Preparation And Electrochemical Performance Of Bifunctional Oxygen Catalysts For Carbon Sulfide

Increasing shortage of energy need of the urgent energy transformation.In order to solve this above problems,exploring sustainable green energy and its related storage/conversion devices is an important means.Zinc-air battery has become a research hotspot because of its advantages such as low cost,high specific energy,green and clean.ORR/OER as the core process of battery reaction,their slow cathode kinetic reaction is an important reason that hinder their further development.The key to solve this problem is to design ORR/OER bifunctional electrocatalysts with high activity and durability.Although noble metal catalysts have good ORR performance,it is costly and often shows a single catalytic performance.Thus it is urgent to design the good ORR/OER bifunctional with high abundance,good stability and low cost for replace noble metal catalysts.The main contents and achievements of this paper are as follows:（1）Using thiourea and Co（No₃）₂as reactants and graphene oxide as the skeleton to construct a three-dimensional metal sulfide catalyst network structure.Porous nitrogen doped sulfide catalyst through ball-milling and high temperature pyrolysis process successfully prepared.Physical spectrum characterization include SEM,TEM,XRD and XPS.Electrochemical performance include CV,LSV and LANDA.The results show that catalyst had the best ORR catalytic performance when the matel content was 0.8g(named Co_0.8S_x-Gra).The ORR reaction process was mainly four electron transfer.However,the ORR performance of the catalyst was still less than that of the commercial 20%Pt/C catalyst.Therefore another transition metal（Ni/Cu/Fe）was introduced to modify the catalyst on the basis of Co S_x-Gra.The results showed that Co/Fe catalyst had better bifunctional performance,and when the ratio of iron salt to cobalt salt was 3:1(Co_0.2Fe_0.6S_x-Gra),Co/Fe catalyst showed the best performance.This may be due to the proximity of Fe atomic sites to Co atomic sites which promoting the adsorption and charge transfer of Co.（2）On the basis of the above work,carbon nanotubes were introduced into the precursor in this paper.The role of carbon nanotubes was to support the structure of GO and prevent the collapse of the catalyst structure supported by GO,which would lead to the deterioration of the performance.Through scanning electron microscopy,transmission electron microscopy,X-ray diffraction,X-ray spectroscopy,Raman spectroscopy,surface area test and other physical spectroscopic characterization,through linear scanning voltammetry,blue electric test and other electrochemical performance tests,the experimental results show that when the ratio of graphene to carbon nanotubes is 1:4(Co_0.2Fe_0.6S_x-Gra/CNT_0.12),the prepared catalyst has significantly better ORR and OER electrocatalytic performance than Co_0.2Fe_0.6S_x-Gra,and its half-wave potential is 0.822V.This is attributed to the two-carbon synergistic effect of carbon nanotubes compounded with graphene.With Co_0.2Fe_0.6S_x-Gra/CNT_0.12catalyst as the cathode catalyst,the maximum power density of the Zn-air battery can reach 366m W cm^-2,and it still maintains good stability after 69 hours of charging and discharging.（3）This paper also prepared Fe-N-C mesoporous carbon materials by hard template method.Through scanning electron microscopy,spherical electron microscopy,X-ray diffraction,X-ray spectroscopy,Raman spectroscopy,specific surface area test and other physical spectroscopy characterization,through linear scanning voltammetry and other electrochemical performance tests,the experimental results show that Fe-N-C has mesoporous structure.In which Fe exists as a single atom.The Co_0.2Fe_0.6S_x-Gra/CNT_0.12and Fe-N-C were characterized by ball milling,Raman spectroscopy,surface area test and other physical spectroscopy,and electrochemical performance tests such as linear sweep voltammetry and blue electricity.The results show that when the ratio of Co_0.2Fe_0.6S_x-Gra/CNT_0.12to Fe-N-C is 2:3,(2 Co_0.2Fe_0.6S_x-Gra/CNT_0.12:3 Fe-N-C)has significantly better ORR catalytic performance than commercial 20%Pt/C catalyst,and its half-wave potential is0.883V.The maximum power density of the Zn-air battery assembled with 2 Co_0.2Fe_0.6S_x-Gra/CNT_0.12:3 Fe-N-C catalyst as the cathode catalyst is up to 420m W cm^-2,and it still maintains good stability after 90 hours of charging and discharging.The excellent electrocatalytic activity and stability of the composite catalyst are largely dependent on the three-dimensional network skeleton structure and the synergistic enhancement effect of multi-dimensional carbon（2D graphene,2D carbon nanotubes and 3D mesoporous carbon）.