Synthesis and characterisation of novel ion conductors

As hydrogen is a renewable energy source, the studies for materials exhibiting fast hydrogen transport can have great potential to be used as electrolytes for electrochemical devices and as strong reducing agents for electrochemical conversion reactions. The alkaline earth metals, AeH2, where Ae = Ca, Sr and Ba are of interest as they exhibit fast hydride ion conductivity which may enable them to be used as solid-state electrolytes in electrochemical devices. BaH2 has a high hydride ion conductivity of 0.2 S cm−1 at 630 °C, which is an order of magnitude higher than other oxide ion conductors at a similar temperature. The in-situ PDF and conductivity study of BaD2 was performed to examine the local deviation from the average crystal structure. The technique using neutron total scattering helped to examine possible short-range correlations between atoms to understand the local structure of BaD2. BaH2 was doped with the monovalent ions Na or Li and its structural and electrical properties, were investigated. LixBa1−xH2−x (x = 0.05, 0.10, 0.15 and 0.20) were synthesised by the solid-state reaction in which Li0.10Ba0.90H1.90 has achieved highest conductivity of 0.38 S cm−1 at 600 °C. LiBaH3 was synthesised by mechanochemical reaction at room temperature and solid-state reaction at high temperature, and their structural and electrical properties were analysed. LiBaH3 has a conductivity of 0.01 S cm−1 at 600 °C. NaxLi1−xBaH3 (x = 0.05, 0.15 and 0.20) were also synthesised by solid-state reaction and their structural and electrical properties were examined. Na0.15Li0.85BaH3 has the highest conductivity of the Na-doped LiBaH3 samples studied, exhibiting a conductivity of 0.03 S cm−1 at 600 °C. Nitridation in LixBa1−xH2−x (x = 0.05, 0.10, 0.15 and 0.20), NaxBa1−xH2−x (x = 0.01, 0.05 and 0.10), LiBaH3 and NaxLi1−xBaH3 (x = 0.05, 0.15 and 0.20) increases their conductivity by 0.02 S cm−1 initially due to exothermic reaction, except the nitridation of BaH2 at 600 °C, where their conductivity decreases by 0.04 S cm−1 upon nitridation due to endothermic reaction.