(Na, Li)2CO3 interaction with Gd-doped ceria in composite electrolytes

Gd-doped ceria (GDC) is often considered as electrolyte for Solid Oxide Fuel Cells or CO2 separation membranes. The efficacy of alkaline carbonates and corresponding mixtures as sintering aids and on the electrical performance... [ view full abstract ]

Gd-doped ceria (GDC) is often considered as electrolyte for Solid Oxide Fuel Cells or CO₂ separation membranes. The efficacy of alkaline carbonates and corresponding mixtures as sintering aids and on the electrical performance was already assessed (1,2). However, despite the claimed chemical stability of GDC in molten carbonates, Gd₂O₃ reacts easily with these salts (3) and the exact effect of carbonates on the surface and grain boundary of GDC is poorly investigated.

This work evaluates the impact of the eutectic mixture of sodium and lithium carbonates (NLC) on the GDC microstructure and electrical properties, using a special cell assembly where GDC pellets are covered in one side by NLC, before firing at various temperatures and times. The microstructures of treated and fracture surfaces were analyzed by scanning electron microscopy. Impedance spectroscopy measurements were performed using in plane Au electrodes to detect possible effects on the electrical properties. Measurements were performed under wet and dry air conditions to check the possible role of vestigial alkaline ions at the surface of the pellets.

The surfaces of samples heat treated with NLC layers show regions with grain reconstruction. A noticeable grain boundary conductivity enhancement was observed for higher treatment temperatures and times. The observed electrical effects are probably related to Gd depletion from the grain boundary.

Acknowledgement: Funding from projects CO2ZERO (POCI-01-0145- FEDER-016654 - PTDC /CTM -CER/6732/2014) and CICECO‐Aveiro Institute of Materials (FCT UID/CTM/ 50011/2013), Portugal FCT/MEC PIDDAC and co-financed by FEDER under the COMPETE 2020 Program, and from CNPq (Program Ciência sem Fronteiras, Brazil).

(1) Nicholas JD, Jonghe LC De. Solid State Ionics. 178 (2007) 1187–94.

(2) Aditya M., Hans-Dieter W. Acta Materialia 103 (2016) 361–369

(3) Loureiro FJA, Rajesh S, Figueiredo FML, Marques FMB. RSC Adv. 104 (2014) 59943–52.