Design And Synthesis Of Mesoporous Co-doped Carbons For Oxygen-electron Catalyze And Conversion

In order to solve the increasing conflicts between economic development and environment pollution,developing a series of efficient and sustainable energy techniques is under urgency.A series of electrocatalytic energy technologies,represented by proton exchange membrane fuel cell?PEMFC?and water splitting system has aroused various attentions.The oxygen reduction reaction?ORR?of the PEMFC and the oxygen evolution reaction?OER?of the water splitting system are key steps.But their overpotentials are high and need noble metal catalysts.At present,the commercial catalysts are Pt/C for ORR,RuO₂ and IrO₂ for OER.However,the high expense,extreme scarcity,low stability impede the widespread application of fuel cells.Recently,more attentions have been paid on the replacement of noble-metal-catalysts with cheap and eco-friendly non-precious-metal catalysts.Compared with metal-based catalysts,non-metallic heteroatoms doped carbon materials are more durable from oxidation and have higher stability.Especially in acidic electrolyte,they have better methanol tolerance.It is found lately that nitrogen doped carbon has outstanding catalytic performance among all series of meta-free catalysts.Nitrogen has similar atomic radius but different electronic configurations with carbon,which endows N-doped carbons with new electronic structures in the minimum lattice mismatch.On the basis of N-doping,importing another heteroatom and forming co-doped carbon can verify the polarities and electronic distribution of the catalyst to further optimize its electro-activity.Although great progress has been made in late years,there are still various problems.1:Some so-called"non-metal catalysts"use precursors or carriers that contain trace metal elements in the synthesis process,which cannot determine true active center.2:Although bifunctional catalysts are already synthesized,their performance is generally splendid sorely in single reaction,and in the other reaction is less effective.3:The preparation processes of the catalyst are complicated,and the precursors are expensive,which inevitably increases the price of the non-metallic catalytic materiasl.In this dissertation,commercialized and accessible non-metal compunds were chosen as N-doped precusors to construct and modify hierarchically porous carbon materials,supported by sacrificed hard-template and self-assembly method.By optimizing the pyrolysis temperature,the graphization degree and transfer of electron can be enhanced,which can condense the active site to synthesize a series of highly-efficient non-mental electrocatalysts.Details are as follows.1:A series of metal-free N,P-doped carbons were synthesized as efficient electro-catalysts for both ORR and OER by hiring mesoporous silica spheres as hard temple and commercial phenoxycycloposphazene as a tri-resource of N,P,and C owing to its pre-existing N-P coupling.Efficient and stable N-P-C electro-catalysts with outstanding performance in both ORR and OER were obtained after the pyrolysis at 1000?and acid-etching.The ORR half-wave potential of N-P-C reached 0.85 V and 0.64 V in the 0.1M KOH and 0.1M HClO₄,separately,superior than reported N,P doped carbon materials in the literature.Moreover,the OER over N-P-C electrodes should reach 10mA·cm^-2 current density,even 30mV lower than typical RuO₂ electrode.The splendid performance makes this series materials a potential substitute for noble-metal electro-catalysts.2:Low-cost melamine and 4-formylphenylboronic acid were assembled into new covalent melamine-boroxine frameworks with Cu?NO₃?₂ as catalysts and temples.Cu@B-N-COFs were synthesized through boronic acid dehydration reaction are well as Schiff-base reaction by a simple one-pot synthesis routine.A series of mesoporous B-N-Cs with unique hollow capsule morphology and high graphization degree were achieved after etching the metal Cu in Cu@B-N-C,which derived from the pyrolysis of Cu@B-N-COFs at 1000?.The ORR half-wave potential of B-N-C reaches 0.85V in alkaline electrolyte.It also served as an advanced electrode material for supercapacitor with a specific capacitance of 230 F/g.This research not only develops a novel copper-assisted thermal conversion pathway of melamine-boroxine frameworks,but also provids a series of reliable metal-free ORR electro-catalysts and capacitor materials with satisfying performance.3:A series of novel N,S-codoped organic frameworks?N-S-COFs?by hiring carbon nanotube as carriers and melamine and 2-Thenaldehyde as precursors in one-pot synthesis.By optimizing the pyrolysis temperature,N-S-C-900 has the most suitable graphitization degree and porosity.The ORR half-wave potential in 0.1M KOH reaches 0.84V.In OER,the potential of N-S-C-900 at 10 mA·cm^-2 is 1.56V.The obtained N-S-C-900 is an efficient bifunctional catalyst in oxygen conversion reaction.