MOF Derived Nitrogen Doped Carbon With Hierarchical Nanostructure For Electrochemical Energy Conversion And Storage

Nowadays,the exploration of rational design and facile synthesis of bifunctional low-cost electroctalysts for both oxygen reduction and evolution reaction(ORR/OER)is central to renewable energy storage/and or energy conversion technologies such as fuel cells and metal air batteries.In the present work a facile and direct growth approach is developed to construct Co embedded Nitrogen-doped carbon nanotubes(Co-NCNTs)via solid pyrolysis of ZIF-67 and Uric acid.In this strategy,The Uric acid were chosen as initiator get the advantage of thermal decomposition at relatively lower temperature(440?)to carbonaceous gases permeate readily into ZIF-67 polyhedron via solid diffusion.These gases serve as carbon-Nitrogen source as well in-situ formed Co metal nanoparticles with increasing pyrolysis temperature for catalytic growth of N-CNTs.Due to preferential generated nanocatlyst on the surface,the subsequent growth of CNTs is directed from inside to outside on each nanotube sphere.Moreover,the UA serve as inducer for the graphitic structure.The resultant well-developed worms like CNTs possess the following unique characteristics.(1)Due to pronounce graphitic structure of one dimensional CNTs present admirable electrical conductivity,and hence improved the electrocatalytic performance.(2)The Co-NCNTs-700 possesses high surface area and the mesoporous structures imply to expose high density of efficient active sites.(3)The core shell particles(Co@NC)located at the tip of each growing CNT could effectively expose the available active sites of the catalyst to the electrolyte.(4)The in-situ formed unique and uniform CNTs structure favourable the electron transport and durability of the as-prepared materials.The combined effect of these remarkable-factors in Co-NCNTs-700 catalyst ensures its outstanding bi-functional electrocatalytic activity for both ORR and OER reactions in alkaline medium.Moreover,Zinc-air battery was design using Co-NCNTs as cathode materials with significant performance,demonstrating its feasibility and potentials for practical applications in energy storage and energy conversion technology.In the second project,instead of direct pyrolysis of solid precursor,firstly the as optimized-ratio of ZIF-67 and Uric acid(2:1)respectively,were mixed via simple solvent thermal method,followed by pyrolysis approach to construct double-shell Nanocages(DSNCs).The Uric acid exhibit relatively large amount of Carbon and Nitrogen species,with increasing pyrolysis temperature the UA decompose into large amount of carbonaceous gasses.The escaping of these gasses results in hierarchical mesoporous outcomes.Moreover,the formation of Co NPs during pyrolysis catalyzed the carbon-organic residual results in the formation of short CNTs on outer shell of the DSNCs.The inner shell consists of Co and N doped mesoporous structure while the outer dense shell consists of N doped graphitic carbon from which the short CNTs are extruded.The resultant DSNCs catalyst shows excellent catalytic activity for oxygen reduction reaction and supercapacitor.When the pyrolysis temperature reaches to 700?,the as prepared(DSNCs-700)catalyst shows the best ORR activity compare to commercial 20%Pt/C catalyst.In addition,the DSNCs-700 was also employed as electrode materials for supercapacitor which possess excellent stability,significant capacitance,and good rate capability at different current densities.