,F-,CO do harm to PEMFC,results in degradation of its performance.For instance, Ni2+ can reduce the conductivity of Nafion membrane,and CO leads to Pt catalyst poisoning,which reduces its catalytic ability.Impurities such as ions and gas have been widely studied,but there is not enough research into the effect of organic impurity,nonionic surfactant Triton X100 for example,on the performance of Nafion membrane.Furthermore,the impurities on the performace of Nafion/PTFE composite membrane,and the method of getting rid of impurities is still lack of attention.In this paper the relation between impurity (Na+,Triton X100) and conductivity of Nafion membrane or Nafion/PTFE composite membrane have been studied by EIS(Electrochemical impedance spectroscopy).Methods of getting rid of impurities in Nafion/PTFE composite membrane have also been introduced,which improves the conductivity of adulterated Nafion/PTFE composite membrane.It draws the conclusion as follows:(1) By mixing Na+ and Triton X100 in Nafion resin solution,a series of Nafion membranes contained different impurity content have been prepared.Doping of Na+and Triton X100 obviously reduces conductivities of Nafion membrane.At the increase of amout of doping,conductivities decrease more linearly.By comparison dpoing equal amout og Na+ and Triton X100,the conductivity of Nafion contained Na+ cause more decrease,which means the effct of Na+ doping is more harmful. (2)Protonation can effectively getting rid of impurities in Nafion/PTFE composite membrane,decreasing the impedance,thus improving the conductivity of composite membrane.Among different methods of protonation,using one of isopropanol or dilute silphuric acid,and deionized water is less effective,while using dilute silphuric acid is better than the former.And using isopropanol,dilute silphuric acid,and deionized water orderly earns best results. After protonation 3 times by using the last method,increase the protonation times,the impedance of Nafion/PTFE composite does not shows obviously change.Which means protonation 3 times can effectively get rid of Na+ and Triton X100 in composite membrane.