Application of murexide as a capping agent for fabrication of magnetite anodes for supercapacitors: experimental and first-principle studies

In this study, we investigate the effectiveness of murexide for surface modification of Fe3O4$$\textrm{Fe}_{3}\textrm{O}_{4}$$ nanoparticles to enhance the performance of multiwalled carbon nanotube-Fe3O4$$\textrm{Fe}_{3}\textrm{O}_{4}$$ supercapacitor anodes. Our experimental results demonstrate significant improvements in electrode performance when murexide is used as a capping or dispersing agent compared to the case with no additives. When murexide is used as a capping agent, we report a capacitance of 4.2 F cm-2$$^{-2}$$ from cyclic voltammetry analysis with good capacitance retention at high scan rates. From impedance measurements, we reveal a substantial decrease in the real part of impedance for samples prepared with murexide, indicating easier charge transfer at more negative electrode potentials, and reinforcing the role of murexide as a capping agent and charge transfer mediator. Density functional theory is used to investigate interactions between the murexide adsorbate and the Fe3O4$$\textrm{Fe}_{3}\textrm{O}_{4}$$ (001) surface, with a specific emphasis on adsorption strength, charge transfer, and electronic properties. This theoretical investigation uncovers a strong adsorption enthalpy of − 4.5 eV and allows us to identify the nature of chemical bonds between murexide and the surface, with significant charge transfer taking place between the Fe3O4$$\textrm{Fe}_{3}\textrm{O}_{4}$$ surface and murexide adsorbate. The transfer of electrons from the Fe3O4$$\textrm{Fe}_{3}\textrm{O}_{4}$$ surface to murexide is recognized as a vital component of the adsorption process. By examining the bonding nature of murexide on Fe3O4$$\textrm{Fe}_{3}\textrm{O}_{4}$$, this research study uncovers insights and proposes a novel bonding configuration of murexide that incorporates a combination of bridging and chelating bonding.Graphical abstract