Nanoporous Pt-Al Intermetallic Compounds Incorpated By Fe Or Co Element And Their Oxygen Reduction Properties

Nowadays,the ordeal we face is the problems brought by the severe environment contamination and the lack of fossil fuel.The key to solve the environmental and energy problems is to looking for a new energy with large reserves,low cost and less pollution.In kinds of new energy,low-temperature proton exchange membrane?PEM?fuel cell has widely used in power station,automotive and portable equipment due to its high efficiency,environmental friendly and rapid running speed features.It has become the succedaneum of fossil fuel.Therefore,how to improve the performance of fuel cells to promote its further development has become a highly anticipated topic.However,the specific activity and stability of Pt/C,the commercial cathode catalyst,largely hinder the development of fuel cell.Because this catalyst has a strong adsorption to the hydroxyl intermediate,which will decrease its specific activity.In the long-term use process,it will turn to coarsening and peeling,then reduce the service life.The cost and reserve of noble metal Pt is also constrain its application.In consequence,we need to find a novel catalyst to replace the Pt/C catalyst with a low price,high catalytic activiy and good stability,which will improve the performance of fuel cells.In recent years,the most common mehod to sovle this problem is the alloying,which is to prepare the binary alloy of Pt-M/Pt by inserting the transitional elements M to Pt,such as Fe,Co or Ni.Although this binary alloy has a higher catalytic activity than Pt/C,it still occur diffusion and dissolution in the acidic electrolyte,which greatly reduce the stability of the catalyst.Therefore,we improved this binary alloy by incorporated amphoteric metal Al to prepare a ternary alloy,and then form nanoporous structure by dealloying.This nanoporous structure could promote the electrocatalysis with the confinement effect,the negative curvature effect and the double charge layer overlap effect.Hence,this paper will focus on the catalytic performance of the nanoporous ternary alloys in the oxygen reduction reaction?ORR?.The main research content and results are as follows:1.Synthesis and catalytic properties of nanoporous?Pt1-x Fex?3Al/Pt intermatallic compounds.Lots of studies have shown that Pt-Fe alloy has a higher catalytic activity than Pt/C,but the catalytic stability is insufficient.Therefore,we firstly prepared master alloy Pt₁₀Fe₂Al₈₈ by alloying method and then,synthhesized nanoporous(Pt_1-xFe_x)₃Al intermatallic compounds by dealloying method.This intermatallic compounds have a bimodal nanoporous structure and an excellent electrocatalytic performance.The specific activity and mass activity of nanoporous(Pt_1-xFe_x)₃Al/Pt intermatallic compounds at 0.9 V?vs RHE?were 3.97 mA cmPt-2 and 1.94 A mgpt-1 respectively,which were 10.2 times and 14.9 times higher than the commercial Pt/C catalyst?0.39 mA cm Pt-2and 0.13 A mgpt-1?.After 40,000 cycles,the half-wave potential??E1/2?of nanoporous?Pt1-x Fex?3Al/Pt intermatallic compounds only shifted 15 mV to the left and the electrochemical specific area?ECSA?still remained 74%.This excellent catalytic activity and stability are derived from the compressive effect and ligand effect produced by Fe and Al atoms.The interaction between them leads to a significant down shift for the d-band center of the Pt atom,which also suppress the diffusion and evolution of Pt atoms on the surface,as well as preventing the corrosion of internal Fe and Al atoms.These features thereby stabilize the catalytic activity.This makes nanoporous?Pt1-x Fex?3Al/Pt intermatallic compounds become a powerful candidate for the next generation fuel cell cathodic catalysts.2.Synthesis and catalytic properties of nanoporous(Pt_1-xCo_x)₃Al/Pt intermatallic compounds.Based on the success of the improvement for Pt-Fe alloy system in our previous work,we have also focused on the Pt-Co system.We adopted the same alloying/dealloying method to insert Al atoms into Pt-Co alloy and finally got nanoporous(Pt_1-xCo_x)₃Al/Pt intermatallic compounds.The results of series of tests showed that at 0.9 V?vs RHE?,nanoporous(Pt_1-xCo_x)₃Al/Pt intermatallic compounds had a half-wave potential??E1/2?of 0.931 V and a specific activity of 3.50 mA cmPt-2 with a mass activity of 1.72 A mgpt-1,which were 9.0 times and 13.2 times higher than the commercial Pt/C catalyst?0.39 mA cmPt-2 and 0.13 A mgpt-1?,respectively.After 50,000 cycles,the half-wave potential only shifted 13 mV to the left.The electrochemical specific area and mass activity were still remained 65% and 61%,respectively.It can be seen that the nanoporous(Pt_1-xCo_x)₃Al/Pt intermatallic compounds could also be used as a cathode catalyst in fuel cell.What's more,the above results show that the design concept and synthesis method of ternary alloys are applicable not only to Pt-Fe system,but also Pt-Co system.In the future,it may also be developed to other alloy systems to offer more possibilities for cathodic catalysts.