Understanding the Aging Degradation of Doped Barium Cerate Proton Conductor in Ambient Air at Room Temperature

As a promising alternative power generation technology, solid oxide fuel cells (SOFC) have been intensively studied during the past several decades [1]. Among all the solid electrolyte candidates, proton conducting materials, e.g., BaCeO₃, exhibit relatively high ionic conductivity at intermediate temperature (< 750 ^oC). Particularly, Zr and Y doped cerate, e.g., BaZr_0.1Ce_0.7Y_0.2O₃ (BZCY) was widely reported to have excellent conductivity as well as adequate stability in resisting concentrated CO₂ up to 30 % with moisture at elevated temperatures typical for SOFC operation [2,3].

Herein, via using a combinations of various electrochemical measurements together with materials characterization techniques including XRD, TEM, SEM, XPS, TG-MS and FTIR, we firstly report that BZCY was prone to a gradual degradation in ambient air at room temperature with considerably minor CO₂ (~0.04%) and humidity (<45% relative humidity). The adsorbed H₂O acted as an effective catalyst that promoted the decomposition of BZCY via reaction with CO₂, subsequently leading to the formation of BaCO₃ nanorods as the major impurity phase, presumably following a microcrucible mechanism. Yttrium (oxy)carbonate and amorphous CeO₂ and ZrO₂ were also produced. It is also confirmed that the doping elements of Ce and Y caused the degradation of BZCY. During the fuel cells tests, the formed impurities on BZCY significantly hindered the electrocatalytic reactions at the electrolyte/electrode interfaces. We also proposed the regeneration and appropriate storage method of the electrolyte materials.

Figure 1. TEM microscopic analysis of: (left) HAADF-STEM image of degraded BZCY with amorphous mixed oxides microcrucible and BaCO₃ nanorods: (right) elemental mapping of Ba, Ce, Zr and Y.

[1]       X. W. Zhou, N. Yan, K. T. Chuang, J. L. Luo, RSC Adv., 4(2014), 118.

[2]       N. Yan, X. Z. Fu, K. T. Chuang, J. L. Luo, J. Power Sources, 254(2014),48.

[3]       L Yang, et. al., Science 326 (2009), 126.