Correlation between Concentrations of Ni and Y in Y-Doped BaZrO3 Electrolyte in Co-Sintered Cells: A Case of Controlled NiO Activity by Using MgO-NiO Solid Solution as Anode Substrate.

Donglin Han,Tetsuya Uda,Kenji Kuno

doi:10.3390/membranes9080095

Abstract

BaZr0.8Y0.2O3-δ (BZY20) is promising to be applied as an electrolyte in fuel cells, electrolysis cells, etc. However, when a half cell composed of a BZY20 electrolyte layer and a BZY20-NiO composite anode substrate is co-sintered (1400–1600 °C), Ni diffuses from the anode substrate into the electrolyte layer. Y content in the electrolyte layer decreases dramatically, since BZY20 cannot be equilibrated with NiO at such high temperature. Such Ni diffusion and Y loss are detrimental to the electrochemical performance of the electrolyte layer. In this work, we added MgO-NiO solid solution into the anode substrate to adjust the NiO activity (aNiO) during the co-sintering process, and used three different co-sintering methods to control the BaO activity (aBaO). The results revealed that by decreasing aNiO in the system, the as-co-sintered electrolyte layer had the composition shifting towards the direction of high Y and low Ni cation ratios. A clear correlation between the intra-grain concentration of Ni and Y was confirmed. In other words, to prepare the electrolyte with the same Y cation ratio, the Ni diffusion into the electrolyte layer can be suppressed by using the MgO-NiO solid solution with a high MgO ratio and a low Ni ratio. Moreover, by increasing aBaO, we found that the Y cation ratio increased and approached the nominal value of the pristine BZY20, when Mg1−xNixO (x = 0.3 and 0.5) was used. In summary, both aNiO and aBaO play important roles in governing the composition of the electrolyte layer prepared by the co-sintering process. To evaluate the quality of the electrolyte layer, both the intra-grain Y and Ni concentrations should be carefully checked.

Highlights

A fuel cell can be regarded as an assembling of cathode, electrolyte and anode layers
The as-synthesized powder was pelletized at 392 MPa and heated at 1600 ◦ C for 24 h in artificial oxygen with subsequent pulverization by ball-milling for 50 h to prepare the powders with improved compositional homogeneity [19]
Should maintain a single phase without anyany compositional change afterafter the Ideally,the theelectrolyte electrolyte should maintain a single phase without compositional change co-sintering process, to fully activate its electrochemical properties. It seems to be difficult the co-sintering process, to fully activate its electrochemical properties. It seems to for be Firstly, a two-phase equilibrium cannot be achieved between BZY20 and NiO

Summary

Introduction

A fuel cell can be regarded as an assembling of cathode, electrolyte and anode layers. The electrolyte is the most important component and needs high ionic conductivity of at least 0.01 Scm−1 [1]. A total of 20 mol % Y-doped BaZrO3 (BaZr0.8 Y0.2 O3−δ (BZY20)) shows proton conductivity of about. 0.01 Scm−1 even at 450 ◦ C [2,3,4] and excellent chemical stability against the reaction with water vapor and carbon dioxide [5,6,7]. BZY20 is one of the most promising electrolyte candidates for intermediate temperature fuel cells (IT-FCs). To minimize ohmic resistance from the electrolyte, one ordinary strategy is to construct an anode-supported structure. The electrolyte layer is supported mechanically by the anode layer, thereby can be thinned to several tens of micrometers. The cell fabrication process faces a severe challenge; during the co-sintering process performed at

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Discussion

Conclusion