Application And Performance Study Of FeCoNi-based High-entropy Electrodes In Solid Oxide Fuel Cells

Solid oxide fuel cells（SOFCs）are all-solid-state energy conversion devices that convert chemical energy from fuel into electrical energy with the advantages of high efficiency,clean and pollution-free.High-entropy materials have been widely used in the field of energy conversion and storage due to their stable crystal structure,adjustable reactive sites and strong synergistic effects between elements.However,the high operating temperature and harsh preparation conditions of SOFCs have made the application of high-entropy materials in SOFCs rarely reported.The main objective of this thesis is to design and develop medium-/high-entropy materials for SOFCs electrodes,to investigate their conformational relationships,electrical behaviors and catalytic mechanisms as SOFCs electrodes,and to lay the foundation for the application of medium-/high-entropy materials in the field of SOFCs.In this work,we used three metal elements of Fe Co Ni as the base elements to build the medium-/high-entropy system,used the strategy of heterogeneous element doping to build the entropy-driven system,conducted some experimental exploration on the synthesis methods of high entropy alloys and medium-/high-entropy spinels,developed Fe Co Ni Cu X（X=Al,Mo）high-entropy alloys and（Fe Co Ni Mn）₃O₄ medium-entropy spinels as SOFCs electrode materials,and their phase structure,conductive properties,electrochemical performance,catalytic mechanism,and electrode reaction kinetics were initially explored and studied.The main research contents are as follows:1.FeCoNiCuX（X=Al,Mo）isoatomic ratio high-entropy alloys with FCC+BCC phase structure was prepared by high-energy ball mill mechanical alloying method,and 60wt%Fe Co Ni Cu X（X=Al,Mo）-40wt%Sm_0.2Ce_0.8O_2-δ（Fe Co Ni Cu X-SDC）metal-ceramic composite electrode was obtained by mechanical mixing for SOFCs anodes.Fe Co Ni Cu X-SDC as SOFCs anode:（1）Achieves conductivity of 168 S cm^-1（X=Al）and 329 S cm^-1（X=Mo）at 800 ℃ under hydrogen atmosphere comparable to conventional nickel-based ceramic anodes;（2）Exhibits excellent methane and CO₂ reforming capabilities;（3）When hydrogen is used as fuel gas,at850 ℃ the maximum power density of LSGM electrolyte-supported single cell is 779 m W cm^-2（X=Al）and 577 m W cm^-2（X=Mo）,respectively,and shows good stability in long-term operation;（4）When methane is used as fuel gas,at 850 ℃,the maximum power density of single cell is 526 m W cm^-2（X=Al）and 473 m W cm^-2（X=Mo）,respectively,and shows good stability in long-term operation,and exhibited superior stability compared to Ni-SDC during long-term operation,indicating that FeCoNiCuX has superior resistance to carbon buildup.The results indicate that the Fe Co Ni Cu X high-entropy alloys constructs a special surface electronic structure with different valence states,which provides a synergistic effect for the catalytic oxidation of hydrogen and methane fuel gases.2.（FeCoNiMn）₃O₄（FCNMO）medium-entropy spinel oxide electrode material was prepared by co-precipitation method:（1）As an air electrode,FCNMO forms more small polarization sub pairs due to the coexistence of different valent metal ions Fe,Co,Ni and Mn in the A and B sites of the spinel structure,which can effectively ensure the electron and oxygen ion transport capacity and promote high temperature stable Oxygen evolution reaction（OER）and oxygen reduction reactions（ORR）;（2）FCNMO is used as a fuel electrode,and the Fe Co Ni@Mn O_x metal oxide heterostructure is constructed by in situ self-assembly method to effectively increase the three-phase boundary（TPB）,and the abundant reactive sites of Fe Co Ni alloys and the good oxygen ion transport properties of Mn O_x synergistically catalyze the oxidation of hydrogen and electrolysis of water.The intrinsic advantages of FCNMO with quadruple effect as a multifunctional electrode material for reversible symmetrical solid oxide batteries were systematically investigated by phase structure characterization,valence analysis,electrode reaction kinetic analysis and electrochemical performance testing,combined with theoretical calculations,and the application potential of entropic spinel oxide in FCNMO as an electrode material for symmetric reversible solid oxide batteries was verified.3.The in situ self-assembly of FCNMO medium-entropy spinel under reducing atmosphere to construct Fe Co Ni@Mn O_x metal oxide heterostructures exhibited ultra-high conductivity(2254.69 S cm^-1 at 800 ℃),which was compounded with SDC to construct FCNMO-SDC composite anodes:（1）FCNMO-SDC exhibited good chemical compatibility before and after reduction;（2）At 850 ℃ with hydrogen as the fuel gas,the maximum power density of the single cell with FCNMO as the anode was 1054 m W cm^-2,and the maximum power density of the single cell with FCNM-SDC as the anode reached 1296 m W cm^-2,and the long-term stability test showed that the FCNMO-SDC composite anode had better stability compared with FCNMO;（3）Relaxation time distribution（DRT）analysis shows that the introduction of SDC can effectively accelerate the charge transfer and the bulk diffusion process of oxygen ions.The results show the potential of using in situ reduction of medium-/high-entropy spinel to construct metal oxide heterostructures as solid oxide fuel cell anodes,providing new insights for exploring new metal oxide heterostructure-type anodes.