Synthesis and Densification of Mo/Mg Co‐Doped Apatite‐type Lanthanum Silicate Electrolytes with Enhanced Ionic Conductivity

Abstract

Apatite-type lanthanum silicate (LSO) electrolyte is one of the most promising candidates for developing intermediate-temperature solid oxide electrolysis cells and solid oxide full cells (IT-SOECs and SOFCs) due to its stability and low activation energy. However, the LSO electrolyte still suffers from unsatisfied ionic conductivity and low relative density. Herein, a new co-doped method is reported to prepare highly purified polycrystalline powders of MgÀ Mo codoped LSO (Mg/Mo-LSO) electrolytes with high excellent densification properties and improved ionic conductivity. Introducing the Mo 6 + and Mg 2 + ions into the LSO structure can increase the number of interstitial oxide ions and improve the degree of densification at lower sintering temperatures, more importantly, expand the migration channel of oxide ions to enhance the ionic conductivity. As a result, the relative density of the fabricated Mo/Mg-LSO electrolytes pellets could achieve more than 98 % of the theoretical density after sintering at 1500 °C for 4 h with a grain size of about 1-3 μm and the EIS results showed the ionic conductivity increased from 0.782 mS • cm À 1 for the pristine LSO to 33.94 mS • cm À 1 for the doped sample La 9.5 Si 5.45 Mg 0.3 Mo 0.25 O 26 + δ at 800 °C. In addition, the effect of different Mo 6 + doping contents was investigated systematically, in which La 9.5 Si 5.45 Mg 0.3 Mo 0.25 O 26 + δ possessed the highest ionic conductivity and relative density. The proposed Mo/Mg co-doped method in this work is one step forward in developing apatite-structured electrolytes offering excellent potential to address the common issues associated with the fabrication of dense, highly conductive, and thermochemically stable electrolytes for solid oxide electrolysers and fuel cells.

The use of silicon in the membrane electrode assembly of fuel cells

“…The difference of the doped cations, especially the ionic radius, results in the difference of cell distortion and restraining O 2À , and then LSO conductivity changes accordingly. Finally, Li et al [71] evaluated the conductivity of co-doped LSO with Mg 2 + and Mo 6 + on Si-site. Compared to the pure LSO, the conductivity of Mg/Mo-LSO was significantly enhanced.…”

“…Co-doped LSO with Mg 2 + and Mo 6 + on Si-site can be readily densified at a relatively low sintering temperature of ~1500 °C, the relative density reaching 98 %, without any sintering aids or additives. [71] On the other hand, Celerier et al [73] reported the use of acidcatalyzed silica sol with TEOS and La(NO 3 ) 3 as precursors for the gel formation to prepare directly LSO powder. These powders can be used directly to form ceramics, allowing a decrease of the sintering temperature of more than 200 °C.…”

Multi-doped ceria-based composite as a promising low-temperature electrolyte with enhanced ionic conductivity for steam electrolysis

“…33 Co-doping the common solid oxide composites with aliovalent transition metal cations is a new approach to improve the densification properties and ionic conductivity of the resulting polycrystalline electrolytes. 34 Considering the protection for the metal support in the fabrication process, the study of sintering behaviour in an inert atmosphere for doping ceria-based composites is necessary. Also, the physicochemical and electrochemical properties for multi-doped ceria-based This journal is © The Royal Society of Chemistry and IChemE 2023 composites were rarely reported.…”