Construction And Electrocatalytic Performance Investigation Of Nitrogen-or Phosphorus-doped Pt-free Composite Electrocatalytic Materials

The large-scale production of many types of fuel cells is currently constrained by the lack of sustainable and efficient catalysts that can replace the less earth-abundant,noble metal-based catalysts,which are commonly used in these renewable energy systems.This burgeoning issue has led to explosive research efforts to find alternative Pt-free catalysts.Nowadays,tremendous progress has been achieved and a few Pt-free catalysts for fuel cells have demonstrated several advantages,such as high activity,long-term stability and excellent tolerance to methanol crossover in this direction.Especially,nitrogen-or phosphorus-doped composite catalysts which as Pt-free catalysts have spawned considerable attention.More importantly,their precursors are widely available,which is helpful for extending commercialization of the catalyst.The thesis mainly focuses on the preparation of low-cost and high-performance catalyst based on the electronic effect of nitrogen and phosphorus.As a result,the construction of nitrogen-or phosphorus-doped Pt-free composite electrocatalytic materials is studied from the two aspects of the modification of the support and the preparation of the composite catalyst.The structures and electrochemical performance are investigated by physical and electrochemical test methods.The thesis is divided into the following three parts:Part ?:PdSn alloy supported on phenanthroline-functionalized carbon as highly active electrocatalysts for glycerol oxidationNitrogen-doped carbon support can facilitate the immobility of nanoparticles due to its special electronic effect,which has been used for the preparation of high-performance electrocatalysts.In this part,phenanthroline is used to direct functionalize carbon?phen-C?for preparing nitrogen-doped carbon support,and different molar ratios of PdSn?Pd:Sn=1:1¹:3?nanoparticles are deposited subsequently.According to the electrochemical results,the Pd₃Sn/phen-C catalyst has the largest electrochemically active surface area(577.2 cm² mg_Pd^-1),best activity and stability among as-prepared Pd_xSn_y/phen-C,Pd/phen-C and Pd/C catalysts for glycerol oxidation.Furthermore,the durability and poisoning tolerance of Pd₃Sn/phen-C are also superior to that of Pd/C.The Pd₃Sn/phen-C would be a potential electrocatalyst for glycerol oxidation.Part ?:An effective Pd-NiOx-P composite catalyst for glycerol electrooxidation:co-existed phosphorus and nickel oxide to enhance performance of PdHighly active and durable catalysts are crucial for the development of direct alcohol fuel cells?DAFCs?.Herein,a phosphorus and nickel oxide co-existed composite catalyst?Pd-NiO_x-P/C?is prepared for glycerol electrooxidation in alkaline media.X-ray photoelectron spectroscopy?XPS?,X-ray diffraction?XRD?and energy dispersive X-ray?EDX?analysis reveal that the phosphorus and nickel oxide are co-existed in the Pd-NiO_x-P/C composite catalyst.Compared with Pd/C catalyst,electrochemical measurements present that it has good electrocatalytic performance with higher electrochemically active surface area(EASA=576.3 cm² mg_Pd^-1),larger peak current(I_p=0.3640 A mg_Pd^-1)and lower activation energy(E_a=21 kJ mol^-1).More importantly,the Pd-NiO_x-P/C exhibits high stability.It will be a promising Pd-based catalyst in DAFCs.Part ?:Preparation of a nitrogen-doped composite from polyaniline-coated Ce?TTA?3Phen for oxygen reduction reactionThe commercial development of fuel cells is still hindered by several critical issues among which the design of highly durable cathode electro catalysts for the oxygen reduction reaction?ORR?remains a formidable challenge.Herein,a polyaniline-coated Ce?TTA?₃Phen complex nanocomposite was prepared and used as an efficient electrocatalyst to solve these challenges associated with ORR.This nitrogen-doped material was prepared from in situ polymerization method with modified Ce?TTA?₃Phen-supported polyaniline?PANI?,followed by carbonization of the latter.The as-prepared nanocomposite exhibits high electrocatalytic activity,stability and tolerance for methanol crossover.This nitrogen-doped nanocomposite can be prepared in a facile procedure,which exhibits a good prospect in the commercial application of fuel cells.