Preparation And Performance Of Cathode Materials For Intermediate-to-low Temperature Proton Conducting Fuel Cell

Solid oxide fuel cell（SOFC）has garnered attracted wide attention because of its various advantages such as low emission of pollutants,high energy conversion efficiency（up to 65%）,noiseless and vibrationless.Traditional oxygen ion conducting SOFC（O-SOFC）is usually operating at the high temperature of 800-1000 ℃.High operating temperature is adopted to facilitate the ion transportation within the electrolyte and fasten the electrode reaction kinetics.However,such high operating temperature also causes several challenges related to poor thermomechanical stability and difficult sealing,resulting in short lifespan and high costs of SOFC.Therefore,numerous studies have been conducted to reduce the operating temperatures to an intermediate-to-low temperature range of 600-800 ℃.Compared with O-SOFC,proton conducting fuel cell（PCFC）is easier to achieve higher conductivity for protons than oxygen ions at the intermediate-to-low temperature range due to the lower activation energy.Hence,PCFC has become a hot research topic in the field of SOFC.However,the actual development of PCFC still has lagged behind the relatively mature O-SOFC.A major obstacle is the lack of suitable cathode materials.This thesis aims to develop cathode materials which are suitable for operation on PCFC,so that it can operate stably under intermediate-to-low temperature and obtain higher output power density.The specific research results are as follows:（1）We successfully developed Ba(Fe_0.6Co_0.4)_1-x(Zr_0.8Y_0.2)_xO_3-δ（BFC（ZY）_x,x=0.1,0.2,0.3,0.4,0.5）cathode materials by adjusting the metal ions of B-site.Then,with Ni-Ba Zr_0.1Ce_0.7Y_0.1Yb_0.1O3-δ（BZCYYb）as anode and BZCYYb as electrolyte,the single cells Ni-BZCYYb|BZCYYb|BFC（ZY）_x supported by anode were made.The phase structure,ORR activity and electrochemical performance of cathode materials were systematically explored.The XRD test results showed that the five powders prepared by ethylene diamine tetraacetic acid-citric acid（EDTA-CA）combined method all presented the cubic perovskite phase structure,and they had good chemical compatibility with the electrolyte BZCYYb.The electrochemical performance test showed that the single cell with BFC（ZY）_0.1cathode material had the highest output power density and the smallest polarization impendance,716.10 m W·cm^-2 and 0.031Ω·cm² at 700 ℃.The stability test showed the single cell Ni-BZCYYb|BZCYYb|BFC（ZY）_0.1remained stable for 30 h at 600 ℃ and constant voltage of 0.54 V,and the power density did not have notable degration.（2）The two-phase composite materials Ba(Fe_0.6Co_0.4)_1-x(Ce_0.8Y_0.2)_xO_3-δ（BFC（CY）_x,x=0.2,0.3,0.4,0.5）were synthesized by EDTA-CA combined method,which self-assembled into two-phase distributed when sintered at high temperature.XRD analysis initially verified the correctness of the design ideas.The single cells Ni-BZCYYb|BZCYYb|BFC（CY）_xwere prepared.The experimental results showed BFC（CY）_0.3 as the cathode had the largest output power density and the smallest polarization resistance,with 0.0165Ω·cm²and 827.9m W·cm^-2 at 700 ℃.The stability test showed that under the conditions of the test temperature of 600 ℃ and a constant voltage of 0.7 V,the single cell Ni-BZCYYb|BZCYYb|BFC（CY）_0.3had been operating at a high current density of 0.918 A·cm^-2 during the period of 30 h.