Synthesis And Electrooxidative Properties Of Pd-based Nanocatalysts For Direct Methanol Fuel Cell Anodes

Direct methanol fuel cell(DMFC)using liquid methanol as fuel is a type of proton exchange membrane fuel cell.Because fuel methanol can directly convert its chemical energy into electrical energy without going through the combustion process,and DMFC does not involve mechanical rotation,it is not limited by the Carnot cycle and has a higher theoretical energy conversion efficiency.In addition,DMFC can work at a lower temperature,has the advantages of environmental friendliness,easy fuel storage and transportation,etc.,showing important potential application prospects.However,the kinetics of methanol oxidation reaction(MOR)at the anode and oxygen reduction at the cathode of DMFC are slow,requiring the use of a large amount of precious metal Pt,which has become an important factor restricting the development of DMFC.Currently,Pt catalyst is the most widely studied anode catalyst for DMFC,but Pt has little reserve on the earth and is expensive.Pd has crystal structure and electronic structure similar to Pt,and its reserves on the earth are dozens of times that of Pt.Therefore,the construction of DMFC anode catalyst based on Pd instead of Pt has important research value and is gradually being favored.The low MOR performance of plain Pd catalysts is difficult to accommodate the large-scale application requirements of DMFC.Several studies showed that Pd-based catalysts show obvious advantages over plain Pd catalyst for MOR.It is believed that in-depth research on Pd-based MOR catalysts is of great significance for promoting the development of DMFC.In this thesis,PdRh alloy nanocrystals,PdRuW nanosheets and Mn₃O₄ particles supported by Pd nanosheets were prepared,and the morphology and structure of these three catalysts were characterized and analyzed.Their electrocatalytic activity and stability have been researched and analyzed.The main contents are as follows:(1)Defective PdRh bimetallic nanocrystals were prepared by solvothermal method.After introduction of Rh into Pd lattice,the obtained defective PdRh NAs showed enhanced peak current density and stability compare to the commercial Pd/C,and the Pd₃Rh₁ NAs exhibited the highest peak current density and best durability.The catalytic activity enhancement mechanism of PdRh NAs should be contributed to the introducedRh providing rich OH^-,which promotes the oxidation of CO-like poisoning species.It is worthy of a note that the introduction of Rh into Pd lattice induce crystalline defects of twisted structures could function as active sites for MOR.(2)The PdRuW NSs catalysts were prepared by one-step method.The study found that the oxidation peak current density of the PdRuW NSs/C catalyst is 1856.9 m A mg^-1_Pd,which is 3.83 times that of the commercial Pd/C;and the electrochemical active area(ECSA)of the PdRuW NSs/C catalyst is better than the commercial Pd/C,which may be because the PdRuW NSs/C catalyst with a two-dimensional nanosheet structure exhibits a larger specific surface area,thereby providing more active sites to participate in the reaction.In addition,the successful incorporation of Ru and W elements makes the electronic synergistic effect between Pd andRu and W promote the improvement of the catalytic activity of PdRuW NSs/C and the improvement of the resistance to CO poisoning.(3)The Pd@Mn₃O₄ NSs catalyst was prepared by a stepwise method.The Mn₃O₄particles loaded on the Pd nanosheets have uniform morphology and are mainly distributed at the edge of the Pd nanosheets.The study found that compared with Pd NSs and commercial Pd/C,the prepared Pd@Mn₃O₄ NSs catalyst shows higher MOR oxidation peak current density,better resistance to CO and electrochemical stability.After a series of characterization studies,the enhancement of the catalytic performance of Pd@Mn₃O₄ NSs can be considered as the synergistic effect between the supported Mn₃O₄ and the nanosheet structure,as well as the electron transfer between Pd and Mn₃O₄.The outstanding stability may be due to the Mn₃O₄ particles distributed on the surface of the Pd nanosheets,and there is a strong force between them to inhibit the agglomeration of the Pd nanosheets.