Preparation Of Au-Based Alloy Electrocatalysts And Its Oxygen Reduction Activity

In recent years,because of the energy shortage crisis,fuel cells have been paid more attention as a clean,economical and efficient renewable energy technology.Oxygen reduction reaction?ORR?has also been extensively studied as a cathode reaction for fuel cells.In this paper,Au-based bimetal alloy catalysts were prepared by magnetron sputtering.It aims to improve the oxygen reduction activity of Au through the interaction of Au and other metal elements.The main research contents and conclusions are as follows:?1?Firstly,Au nano-electrocatalysts were prepared by magnetron sputtering,and the ORR activity of the different particle sizes of Au nanoparticles were investigated.For ORR,electrochemical analysis has shown that the initial potential of Au prepared by magnetron sputtering and liquid phase reduction?Au/C?is the same,and the half-wave potential of them is close.As for the electron transfer processes,they have not only 2e process but also4e process.This indicates that the oxygen reduction activity of Au prepared by magnetron sputtering is closed to Au/C prepared by liquid phase reduction.The ORR activity increases with the increase of particle size in the range of 4.25nm-11.22nm.?2?In order to further improve the ORR activity of Au,an AuCo alloy catalyst was prepared by magnetron sputtering.It was found that the initial potential of AuCo was0.967V,which was positive shifts of 47mV than Au.The half-wave potential was 0.862V,which was positive shifts of 32mV than Au.Compared with Pt prepared by magnetron sputtering,the initial potential of AuCo is the same asthat of Pt,but the half-wave potential is 12mV higher than that of Pt.However,the kinetic current density of AuCo(0.23mA cm^-2 at 0.85V vs.RHE)is less than that of the Pt(0.27mA cm^-2 at 0.85V vs.RHE).In addition,the ORR activity of AuCo with different proportions was also investigated.It was found that the ORR activity of AuCo increased first and then decreased with the increase of Co content.Among them,when the molar ratio of Au to Co is 46:54,it has the optimal oxygen reduction activity.The ORR activity of AuCo is improved because the electronic structure of Au has been changed during the alloying process.?3?Although the ORR activity of AuCo is significantly higher than that of Au,there is still a little lessthan that of Pt.In order to further improve the catalytic activity of Au,the AuFe alloy catalyst was further prepared by magnetron sputtering.Electrochemical analysis results have shown that the addition of Fe could actually improve the ORR activity of Au,and the Fe content could also affect its oxygen reduction activity.Au₆₇Fe₃₃has the optimal ORR activity,and its initial potential is 0.974V,which is positive shifts of30mV,4mV,7mV than that of Au,Pt and AuCo,respectively.The half-wave potential of Au₆₇Fe₃₃ is 0.870V,which is 40mV?15mV and 8mV higher than that of Au?Pt and AuCo,respectively.According to the XRD and XPS results,the remarkably ORR activity of AuFe is owing to the electron effect between Au and Fe in the process of AuFe alloy formation.The loss of electrons on the Au surface leads to an increases in the O binding energy,so the O adsorption capacity is improved.?4?Through previous researches,it was found that AuCo and AuFe did significantly increase the ORR activity of Au,and the ORR activity of AuFe was significantly better than that of Pt.However,it is not enough to merely improve the ORR activity,and it is also important to obtain a bifunctional catalyst having both oxygen reduction and oxygen evolution reactivity.Therefore,the AuIr alloy catalyst was successfully prepared by magnetron sputtering.XRD results showed that the characteristic diffraction peak of AuIr?111?was continuously shifted positively with the increase of Ir content,which indicated that AuIr alloys were successfully prepared.Electrochemical analysis has shown that the ORR initial potential of AuIr is 0.92V,and the half-wave potential is 0.80V,and the number of transferred electrons is 4.12.It is indicated that the oxygen reduction activity of Au can be increased by the addition of Ir,and the electron transfer process is also changed from 2e reaction to 4e reaction.At the same time,AuIr also has good oxygen evolution activity.When the current density is 10mA cm^-2,the overpotential of AuIr is290mV,butthe overpotential of Ir is 300mV.The overpotential of AuIr is close to Ir,indicating that AuIr has better OER activity.The surface electronic structure of Au is changed because of the addition of Ir,so the ORR activity is improved.On the other hand,Ir itself has good OER activity.So AuIr is a bifunction electrocatalyst with excellent ORR and OER activity.