Preparation And Properties Of Pt Supported On Divalent Metal Doped Ceria

Among the fuel cells,the energy density of most fuel cells is low.After hydrogen,the next best fuel in terms of energy density is methanol.Direct methanol fuel cell?DMFCs?has the advantages of high efficiency,low pollution,convenience and practicality,and is an ideal power source for portable electronic equipment and electric vehicles.Over the past few decades,a great deal of effort has been devoted to promoting the large-scale commercialization of DMFC.However,there are still some unresolved obstacles that greatly hamper its widespread application.As a commonly used anode catalyst,the main drawback of Pt-based catalyst is that it is susceptible to the toxicity of methanol electrocatalytic oxidation intermediates,and the migration and agglomeration of platinum nanoparticles on the carrier will also lead to poor durability of the catalyst.In order to overcome these problems,some co-catalytic materials need to be introduced to improve the electrocatalytic performance of Pt catalysts.Among them,metal oxides?MOx?and their compounding as hybrid carriers have been widely studied because of their excellent performance in improving the performance of platinum catalysts.Among various MOx hybrid carriers,CeO₂ composites have been widely concerned because of their unique characteristics of CeO₂.A large number of studies have shown that the electrocatalytic oxidation performance of Pt/CeO₂ catalysts to alcohol is significantly improved compared with commercial Pt/C catalysts.The Platinum Catalyst deposited on the CeO₂ carrier not only has high dispersion due to the anchoring effect of CeO₂,but also has good oxidation properties of methanol because the platinum surface is easy to release the poisoned intermediates.However,the concentration of oxygen vacancy in pure CeO₂ is low,which limits its synergistic catalysis to methanol oxidation.The addition of other metal oxides can promote the catalytic activity and stability of Pt catalyst to the electrocatalytic oxidation of methanol by means of double functional groups and synergy.The concentration of oxygen vacancy in CeO₂ can be effectively increased by doping appropriate doping agent.After doping,CeO₂ has more oxygen vacancy,which shows better catalytic/co-catalytic performance and high stability in many catalytic reactions.Using Cu as a dopant,and the combination of Cu and CeO₂ can improve the catalytic performance of the system.Cu²⁺and CeO₂ contact,through the Ce⁴⁺/Ce³⁺oxidation reduction process,promote the formation of Cu⁺,the electronic transfer to Cu²⁺formation Cu⁺.This enhances the adsorption of CO-ads,resulting in excellent catalytic activity when doped with Cu²⁺,and significantly improves the catalytic effect due to the uniform integration of Cu²⁺into the CeO₂ lattice.Copper ions are migrated from CeO₂ crystals,clustered on the surface of CeO₂,and the coordination environment is low,which improves the reduction of Ce⁴⁺/Ce³⁺.It is beneficial to improve the catalytic performance of the catalyst.Sn is used as a doping agent to maximize the synergistic catalysis of CeO₂ to methanol electrocatalytic oxidation.First,the redox behavior of Sn(Sn⁴⁺/Sn²⁺)can improve the OSC of CeO₂,which is beneficial to the oxidation of the CO of intermediates of methanol electrocatalytic oxidation reaction.Secondly,adding Sn to the CeO₂ lattice can increase the specific surface area of the composites,which is beneficial to better dispersion and anchoring of Pt and improve the durability of the catalyst.Finally,Sn can improve the electrical performance of CeO₂,which is helpful to improve the electrocatalytic activity of catalyst.Based on the above analysis,a series of divalent metal doped cerium oxide nano-fiber?NFs?containing Pt catalysts were synthesized to study the electrocatalytic properties of methanol.The main research contents are as follows:Part ?:the effect of Cu doped Pt/CeO₂ catalyst on the catalytic oxidation properties of methanol.Pt/CeO₂ and a series of Pt/CuO-CeO₂(Pt/Cu_x-Ce_1-x)catalysts were prepared by electrostatic spinning combined with impregnated reduction.X-ray diffraction?XRD?,Scanning electron microscope?SEM?,Transmission electron microscope?TEM?,X-ray Energy spectrometry?EDS?were used to characterize the structure and composition of Cu_x-Ce_1-x NFs and Pt/Cu_x-Ce_1-x catalysts.The content of Pt in Pt/CeO₂ and Pt/Cu_x-Ce_1-x catalysts was about10 wt.%.It is found that the average particle size of Pt nanoparticles on Cu_x-Ce_1-xNFs is significantly smaller than that of Pt particles on pure CeO₂ NFs.The results of SEM showed that the diameter of fiber was significantly smaller after calcination,and the distribution on Cu_x-Ce_1-x NFs was more uniform than that of Pt nanoparticles on CeO₂ NFs.It is further shown that Cu_x-Ce_1-x NFs is more favorable to the dispersion and deposition of Pt nanoparticles.The catalytic properties of the catalyst for methanol oxidation reaction were evaluated by cyclic voltammetry?CV?,CO stripping voltammetry and chronoamperometry?CA?.The results of electrochemical test show that with the increase of Cu doping,the catalytic activity of Pt/Cu_x-Ce_1-x to methanol increases gradually,and the Pt/Cu_0.3-Ce_0.7 has the greatest catalytic activity.Moreover,compared with commercial Pt/C and Pt/CeO₂ catalysts,the catalytic activity of Pt/Cu_x-Ce_1-x catalyst,the ability to resist poisoning and stability were significantly improved.The experimental results show that the doping of Cu is an effective method to improve the catalytic properties of Pt/CeO₂.Part ?:The effect of Sn doped Pt/CeO₂ catalyst on the catalytic oxidation properties of methanol.SnO₂-CeO₂(Sn_x-Ce_1-x)NFs with different Sn/Ce atoms ratio was prepared by electrostatic spinning method,and its Pt catalyst was prepared by impregnation reduction method.The content of Pt in Pt/Sn_x-Ce_1-x Catalyst is about 20 wt.%.The crystalline facies,microstructure and chemical composition of Pt/SnO₂-CeO₂(Pt/Sn_x-Ce_1-x)were characterized by XRD,SEM|,TEM and EDS.Compared with Pt on CeO₂ NFs,the lattice of Pt on CeO₂-MO_x NFs shrinked,and the cell parameters and interplanar spacing became smaller.The lattice parameter of Pt in Pt/Sn_0.3-Ce_0.7 is 0.3772 nm by Jade software,which is less than the lattice parameter?0.3995 nm?of Pt in Pt/CeO₂ Catalyst.The decrease of lattice parameters indicates the interaction between Pt and composite metal oxides.Pt has the strongest interaction with the Sn_0.3-Ce_0.7 NFs carrier,and the Pt particle size order on NFs is:Sn_0.3-Ce_0.7 NFs>Sn_0.5-Ce_0.5NFs>Sn_0.2-Ce_0.8 NFs>Sn_0.1-Ce_0.9 NFs.SEM results show that after calcination,the fibers become discontinuous,deformed and the surface becomes rough,and the distribution on Cu_x-Ce_1-x NFs is more uniform than that of Pt nanoparticles on CeO₂ NFs.The Pt particle size is closely related to the composition of the carrier NFs,compared to the individual metal oxides,composite oxide NFs is more likely to form a small particle size Pt.By using CV,CO stripping voltammetry and CA to evaluate the catalytic properties of Pt/Sn_x-Ce_1-x to methanol,it was found that the catalytic activity,anti-poisoning ability and stability of Pt/Sn_x-Ce_1-x catalyst were significantly higher than that of Pt/CeO₂ catalyst.Among them,Pt/Sn_0.3-Ce_0.7 catalyst showed the best catalytic activity,anti-poisoning ability and stability to methanol.In summary,the electrocatalytic properties of Pt catalysts were significantly improved by introducing CuO,SnO₂ and CeO₂ Composite as co-catalytic materials,which weakened the toxic effect of intermediates CO,and compared with commercial Pt/C catalysts and Pt/CeO₂catalysts,Pt/CuO-CeO₂ catalysts and pt/The electrocatalytic oxidation performance of SnO₂-CeO₂ catalyst to alcohol was significantly improved.The experimental results show that the doping of Cu and Sn is an effective method to improve the catalytic properties of Pt/CeO₂.