Structural and electrochemical properties of hydrogen titanium oxides

Hydrogen titanium oxide H2Ti6O13 was prepared from Li2Ti6O13 as a parent compound via Li+/H+ ion exchange in acidic solution at 60 °C. It crystallizes in the monoclinic system, space group C2/m, and the lattice parameters of a = 14.6604(3) Å, b = 3.74109(8) Å, c = 9.2487(2) Å, and β = 96.956(2)°. The crystal structure of H2Ti6O13 was refined to the conventional values of Rwp = 3.12% and Rp = 2.45% with a fit indicator of GOF = Rwp / Re = 1.39 by Rietveld analysis using powder neutron diffraction data. The basic (Ti6O13)2 − framework in H2Ti6O13 was maintained nearly unchanged from that in the parent Li2Ti6O13. The hydrogen site in the tunnel space was refined with the strict O3H1 distance of 0.94(1) Å in H2Ti6O13. The structural stability of H2Ti6O13 was confirmed by bond valence sums and 1H-MAS NMR measurement. The total protonic conductivity in H2Ti6O13 was estimated to be σtotal = 8.32 × 10− 6 S cm− 1 at room temperature from the results of AC-impedance measurements. This value is comparable to that of the well-known good protonic conducting ramsdellite-type H2Ti3O7.