Synthesis And Electrochemical Properties Of Delafossite-based Composite Nanomaterials

Energy crisis and environmental pollution are the challenging problems all over by the whole world in the path of sustainable development.Solid oxide fuel cell(SOFC)is an efficient and environmentally friendly energy conversion technology.At present,high temperature(750 ^oC)and manufacturing cost restricted its commercialization process.In order to make SOFC more competitive,people are committed to looking for low temperature,high performance,low cost SOFC key materials.The ohmic resistance of electrolyte and the interfacial polarization resistance of electrode are important factors to determine the performance of SOFC.Therefore,the development of new electrolytes and electrode materials is the focus of SOFC.In this thesis,the relationship between the structure morphology and electrochemical performance of delafossite composite nanomaterials was studied,showing the application prospect of delafossite composite nanomaterials in the field of low temperature SOFC.The innovation points of this thesis include:Low-cost delafossite composite materials used as electrolytes in SOFC have excellent performance,which provides a new idea for the application of natural mineral materials in SOFC;by introducing the second phase to construct heterogeneous interface,the electrochemical performance of delafossite fuel cell was further improved,the influence of heterogeneous interface on the ion transport and battery performance of SOFC at low temperature was discussed;The electrochemical behavior of oxygen reduction reaction(ORR)was discussed by constructing Cu Fe O₂-Ni_0.8Co_0.15Al_0.05Li O_2-?(NCAL)composite cathodes.The main research results of this thesis are as follows:1.The effect of structure and composition of natural delafossite(CF)electrolyte on ion conduction was investigated.After crushing,dressing,grinding,sieving and high temperature treatment,natural delafossite(CF)was assembled as an electrolyte in fuel cell for electrochemical testing.At 550 ^oC,the open-circuit voltage(OCV)and maximum power density of the natural delafossite fuel cell can reach 1.04 V and 423m W cm^-2.It is found that in delafossite,protons conduct in Cu-O layer through the reduction and oxidation cycle of Cu⁺-(Cu-H)⁺.2.The influence of composite structure and composition of delafossite composite electrolyte on the performance of low temperature SOFC was explored.After the composite of natural delafossite and nanomaterial,the electrical conductivity increases significantly and the electrode polarization decreases effectively.After CF-LZSDC composite was prepared by natural delafossite(CF)and Li_xZn O-Sm_0.2Ce_0.8O_2-?(LZSDC)composite,CF-LZSDC was used as electrolyte,and fuel cell devices were assembled for testing.The relationship between the composition of CF-LZSDC composite and ion conduction was studied.It was found that the conductivity of the electrolyte increased to 0.312 S cm^-1 and the electrode polarization of the fuel cell decreased,thus improving the electrochemical performance of the overall fuel cell.At 550 ^oC,the OCV of CF-LZSDC fuel cell can reach 1.14 V,and the maximum power density can reach 637 m W cm^-2.In this thesis,a series of CF-LZSDC fuel cells with different compaction pressures were prepared,and the effects of compaction pressures on the morphology and electrochemical performance of fuel cells were studied.Optimal compaction pressure can effectively optimize fuel cell performance through maximum contact and optimized continuous path.3.The effect of semiconductor charge separation on the electrochemical performance of SOFC devices was discussed by constructing a heterojunction for synthesizing Zn O-Cu Fe O₂ composite electrolyte.Zn O-Cu Fe O₂ composite nanomaterials were synthesized and Zn O-Cu Fe O₂ was used as electrolyte to assemble fuel cell devices for testing.Zn O-Cu Fe O₂ nanocomposites can be used to construct heterojunctions for charge separation and blocking electron transport.At 550 ^oC,the OCV of Zn O-Cu Fe O₂ cell can reach 1.03 V,and the maximum power density can reach 468 m W cm^-2.The introduction of heterojunction improves the performance of SOFC.4.A new type of Cu Fe O₂-NCAL composite cathode was constructed and its catalytic effect on low temperature oxygen reduction reaction was discussed.Cu Fe O₂-NCAL composite nanocathode material was synthesized,and the effect of cathode composition on ORR was studied.At 600 ^oC,the NCAL/Ce O₂/Cu Fe O₂ cell has an OCV of 0.89 V and a power output of 289 m W cm^-2.When the same amount of NCAL is combined with Cu Fe O₂,the fuel cell can obtain an OCV of 1.02 V and a power output of 523 m W cm^-2 at 600 ^oC.This work reveals the feasibility of using delafossite based composites as SOFC electrolytes and electrodes,making SOFC a more economically competitive energy conversion technology.This study provides a new way for the development of low temperature solid oxide fuel cells with good market prospect using natural mineral composite materials.