| Summary: | Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub>–Fe<sub>3</sub>O<sub>4</sub>–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<sup>−2</sup> in a neutral Na<sub>2</sub>SO<sub>4</sub> 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 Fe<sub>3</sub>O<sub>4</sub> nanoparticles. The superparamagnetic behavior of the Fe<sub>3</sub>O<sub>4</sub> 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<sup>−2</sup>. An asymmetric device was proposed and fabricated, which contained a Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub>–Fe<sub>3</sub>O<sub>4</sub>–carbon nanotube negative electrode and a polypyrrole–carbon nanotube positive electrode for operation in an Na<sub>2</sub>SO<sub>4</sub> 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.
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