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.

Niobium compounds show considerable structural diversity and can be classified as binary compounds, alkali niobates, or complexes. Although niobium oxides have shown promising results as battery anodes, the perovskite structures are rarely utilized for electrochemical energy storage applications due to their low electrical conductivity. Therefore, this study reports the synthesis of a novel mixed perovskite, Nax(Nb0.5W0.5)O3, through a green, collagen-assisted route. FTIR analysis indicated that the synthesis is facilitated by the possible complexation of the niobium precursor within the protein structures. Furthermore, Rietveld refinement confirmed the formation of a mixed compound consisting of 97% Nax(Nb0.5W0.5)O3 and 3% (Na0.75Nb0.25)WO4. FEG-SEM characterization revealed nanoparticles with an average minimum Feret diameter of 95.03 nm. Postactivation XPS analysis of the electrodes revealed that the charge storage occurs via intercalation-type pseudocapacitance. Another significant aspect is the stabilization of tungsten in the +6 oxidation state, leading to an enhanced theoretical maximum capacity of 270.9 mAh g–1. Finally, galvanostatic charge and discharge confirmed the energy storage process, demonstrating a capacity of 243 mAh g–1 at 200 mA g–1 in an aqueous sodium-ion electrolyte. This enhanced performance is likely attributed to improved material conductivity resulting from the reduction of the bandgap from 3.4 eV (NaNbO3) to 3.04 eV and an Rct of 0.48 Ω by electrochemical impedance spectroscopy.