Controllable Design Of Platinum-based Catalysts And Research On Their Electrocatalytic Performance

The rapid development of society relies on a large amount of energy consumption.While traditional fossil energy is depleting day by day,it also causes irreversible damage to the environment.In order to achieve sustainable development,scientists have been seeking to achieve more efficient and environmentally friendly energy conversion and storage technologies,such as water electrolysis,fuel cells and metal-air batteries.The core technology of these systems lies in electrochemical reactions,of which catalysts are the most important modules.Catalysts play a crucial role in both hydrogen evolution reaction（HER）and oxygen reduction reaction（ORR）.At present,Pt is the single-element catalyst with the best performance for HER and ORR reactions,but its shortcomings are also very prominent,its limited reserves and high cost,which also hinder the development of these advanced energy conversion technologies.Therefore,in order to improve the activity and stability of Pt in HER and ORR,a variety of Pt-based catalysts were explored and designed in this dissertation,which effectively improved the kinetics of the HER and ORR.In situ transmission electron microscopy was used to explore the factors of the performance difference of Pt-based alloy catalysts in membrane electrode assembly.Based on this,in this dissertation,a variety of Pt alloy ORR catalysts were synthesized,which enhanced the catalytic activity of the ORR reaction and improved the stability of the catalysts.The main research content is divided into the following four parts:1.Hydrogen economy,as the most promising alternative energy system,relies on hydrogen production through sustainable water splitting which in turn relies on the high efficient electrocatalysts.The hydrogen evolution performance of platinum catalysts can be further improved by alloying,Pt Au Cu A1-phase alloy has been predicted to be a promising electrocatalyst for hydrogen evolution.As such preferred phase of Pt-Au-Cu is not thermodynamically favored,herein,we stabilize Pt Au Cu alloy by engineering the high-entropy phase in the form of nanowire.DFT calculations indicate that,in comparison with the ordered phase and segregated phases with discrete hydrogen binding energy,the high-entropy phase provides a diverse combination of site composition to continuously tune the hydrogen binding energy,and thus generate a series of highly active sites for the hydrogen evolution.Reflecting the theoretical prediction,electrochemical tests show that the A1-phase Pt Au Cu nanowire significantly outperforms its nanoparticle counterpart with phase segregation,toward the electrocatalysis of hydrogen evolution,offering one of the best hydrogen evolution electrocatalysts.2.The sluggish cathode oxygen reduction reaction is a major factor limiting stack output in the fuel cells.Although alloying can significantly improve Pt’s performance by improving kinetic current and reducing overpotential in single cells,many Pt-based alloy catalysts still perform poor performance in membrane electrodes assembly,outputting low voltage and power density.In order to explore the deactivation mechanism of Pt-based alloys in electrochemical tests,the Pt Ni rhombic dodecahedron with slight phase separation was taken as the research object,the structural and compositional evolution at oxygen reduction potential was explored by in situ transmission electron microscopy.At0.8 V vs.RHE,electrochemical corrosion of the Pt Ni₃ rhombic dodecahedron was clearly observed from the corners,and finally,the Pt₃Ni with nanoframe structure formed.The corrosion of Ni is also the main reason for affecting the performance of the membrane electrode.This work provides an intuitive idea for designing stable ORR catalysts.3.Improving the stability of Pt-based nanocatalysts in electrochemical tests has become a key factor for ORR.In pursuit of ORR with high efficiency,more attention should be paid to the durability of catalysts.The transformation of solid solution alloys into ordered intermetallic compounds has proved to be an effective means.In this work,Mo-doped Pt In alloy nanowires were first synthesized,which exhibited excellent ORR catalytic activity.To further improve its stability,the catalyst was coated with silica and annealed at a high temperature to complete the ordered phase transition.The electrochemical tests show the ordered 1-D Mo-Pt₃In exhibited ultra-high activity,meanwhile,the half-wave potential only negatively shifted 1 m V after 10,000 cycles,and the mass activity decayed by less than 1%,indicating its strong stability.4.Developing efficient platinum-based electrocatalysts with super durability for the oxygen reduction reaction（ORR）is highly desirable to promote the large-scale commercialization of fuel cells.Although progress has been made in this aspect,the electrochemical kinetics and stability of platinum-based catalysts are still far from the requirements of the practical applications.Herein,Pt Pd Fe Co Ni high-entropy alloy（HEA）nanoparticles were demonstrated via a high-temperature injection method.Pt Pd Fe Co Ni HEA nanocatalyst exhibits outstanding catalytic activity and stability towards ORR due to the high entropy,lattice distortion,and sluggish diffusion effects of HEA,and the HEA nanoparticles delivered a mass activity of 1.23 A/mg _Pt and specific activity of 1.80m A/cm ²_Pt,which enhanced by 6.2 and 4.9 times,respectively,compared with the values of the commercial Pt/C catalyst.More importantly,the high durability of Pt Pd Fe Co Ni HEA/C was evidenced by only 6 m V negative-shifted half-wave potential after 50,000cycles of accelerated durability test（ADT）.