Macrocyclic Compounds Derived Porous Multi-doped Carbons With Efficient Oxygen Electroreduction Performance

Proton exchange membrane fuel cells?PEMFCs?are energy conversion devices and power sources with high-efficiency and low-emission.One major bottleneck for the high power output of the fuel cell lies in the sluggish kinetics of oxygen reduction reaction?ORR?at cathode.The most common catalyst to accelerate the ORR is the Pt-based catalysts.However,the high cost and scarcity of Pt impedes the widespread application of fuel cells.Therefore,exploring non-precious metal electrocatalysts?NPMCs?with abundant storage for the replacement of the Pt-based catalysts,optimized their structure,morphology,composition to improve ORR performance,become popular concerns in the area of materials and energy research to promote the large-scale application of PEMFCs.Among various NPMCs,non-precious metal macrocyclic compounds derived carbons materials on phthalocyanines and porphyrins are particularly attractive.These macrocyclic compounds not only contain rich contents of carbon and nitrogen,but their centers often have M-N4 centers formed by metals and nitrogen,and some M-N4centers can be retained on the surface of pyrolyzed carbon materials and become active sites of ORR,especially in acid.However,macrocyclic compounds are generally expensive,except for cheap and commercialized phthalocyanines and porphyrins,and are pyrolyzed directly or loaded on the surface of the carbon to be pyrolyzed.It is often difficult to obtain efficient ORR electrocatalyst comparable to Pt-based materials,due to insufficient surface area or lower active site density.If the cheap phthalocyanine and porphyrin macrocyclic compounds are used as precursors,the high active NPMCs are constructed by the optimization of the pyrolysis methods,doping species of metal and non-metal,and precursor structure and composition.It is of great significance to promote the preparation of highly efficient and stable NPMCs and the application of PEMFCs.In this dissertation,commercialized and cheap phthalocyanines and porphyrins non-precious metal macrocyclic compounds were chosen as precursors to construct and regulate hierarchically porous formation of derived carbon materials,supported by sacrifice the hard template and self-assembly method.The heat-treatment is optimized to control the degree of graphitization and electric conductivity.Meanwhile,the types of multi-doped metals in N-doped carbon materials are controled to regulate the active site density and the active site center.Our aim is to optimize balance between active site density and capability for mass and charge transport to prepare efficient and stable oxygen reduction electrocatalysts derived from non-precious metal macrocyclic compounds.Details are as follows:1:The highly efficient and stable ordered mesoporous Cu-based ORR catalysts?Cu-N-C?were obtained by using commercialized and cheap copper phthalocyanine as a precursor and the mesoporous KIT-6 silicon as the hard template to pyrolyze at a high temperature of 1000°C.The prepared Cu-N-C catalyst was superior to Cu-based electrocatalysts reported in the past for ORR,with 0.82 V half-wave potential in 0.1M KOH and 0.72 V half-wave potential in 0.1 M HClO4.For further study of the central metal on ORR activity,it was found that the order of activity was as follows:Cu>Fe>Co>Zn H at 1000?,which was different from that of 900?.It was also found that the ORR catalytic performance of Cu-N-C could be futher enhanecd by co-doping few Fe species into the carbon framework?Fe?1?-Cu?3?-N-C?.It revealed about 30 mV higher half-wave potential and better stability than Cu-N-C catalyst in both alkaline and acidic media.Moreever,the electrocatalysts prepared by this method can be produced at a scale of over 15 g in laboratory,and the half wave potential was even increased by 10 mV.The high-efficiency ORR performance and scalable synthesis of Cu-N-C and Fe?1?-Cu?3?-N-C catalysts enabled them to be the potential substitutes to Pt-based eletrocatalyst for ORR.2:A double metal and double non-metal co-doped carbon material?Co?1?-Cu?3?-N-S-C-900?waspreparedbycobalttetrasulphonated phthalocyanine?CoTSPc?and copper disulphonated phthalocyanine?CuDSPc?as precursors,nano-silica spheres as sacrificial hard templates,chitosan as a binder and graphene oxide as an electrical conductivity enhancer.The material ratio of CoTSPc,CuDSPc,chitosan,graphene,and nano-silica spheres,and the heat treatment conditions were further optimized.It was found that Co?1?-Cu?3?-N-S-C-900 has good nanoporous structure and high degree of graphitization.The half-wave potential of the Co?1?-Cu?3?-N-S-C-900 reaches 0.85V under alkaline conditions,close to the commercial Pt/C,and the stability was better than Pt/C.3:A three-dimensional iron-based covalent porphyrin polymer?Fe-CPP?with rigid and flexible structure was rapidly synthesized through the one-pot polymerization reaction between cheap pyrrole and self-made tris?4-formylphenyl?amine?TFPA?.Among them,the N-centered TFPA pyramid structure is flexible,while the formed Fe-porphyrin block is rigid.The structure,composition and properties of the carbon materials were characterized after optimizing the heat treatment of the Fe-CPP.The obtained Fe@Fe-N-C at 900?C?Fe@Fe-N-C?showed high graphitization degree and hierarchical pore structures with specific surface area of 752 m² g^-1.The ORR half-wave potential of?Fe@Fe-N-C?reached about 0.83V in KOH and 0.73V in HClO4 solution with high limiting current density,making it the advanced carbon-based non-precious metal nanocatalysts?NPMCs?for the ORR.