Study On Pt/Pt Alloy Catalysts Derived From MOF For Oxygen Reduction Reaction

Fossil fuel resources are restricted as well as unavoidably cause geological harm,environmental pollution,and greenhouse effects,bringing about the steady deterioration of our environment.Therefore,it is demanding to search for clean,sustainable,and feasible new energy for our use.Fuel cells and metal-air batteries are drawing huge attention among various promising power technologies due to their low cost,environmental harmony,and high energy density.However,their commercial applications have been truly hindered by a poor oxygen reduction reaction(ORR).As an extensively used ORR catalyst,Pt/C is one of the most favorable catalysts with high catalytic activity.Nevertheless,the high cost and poor durability problems hinder its large-scale commercial applications.Recently,alloying of Pt with other non-precious metals are attracting massive attention from researchers.Alloying of Pt with transition metal is a valuable way to increase the mass activity and reduce the Pt loading,but carbon support corrosion still exists.The synthesis of Pt/C with low loading and superior durability is still a significant challenge.In this research,we utilized different ways to solve these problems.We synthesized pure Pt catalysts and Pt alloy catalysts by using pyrolyzed metal-organic frameworks(MOFs)as a carbon support material.The content of this thesis is as follows:(1)A simple impregnation method was used to synthesis pure Pt catalysts by encapsulating ultrasmall Pt nanocrystals inside pyrolyzed UiO-66-NH2 metal organic frameworks.The corrosion of carbon support is the main problem for the degradation of commercial Pt/C.MOFderived NC was utilized as carbon support.The unique interaction between Pt and carbon support was observed by Pt-N bonding,which results an improved electrocatalytic activity.This Pt/N-C displays fantastic ORR activity and durability in alkaline solution with a half-wave potential of 0.90V(vs.RHE),limited diffusion current density of 5.5 mA cm-2,and only 5 mV deterioration in half-wave potential after testing 20,000 CV cycles.Besides,it also shows impressively good performance in acidic solutions.In addition,Zn-air battery assembled by the Pt/N-C air electrode displays excellent battery performance,including a high specific capacity of 825 mAh g-1,a high peak power density of 372 mW cm-2,and 208 hours long-cycle life.The improved performance of Pt/N-C may be due to its novel encapsulation structure,large surface area,high porosity,and including Pt-N bonding(unique interaction between Pt and carbon support).This offers a new innovative approach for developing noble metal-based catalysts with unusual activity,stability and a promising future for applications in metal-air batteries and fuel cells.(2)Metal-Organic Frameworks-derived PtNi based catalysts were synthesized by utilizing pyrolyzed-MOF as a carbon-supported material.The novel PtNi nanoparticles have been successfully synthesized with an average diameter of 3.1 nm.The as-synthesized Pt1Ni1/NC catalyst showed superior ORR activity than commercial Pt/C in both alkaline and acidic solutions.Pt1Ni1/NC showed a high mass activity of 2.16 A mg Pt-1,superior to Pt/C(0.105 A mg pt-1)in 0.1 M KOH and showed a high mass activity of 1.09 A mg Pt-1,superior to all other catalysts and Pt/C(0.101 A mg Pt-1)in 0.1 M HClO4 solution.Likewise,Zinc-air batteries(ZABs)assembled with Pt1Ni1/NC displayed high specific capacity and energy density(882 mAh gzn-1,1102 Wh kgzn-1).In addition,it showed a high peak power density of 464 mW cm2 superior to commercial catalysts.This work offers a new approach to synthesizing Precious metal-based catalysts with outstanding activity,durability,and promising applications in fuel cells and metal-air batteries.(3)Novel PtRu single-atom catalysts were synthesized by utilizing pyrolyzed-MOF as a carbon-supported material.The as-synthesized PtRu SAs/NC catalyst showed improved ORR activity in both alkaline and acidic solutions.