Controlled Synthesis Of Supported Alloy Catalysts And The Effects Of Composition And Structure On Electrocatalytic Performance

Supported platinum catalyst is an indispensable catalyst material for cathodic oxygen reduction reaction(ORR)in new energy installations.The current commercial Pt/C catalyst has poor specific activity and long-term durability,and its performance has not yet reached the requirements for large-scale commercial applications of proton exchange membrane fuel cells and metal-air batteries.Therefore,the development of oxygen reduction catalysts with low cost,high activity,and good durability are the focus of research.Alloying and interfacial control are currently two main strategies for improving the catalytic activity of supported catalysts.In this subject,platinum-palladium-copper(PtPdCu)ternary alloy catalysts are synthesized by a carbon-assisted galvanic replacement reaction with self-made copper nanowires as templates.Its morphological structure and electrochemical activity are provided,which provide a new idea for batch preparation of alloy catalyst.The main research results are as follows:(1)First,the hollow nitrogen-doped carbon microsphere carrier was prepared by solid phase etching,which use the carbon-cobalt tetroxide hybrid sample as the raw material.By analyzing its morphology,structure and composition,it was found that the hollow carbon microspheres exhibit a typical graded porous structure with a relative specific surface area of 438.51 m2 g-1.The deconvolution of Raman spectra demonstrates that the hollow nitrogen-doped carbon microspheres contains in-plane defects,stacking defects and nitrogen atom doping.XPS results show that the nitrogen content is 4.19 at%(relative to carbon atoms).In alkaline media,the hollow nitrogen-doped carbon microspheres exhibit excellent catalytic activity and stability,with a half-wave potential of 0.88 V vs.RHE.This study provides a carrier material for subsequent interface adjustment of low platinum alloys.(2)An unsupported platinum-palladium-copper(PtPdCu)catalyst was synthesized by galvanic replacement method using self-made one-dimensional copper nanowires as a sacrificial template material in one step in ethylene glycol system.The catalyst has a self-supporting one-dimensional nanotube morphology,and each metal element on the surface mainly exists in the form of zero valence.In acidic medium,the unsupported catalyst with alloy ratio Pt33Pd13Cu54 shows the best catalytic activity,with a half-wave potential of 0.85 V vs.RHE.Alloying causes a negative shift of the Pt 4f peak position in the alloy,indicating that the electrons transfer from Cu and Pd to Pt,which changes the electronic structure of the active site and affects the catalytic activity.(3)The carbon-supported PtPdCu catalysts were successfully prepared via a carbon-assisted galvanic replacement reaction by adding carbon carrier material to the conventional galvanic replacement system.Changing the type of carbon carrier will affect the catalytic activity of the composite sample,of which carbon black is the most economical and efficient carrier.In the supported catalyst,the alloy nanoparticles are uniformly dispersed on the carbon support,with the average particle size about 1.88 nm.Each metal element mainly exists in the form of zero valence,and the surface has a Pt skin structure.ICP test showed that the mass ratio of Pt in the composite sample is 11.9%.In 0.1 M HClO4,the supported PtPdCu sample exhibits excellent oxygen reduction performance,with a half-wave potential of 0.91 V vs.RHE,which is 30 mV higher than the commercial Pt/C.The improvement of catalytic activity mainly comes from the alloying and interface structure regulating the electronic structure of the alloy.(4)Using experimental research and DFT theoretical calculation methods,the origin of the oxygen reduction activity of the supported alloy catalyst was deeply analyzed,and the corresponding relation theory between the activity and the catalyst interface structure was preliminary established.Compared with the supported PtCu alloy catalyst,it is shown that the incorporation of Pd changes the electronic structure of Pt and hinders the extraction and deactivation of the surface Pt and internal Cu.Comparison with the unsupported PtPdCu shows that not only does the carbon carrier provide a fast electron transport channel,the special alloy-carbon carrier interface in the hybrid sample affects the electronic structure of the active site Pt.Calculated by density functional theory(DFT),the lattice of the alloy cluster shrinks,and the center of the d-band of Pt is appropriately negatively shifted,so that the adsorption and desorption of oxygen-containing groups achieves a good balance,making the ORR reaction more likely to occur on the surface of the hybrid sample.