The Study On The Catalytic Properties Of Perovskite Oxide-based Composites On Oxygen Reduction Reaction(ORR)

Scince the 21st century,the excessive and unreasonable utilization of fossil fuels and the issues of energy shortage have been seriously influenced the human social life,seeking for green clean renewable energy is extremely urgent.Fuel cell,a kind of way to obtain green renewable energy,has caught more and more attention.Oxygen reduction reaction(ORR)is a common cathode reaction in fuel cell and the long-term stability of expensive commercial cathode catalyst Pt/C is not ideal,which constrains the large-scale application of fuel cell.Therefore,design a new type of ORR catalyst that can replace Pt/C has become key issue.Perovskite oxides with stable structure and flexible composition,high oxygen utilization and low price have very good prospect in application as ORR catalysts.But in current research,the promotion of the ORR activity catalyzed by perovskite oxide is limited to small oxygen adsorption energy and low conductivity.Therefore,we consider to combine perovskite oxides with other materials(such as carbon materials,g-C3N4,etc.)to improve their ORR performance from the two aspects of electrical conductivity and oxygen adsorption ability.Based on the above consideration,this thesis is carried out according to the following two attempts:Ⅰ.The study on oxygen reduction reaction(ORR)performance catalyzed by perovskite-carbon compositesWe selected LaMnO3 as model perovskite oxide and phenolic resin as carbon sources to fabricate a series of composites with various carbon contents.The results show that interaction exists between LaMnO3 and carbon by means of Mn-O-C bond.After composited with carbon,the catalytic activity on ORR and utilization of oxygen for LaMnO3 are significantly improved.The optimal catalytic performance is achieved with the amount of phenolic resin of 10 mg.The results further confirmed that in ORR process oxygen molecule preferentially adsorbed on carbon to generate intermediate H2O2,which was then transferred to the surface of LaMnO3 and further reduced to OH-.On the one hand,large O2 adsorption energy for carbon accelerated the adsorption of oxygen molecules.On the other hand,the active sites on the surface of the LaMnO3 were utilized for the H2O2 reduction,without being occupied by adsorbed oxygen molecules.These factors were the main reasons for the improvement of ORR performance for the carbon-LaMnO3 composites.II.The study on oxygen reduction reaction(ORR)performance catalyzed by perovskite-g-C3N4 compositesWe prepared a series of LaMnO3-g-C3N4 composites with different contents of g-C3N4.The crystal structure of the composites remains perovskite type,which showed that of the high chemical stability of g-C3N4 helped to fabricate single phase perovskite composites.The results turned out that the Mn-O-C interaction existed between g-C3N4 and LaMnO3 and the interaction could make some g-C3N4 broken into small sheets and attached on the surface of LaMnO3.The study on the ORR activity showed that the combination of g-C3N4 with LaMnO3 could improve the performance apparently and the oxygen utilization was still high.O2 molecules were adsorbed and activated on the g-C3N4 preferentially and reduced to H2O2,which then transferred to the surface of LaMnO3 and further reduced to OH-.The adsorption and activation of O2 happened on g-C3N4 made facilitated the active sites on LaMnO3 surface available for the reduction of H2O2,inhibited the accumulation of intermediates and enhanced the catalytic performance.