An unprecedented hybrid polyoxometalate based on niobium oligomers: A notable application as redox supercapacitor electrode

An unprecedented polyoxoniobate (PONb) oligomer was obtained by addition of a methylene blue (MB) dye solution over the PONb solution formed a blue nanogel that was converted into a stable blue solid through a lyophilization process. The new solid composite, so-called blue polyoxoniobate (blue-PONb), presents a two-dimensional (2D) morphology with electrochemical performance that stand out among the materials used in redox supercapacitor technology. This new material was evaluated as supercapacitor electrode showing a high areal specific capacitance and power density that reaches 110.50 mF cm(-2) and 8.49 mW cm(-2). In addition, in this composite the redox additive (MB) and the PONb presented a peculiar electrochemical behavior, the reduction of the niobium species and the transfer of electrons necessary for the accumulation of charge occurring simultaneously. As a result, blue-PONb electrode maintains the cycling performance with high coulombic effi-ciency (similar to 99 %) over the 50,000 cycles evaluated. Here, the origins of the electrochemical stability and the mechanism of operation of the blue-PONb electrode are analyzed and discussed. Finally, this work presents a PONb as a new and promising class of redox-capacitive materials with matrix/redox shuttle synergism.

Automated summary

A stable blue solid composite, called blue polyoxoniobate (blue-PONb), was obtained by converting a methylene blue (MB) dye solution into a blue nanogel through a lyophilization process. This new material, blue-PONb, exhibits exceptional electrochemical performance and serves as a promising supercapacitor electrode, demonstrating high areal specific capacitance and power density. It also maintains high cycling performance with a coulombic efficiency of approximately 99% over 50,000 cycles. The electrochemical stability and operational mechanism of the blue-PONb electrode are analyzed and discussed in this study, presenting PONb as a new and promising class of redox-capacitive materials with matrix/redox shuttle synergism.