Preparation Of Novel Platinum Based Alloy Nanocatalysts And Their Application In Hydrogen Energy Electrocatalytic Technology

Hydrogen is one of the most promising energy carriers for achieving carbon neutrality.The hydrogen energy electrocatalytic technology is required in production and utilization of hydrogen.Among them,the hydrogen evolution reaction(HER)in water electrolysis and the oxygen reduction reaction(ORR)in proton exchange membrane fuel cells are two important cathode reactions.Platinum-based catalysts are the most studied cathode catalysts,and it is still a challenge to improve its mass activity and stability to meet the needs of large-scale commercial applications.Platinum-based alloy nanocatalysts can effectively improve the catalytic activity of platinum and reduce the loading of platinum,which are considered as the ideal HER and ORR catalysts.Hightemperature pyrolysis reduction is a commonly used strategy for preparing alloy nanocatalysts,such as fixed bed pyrolysis(FBP),which faces the incompatible contradiction between component control of homogeneous alloys and ultra-small particle sizes.Therefore,this paper focuses on ultra-small alloy nanocatalysts systems and develops a new pyrolysis reduction strategy based on the study of the nucleation and growth mechanism of alloy nanoparticles,which allows for the controlled synthesis of highly dispersed,multi-component homogeneous alloy nanocatalysts with ultra-small particle size.Furthermore,strategies such as structural regulation and component optimization had been adopted to improve the activity and stability of alloy nanocatalysts,achieving the following research results:1.Based on the study of nucleation and growth mechanism of alloy nanoparticles,a fast moving bed pyrolysis(FMBP)strategy was developed.The investigation of the nucleation mechanism indicated that the extremely fast heating rate would lead to high nucleation temperature,which resulted in small critical excess free energy and critical nucleation radius,so that the metal precursor could be reduced to nucleation at the same time.The investigation of the growth mechanism indicated that the extremely fast heating rate made the system have a high degree of supersaturation,so that the growth of alloy nanoparticles was narrow in size distributions.Therefore,FMBP with an extremely fast heating rate(125 K/s)could be used to prepare small sized homogeneous alloy nanoparticles.2.In order to adjust the components and supports of alloy nanoparticles in a wide range to obtain efficient and stable alloy nanocatalysts,a variety of incompatible metal elements can be formed into multicomponent homogeneous alloy nanocatalysts with ultra-small particle size(1-5 nm)and high dispersion by improving the the process parameters of FMBP,which was basing on the research on nucleation and growth mechanism of alloy nanoparticles.And FMBP strategy is not limited by the type of metals(up to ten)and supports(γ-Al2O3,zeolite,carbon substrates).Representative quinary alloy nanocatalysts(FeCoPdlrPt@GO)of FMBP synthesis had a smaller HER overpotential(η10=42 mV),and its mass activity(9.1 mA μgPt-1)was about 26 times of commercial Pt/C.Furthermore,FeCoPdIrPt@GO exhibited a long stability of 150 hours at a high current of 100 mA cm-2 without obvious fluctuation.3.In order to improve the atomic utilization rate of Pt and further enhance the ORR activity of Pt-based nanocatalysts,a ternary alloy nanocatalysts(VCo-Mo-PtCoMo)with double surface Co and Mo defects were synthesized by combining FMBP strategy and etching process.The ORR specific activity(0.89 mA cm-2)and mass activity(0.57 A mgPt-1)of VCo-Mo-PtCoMo were 7.4 times and 5.2 times that of commercial Pt/C,respectively,and the mass activity was further improved to 0.77 A mgPt-1 after 10,000 cycles.The investigation of the catalytic mechanism indicated that the compressive strains caused by the double surface defects optimized the electronic structure of Pt,weakening binding energy between active sites and*OH,thus enhancing the ORR activity of the catalysts.The improvement of stability can be attributed to the formation of Mo-Pt and Mo-Co bonds,as well as the formation of surface Pt shell.4.In order to improve the ORR stability of alloy nanocatalysts,Pt3FeCoNiCux were determined to quinary high entropy alloy nanocatalysts with excellent thermodynamic stability according to the Hume Rothery rule.The quinary high entropy alloy nanocatalysts(Pt3FeCoNiCux)were synthesized by FMBP,and the relationship between Cu content and ORR catalytic performance was systematically studied.The catalysts exhibited the best stability(the half-wave potential showed a decreased potential of 1 mV after 30,000 cycles)at x=0.75,which may be attributed to the high entropy and slow diffusion effects of high entropy alloy catalysts.The investigation of the catalytic mechanism indicated that the Cu optimized the electronic structure of Pt and reduced the energy barrier of the formation step of*OOH intermediates,thereby increasing ORR activity.