| With the extensive use of fossil energy,the energy crisis and the greenhouse effect have been become more serious.Therefore,the development and utilization of clean and renewable energy technologies are of great practical significance to the establishment of an environmentfriendly and sustainable society.Proton exchange membrane fuel cell(PEMFC)is an energy conversion device that can directly convert chemical energy in fuels into electrical energy.Due to its high and efficient conversion,low operation temperature,and being environmental friendly,it is recognized as the most promising new energy technology in the 21 st century.At present,in order to solve the problem of slow kinetics of the cathodic oxygen reduction reaction(ORR),Pt/C catalysts are widely used in PEMFC as cathode and anode catalyst.However,its high cost,scarcity of resources and insufficient stability under acid and high potential have become a problem that urgently needs to be solved for the large-scale commercialization of PEMFC.Therefore,the development of Pt-based catalysts with high ORR activity,high durability and low Pt loading is of great significance for promoting the development of fuel cell technology and its application.During the past decades,researchers around the world have carried out a lot of research works on low-Pt and non-Pt catalysts,and have also made many important progresses and achievements.Among the various catalysts,the core-shell structured catalyst is a widely recognized low-platinum catalyst which can not only greatly reduce the loading of platinum,but also greatly improve stability of the platinum-based catalyst.Among them,the new coreshell structure platinum-based catalyst using nitride nanoparticles rather than other expensive noble metal nanoparticles as the core exhibits outstanding economic efficiency and excellent stability/durability.Compared with other types of core-shell structured catalysts,it has greater comprehensive advantages in terms of cost,performance and stability.On the basis of the previous research work of our research group,this thesis conducts further in-depth research on this type of core-shell structured catalyst with nitride nanoparticles as core and explores the scale-up preparation and its related problems.The specific research works and its results are as follows:(1)The carbon nanotube-supported titanium nitride nanoparticles were prepared by a solvothermal-nitridation procedure,and then thin layer of Pt was deposited on the surface of the nitride nanoparticles by a pulse electrodeposition technology developed in our group,and Ti N@Pt/CNTs core-shell structured catalyst with titanium nitride nanoparticles as core was prepared.Meanwhile,the effects of various preparation parameters or conditions on the performance of the catalyst were investigated.It is showed that the Ti N@Pt/CNTs catalyst(containing 16wt% Pt)prepared under our optimized conditions exhibits excellent ORR catalytic performance,and its mass activity can reach 0.23 A/mg Pt,which is almost three times that of the commercial Pt/C(0.08 A/mg Pt);Furthermore,the stability or durability of the catalysts is evaluated by an accelerated durability test(ADT)protocol issued by US Department of Energy,it is found that the half-wave potential of the Pt/C catalyst decreased by 45 m V after10,000 cycles of ADT,while the half-wave potential of Ti N@Pt/CNTs only decreased by 5 m V.In addition,it is revealed by XPS results that the binding energy of Pt in Ti N@Pt/CNTs is negatively shifted by 0.4 e V relative to Pt/C.Then,we also studied the effect of doping different elements(Cr,Mn,W,Mo)in titanium nitride on the performance of the catalyst,and we found that the Ti Mo N@Pt/NCNTs catalyst prepared by doping 11wt% molybdenum exhibits the highest mass specific activity of 0.37 A/mg Pt,which is almost 5 times that of the commercial Pt/C.(2)In the bases of our successful preparation of Mo-doped Ti Mo N@Pt/NCNTs catalyst,we attempted to the scale-up preparation of the catalyst through developing the apparatus and process.First,Ti Mo N/NCNTs precursors were prepared by solvothermal-nitridation method,and then Ti Mo N@Pt/NCNTs were amplified by pulse electrodeposition technology,in which glassy carbon sheet with large surface area is used as cathode instead of using of small-area glassy carbon electrode,and the electrode area is 20 times that of the glassy carbon electrode,realizing the amplified preparation of the catalyst.It is showed by electrochemical tests that the electrochemical active surface area of the amplified Ti Mo N@Pt/NCNTs catalyst is lower than that of the Pt/C and the micro-prepared Ti Mo N@Pt/NCNTs,and the reduction peak potential of Pt-O is negatively shifted by 30 m V and 100 m V respectively,relative to that of the Pt/C and Ti Mo N@Pt/NCNTs,and its mass specific activity(0.03 A/mg Pt)is also much lower than the0.37 A/mg Pt of the micro-prepared Ti Mo N@Pt/NCNTs catalyst.Although the activity of the obtained catalyst still needs to be improved,our suggested method may provide a new pathway to resolve the problems of large scale preparation of core-shell structure,including low yield of prepared catalyst and difficulty in collecting catalysts eta,which have plagued electrodeposition technology for a long time. |
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