Preparation And Electrochemical Actinvity Of Graphene Based Perovskite Composites

Perovskite can be used as a substitute for precious metal catalyst because of their high catalytic activity, oxidation resistant, stable in alkaline solution and high conductivity to solve the limitation of production scale and application problems for metal air battery. Graphene is a two-dimensional carbon material with a single carbon atom thick. It can be used as the ideal support material for catalyst because of its large specific surface area, excellent electrical conductivity and chemical stability. Compositing perovskite with graphene acting as the support materials of semiconductor nanoparticles, not only can effectively suppress the aggregation of nanoparticles but also function as electron transfer channels. Therefore, the composite can produce new synergistic effect, and has broad application.This prepared graphite oxide by improved Hummers method, and restored the graphite oxide by thermal stripping to obtain graphene material. Through the use of a sol-gel method, i.e. mixing the graphene suspension and nitrate solution, the composites of La Mn O3/graphene, La1-xCaxMn O3/graphene with different content of Ca doping in A site(x=0.1, 0.2, 0.3, 0.4, 0.5) and La Mn1-xCoxO3/graphene with different content of Co doping in B site(x=0.05, 0.10, 0.15) were produced.The decomposition behaviors of La Mn O3/graphene precursor and the calcined La Mn O3/graphene sample were analyzed using the TG-DSC technique. Compositing La Mn O3 and graphene leads to the formation of porous structure, which was observed by FE-SEM analyses. BET results demonstrated the larger specific surface area of La Mn O3/graphene than that of pure La Mn O3. The best process condition was obtained using the electrochemical characterization technique, and the optimal percentage of graphene in the composite is determined to be 10 wt%.The phase composition of the composites with doping in A and B sites was characterized by XRD ananlysis, and results indicated that the substitution of different valence elements does not change the perovskite-type structure. The electrochemical characterization of modified powders was performed by a series of electrochemical measurements. Results demonstrated that the electrocatalytic activity was optimized, when the doping amounts of Ca and Co are 0.4 and 0.1, respectively. The electron transfer numbers of the two composite powders were 3.60 and 3.87, respectively, and OH-(four electrons transferred) and HO2-(two electrons transferred) coexisted for the ORR, indicating the composite powders with doping in A and B sites possessed very high ORR catalytic activities.