Universal Synthesis Of Small-sized Platinum-based Intermetallic Compounds Nanoparticles And Their Catalytic Properties

Platinum-based intermetallic compounds(IMCs)with defined stoichiometry and crystal structures display distinct magnetic,superconducting,and chemical properties compared to their disordered solid solution structure.In particular for catalysis applications,the site isolation of the active metal in the ordered structures affords intriguing geometric and electronic properties that often lead to significant enhancement in activity,selectivity,and stability.Moreover,the regular structure of IMCs ensures homogeneity of the active sites,which is beneficial for studying the underlying relationship between structure and performance,and further guiding the structural design of the new high performance catalyst.However,the synthesis of IMCs often requires high temperature treatment to overcome the energy barrier that transforms from disordered structure to ordered structure,which inevitably causes the nanoparticles to undergo severe agglomeration,Oswald ripening and sintering,resulting in large particles and broader size distribution and thus greatly reduce the activity and selectivity of the catalyst.Although some methods for synthesizing small-sized IMCs have been reported,to date there is still no general method for the controllable synthesis of sub-5 nm IMCs.The purpose of this paper is to use mesoporous sulfur-doped carbon as support to synthesize small-sized platinum(Pt)-based IMCs by simple wet-impregnation method,based on the strong metal-support interaction.And then,the ordered Pt-based catalysts prepared thereby are applied in electrocatalysis and heterogeneous catalysis in order to gain good catalytic performance and to understand the relationship between structure and performance.In the first chapter,combining with typical examples,the synthesis methods for platinum-based IMCs nanoparticles and their applications for electrocatalysis and heterogeneous catalysis were summarized.In the second chapter,with the mesoporous sulfur-doped carbon(meso-S-C)as supports,which were fabricated by carbonization of molecular precursors with silica nanoparticles as templates according to our previous work,45 Pt-based IMCs with average particle sizes of less than 5 nm were prepared.We found that the strong chemical interaction between sulfur and Pt and the physical confinement effect of the mesoporous structure could restrain the agglomeration and sintering of metal nanoparticles at high temperature up to 1100 ?,therefore guaranteeing the synthesis of small-sized Pt-based IMCs.The ordered structure of the obtained IMCs nanoparticles was confirmed by X-ray diffraction(XRD),high-angle annular dark-field scanning transmission electron microscope(HAADF-STEM),and extended X-ray absorption fine structure(EXAFS).The formation mechanism of small-sized IMCs on the meso S-C support was also explained by combining the characterization data of HAADF-STEM,energy dispersion spectrum(EDS)mapping and line scanning.The synthesis of Pt-based IMCs nanoparticle library supplies a perfect platform for exploring the structure/performance relationship of IMCs.The synthesis strategy based on the strong metal-S interaction may provide new insights for synthesizing other small-sized alloy or IMCs nanoparticle catalysts.In the third chapter,the electrocatalytic performances for the oxygen reduction reaction(ORR)of several Pt-based IMCs were demonstrated.The addition of second metal M can shorten the Pt-Pt bond,so that d-band center down-shift relative to the Fermi level,thereby weakening the adsorption of the oxygenated species on metal surface,thus increasing the catalytic activity of the catalyst(the mass activity of our best sample for ORR is close to 8 times higher than that of the commercial Pt/C catalyst).Meanwhile,as the order degree of the IMCs increases,the electronic and geometric effects increase,resulting in an improved catalytic activity.In addition,the decrease of the proportion of Pt atoms in IMCs leads to the change of crystal structure and the increase of electronic effect caused by the increase of Pt-M coordination number,thereby increasing the catalytic activity,while the inner metal M is more susceptible to corrosion and the stability is degraded.In the fourth chapter,the catalytic performances for selective hydrogenation of 4-chloronitrobenzene of several Pt-based IMCs were demonstrated.The addition of second metal M changes the adsorption characteristics of Pt that the adsorption of C-CI bond is repulsive,while the electron-enriched Pt sites induced by the electrons transfer from metal M to Pt greatly increase the activation energy of the dechlorination reaction,thereby inhibiting the side reaction of dechlorination and improving the selectivity.With different metal M,the electronic states of Pt in different Pt-based IMCs are changed.The catalytic activity incrases with the oxidation state of Pt in these IMCs.In the fifth chapter,the structure of sulphur and nitrogen co-doped porous carbon matrix confined antimony/germanium(Sb/Ge)nanoparticles was constructed and applied to lithium/sodium ion batteries.Sulfur and nitrogen co-doped porous carbon matrix can not only alleviate the volume expansion of Sb/Ge nanoparticles during circulation,but also promote electrolyte infiltration,increase electron conductance and ionic conductance,leading to enhanced structural stability and cyclability of the Sb/Ge nanoparticles.In addition,sulfur and nitrogen co-doping introduced more defects and active sites to the carbon framework,thereby improving the interfacial adsorption and electrochemical behaviors.This special structure could offer an effective and general approach to improve the electrochemical performance of these alloy-type electrode materials(Sn,Pb and so on)with huge volume change in the energy storage area.