The Synthesis And Application Of Electrocatalyst Based On Selected 3d Transition Metal Sulfide

The incremental demand for energy and the increasingly serious environmental crisis has prompted the continuous researches on excellent renewable energy conversion and storage systems.Microbial fuel cells?MFCs?and rechargeable zinc air battery are considered as the next generation of clean energy equipment owing to the property of environmental benefit and high security.Cathode catalyst is vital for the performance of the above batteries,since kinetics of both oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?are inert due to adsorption and desorption of oxygen on electrode,formation of intermediates and mass transfer process of reactants.Traditional noble metal catalysts are widely deemed to be effective in reducing the intermediate barrier of oxygen reaction while the high cost,scarce distribution and poor durability of these catalysts have greatly limited their application in mass production.Therefore,it is extremely urgent to design and prepare cathode catalyst based on low cost,easy accessibility to raw materials,and with high catalytic efficiency besides stability.In this paper,nitrogen doped hollow spheres as substrate and transition metal sulfides as active sites were combined and synthesized by means of template method,chemical bath deposition and hydrothermal method.And their applications as cathode catalysts in microbial fuel cell and even in zinc-air rechargeable battery were explored.The specific work is as follows:?1?Phenolic resin coated silica sphere template was synthesized based on typical Sto?ber method.After carbonization in N₂ and removal of silicon sphere,the phenolic resin was transformed into hollow carbon sphere with mesoporous channels and nitrogen doped active sites.Co₉S₈ nanoparticles with high catalytic activity of ORR were later modified on the surface of hollow carbon sphere,so the Co₉S₈/NHCS with cooperative interface structure was constructed.Co₉S₈/NHCS exhibited good catalytic activity,stability and methanol resistance in both alkaline and neutral electrolyte.In application of cathode in MFC device,the maximum power density was 704±2mW m^-2,as the chemical oxygen demand?COD?removal rate was 96.28±0.50%.?2?As the synthesis of Co₉S₈/NHCS,nitrogen-doped carbon hollow spheres with a bowl-shaped structure were obtained by adjusting the concentration of phenolic resin precursor.Next the Fe doped Fe _XCo_9-XS₈-NHCS was synthesized with introduction of iron into the growth process of sulfide nanoparticles.The iron replacement site of octahedron and tetrahedron was found in connection with the bond length of metal-sulfur bond,which could be simply regulated via the ratio of concentrations of iron and cobalt precursors.Fe_XCo_9-XS₈-NHCS demonstrated superior catalytic activity with half-wave potential of of0.803 V?vs RHE?for ORR and the potential of 1.531 V?vs RHE?as current density reaching10 mA cm^-2 during OER.In application of cathode in Zinc-air battery,the Fe_XCo_9-XS₈-NHCS achieved superior performance with the power density was 102 mW cm^-2.Besides,the maximum power density of MFC used Fe_XCo_9-XS₈-NHCS as cathode reached 791±42 mW m^-22 after 30 cycles.