Electrical Properties of Hollandite-Type Ba1.33Ga2.67Ti5.33O16, K1.33Ga1.33Ti6.67O16, and K1.54Mg0.77Ti7.23O16.

Electrical conductivity and electrochemical catalytic activity for H2 oxidation of Ti-based hollandite-type Ba1.33Ga2.67Ti5.33O16 (BGT), K1.33Ga1.33Ti6.67O16 (KGT), and K1.54Mg0.77Ti7.23O16 (KMT) were investigated, along with the chemical stability of KMT under H2 at elevated temperature. BGT, KGT, and KMT crystallized in a tetragonal structure with the space-group I4/ m. The electrical conductivity in H2 increases with increasing Ti content, and the highest total electrical conductivity of 2 S/cm at 800 °C in H2 was observed for KMT. KGT:Fe (1:1) + 20% LSGM + 30% porosity composite electrode showed the lowest area specific resistance of ca. 1.6 Ω cm2 at 800 °C for hydrogen oxidation reaction (HOR) under the open circuit condition. Moderate catalytic activity for HOR could be attributed to poor oxide ion conductivity and exclusion of potassium and hydrogen uptake in H2 at elevated temperature. Bond valence sum mismatch map calculation showed that the ionic transport happens along the 1D channel of c-axis in the hollandite oxides.