Modification And Energy Conversion Performance Of Carbon-based Nanocatalyst

Scientific research and application technology all over the world are committed to the development of new types of energy conversion technologies,such as electrolytic water and fuel cells.Constrained by the slow kinetics of oxygen evolution reaction?OER?,hydrogen evolution reaction?HER?and oxygen reduction reaction?ORR?,the application of large-scale industrialization is difficult in these fields.Development of low cost non-precious metals?transition metal and non-metal?catalyst with excellent performance is the key to solve the problem.Based on non-noble metal carbon-based nanocatalyst in the application of OER,HER and ORR,this work deeply discusses the modification and construction of catalyst,systematically analyses the influence catalyst structure on catalytic activity,and provides a reference for the industrial application of nonnoble metal carbon-based nanocatalyst.1.Synthesis of Co@Co₃O₄ core-shell particle encapsulated N-doped mesoporous carbon cage hybrids for electrocatalytic water oxidationMetal organic frameworks?MOF?are self-assembled by metal ions or clusters and organic ligands through coordination bonds,which have the advantages of high specific surface area,tunable pore size and shape.Based on these facts,in this part of work,a unique electrocatalyst comprising Co@Co₃O₄ core–shell nanoparticle encapsulated N-doped mesoporous carbon cages is successfully synthesized by employing three-dimensional zeolitic imidazolate framework?ZIF-9?as MOF materials and ZIF-9/graphene oxide?GO?as the precursor.The researches show that:?1?During high temperature pyrolysis process,the periodic arrangement of Co2+ and organic ligands in MOF scaffolds leads to a homogeneous distribution of in situ formed Co nanoparticles and nitrogendoped porous carbon.Besides,the formed porous carbon can in situ encapsulate the Co nanoparticles,resulting in the specific carbon-cage structure;?2?Co nanoparticles can be regulated and controlled to form Co@Co₃O₄ as well as the Co₃O₄ nanoparticles by changing the method of heat treatment;?3?Nitrogen doped mesoporous carbon cage itself has certain OER performance;?4?MOF-derived electrochemical catalysts have the inherent high surface area and pore structure resulting from MOF;?5?GO has important influence on the morphology and activity of the catalyst;?6?The Co cores in Co@Co₃O₄ provide an alternative way for ultrafast electron transport and enhance OER performance.2.MOF derived Co₃O₄ nanoparticles embedded in N-doped mesoporous carbon layer/carbon nanotube composites: extraordinary bi-functional electrocatalysts for OER and ORRBased on the advantages of MOF as the pyrolysis precursor,this section mainly synthesizes Co₃O₄ nanoparticles embedded N doped mesoporous carbon layer/carbon nanotube?CNTs?composites by two step heat treatment method.The composites not only have good electrocatalytic activity and stability toward OER,but also can be used as a good performance ORR electrocatalyst.The composites catalyze OER with an onset potential of 1.50 V and an over-potential only of 320 mV to achieve a stable current density of 10 mA cm2.The same hybrids also exhibit ultrahigh ORR activity with an onset potential of 0.89 V,a half-wave potential?E1/2?of 0.81 V,limited current density of 4.4 mA cm-2,and the electron transfer number is calculated to be 3.8-3.9,indicating that ORR follows the first-order reaction kinetics and O2 is directly reduced to OH-.The results show that MOF derived materials can be used as bifunctional electrocatalysts for OER and ORR.3.Nitrogen-doped mesoporous carbon nanosheet/carbon nanotube hybrids as metal-free bi-functional electrocatalysts for water oxidation and oxygen reductionHeteroatom doped carbon material with a large surface area and pore structure has outstanding electrocatalytic properties.In this part,N-doped mesoporous carbon nanosheet/carbon nanotube?CNTs?hybrid material is synthesized by high temperature pyrolysis process.A biomass,non-toxic glucose,is used as the carbon precursor owing to its abundance and low price.Urea is introduced as the nitrogen source.The surface area of the resulting material can reach 594.1 m2 g-1 and the N content can reach 10.7 at%,in which the graphite and pyridine N is 69.3%.Research shows that CNTs are embedded in the carbon layer,not only can accelerate the electron transfer,but also can play a separate role,restraining the aggregation and stacking of N doped mesoporous nanosheets,and create more space for the mass transfer and active site exposure.At the same time,CNTs and N doped mesoporous nanosheets have synergistic effect.The electrochemical test results show that the material not only exhibits excellent OER performance,but also has good catalytic effect on ORR.4.Ultrafine Co2 P nanoparticles encapsulated in nitrogen and phosphorus dual-doped porous carbon nanosheet/carbon nanotube hybrids: high-performance bifunctional electrocatalysts for overall water splittingCobalt-based phosphides carbon hybrid nanomaterials have received considerable attention for both OER and HER.The current prevailing strategy for manufacturing such materials is the high temperature pyrolysis and followed by phosphidation,existing various inherent problems.Based on the above work in the third part,this part of work design and synthesize ultrafine Co2 P nanoparticles encapsulated in nitrogen and phosphorus dual-doped porous carbon nanosheet/carbon nanotube hybrids.With the addition of phosphoric acid,not only the ultrafine Co2 P nanoparticles embedded in the carbon layer can be formed in the pyrolysis process,but also the N and P in situ double-doping in the carbon layer can be realized.The research shows that the catalyst has fully exposed active sites and affords a large electrochemically active surface area,and not only has excellent catalytic performance in OER,but also can effectively catalyze HER in both acidic and alkaline conditions.