| The increasing global concerns about the environmental issues and the depletion of fossil fuels have triggered an urgent demand to develop clean and high efficient energy conversion and storage technologies.Direct methanol fuel cells?DMFCs?as a green conversion device has been attracting increasing attention in recent decades.As we all know,the oxygen reduction reaction?ORR?is an important factors limiting the performance of fuel cells.Pt or its alloys are widely used as effective catalysts for ORR.Owing to the high cost and quickly declining activity of Pt,alternative catalysts have been actively pursued.Combining with the compositional effects,the accurate design of nonprecious metal catalysts with 3D porous nanostructures plays a significant role in further enhancing ORR performance.These 3D porous architectures are able to provide higher specific surface areas and larger pore volumes,not only maximizing the availability of electron transfer within the nanosized electrocatalyst surface but also providing better mass transport of reactants to the electrocatalyst.In this dissertation,we designed and synthesized three hybrids of cobalt-based nanocrystals and graphene aerogels,including CoCO3/NGA,Co3O4/NG and Co/GA.The probable structural information of catalysts was explored by scanning electron microscope?SEM?,transmission electron microscope?TEM?,X-ray diffraction?XRD?and X-ray photoelectron spectroscopy?XPS?techniques.The electrocatalysts were coated onto the glassy carbon electrode for electrochemical ORR measurements by using cyclic voltammetry?CV?,linear sweep voltammetry?LSV?and rotating disk electrode?RDE?techniques.The results showed that the prepared catalysts possessed not only excellent activity but also good tolerance to methanol crossover favorable for ORR.Prospectively,our present work may pave a new way to develop earth-abundant,low-cost and high-performance electrocatalysts for direct methanol fuel cells. |
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