Metal Materials Supported On Pyridyne Cycloaddition Of Graphene And Their Electrocatalytic Performance

In recent years, proton exchange membrane fuel cells (PEMFCs) are promising candidates for clean and efficient energy conversion amidst the impending global energy crisis, resulting from their high energy-conversion efficiency, low temperature of operation, and environmental benefits. Catalysts for oxygen reduction reactions (ORR) are the major focus of chief renewable energy technologies in fuel cells. It has been well known that Pt and its alloy are known as efficient catalysts for ORR. However, the prohibitive cost and scarce reserves of Pt have hampered the widespread use of PEMFCs. Therefore, partial or complete replacement of Pt metal is of interest and much progress has been made so far. Here, we prepared differet types of metal/graphene bi-functional catalysts, and the characterization and electrochemical performance of catalysts were thoroughly identified and analyzed. The detailed contents and conclusions are as follows:(1) Pyridyne precursors were prepared by organic synthesis methods, and then we developed an approach for obtaining "external" nitrogen doped graphene (PyNG) via pyridyne cycloaddition. The PyNG material exhibited moderate ORR performance. And XPS measurements indicated the nitrogen functional groups correspond to pyridine-N. This phenomenon is attributed to pyridyne cycloaddition modulation, which causes PyNG to have unique chemical and electronic structures. The DFT calculations revealed that the ortho-carbon of the "external" nitrogen could be a possible adsorption and catalytic site because of its unique electronic properties. The results provided us with an idea that dispersing metal materials on PyNG which can act as a high surface area active support.(2) A new type of hybrid material consisting of iron phthalocyanine (FePc) coordinated with pyridyne cycloaddition of graphene sheets as a high-performance electrocatalyst for ORR were fabricated. Electrocatalytic properties of the catalyst for ORR in alkaline have been investigated by cyclic voltammetry (CV) experiments, rotating disk electrode (RDE) measurements and chronoamperometry. The prominent features of the Fe-PyNG hybrid include high electrocatalytic activity, superior durability, and better performance than Pt/C toward ORR in alkaline media. These features potentially make Fe-PyNG an outstanding nonprecious metal cathode catalyst for fuel cells. The incorporation of Fe ion and pyridine-N afforded effective bonding and synergetic coupling effects, which lead to significant electrocatalytic performance. (3) The Pt@Au alloy nanorods were fabricated with the as-prepared gold nanorods for platinum growth, using a mild reducing agent, ascorbic acid, in the presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB) and silver ions. Then, we successfully developed a novel and efficient approach for decorating Pt@Au nanorods on PyNG, which can serve as feasible Pt alternatives for ORR. The Pt@Au-PyNG exhibited excellent electrocatalytic performance, with superior methanol tolerance and enhanced electrocatalytic stability than Pt/C toward ORR. This result can be attributed to the strong coupling effects between the Pt@Au NRs and PyNG.In this thesis, we present facile and efficient approach for preparing novel metal/graphene hybrids, but also we believe that our present strategy could open the door toward fabrication of varying kinds of metal complexes/N-doped carbon materials hybrids that will have broad application in the field of catalysts, batteries, and supercapacitors.