A conceptually new approach has been developed for the fabrication of magnetite (Fe₃O₄)‐decorated carbon nanotubes (M‐CNTs) for negative electrodes of electrochemical supercapacitors. M‐CNTs were prepared by an ultrasonic‐assisted chemical synthesis method, which involved dispersion of functionalized CNTs in water, Fe₃O₄ formation on the CNTs surface, and particle extraction through liquid‐liquid interface (PELLI). Palmitic acid was found to be an efficient new extractor for PELLI. The slurries produced after drying and redispersing M‐CNTs and slurries obtained using PELLI were used for electrode fabrication. The electrodes prepared using PELLI showed superior performance due to reduced particle agglomeration. Testing results provided an insight into the influence of Fe₃O₄/CNTs mass ratio on the capacitance and capacitance retention at high charge‐discharge rates. A capacitance of 5.82 F cm⁻² (145.4 F g⁻¹) was achieved in Na₂SO₄ electrolyte using electrodes with high active mass of 40 mg cm⁻² and ratio of active mass to current collector mass of 0.6. Good electrochemical performance was achieved at low impedance. The capacitance of the negative M‐CNTs electrodes was comparable with capacitance of advanced positive MnO₂‐CNTs electrodes, which was beneficial for the fabrication of asymmetric devices. The asymmetric device has been fabricated, which showed promising performance in a voltage window of 1.6 V.

Ti₃C₂T_x–Fe₃O₄–carbon nanotube composites were prepared for electrochemical energy storage in the negative electrodes of supercapacitors. The electrodes show a remarkably high areal capacitance of 6.59 F cm⁻² in a neutral Na₂SO₄ electrolyte, which was obtained by the development of advanced nanofabrication strategies and due to the synergistic effect of the individual components. Enhanced capacitance was achieved using the in-situ synthesis method for the Fe₃O₄ nanoparticles. The superparamagnetic behavior of the Fe₃O₄ nanoparticles facilitated the fabrication of electrodes with a reduced binder content. Good mixing of the components was achieved using a celestine blue co-dispersant, which adsorbed on the inorganic components and carbon nanotubes and facilitated their co-dispersion and mixing. The capacitive behavior was optimized by the variation of the electrode composition and mass loading in a range of 30–45 mg cm⁻². An asymmetric device was proposed and fabricated, which contained a Ti₃C₂T_x–Fe₃O₄–carbon nanotube negative electrode and a polypyrrole–carbon nanotube positive electrode for operation in an Na₂SO₄ electrolyte. The asymmetric supercapacitor device demonstrated high areal capacitance and excellent power-density characteristics in an enlarged voltage window of 1.6 V. This investigation opens a new avenue for the synthesis and design of MXene-based asymmetric supercapacitors for future energy storage devices.

The purpose of this investigation was the development of a new colloidal route for the fabrication of Mn₃O₄ electrodes for supercapacitors with enhanced charge storage performance. Mn₃O₄-carbon nanotube electrodes were fabricated with record-high capacitances of 6.67 F cm⁻² obtained from cyclic voltammetry tests at a scan rate of 2 mV s⁻¹ and 7.55 F cm⁻² obtained from the galvanostatic charge–discharge tests at a current density of 3 mA cm⁻² in 0.5 M Na₂SO₄ electrolyte in a potential window of 0.9 V. The approach involves the use of murexide as a capping agent for the synthesis of Mn₃O₄ and a co-dispersant for Mn₃O₄ and carbon nanotubes. Good electrochemical performance of the electrode material was achieved at a high active mass loading of 40 mg cm⁻² and was linked to a reduced agglomeration of Mn₃O₄ nanoparticles and efficient co-dispersion of Mn₃O₄ with carbon nanotubes. The mechanisms of murexide adsorption on Mn₃O₄ and carbon nanotube are discussed. With the proposed method, the time-consuming electrode activation procedure for Mn₃O₄ electrodes can be avoided. The approach developed in this investigation paves the way for the fabrication of advanced cathodes for asymmetric supercapacitors and multifunctional devices, combining capacitive, magnetic, and other functional properties.

A novel approach has been developed for the fabrication of Fe₃O₄ decorated multiwalled carbon nanotubes (MWCNT) for energy storage in negative electrodes of electrochemical supercapacitors. Synthesis of Fe₃O₄ was performed in the presence of MWCNT, dispersed using various cationic and anionic polyaromatic dispersants. The comparison of experimental results obtained using different dispersants provided an insight into the influence of the chemical structure of the dispersant molecules on the microstructure of the Fe₃O₄-MWCNT materials. It was found that positively charged groups and chelating catechol ligands of the dispersants facilitated the formation of Fe₃O₄ decorated MWCNT with low agglomeration. The Fe₃O₄ -MWCNT materials, prepared using different dispersants were used for the fabrication of electrodes with mass loading of 40 mg cm⁻². The highest capacitance was obtained in 0.5 M Na₂SO₄ electrolyte for Fe₃O₄ decorated MWCNT prepared using cationic celestine blue dye as a dispersant. Improved cyclic voltammetry profile was obtained using FeOOH as an additive. Asymmetric devices were fabricated and tested based on the Fe₃O₄ decorated MWCNT negative electrodes and MnO₂-MWCNT positive electrodes.