Preperation And Perfromance Of In-situ Growth Iron-nickel Alloy Nanoparticles-oxides Composite Anode For Solid Oxide Fuel Cells

Solid oxide fuel cells(SOFCs)are able to convert various fuels(including hydrogen,hydro-carbon fuels,syngas and even pulverized coal)into electricity with high efficiency and low emission without combustion,which have also the advantages of using noble metal-free catalysts,all solid-state system and promising fuel flexibility.The main limitations of SOFCs for long-term utilization are the problems faced by the conventional nickel-based cermet anodes such as redox-cycling instability,tendency towards agglomeration of Ni particles at high temperature and low coking resistance as well as sulfur resistance.Redox-stable oxide anode materials such as LSCM and SFM have shown reasonable coking and sulfur resistance,while suffered from rather low electrochemical activities.Many perovskite oxides have been reported to be able to convert to composite anode materials by exsolving endogenous metallic nanoparticles socketed into the parent oxide substrates through in situ reduction,therefore exhibit highly enhanced electric conductivity and catalytic performance.Furthermore,the strong interaction between the metallic nanoparticles and the oxide substrate further suppresses the agglomeration,and allow the materials to be regenerative through redox-cycling,which are therefore proved to be promising SOFC anode materials.Firstly in this work,a redox reversible composite anode reduced-La0.4Sr0.6Fe0.75Ni0.1Nb0.15O3-?(R-LSFNNb0.15)with Fe-Ni alloy nanoparticles in situ growth on SrLaFe04-type and LaFeO3-type oxide substrates has been prepared by reducing perovskite oxide material La0.4Sr0.6Fe0.75Ni0.1Nb0.15O3-?(LSFNNb0.15)at high temperature.Further characterizaiton show the Fe-Ni alloy nanoparticles have a structure of Ni-enriched core covered by Fe-enriched surface,which are in favor of suppressing agglomeration and coking.Such R-LSFNNb0.15 composite anode has shown promising electrocatalytic performance to fuel oxidation,ScSZ(250?m)electrolyte supported SOFC single cells based on R-LSFNNbO 15 anodes achieves maximum power densities of 709?628 and 639 mW cm-2 at 800,respectively in wet H2(3%H2O),50%H2-CO and H2 with 50ppm H2S,also showing stable power output during 100h operation at 800 ? under 0.7V,indicating that R-LSFNNb has promising stability and coking and sulfur resistance as anode of SOFCs.The electrochemical impedance spectra of anode suggest that the gas conversion in the anode at low frequency range is the rate limiting process of hydrogen oxidation process on the anode. Furthermore,the effect of Nb substitution is investigated by studying on La0.4Sr0.6Fe0.8Ni0.25-xNbxO3-?(LSFNNbx;x=0,0.08,0.15,0.22)series materials.The results prove that Nb substitution lead to increasing sintering temperature of material preparation,deacreasing thermo-expasion coefficiency,and decreasing total valence of other B site elements.The stability of the materials under reducing conditions is shown to be improved by Nb substitution,therefore with increasing Nb substitution ratio the in-situ exsolved Fe-Ni alloy nanoparticles show smaller and more uniformed sizes and lower distribution density,indicating Nb substitution is an important factor in controlling the exsolution process of metallic nanoparticles.As a result,LSFNNb0.08 anode shows the lowest polarization resistance of 0.349 ? cm2 in H2-Ar at 800?,ScSZ(180?m)electrolyte supported SOFC single cell based on R-LSFN and R-LSFNNb0.15 achieve maximum power densities of 741 and 826 mW cm-2,respectively at 800?.Therefore,Nb substitution is proved to be a key factor in controlling the construction of the composite anodes,the sizes and micro-structure of exsolved metallic nanoparticles and the distribution of nanoparticles on oxide substractes.This conclusion provides theoretical basis for the design,tailoring and controllably preparing SOFC anode materials with favorable structure and performances.