Pseudocapacitive Behavior of Protonic Niobate Nanowires in Aqueous Acidic Electrolyte

Abstract

Niobium-based oxides are being increasingly evaluated as materials for energy storage applications. Additionally, the use of these oxides as cathodes in aqueous electrolytes has shown promise. Based on this, the pseudocapacitive behavior of protonic niobate nanowires in an aqueous acidic electrolyte (1 M H2SO4) was evaluated for the first time. The material was obtained in two simple sequential steps. First, hydrothermal synthesis resulted in sodium niobate; second was ionic exchange (in two concentrations of 2 M and 0.1 M HNO3), where the protonic niobate was obtained. The resulting protonic niobate was characterized by FEG-SEM, the results demonstrated that the morphology of the oxide was concentration-dependent in the ionic exchange step, and EDS analysis was used to validate the procedure. Using DRX, Raman spectroscopy, and FTIR analysis, the transformation of sodium niobate to protonic niobate was evidenced. The electrochemical tests demonstrated that the protonic niobate presented pseudocapacitive behavior when employed as the cathode in 1 M H2SO4, and the ionic exchange in 2 M HNO3 promoted a better specific capacitance, reaching 119.8 mF·cm−2 at a 1 mA·cm−2 current density.