Electrochemical Performance And Preparation Of NdBaFe_2-xM_xO_5+δ（M=Mn,Nb） Cathodes Materials

With the rapid development of the world economy, large quantities of new energy conversion technologies have emerged to decrease the environmental pollution and to meet the increasing energy demand. Solid oxide fuel cell(SOFC) is particularly competitive candidate due to its high power conversion efficiency, low emissions and excellent fuel adaptability, etc.However, the operating temperature of conventional SOFC based on yttrium-stabilized zirconia(YSZ) electrolyte is as high as 800-1000 °C, which leads to interfacial reactions, thermal expansion mismatch among the components, difficulty in the choice of sealing and bonding materials and so on. Therefore, intermediate temperature SOFC(IT-SOFC) has received tremendous attention around the world. However, the decrease of operating temperature results in the rapid increase of the polarization resistance of cathode-electrolyte interface. Consequently, significant efforts have been devoted to the development of excellent electrolyte and cathode materials for IT-SOFCs.Desirable electrolyte materials must possess both high ionic conductivity and sufficient chemical stability. Recently, a new composition Ba Zr0.1Ce0.7Y0.2O3-α(BZCY) has been extensively used as electrolyte material for IT-SOFC since it shows both adequate proton conductivity and sufficient chemical stability.Based on the above, this paper focused on cobalt-free double-perovskite cathode materials and the electrochemical performance of single cells. Main studies and results of this paper are as follows:A series of cobalt-free cathode materials Nd Ba Fe2-x Mnx O5+δ(0.00 ≤ x ≤ 0.30) were prepared by a citric acid-nitrate process, and the XRD results showed that they were double-perovskite phases with a cubic structure. The conductivities of Nd Ba Fe2-x Mnx O5+δ(0.00 ≤ x ≤ 0.30) ceramic pellets were determined by impedance spectrometry as functions of temperature(300-800 °C) and oxygen partial pressure(1-10-10 atm). The conductivity increased with increasing temperature up to 550 °C and decreased with further increasing temperature. The conductivity increases with increasing Mn doping level up to 0.1 and then decreases with further increase of Mn doping level. Among the tested samples, the sample of x = 0.1 has the highest conductivity of 114 S cm-1 at 550 °C. Nd Ba Fe1.9Mn0.1O5+δ(NBFM10) was mainly a p-type electronic conductor in the oxygen partial pressure range tested. The single cell Ni O-BZCY | BZCY | BZCY-NBFM10 was assembled and tested from 500 °C to 700 °C with H2 as fuel and air as oxidant. The peak power density was 453 m W cm-2 and the interfacial polarization resistance Rp was only 0.06 Ω cm2 at 700 °C.A novel series of cobalt-free cathode materials Nd Ba Fe2-y Nby O5+δ(0.00 ≤ y ≤ 0.30) prepared by a solid state reaction method were double-perovskite phases with a cubic structure. The Nd Ba Fe1.9Nb0.1O5+δ(NBFNb10) ceramic pellet was used to investigate its conductivity in N2、Air and O2 as function of temperature(300-800 °C) by AC impedance method. The conductivities of NBFNb10 increased with the increasing oxygen partial pressure. The maximum conductivities of NBFNb10 are observed to be 101 S cm-1 under nitrogen, 109 S cm-1 under air and 119 S cm-1 under oxygen at 450 °C, respectively. The H2/air fuel cell utilizing the NBFNb10-BZCY composite cathode and Ni O-BZCY composite anode as well as BZCY electrolyte membrane was assembled and tested at 500-700 °C. The peak power density of the cell reached 392 m W cm-2, and the interfacial polarization resistance Rp was 0.14 Ω cm2 under open circuit conditions, at 700 °C.These above results indicated that NBFM10 and NBFNb10 were promising cathode materials for application in proton-conducting IT-SOFCs.