Preparation And Properties Of Carbon-based Oxygen Reduction Catalyst For Zinc-air Battery

Nowadays,under the background of the energy crisis and a new generation of energy conversion and storage devices constantly updated,zinc-air batteries（ZABs）using carbon-based metal materials as electrode catalysts have large specific energy,high rate performance,cheap of materials,technology mature and other advantages,has been widely concerned by people and the country’s strong support.The performance of ZABs depends on the kinetics of oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）.However,the catalytic reaction mechanism of ORR and OER is relatively complex,which is affected by factors such as the type of catalytic material,molecular structure,and the synergy between catalyst nanoparticles clusters,resulting in low electrocatalytic reaction activity and severely limiting the applicability of ZABs.In recent years,researchers in the field of industrial catalysis have constructed stable and efficient ORR and OER catalysts by developing and designing the structure of the catalyst and enhancing the interaction between the reactive site and the support,resulting in excellent performance of ZABs,but there are still falls short of the commercialization target.Based on this,this thesis combines the advantages of noble metals,transition metal-based materials and carbon materials,and uses a simple and effective preparation method to design and construct a variety of carbon-based composite materials for ORR catalytic reaction and zinc-air battery testing.The main research contents are as follows:1.Firstly,using the physical properties of biomass carbon starch gelatinization,platinum nanoparticles were grown in situ on the gel surface using starch as carbon carrier by simple freeze-drying method,and a catalyst with cheap and good catalytic performance Pt@C was obtained.The chemical composition,structure and morphology of the prepared materials were characterized by XRD,SEM,TEM,BET and XPS,and their stability and electrochemical performance of ORR were investigated by electrochemical test.Among them,Pt@C-800 has a large specific surface area(494.324 m~2 g^-1)and good catalytic performance,which is attributed to the unique structure of its biomass starch carbon carrier.This study provides a new theoretical support for the preparation of platinum carbon noble metal catalysts with high availability and easy availability.2.Here,the carbon-based non-precious metal composite nanomaterial catalyst Co/Co₉S₈/CNTs was successfully prepared by hydrothermal-pyrolysis method using corn starch as carbon source,thiourea as sulfur source,and cobalt hexahydrate as transition metal cobalt source.Using modern physical characterization methods,the microstructure and crystal structure of the prepared catalysts were analyzed.The results show that the Co/Co₉S₈/CNTs（900℃）catalyst not only has a large specific surface area(300.809 m~2 g^-1),but also its excellent ORR catalytic performance（onset potential of 1.0 V,half-wave potential can reach 0.86 V）is comparable to that of commercial Pt/C（onset potential of 0.97 V,half-wave potential of 0.85 V）,and its ORR mechanism path is close to the four-electron process,and it has better methanol tolerance and stability.Its excellent catalytic performance benefits from the large specific surface area and good pore structure of the composite,as well as the synergistic effect of better elemental composition ratio and sulfur atom doping.This study proposes a design method of carbon-based non-precious metal composites to improve the properties of ORR catalysts,which provides a promising preparation method for the development of non-precious metal catalysts that can replace Pt/C.3.In the end,using a combination of one-pot hydrothermal and high-temperature pyrolysis method,Co/Co₉S₈ nanoparticles were successfully anchored on the 3D carbon matrix（NSG/CNTs）with N and S double doping,using cobalt salt as non-noble metal cobalt source,melamine as a high nitrogen carbon source,thiourea as a sulfur source,and MWCNTs were used to further enhance the conductivity.A low-cost Co/Co₉S₈@NSG/CNTs（600℃）catalysts with excellent performance were prepared.Co/Co₉S₈@NSG/CNTs（600℃）catalyst not only has good ORR performance（half wave potential of 81.4 m V,which is only 30 m V lower than commercial Pt/C）,small tafel slope(84.0 m V dec^-1),but also has better stability and methanol tolerance in alkaline electrolyte,and has been successfully used in the application test of ZABs.Assemble a zinc-air battery with this catalyst and test its applicability in energy conversion devices,the battery showed high open circuit potential（OCP is 1.33 V）and good cycle stability and durability.This work provides a simple,stable and efficient method for the synthesis of doped non-noble metal catalysts with good stability and cost-effective.