A Novel Mixed Perovskite-like Alkali Niobium Tungsten Oxide (Na x (Nb0.5W0.5)O3) Synthesized by a Sustainable Collagen Dispersion Process.

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, Na x (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% Na x (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 R ct of 0.48 Ω by electrochemical impedance spectroscopy.