Design And Regulation Of Ruddlesden-Popper Type Air Electrode For Solid Oxide Cell

In recent years,solid oxide cell(SOC)has been widely concerned as an energy conversion device.There are two reversible working modes in SOC since the electrode reaction is reversible.One is the discharge process consuming chemical energy,called fuel cell mode(FC),and the other obtains chemical energy from applied electricity energy,which is called the electrolysis cell(EC)mode.Wherein,the SOC,which with proton conducting electrolytes of BaZrO3-δ or BaCeO3-δ based perovskite oxides is referred to as proton-conducting solid oxide cell(PSOC).The polarization loss of SOC under the two operating modes,with Ni-based fuel electrode,mainly comes from the air electrode.Because the energy barriers required for oxygen reduction reaction(FC mode)and oxygen evolution reaction(EC mode)on air electrodes are higher than those of hydrogen oxidation reaction(FC mode)and hydrogen evolution reaction(HER,EC mode)on fuel electrodes.Therefore,highly efficient and stable air electrode is the key factor to achieve cells with better performance at lower temperatures.Researchers usually use cobalt-based simple perovskite oxides,such as La0.6Sr0.4Co0.8Fe0.2O3-δ(LSCF),as air electrodes in order to pursue high efficiency of SOC.But perovskite oxides with high cobalt content tend to be accompanied by hightemperature phase transition,element segregation,activity decay and other unstable problems,especially under high water pressure electrolysis and CO2 atmosphere conditions.In recent years,Ruddlesden-Popper(R-P)type oxides(An+1BnO3n+1)have received widespread attention.Cobalt-free An+1NinO3n+1(A=La,Pr)is a type of classic air electrode materials with excellent structural stability and high conductivity.However,its surface activity decreases due to the high inertness of rock salt layer and the long-term treatment under high-temperature.To confront the problems mentioned above,innovative strategies of doping modification,single atom modification and non-metallic activation are successfully applied to design novel efficient,and stable air electrode materials based on La2NiO4+δ(LNO)and Pr4Ni3O10+δ(PNO)R-P oxides.This thesis consists of six parts:In Chapter 1,the basic working principle and the development of key materials are introduced based on the background of SOC,and the development and research status of air electrode materials in the application of PSOC are also introduced.The optimization methods of air electrode materials are briefly described,based on which the theme and research contents of this thesis are proposed.In Chapter 2,La2-xCaxNiO4+δ are obtained by partially replacing the A site ion(La3+)with Ca2+ which has lower valence,to explore the impact of low valent doping on the structure,catalytic activity,and stability of LNO as PSOC air electrode.The La2xCaxNiO4+δ has good chemical compatibility with electrolyte and excellent chemical stability.The experimental results show that an appropriate amount of Ca doping can improve the electron-hole concentration of the material,optimize the conduction mechanism,and thereby improve the catalytic activity.In addition,accelerating oxygen reduction reaction of air electrode can effectively improve the output performance of PSOC.In Chapter 3,a customized route for single atom catalyst(SAC)is innovatively reported based on the surface modification strategy with single-atoms.Platinum(Pt)is selected as dispertant and Pr4Ni3O10+δ(PNO)as the matrical granule.Pt1-PNO with different Pt loading amounts are successfully prepared,and the experimental results show that Pt is in an isolated monoatomic form on the surface of PNO.The stability tests of Pt1-PNO in different atmospheres at 700℃ show that Pt1-PNO has excellent chemical stability and anti-sintering ability.More importantly,1Pt1-PNO(100 g)prepared on a large scale still maintains high catalytic activity,which is very rare in SAC related reports.Ultimately,we extend the systhesis route to other SAC systems and successfully obtained ruthenium(Ru),palladium(Pd),iridium(Ir)and iron(Fe)SACs.These finding points a new direction for the surface modification of air electrodes.In Chapter 4,Pt1-PNO air electrode materials with excellent stability are successfully obtained through the SAC customized route.This chapter further analyzes the electronic structure,formation mechanism,electrocatalytic principle,and other properties of Pt on PNO surface,combining DFT theoretical calculation with experimental operation.The experimental results show that Pt forms two types of monatomic functional sites,Pt-O-Ni(2)and Pt-O-Ni(4),on the surface of Pt1-PNO through the principle of covalent metal strong interaction(CMSI),and the ratio of these two sites can be effectively regulated.Interestingly,Pt-O-Ni(4)plays a positive role in ORR and OER processes,while Pt-O-Ni(2)is negative.The electrochemical test results also demonstrate that 1 Pt1-PNO is the best one among Pt1-PNOs,using which the output performances of single cell are twice of that PNO at 700℃ both in FC and EC mode.The design of active sites at the atomic scale provides a new thinking for the research of the electrochemical mechanism of SOC.In Chapter 5,the in-depth research of surface activation using non-metallic elements with high economic benefits is very novel and valuable,compared to the scarce and expensive Pt.Based on the acid-base proton theory,this chapter innovatively replaces the traditional metal with non-metallic heteroatom boron(B)for Pr4Ni3O10+δ(PN)surface modification,expecting to increase the Br?nsted acid(proton acid)content on the surface of the air electrode by utilizing the unique properties of B,thereby achieving the goal of improving catalytic activity.The 0.5at.%B-loaded PN(expressed as 0.5B-PN)powder is successfully obtained by the material synthesis route proposed in Chapter 3.It is identified that the modification of B would enhance the hydration ability of the material surface,promote the chemical adsorption of H2O,and further convert it into Br?nsted acids(proton acids),achieving an effective increase in the surface proton concentration.And the CO2 corrosion resistance of 0.5B-PN surface is improved.The content of active oxygen species on the surface of 0.5B-PN increases,and there may be more interstitial oxygen defects in the 0.5B-PN based on the charge conservation theory.The maximum power density of PSOC using 0.5B-PN as air electrode increased by 103.9%compared to PN at 700℃,and is comparable to that of 1Pt1-PNO.This work provides a new research idea for the surface electron regulation and optimization of non-metallic elements.Chapter 6 summarizes the innovation and breakthrough of the scientific research content of this thesis,analyzes the expandable experimental design of the four works,and looks forward to the research hotspot of SOC in the field of energy and catalysis in the future.