Graphical At the boundary : SrZr 0.9 Y 0.1 O 3− δ has high proton transport number in wet oxygen, moderate proton conductivity and high chemical stability. Its grain boundary has lower proton transport number than that of bulk, possibly due to decreased proton mobility and tunnelling of electron holes across the grain boundary. Proton conducting acceptor-doped SrZrO 3 has a history as long as that of BaZrO 3 , but has attracted less interest. Inspired by its higher transport number of ionic conduction in wet oxygen revealed by our recent work, we here explore further aspects of doped SrZrO 3 as electrolyte in proton ceramic electrochemical cells. In-situ high temperature XRD (HT-XRD) analysis of SrZr 0.9 Y 0.1 O 3− δ (SZY10) indicated an anisotropic chemical expansion of hydration, stronger along the b than the a direction, and negative in the c direction. A systematic electromotive force (EMF) and impedance spectroscopy study as a function of and allowed determination of partial conductivities of electron holes and ions (mainly protons) in bulk (grain interior) and grain boundaries. Enthalpies and preexponentials were determined and interpreted for bulk and grain boundary partial conductivities based on defect chemistry and a brick layer model. The hole conductivity in bulk is modest and ensures high ionic transport numbers in oxidizing atmospheres, while grain boundaries exhibit lower ionic transport numbers from a relatively higher hole conductivity attributed primarily to tunnelling past the deepest part of the space charge region. Y-doped SrZrO 3 (SZY) materials exhibit lower proton conductivities but excel over Y-doped BaZrO 3 (BZY) in terms of thermal expansion compatibility with electrode materials and higher ionic transport numbers in oxidizing atmospheres and may hence be candidates for functional layers between BZY-based electrolytes and positrodes in proton ceramic electrochemical cells.
BaZr 0.9 Y 0.1 O 3-δ (BZY10) is a popular composition for the electrolyte in protonic ceramic cells, due to its relatively high proton conductivity, excellent chemical stability, and good compatibility with NiO negatrode substrate during high temperature co-sintering. The microstructure of BZY10 is highly dependent on sample processing, leading to large discrepancy of the electrochemical performance of BZY10 in literature. In this work, three BZY10 samples were prepared by different sample processing and sintering conditions, and the grain interior (bulk) and grain boundary partial conductivities of protons and holes were separated. The sintering processes influenced the transport properties of pristine BZY10 samples significantly, and longer sintering time at high temperature (1650 – 1700 °C) leads to lower proton conductivity in both bulk and grain boundary. However interestingly, longer sintering time resulted in higher ionic transport number of bulk conduction, but lower ionic transport number of grain boundary conduction, possibly due to increasing Ba-deficiency in bulk by longer annealing at high temperature. Besides, adding ZnO into BZY10 decreased the proton conductivity in both bulk and grain boundary, but its ionic transport number of bulk conduction increases. A further analysis based on the theory of space charge layer indicated that adding ZnO leaded to decreased Schottky barrier height in the grain boundary core, and the highest Schottky barrier height was observed in the pristine sample which was sintered for longer time. The results obtained in this work suggest a potential strategy to regulate the transport properties of BZY10 by choosing appropriate approaches for sample processing to control the microstructure and local composition of the polycrystalline BZY10 ceramic electrolyte.
危险品化学品经营许可证（带存储）