Synthesis and electrochemical behaviors of nano-network NaHTi3O7 thin films on Ti/Si prepared by a hydrothermal-galvanic couple method

Nano-network NaHTi3O7 thin films have been successfully synthesized over Ti-coated Si substrates by a hydrothermal-galvanic couple method in 4 M NaOH solutions at temperatures above 60 °C. This is the first report to make nano-network NaHTi3O7 thin films in low concentration NaOH solutions at reaction temperatures below 100 °C. The thickness and porosity of NaHTi3O7 films increased rapidly with the reaction temperature. The nano-network morphology allows sodium ions to be easily inserted into and extracted out of the NaHTi3O7 thin films. The mixed valence states of titanium (Ti+ 3/Ti+ 4) also play an important role on charge balance during the insertion and extraction processes. Charging and discharging performance reveals that the NaHTi3O7 films exhibited potentials in the applications of ionic devices.