Preparation And Electrocatalytic Performance Of Palladium-tin Alloy Nanocrystal

Direct ethanol fuel cells are currently one of the sustainable energy sources,offering high energy density,low operating temperature,and no pollution.However,there are still some issues with the practical application,such as high costs（due to the high catalyst price）,and power to enhance in two areas.Because the anode catalyst is primarily responsible for solving the aforementioned issues,the search of low-cost and high-efficiency catalysts has become a driving force behind the widespread use of direct ethanol fuel cells.Pd and Pd-based catalysts have low costs and plentiful reserves,and alloyed PdSn catalysts can boost activity while lowering costs.As a result,PdSn alloys have a lot of research potential.In order to prepare catalysts with high activity,stability,and low cost,the study of PdSn alloy preparation methods and catalytic mechanisms broadens the range of catalysts available,both in terms of simplifying the synthesis process and understanding the relationship between catalyst structure and properties.The thesis reported three types of Pd-Sn intermetallic catalysts,PdSn nanoparticles（NP）and PdSn nanowire mesh alloys（NW）utilizing distinct simple and low-temperature synthesis methods and the structure,shape,and electrochemical performance were studied.（1）By using sodium hypophosphite as a reducing agent and a simple and low temperature（120℃）oil bath,palladium acetylacetonate and stannous chloride dihydrate were co-reduced in ethylene glycol solution.We obtained three intermetallic compound nanowire mesh structures:Pd₃Sn₂-P63/mmc in hexagonal crystal system,PdSn-Pnmb in orthorhombic crystal system and PdSn₂-Aba2 in orthorhombic crystal system.Then,controlling the crystalline phase of products was achieved by manipulating the ratio of precursors.More importantly,the transformation from pure phase to mixed two-phase can be completed with adequate control of the feeding ratio,allowing both single-phase and two-phase catalysts to be efficiently managed for synthesis.The study of the catalytic oxidation for ethanol revealed that the intermetallic compounds have higher activity and stability than the pure Pd-Fm3m catalyst.Moreover,PdSn-Pnmb catalyst has the largest electrochemically active specific surface area,excellent electrocatalytic activity(4857m A mg _Pd^-1)and remarkable stability to the electrooxidation reaction of ethanol,which can be attributed to its optimal electronic structure.（2）A simple and low-temperature one-pot approach was used to make PdSn nanoparticle（NP）alloys,in which cetyltrimethylammonium bromide plays a significant role in the formation and dispersion of the alloys.To aid the asynchronous reduction of Pd²⁺and Sn²⁺,we replaced the strong reducing agent of dihydrogen hypophosphite with L-ascorbic acid,which helped to the production of PdSn alloys.In terms of catalytic activity and stability for ethanol,the PdSn alloys outperformed the pure Pd catalyst.Furthermore,when the feeding ratio was 1:1,the PdSn-15 NP nanoparticles had the maximum current density and the best stability for ethanol electrooxidation,owing to their lower electron transfer energy barrier,improved coordination environment,and toxicity resistance.（3）When compared to the oil bath approach,the ambient temperature dropwise addition method for manufacturing PdSn catalysts offers the advantages of simpler conditions and cheaper cost.The metal salt precursors were reduced to generate PdSn nanowire mesh alloys under ambient conditions with the help of strong reducing agents（sodium borohydride）and cetyltrimethylammonium bromide.Morphological and dimensional studies revealed that the addition of Sn components had a significant impact on particle size and dispersion.The performance of ethanol catalytic oxidation was further explored.The activity and stability of the PdSn alloy were increased as compared to Pd NW,owing to the synergistic effect of the Pd and Sn atoms.Additionally,the PdSn-5 catalyst even showed higher activity and better stability,surpassing the other PdSn catalysts,which was attributed to its smaller particle radius and better dispersion.As a result,the synergistic effect and the morphological effect are complementary to each other for improving the performance of the catalysts.