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

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 Mg-Mo co-doped LSO (Mg/Mo-LSO) electrolytes with high excellent densification properties and improved ionic conductivity. Introducing the Mo6+ and Mg2+ 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-1 for the pristine LSO to 33.94 mS ⋅ cm-1 for the doped sample La9.5 Si5.45 Mg0.3 Mo0.25 O26+δ at 800 °C. In addition, the effect of different Mo6+ doping contents was investigated systematically, in which La9.5 Si5.45 Mg0.3 Mo0.25 O26+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.

Chitosan/halloysite beads fabricated by ultrasonic-assisted extrusion-dripping and a case study application for copper ion removal.

Development of new materials for different applications especially as bio-composites has received great attention. This study concentrates on development of a biopolymer based on chitosan (CT) and halloysite nanotubes (HNT) and evaluates the copper removal intake as a potential application of this bio-composite. In this study, CT/HNT beads were prepared by ultrasonic-assisted extrusion-dripping method for the first time. Two sources of HNTs (i.e. Dragonite and Matauri Bay) were added into a chitosan solution (2wt.%) at various loading fractions (25, 50, 75wt.%). The effect of ultrasound as a mixing device was also studied by varying the amplitude at constant frequency of 25%, 50% and 75%. Characteristics and physical properties of the prepared CT/HNT beads were also analyzed by SEM, FTIR, TGA and BET the results show that introducing HNT to chitosan increases the adsorption capacity toward copper ions; however HNT loading fraction above 50wt.% resulted in a decrease in adsorption capacity attributed to limited accessibility of the amino groups. The adsorption capacity of the CT/HNT beads prepared from Dragonite source had a larger adsorption capacity of 14.2mg/g as compared to that of Matauri Bay, 10.55mg/g. It was observed that the adsorption capacity of the beads toward copper ions decreased when the loading fraction of HNT is increased at constant ultrasound amplitude. The result of this study helps to understand the links between the characteristics and adsorption abilities of CT/HNT beads.