Study On The Correlation Between Microstructure And Electrocatalytic Performance Of Low Platinum Alloy Nanomaterials

The development of economical and efficient fuel cell technology and hydrogen production technology is an important way to solve the global energy and environmental crisis.High-performance electrodes based on low-platinum alloy nano-electrocatalytic materials is one of the keys to the rapid industrial application of this technology.The correlation between the microstructure of low-platinum alloy catalytic materials and its electrocatalytic performance is the theoretical basis for designing and obtaining corresponding high-efficiency nano electrocatalytic materials.In this paper,alcohol oxidation reaction and hydrogen evolution reaction are used as electrocatalytic reaction models.Density functional theory combined with cluster expansion method are used for the design of the microstructure of platinum alloy catalysts.The coupling competition reaction of microfluidics and coupling field technology are developed for the high-precision online regulation of alloy composition,size,morphology,surface and interface microstructure and electronic states,etc.Combining experiments with theoretical calculations,the correlation between the microstructure of the nanocatalysts and the electrocatalytic performance is studied.By studying the proportions of elements in the surface and inner layers of platinum-based nanoalloys,the formation of periodic defects is found,and the generation of ultrafine grains at low platinum content and low annealing temperature.More active sites are provided at the grain boundaries and the electrocatalytic performance is greatly improved.The external magnetic field can further improve the catalytic performance by controlling the electron and spin state on the surface of the catalyst.Finally,low-Pt alloy catalysts with high-efficiency for the electrocatalytic oxidation of alcohols and the electrocatalytic hydrogen evolution reaction was developed.The details are as follows:1.Microstructure regulation of nanomaterials is realized through the high precision and controllable competitive reaction in programmed microfluidics.FePt@(Fe1-xPtx)Oy(OH)z nanocrystals,which is highly dispersed on carbon black and has abundant vertexes/terraces/steps are synthesized.The catalysts show excellent electrocatalytic methanol oxidation performance.The effects of annealing process,carbon mixing method,etching process and Fe/Pt composition ratio on the microstructure and performance of the nanocatalyst are systematically studied.Based on the density functional theory and the cluster expansion method,the annealing process and the reasons for the difference in catalytic performance of catalysts with different Fe/Pt ratios are explained.It is found that the annealing process increases the degree of order of the alloy,improves the synergy between Pt and Fe atoms.A Pt-rich surface layer and Fe-rich subsurface layer structure is formed at the same time,which enhances its stability.When the Fe/Pt atomic ratio is 2/1,the Fe2Pt phase is generated inside the nanoclusters under low-temperature annealing conditions,which spontaneously produces periodic defects and promotes the generation of ultrafine crystal grains and a large number of grain boundaries on the catalyst surface.Compared with the Pt atoms on the(111)plane,the generalized coordination number of the Pt atoms at the concave interface at the grain boundary is increased,providing active sites closer to the optimal Gibbs free energy of the hydroxyl group.The coordination number of Pt atoms at the convex interface is lower,which makes it easier to adsorb methanol,ethanol and other small molecular species,increasing the number and residence time of the adsorbate at the convex grain boundary,improving the catalytic efficiency of Pt atoms near the convex grain boundary.Further change the way of mixing carbon and added alloying elements.The carbon black and the Ni metal salt solution are mixed in advance,so that the nucleation-growth process of the nano-particles occurs directly on the carrier carbon black.A PtNix/C catalyst with enhanced interaction between the support and carbon black was synthesized,which promoted the electron transfer between the main body of the catalyst and the support carbon black.The research was carried out using the electrocatalytic oxidation of ethanol and the electrocatalytic hydrogen evolution reaction as a model,and it was found that the optimal activity and stability were achieved when the Pt/Ni ratio was 1/3.The goal of low platinum and high efficiency has been achieved.2.Tungsten oxides,manganese oxides and PtNi nanocrystals are used to construct PtNi/WO3/C and PtNi-MnOx/C composite catalysts with neighboring and heterogeneous structures.The synergy and interfacial interaction between the metal oxide and PtNi are used to change the Gibbs free energy of hydrogen adsorption and the rate of hydrogen adsorption and desorption on the catalyst,thereby realizing the improvement of the catalytic hydrogen evolution performance.The introduction of WO3 will weaken the strength of the Pt-H bond and provide functional sites for hydrogen desorption.The interface between MnOx and PtNi promotes the transfer of electrons between the two components.At the same time,the electronic interaction between PtNi and MnOx changes the electronic structure of PtNi,which in turn promotes the improvement of its hydrogen evolution stability.3.The magnetic field is coupled with the fluid field to realize the online regulation of the kinetic parameters during the synthesis of nanomaterials.Taking Fe2Pt nanoclusters as the research model,more Pt2+ is reduced to Pt0 under a magnetic field,which makes the surface active sites of nanocrystals greatly increase on the basis of maintaining the original polycrystalline structure.And during the formation of nanoclusters,Lorentz force changes the direction of charged nanocrystals.This continuous change is similar to an alternating magnetic field is applied to the fluid and leads to the generation of local eddy currents,further regulate the electron and spin state on the surface of the catalyst.By comparing the ethanol electrocatalytic oxidation performance of the nanoparticles synthesized under a magnetic field and a non-magnetic field,it is found that the nanoparticles synthesized under a magnetic field show more excellent activity and stability.The green and effective regulation of the microstructure of low platinum alloy nanomaterials and the improvement of catalytic performance are realized.