Performance of Ceria-Based Composite Electrolytes

Ceria-based composites, including mixtures of alkaline carbonates, are promising electrolytes for fuel cells and CO2 separation membranes [1]. Multiple ionic charge carriers (e.g., oxide, carbonate, alkaline) and a high... [ view full abstract ]

Ceria-based composites, including mixtures of alkaline carbonates, are promising electrolytes for fuel cells and CO₂ separation membranes [1]. Multiple ionic charge carriers (e.g., oxide, carbonate, alkaline) and a high conductivity, exceeding 0.1 S/cm at 500 °C, justify this interest.

In this work composites with distinct compositions and microstructures were studied to identify the relationships between composition, microstructure and electrical performance. Tested materials involved eutectic mixtures of Li and Na or Li, Na and K carbonates, and CGO (Gd-doped ceria). Processing routes involved either joint milling of all constituents before uniaxial pressing and firing, or a two-step process with initial consolidation of the ceramic backbone before impregnation with the molten phase. All cells (composites but also oxide backbones) were studied by impedance spectroscopy (250-650 °C range) and scanning electron microscopy (SEM).

The distinct composites showed a high temperature conductivity strongly influenced by the molten phase composition, dominating their electrical performance. Distinct ceramic skeleton characteristics could be easily perceived from low temperature impedance spectroscopy data and SEM. Proper handling of this information could be used to determine the conductivity of both phases and identify their adequacy for fuel cells or CO₂ separation membranes (with distinct figures of merit for the total conductivity or ambipolar conductivity, respectively). 

Acknowledgments: Work performed with funding from projects CO2ZERO (POCI-01-0145 -FEDER- 016654 - PTDC/CTM - CER/6732/2014), MOCO3 (M-ERA.NET2 2016 - MOCO3-0009/2016) and CICECO‐Aveiro Institute of Materials (FCT UID/CTM/50011/ 2013), based on Portuguese funds from FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement.

References

[1] Y. Li, Z. Rui, C. Xia, M. Anderson, Y.S. Lin, Catalysis Today, 148 (2009) 303-309.