Electrochemical Control And Catalytic Performance Of PdPt Alloy Nanocrystals

With the rapid development of industry and the dramatic increase in population,traditional fossil fuels can no longer meet human needs.Energy security and environmental issues have become increasingly prominent.One of the major challenges is finding efficient and clean energy for the replacement of traditional fossil fuels.Direct alcohol fuel cells(DAFCs)hold the advantages of high energy density,low operating temperature,cheap liquid fuel,ease of handling and friendliness to the environment.However,DAFCs are still far from commercial application to date due to the high cost and unsatisfactory efficiency of the catalysts.Therefore,exploring high activity and high stability catalysts is of great significance for direct alcohol fuel cells.In this thesis,we used electrochemical methods to developed a variety of morphologies of palladium-platinum alloy nanocatalysts.It was found that the electrocatalytic performance of the alloy catalysts was significantly improved.The main results are as follows:1.The screw-like PdPt nanowires(PdPt NWs)with tunable composition were successfully prepared for the first time by using electrochemical square wave potential(SWP)method.Through SEM and TEM characterization,we found the prepared nanowires have a rough surface and a zigzag-like structure,and the surface was surround with high index crystal planes such as {211} and {311}.The SEM-EDS and XPS determined the nanowires consisted of Pd and Pt.The two elements distributed evenly within the nanoparticle by using STEM-mapping.Alloy nanowires exhibited excellent catalytic activity and good stability for the oxidation of methanol and ethylene glycol.Experimental' results show that the catalytic performance of nanowires is closely related to their composition.Pd1Pt1 NWs exhibit the excellent catalytic activity for methanol oxidation.The current density is 2.4 times that of Pt tetrahexahedron and 5.4 times that of commercial Pt/C.For ethylene glycol oxidation,the current density is 2.7 times that of commercial Pt/C and 4.1 times that of commercial Pd/C.The stability of Pd1Pt1 nanowires is also higher than that of Pt tetrahedron and commercial catalysts.The oxidation process was studied by In situ FTIR.It was revealed that their ability towards CO-tolerance is highly improved,and their capability of cleaving the C-C bond of EG is greatly promoted.The reason for the increased catalytic activity of PdPt NWs can be attributed to the synergetic effect and modified electronic states of Pd and Pt.2.The palladium-platinum alloy concave cube(CC-PdPt)with a high-index crystal plane {hkO} and the palladium-platinum alloy octahedron(OH-PdPt)with a low-index crystal face {111} were controlled by electrochemical SWP method.We explored the performance for alcohol oxidation by controlling the composition of CC-PdPt and OH-PdPt to be same.It was found that,for the oxidation of monohydric alcohols such as methanol and ethanol,the CC-PdPt exhibited excellent catalytic activity,and the highest current densities thereof were 7 times and 3.4 times that of commercial Pt/C,respectively.For the oxidation of glycerol,the OH-PdPt showed better catalytic activity,which was 4.5 times that of commercial Pt/C,and its anti-poisoning ability was improved.In this paper,the PdPt NWs with different compositions and the CC-PdPt and OH-PdPt with the same composition of palladium-platinum alloys were synthesized by electrochemical methods.Studies have shown that these catalysts have different catalytic properties for oxidation of methanol,ethanol,ethylene glycol and glycerol,and have obvious structural and compositional effects This study is of significant importance both for electrocatalysis and fuel cells to design and synthesize catalysts with high performance.