Preparation And Property Of Perovskite-type Metal Oxides As Electro-catalysts

With the increasing emphasis on environmental protection and energy conservation,the research and development of green chemical power/storage equipment has received more and more attention.Among them,alkaline fuel cells,solid oxide electrolysis cells?SOEC?and zinc air fuel cells are the focuses in recent studies.In the working process of zinc-air fuel cells,the overpotential required for the reaction?such as oxygen evolution reaction,abbreviated as OER?is too high,so it is necessary to add catalysts to make the reaction proceed rapidly.However,the catalysts recently used in the air electrode of the zinc-air fuel cell are noble metal oxides?such as IrO₂ and RuO₂?,and the expensive price seriously hinders the commercial development of the zinc-air fuel cell.Mixed transition metal oxides,such as perovskite type oxide,pyrochlore or similar structure,these oxygen non-stoichiometric mixed metal oxides have been found to have high OER catalytic activity.Perovskite-type metal oxides have recently been extensively studied for their ease of doping,excellent performance,and low cost.The preparation and properties of perovskite-type metal oxide electrocatalysts for catalytic OER reaction in alkaline solutions were investigated in this paper.Firstly,we investigated the effect of A-site ion vacancies on the structure and properties of Sr_1-xNb_0.1Co_0.7Fe_0.2O_3-?.The prepared Sr_1-xNb_0.1Co_0.7Fe_0.2O_3-??x=0.02,0.05,0.1?catalysts containing different A-site ion vacancy concentrations,we found that the crystal lattice contracted and the state of oxygen changed.After the introduction of the A-site ion vacancy,the catalytic performance has been significantly improved.Among them,Sr_0.95Nb_0.1Co_0.7Fe_0.2O_3-?has the best catalytic performance(the overpotential is 0.42 V at a current density of 10 mA cm^-2 compared to 0.46 V of the original SrNb_0.1Co_0.7Fe_0.2O_3-?catalyst).The increased oxygen vacancy concentration,smaller electron and ionic resistance,and bigger electrochemical specific surface area are responsible for the higher catalytic performance of the catalysts after introducing the A-site ion vacancies.Introducing A-site ion defects as a simple and efficient strategy for improving the electrocatalytic activity of perovskite-type metal oxides was studied in this chapter and the results proved the feasibility and reliability of this strategy.Secondly,we studied the doping of B-site non-metallic elements of perovskite-type metal oxides,and prepared S-doped SrCo_1-xS_xO_3-??x=0.02,0.04,0.06,0.08,0.1?catalysts.It was found that doping S element can stabilize the cubic structure at room temperature,of which SrCo_0.98S_0.02O_3-?possesses the best catalytic performance and better stability than the original SrCoO₃.The better catalytic performance of SrCo_0.98S_0.02O_3-?is contributed to it's better conductivity and larger electrochemical specific surface area,and the improvement of stability further demonstrates its practical value.This chapter demonstrates the feasibility of non-metallic element doping to improve the performance of perovskite-type metal oxide electrocatalysts.It is a cheaper and efficient doping strategy than traditional transition metal element doping.Finally,a cobalt-free perovskite-type metal oxide electrocatalyst SrFeO₃ was prepared by three different methods:solid phase,sol gel and microemulsion method.The SEM was observed by scanning electron microscopy.The catalyst particles prepared by the glycine method are obviously smaller than the solid phase method,and are more uniform without obvious agglomeration;the catalyst particles prepared by the microemulsion method are finer and have a cotton wool shape appearance.Nitrogen adsorption desorption experiments were carried out to test the specific surface area of the catalysts prepared by the three methods.The microemulsion method has the largest BET specific surface area of 21.50 m²/g,which is much larger than that of the catalyst powders prepared by the glycine method and the solid phase method.The result of the electrochemical specific surface area?ECSA?is in agreement with the BET results.The SrFeO₃ prepared by the microemulsion method with larger specific surface area can expose more catalytic sites to the electrolyte during the catalytic process,so it has better catalytic performance.