Preparations And Properties Study Of Pt-based Alloy For Oxygen Reduction Reaction

Low-temperature fuel cell is a device that directly converts chemical energy into electrical energy.It has been considered as an ideal clean power source because of its advantages such as high energy conversion rate,quick start-up,quiet and no noise.However,due to the slow kinetics of cathodic oxygen reduction,it is necessary to increase the platinum-based catalyst to accelerate the rate of cathode reaction.However,the high price of platinum and the scarcity of sources have directly increased the cost of fuel cells,which has severely hindered their large-scale commercial production.In recent years,due to the oxygen reduction catalytic activity of carbon-based non-precious metals catalysts,researches about carbon-based non-precious metals have achieved a lot,but at present there is still a considerable gap for practical applications.Nanoparticles?carbon materials loaded platinum?Nanoparticles are currently the only commercially-available fuel cell catalysts and one of the most active catalysts in each metal.Platinum is an essential element for catalyzing oxygen reduction reactions.The development of its alloy system highlights its irreplaceable importance both in reducing costs and improving catalytic efficiency.Based on all the facts,this article starts with Pt/Ni and Pt/Co alloy catalysts,a series of alloy nanocrystal catalysts supported on carbon materials have been designed and prepared under different conditions.The influences of different reaction conditions on the catalytic oxygen reduction activity of each catalyst have been analyzed and compared in detail.And a simple and easy-to-implement preparation method was explored to prepare the optimal reaction conditions for the oxygen reduction catalyst of the Pt/Ni alloy system and the Pt/Co alloy system.The main research contents and achievements of the paper are as follows:?1?H₂PtCl₆·6H₂O and Ni?CH₃COO?₂·4H₂O as metal precursors,Ketjen Black as the carbon-based material,the Pt/Ni alloy nanocrystal catalyst supported on carbon material was prepared by one-step reduction.By studying the relationships between reaction temperature,reaction time,orders of adding carbon-based materials,and ratios of platinum and nickel in metal precursors and their properties,it is concluded that the Pt₃Ni/C with best ORR performance can be prepared under reaction temperature at 160°C and the reaction time of 12h.This kind of one-step reduction method can be used to prepare highly uniformly dispersed20 wt%Pt₃Ni/C alloy nanocrystal catalyst with the best performance and complete morphology.The average particle size is about 3.9±0.7 nm,the onset potential is 0.952 V?vs.RHE?comparable to commercial Pt/C,and the limit current density is about 5.7 mA cm^-2.?2?The Pt/Co alloy nanocrystal catalysts supported on carbon materials can also be obtained by the above one-step reduction,in Pt/Co alloy system,we systematically studied influences and differences of different cobalt sources together with additives like polypyrrolidone?PVP?and benzoic acid in ORR catalytic synthesis and performance.It is concluded that with the reaction temperature of 170°C and the reaction time of 12 h and benzoic acid as dispersant and stabilizer,highly-active and highly-loaded 40 wt%Pt₃Co/C alloy nanocrystal catalyst with excellent high degree of uniform dispersion can be prepared,and the average particle size is about 2.2±0.1 nm.The onset potential is 1.083V?vs.RHE?,0.133 V higher than that of commercial Pt/C?0.95 V vs.RHE?,and its specific activity and massive activity are over 5 times than that of commercial Pt/C.After 30,000 s stability test,the limiting current density can still maintain 92%,far exceeding the 60%stability of commercial Pt/C.