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Hydrothermal And Solvothermal Synthesis Of Precious Metal-based Catalysts And Their Electrochemical Performance

Posted on:2021-03-19Degree:MasterType:Thesis
Country:ChinaCandidate:Y WangFull Text:PDF
GTID:2431330647458294Subject:Physical chemistry
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The problem of energy shortage and environmental pollution caused by the burning of fossil fuels is becoming increasingly serious,and people's demand for clean and efficient energy conversion devices is increasing.Fuel cells have received widespread attention in energy conversion due to their advantages such as environmental protection and high conversion efficiency.Noble metals platinum and palladium are good fuel cell catalysts,but the high price,poor catalytic activity and poor stability have hindered the development of commercialization of fuel cells.By doping other metal atoms or synthesizing electrocatalysts with special sructures,morphologies and components,researchers can maximize the utilization of noble metal atoms,reduce the production cost of catalysts,and improve the catalytic activity and stability of catalysts.In this thesis,three different noble metal-based catalysts with different morphologies are designed and controllably synthesized by hydrothermal method and solvothermal method,and their applications in formic acid fuel cells are explored.The specific research contents are as follows:1.Heterostructure assembly PdAg/Ag nanowires are synthesized with Ag NO3,K2PdCl4 as metal precursors,and amine-terminated poly?N-isopropylacrylamide??PNIPAM-NH2?as a structure-directing agent.Studies have shown that PdAg/Ag nanowires are one-dimensional wavy ultrafine heterostructure nanowire structures composed of PdAg alloys and pure Ag substance alternately connected.Electrochemical tests show that compared with commercial Pd black catalysts,PdAg/Ag nanowires have better catalytic activity and stability of formic acid oxidation.The mass activity of PdAg/Ag nanowires is 500.6 A g-1,which is 1.79 times that of commercial Pd black catalysts.The electrochemical active area?ECSA?is 9.1 m2 g-1,which is 1.2 times that of the commercial Pd black catalyst.In the CO stripping voltammetry curve,the initial oxidation potential and oxidation peak potential of PdAg/Ag nanowires are negatively shifted by 90 m V and 70 m V,respectively,compared to the commercial Pd black catalysts.After 3000 s chronoamperometry,the current density of the PdAg/Ag nanowires remain at 190 A g-1,which is about 4 times the current density of the commercial Pd black catalysts after stabilization.The superior catalytic activity and stability of heterostructure PdAg/Ag nanowires can be attributed to the interfacial effects of heterostructures,the anisotropy of one-dimensional materials,and the synergistic effects of alloys.2.Based on the previous work,hexamethylenetetramine?HMTA?is further introduced,and porous Pd2Ir alloy nanosheets are synthesized using K2PdCl4 and IrCl3as metal precursors.Studies have shown that porous Pd2Ir alloy nanosheets are self-assembled from one-dimensional wavy nanowires,exhibiting the morphology of porous two-dimensional nanosheets.Electrochemical tests show that porous Pd2Ir alloy nanoplatelets have better formic acid oxidation catalytic activity and stability than commercial Pd black catalysts.The mass activity of porous Pd2Ir alloy nanosheets is506.1 A g-1,which is 2.4 times that of commercial Pd black catalysts.ECSA is 13.6 m2g-1,which is 1.7 times that of commercial Pd black catalyst.In the stripping voltammetry curve of CO,the initial oxidation potential and oxidation peak potential of porous Pd2Ir alloy nanoplatelets are negatively shifted by 105 m V and 89 m V,respectively,compared with the commercial Pd black catalyst.After 3000 s chronoamperometry,the current density of the porous Pd2Ir alloy nanoplatelets are maintained at 125 A g-1,which is about 3.9 times the current density of the stabilized commercial Pd black catalyst.The superior catalytic performance of porous Pd2Ir alloy nanosheets can be attributed to the two-dimensional porous structure,which can improve electron transport,make the catalyst less prone to Osterwald ripening,and avoid loss of activity.In addition,the synergy of the alloy is also conducive to the improvement of catalytic performance.3.Cu5Pt dodecahedron nanoframes are synthesized by using Cu?NO3?2 and H2PtCl6 as metal precursors.Among them,cetyltrimethylammonium bromide?CTAB?is used as an oxide etchant as the key to the successful synthesis of the frame structure.Studies have shown that Cu5Pt nanoframes have very low Pt content and hollow dodecahedron nanoframework structure.Electrochemical tests show that compared with commercial Pt black catalyst,Cu5Pt dodecahedron nanoframes have more excellent formic acid oxidation catalytic activity and stability.Cu5Pt dodecahedron nanoframes have mass specific activity of 193.85 A g-1,which is 4.86 times that of the commercial Pt black catalyst.ECSA is 17.8 m2 g-1,which is slightly higher than the commercial Pt black catalyst(17.5 m2 g-1).In the stripping voltammetry curve of CO,the initial oxidation potential and oxidation peak potential of the Cu5Pt dodecahedron nanoframes are negatively shifted by 18 m V and 34 m V,respectively,compared to the commercial Pt black catalyst.After 3000 s chronoamperometry,the Cu5Pt nanoframes reach a stable current density of 43.20%,i.e.46.27 A g-1,which is 5.51 times the current density of the commercial Pt black catalyst after stabilization.The superior catalytic performance of Cu5Pt dodecahedron nanoframes can be attributed to the dodecahedron frame structure.This structure has multiple boundaries and atomic steps,which provides a rich catalytic active site for electrocatalysis.In addition,the frame structure can also maintain good structural stability and catalytic stability.
Keywords/Search Tags:fuel cell, formic acid oxidation reaction, hydrothermal method, solvothermal method, palladium-based catalyst, platinum-based catalyst
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