FeN/C As Cathode Electrocatalyst Toward Oxygen Reduction Reaction In Proton Exchange Membrane Fuel Cell

Proton exchange membrane fuel cell?PEMFC?has been achieved great progress in recent years due to its advantages such as convenience,high efficiency and low working temperature.However,its commercialization is still hindered by high cost and duration.Pt-based catalysts are widely used as cathode electrocatalyst due to the sluggish reaction kinetics on oxygen reduction reaction?ORR?.It is crucial to research and develop low-cost non-noble metal catalysts with high activity and good stability since Pt is scarce and very costly.The activity of FeN/C as ORR catalyst was investigated in this dissertation.The effects of key parameters on ORR activity of the catalysts were investigated by the kinds of electrochemical techniques.The key parameters including iron precursor,nitrogen precursor and carbon support,as well as temperature,duration time and atmosphere in pyrolysis.The stability of the catalyst with better performance was explored by accelerated durability test.The structure and physical characteristics of catalysts and catalysts precursors were studied by an array of techniques such as Brunauer-Emmet-Teller?BET?surface area and pore size distribution measurements,thermo gravimetric analysis?TGA?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?,and X-ray photoelectron spectroscopy?XPS?etc.The dependence of catalytic performance on structure was studied on the basis of the structural characterizations and electrochemical measurements.The main results of the research works are as follows:1.The type and content of nitrogen and iron sources in catalyst precursor had obvious effects on ORR activities of the catalysts.The catalyst had best ORR activity using 1,10-phenanthroline?phen?,ferric chloride,and Black Pearl 2000?BP?as catalyst precursor,with the ratio of phen/BP was 20/80 and the nominal Fe content in the catalyst precursor was 1 wt.%.The results of TEM,BET,XRD,TGA and XPS show that the particle size,specific surface area of the catalyst,the thermal stability of catalyst precursor and the content of N on the surface of the catalyst are the main factors affect ORR activity of the catalyst.2.The specific surface area and pore structure of carbon support had significant effects on ORR activity of FeN/C catalyst.The catalyst using BP as carbon support had better ORR activity compared to XE-2 and EC300JD,etc.Meanwhile,the conditions of heat treatment have great influence on ORR activity of the catalyst.The catalyst has the best ORR activity when the catalyst precursor was subjected to a second heat treatment in NH₃ at 950°C for 10 min.TEM,BET and XPS tests show that a second heat treatment can significantly change the particle size and morphology of the catalyst,as well as Fe and N content on the surface of the catalyst,which affect ORR activity of the catalyst.3.The stability of the catalysts with and without a second heat treatment were preliminarily studied using accelerated durability test.the results of electrochemical measurements and TEM characterization indicated that the increase of particle size and the reduction of nitrogen content were the possible reasons for the catalyst performance degradation.