凯发

Recently, carbon based catalysts have been extensively studied as a cathode material in Polymer Electrolyte Membrane Fuel Cells (PEMFCs) due to their intrinsic properties such as high surface area and high conductivity. In acidic media,however, the development of carbon-based catalysts outperformingPt as an ORR catalyststill require further exploration. Moreover, carbon corrosion is one of the major issues in PEMFC, which causes the low stability in carbon based catalysts. Thus, designing a catalyst with both activity and stability would be desirable when searching for potential catalysts in PEMFC. Herein, new approaches to advance the nature of carbon-based materials as ORR catalyst are presented. First of all, through a series of physical and chemical modifications, the hybrid structure of tailored nanodiamondgenerated a synergic property of both activity and stability.[1] Our optimized tailored nanodiamond catalyst showed a high current density which is about 73 % to that of Pt/C catalyst. Moreover, the catalyst retained a 96.8 % of performance even after harsh operations (0.6 - 1.4 V) of Accelerated Degradation Test (ADT), which was superior to that of Pt/C catalyst (retained 27 %). Through the modification, the sp3-hybridized diamond structure was deliberately preserved at the core to retain stability, while the modification of the sp2-hybridized at the surface carbon layers by the construction of defect and edge sites enhanced the catalytic activity within the catalyst material.Secondly, morphologically modified graphenebased catalysts were developed. In previous reports, our group suggested following morphological descriptors that can determine ORR activity of graphene based catalyst; defect sites for efficient heteroatom doping, small size to elevate electropotential, and ribbon-like structure to form porous electrode surface.To satisfy the suggested conditions with simple synthesis procedure, stacked-cup carbon nanofiber surrounded by graphitic walls was selected as a parent material of graphene catalyst.[2]The prepared catalyst exhibited 0.72 V of half-wave potential with 1.56 mA mg-1 and 9.75 mA m-2of mass and specific activities, respectively, at 0.75 V in acid media. Finally, polyaniline/graphene self-assembly catalyst is synthesized to utilize basal plane of the graphene which was recognized as an active site in case of graphene-based catalysts. Polymerized polyaniline between graphene layers prevent their restacking and thereby layer-by-layer structure of polyaniline and graphene enhances ORR activity in acidic media.