Sodium niobates and protonic niobates nanowires obtained from hydrothermal synthesis : electrochemical behavior in aqueous electrolyte

Niobium-based oxides can be used in several applications due to a diverse set of properties. In this work, Na2Nb2O6.H2O sodium niobate nanowires were obtained by hydrothermal synthesis at low temperature. Dehydrated sodium niobate (Na2Nb2O6) and sodium niobate with perovskite structure (NaNbO3) were obtained by submitting Na2Nb2O6.H2O to heat treatment (350 °C and 500 °C, respectively). To obtain protonic niobates, sodium niobates were immersed in nitric acid in order to promote ion exchange reactions. From this procedure, protonic niobates (H3O)2Nb2O6.H2O and (H3O)2Nb2O6 were obtained. The sample NaNbO3 did not undergo any transformation. Cyclic voltammetry tests carried out in a neutral aqueous solution 1 M Na2SO4 showed a wide potential window for both niobates (sodium and protonic). However, the protonic niobate samples (H3O)2Nb2O6.H2O and (H3O)2Nb2O6 presented much higher current density values than the sodium niobates. This result can be related to a structural rearrangement that allowed a significant increase in the intercalation of sodium Na + ions from the electrolyte into the structure of these protonic niobates, when polarized. Therefore, in this work, it was demonstrated that it is possible to obtain protonic niobates from sodium niobates, as well as, it was verified the distinct electrochemical behavior between these materials