Syntheses, properties and applications of framework titanium phosphates with open structures

A new layered hydrogen titanium phosphate (HTP) was synthesized by ion exchange of a precursor material NMe{dollar}sb4{dollar}TP. This precursor, which was prepared from a hydrothermal reaction employing tetramethylammonium as a templating cation, also has a layered structure. The chemical formula of HTP was proposed as TiO{dollar}sb2{dollar}(H{dollar}sb2{dollar}PO{dollar}sb4{dollar})(H{dollar}sb3{dollar}O). This was derived using {dollar}sp{lcub}31{rcub}{dollar}P magic angle spinning solid state NMR, structural considerations, and other supplemental methods. A model for the structure of HTP was proposed in this study. HTP is capable of undergoing amine and redox lithium intercalations and the reactions show excellent reversibility. Each formula unit of HTP can take up one amine molecule or two lithium cations. Amines intercalate into HTP with a bilayer conformation and tilt at an angle of about 55 degrees relative to the layer slabs. Metal cations can also be incorporated into HTP under carefully controlled pH conditions or from the amine intercalates. The conductivity of the lithium cations intercalated into HTP was studied by ac impedance spectroscopy and is comparable to that of the NASICON type compounds. A Li/LiClO{dollar}sb4{dollar}/HTP electrochemical cell was constructed and its discharge was studied. The discharge potential ranges between 2.6 and 1.8 volts and the energy density of this cell was estimated to be about 550 W*h/kg for the pure HTP material.; The three dimensional titanium phosphates with the NASICON structure were also studied in this work. The hydrothermal process was used and investigated for the synthesis of MTi{dollar}sb2{dollar}(PO{dollar}sb4{dollar}){dollar}sb3{dollar}, where M = Li{dollar}sp+{dollar}, Na{dollar}sp+{dollar}, K{dollar}sp+{dollar}, Ag{dollar}sp+{dollar}, or Cu{dollar}sp+{dollar}. Pure products were obtained under milder conditions than reported before. A comparison on the syntheses and properties of these NASICON compounds prepared from different processes is given.