Research On The Construction Of Oxygen Reduction Catalysts For Non-precious Metal Fuel Cells Based On Biomolecules

Fuel cell is electrochemical device converting chemical energy into electric energy.Different from batteries,it can keep working as long as fuel and oxidant are supplied.Among kinds of fuel cells,proton exchange membrane fuel cell(PEMFC)has been most actively developed,because of its low operational temperature,high power density,and no environmental pollution.However,a large number of precious metal platinum are required to catalyze the oxygen reduction reaction(ORR)at the cathode,which limits its commercialization.Highly active,low cost and durable ORR catalyst is essential for the further development of PEMFC.Carbon materials doped with heteroatoms,like N,P,B and S,etc,has been demonstrated to show high electrocatalytic activity and stability for oxygen reduction reaction,in which N atoms doped carbon material was particularly attractive.Furthermore,the adaptation of N/S co-doped catalysts was increasingly reported in recent years.It is believed that the introduction of S atoms can further improve the activity of the catalyst accounting from its favorable formation additional active sites.Herein,in this thesis,we proposed two new N/S coped carbon catalystsfrom biomolecules precursors and methods of preparation.And the electrochemical activities of the catalysts were systematically studied.It mainly includes as the following parts:First part,the research progress of ORR non-precious metal catalysts for fuel cells,with focuses on several important components of non-precious metal catalysts,including carbon supports,nitrogen-containing precursors and transition metal precursors is reviewed with our motiviation and main finding.Second part,raw materials and chemical reagents in need,applied instruments,the electrochemical test procedure and the method of evaluation of ORR catalyst are included.Third part,we use biomicromolecule L-cysteine(L-Cysteine,L-Cys)as nitrogen source precursor,and commercial carbon black as carbon sources,and ferric chloride to make a novel N/S co-doped ORR catalyst C/L-Cys/Fe synthesized through one-step high-temperature carbonization.The structure and morphology of the catalysts were characterized by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).The results show that the catalyst is granular and the carbon layer has an ordered graphite structure.X-ray photoelectron spectroscopy(XPS)analysis showed the existence of different chemical bonds of N and S,which indicates the feasibility to synthesize N/S co-doped carbon ORR catalysts by using L-Cys as precursor.It was found that the catalyst C/L-Cys/Fe exhibited good stability and excellent catalytic activity in the alkaline electrolytes.With a high loading,the catalyst is quite active compared with commercial catalyst Pt/C in term of onset/half wave voltage,and limiting current density.The K-L equation shows that the ORR is a four-electron process that O2 is directly reduced to H2 O or OH-,further indicating high activity of prepared C/L-Cys/Fe.Last part,N/S co-doped ORR catalyst CNT/BSA/Fe was prepared by heat-treatment of bovine serum albumin(BSA),carboxylated carbon nanotubes(CNT)and ferric chloride.The prepared catalyst has excellent catalytic performance in alkaline electrolytes,and it can show high activity as much as the commercial Pt/C catalyst at high catalyst loading.The catalyst also exhibits good stability in 20 k cycling testing.The oxygen reduction reaction is a four-electron process according to K-L equation.XPS datas show the existence of pyridine-like nitrogen,graphite-like nitrogen and pyrrole-like nitrogen in the catalyst.Large amouts of pyridine and co-doping with S atom could explain why the catalyst has good performance for ORR reaction.