Systematic study of ionic conduction in silver iodide/mesoporous alumina composites 2: effects of silver bromide doping

In our preceding paper (Y. Fukui et al., Phys. Chem. Chem. Phys., 2023, 25, 25594-25602), we reported a systematic study of the Ag+-ion conducting behaviour of silver iodide (AgI)-loaded mesoporous aluminas (MPAs) with different pore diameters and AgI-loading ratios. By optimising the control parameters, the Ag+-ion conductivity has reached 7.2 x 10-4 S cm-1 at room temperature, which is more than three orders of magnitude higher than that of bulk AgI. In the present study, the effect of silver bromide (AgBr)-doping in the AgI/MPA composites on Ag+-ion conductivity is systematically investigated for the first time, using variable-temperature powder X-ray diffraction, differential scanning calorimetry, and electrochemical impedance spectroscopy measurements. The AgBr-doped AgI/MPA composites, AgI-AgBr/MPA, formed a homogeneous beta/gamma-AgI-structured solid solution (beta/gamma-AgIss) for the composites with AgBr <= 10 mol%, above which the composites underwent a phase separation into beta/gamma-AgIss and face-centred cubic AgBr solid solutions (AgBrss). The onset temperature of the exothermic peaks attributed to the transition from alpha-AgI-structured solid-solution phase to beta/gamma-AgIss or AgBrss decreased with increasing the AgBr-doping ratio. The room-temperature ionic conductivity of the AgI-AgBr/MPA composites exhibited a volcano-type dependence on the AgBr-doping ratio with the highest value (1.6 x 10-3 S cm-1) when the AgBr content was 10 mol%. This value is more than twice as high as that of the highest conducting AgI/MPA found in our previous study. A systematic study of Ag+-ion conducting behaviour in AgBr-doped AgI/mesoporous alumina (MPA) composites was conducted. The highest conductivity was found when the AgBr content was 10 mol% (1.6 x 10-3 S cm-1 at 25 degrees C).