Research On Double-Pervoskite Based Triple Conductive Cathode Materials For Proton Conducting Solid Oxide Fuel Cell

Solid oxide fuel cell（SOFC）is an energy conversion device that converts the chemical energy stored in fuels directly to electric power with the advantages of high efficiency,low emission,and fuel flexibility.However,the high working temperature（above 800℃）restricts the commercialization of traditional SOFC,due to the difficult material selection,sealing,operation,maintenance,and high cost.Decreasing the working temperature is the current research trend.The proton-conducting solid oxide fuel cell（H-SOFC）has the advantages of low activation energy for carrier conduction and high fuel concentration in the anode,and shows broader application prospects at medium-to-low working temperatures.The H-SOFC demands a stable cathode with triple conductivity of protons,oxygen ions,and electrons at the same time.However,the states-of-the-art cathode could not meet these requirements,most of them present one or some of the following drawbacks including mismatched CTE with electrolyte,low proton absorption concentrations,and slow proton conduction.In this work,three kinds of composite or single-phase cathode materials were proposed and investigated to overcome these problems by surface modification and low-electronegativity element doping.The conclusions are made as follows:（1）The triple conducting cathode,PrBa Co₂O5+δ@Ba Zr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ（PBC@BZCYYb）,was prepared by impregnating the PBC particles on the surface of BZCYYb skeleton.The effect of PBC impregnation amount on the electrode performance was investigated.The loading of PBC with 36 wt%boosted the electrochemical performance of cathode best with its abislity to improving oxygen reduction reaction.However,higher PBC loading reduced the performance because it reduced the porosity and proton transportation ability of cathode.The peak power density of the anode-supported single cell was 0.49 W cm^-2 at 750℃ with the optimal loading of PBC@BZCYYb as cathode.（2）Zn-doped PrBa_0.9Ca_0.1Co_2-xZn_xO5+δ（x=0,0.05,0.1,and 0.15,designated as PBCCZy,y=00,05,10,and 15）were prepared and investigated,as it is recognized that doping lower cation electronegativity elements could improve proton transportation ability of PBC.The Zn-doping increased the concentration of oxygen vacancy and binding energy of lattice oxygen for PrBa_0.9Ca_0.1Co₂O5+δ,which the former was in favor of the uptake of proton and the latter was un-favor.Therefore,the proton uptake ability of PBCCZy firstly decreased and then improved with the Zn contents increased.Besides,the rate of surface exchange and bulk transportation for oxygen ion and proton of PBCCZ15 was much higher than that of PBCCZ00.The Zn-doping could not reduce the CTE of PBCCZy,all around21.3×10^-6 K^-1.The peak power density of single cell reached 0.89 W cm^-2 at 700℃ with PBCCZ15-BZCYYb as cathode material.The electrochemical performance of single cell could keep stable within 50 h under 400 m A cm^-2 at 600℃.This work confirmed that reducing the cation electronegativity of material could effectively improve its proton absorption and transportation ability.（3）K-doped PrBa_1-xK_xFe_0.9Zn_0.1O₅₊δ（x=0 and 0.1,designated as PBKFZy,y=00 and10）were prepared and investigated to obtain a single-phase triple conductive cathode material with low CTE.K-doping could simultaneously increase the concentrations of oxygen vacancy and reduce the binding energy of lattice oxygen,effectively improving the rate of surface exchange and bulk transportation for proton and oxygen ion of PBKFZ00.The maximum proton absorption concentration of PBKFZ10 was 6 mol%,higher than 2mol%of PBKFZ00.Besides,the CTE of PBKFZ00 was decreased from 18.3×10^-6 K^-1to16.1×10^-1 K^-1 by K-doping.The single cell with PBKFZ10 as cathode showed a peak power density with 1.4 W cm^-2 at 700℃,which was the highest performance among Co-free cathode materials in literature.the single cell operated stably for 75 h under 400 m A cm^-2at 600℃,indicating a good electrochemical performance and stability at medium and low temperatures.