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.