Synthesis Of PtNi Alloy Nanocatalysts For Oxygen Reduction Reaction

In the development of science and technology and the process of industrialization in the 21st century,the energy crisis and environmental pollution caused by the rapid consumption of fossil energy are becoming more and more serious.It is urgent to find new alternative energy sources.Proton exchange membrane fuel cell(PEMFC),as an efficient device for converting hydrogen energy into electricity,can not only alleviate the energy crisis but also protect the environment.Thus,PEMFC is known as the final solution to energy and environmental problems in the 2cst century.At present,one of the key factors restricting the commercialization of PEMFC is the cost of using precious metal Pt as catalysts.So current research focusing of PEMFC is how to improve the oxygen reduction reaction(ORR)performance of platinum catalysts and reduce the use of precious metal Pt at the same time.In the past decade,researchers have conducted extensive research by doping cheap transition metal into Pt or preparing Pt-free catalysts.Among all the Pt-based catalysts,Pt-Ni alloy catalysts show superior catalytic activity and stability in ORR test,which demonstrates that the cathodic ORR can be greatly accelerated by using Pt-Ni alloy catalysts to reduce the overpotential of ORR.The doping of Ni not only reduces the cost of platinum,but also improves the ORR performance of the catalysts,which shows a broad application prospect in the field of PEMFC.In this paper,a series of studies have been carried out on the design,preparation and synthesis of Pt-Ni alloy nanocatalysts and on the characterization of their corresponding ORR performance.The main results are as follows:(1)Through thermodynamic control,monodispersed Pt-Ni alloy nanocatalysts were successfully synthesized using simple chemical impregnation method.The experimental results show that the size of PtNi nanoparticles is only 2.8 nm.The proportion of Pt and Ni and the amount of surfactant triethylamine play a vital role in determining the size and size distribution of PtNi nanoparticles.ORR measurements showed that the Pt-Ni catalyst had excellent electrochemical surface area(98.9 m2/gpt).Mass activity and specific activity of PtNi nanoparticles were nearly twice as high as that of commercial Pt/C catalyst(JM,60wt%).Moreover,0.5 M sulfuric acid+400 degree annealing treatment can effectively improve the catalytic stability of monodispersed PtNi crystals.It is also found that the power density of PtNi nanocatalyst was better than that of commercial Pt/C catalysts at 0.65V.The doping of Ni greatly improved the catalytic activity and reduced the cost of Pt making PtNi catalysts become a potential catalyst for PEMFC.(2)Through thermodynamic control,PtNi alloy nanocatalyst with octahedral morphology was successfully synthesized by solvent thermal method.The results show that sodium benzoate could effectively reduce the particle size of PtNi octahedral nanocrystals and promote the formation of regular octahedrons.The mass ratio of Pt(acac)2 to Ni(acac)2 can greatly affects the productivity of PtNi nanocrystalline octahedron.When the mass ratio of Pt(acac)2 and Ni(acac)2 is 2:1,higher yield of octahedral structure can be obtained.In the accelerated stability test,PtNi octahedron nanostructure showed excellent stability,the electrochemical activity area decreased by only 18.3%,and the half-wave potential loss of oxygen reduction curve was only 10mV.