High-performance multi-dimensional nitrogen-doped N+MnO₂@TiC/C electrodes for supercapacitors

Intercalation of alkali cations (Na⁺, K⁺, etc.) or protons (H⁺) on the surface of MnO₂ can improve the theoretical pseudocapacitance in the redox reactions. However, the poor electrical conductivity and vulnerability to agglomeration and dissolution during the redox reactions on MnO₂ have hampered practical application. In this work, a network composed of TiC/C nanowires is prepared on Ti₆Al₄V to produce a conductive three-dimensional substrate on which two-dimensional MnO₂ nanosheets are fabricated to form a multi-dimensional MnO₂@TiC/C composite electrode. The three-dimensional TiC/C nanowire network increases the specific surface area between the active species and electrolyte and electron transport efficiency to yield a specific capacitance of 284.8 F g⁻¹ or 76.0 mAh g⁻¹. To further improve the conductivity and increase the active sites on the pseudocapacitive materials, nitrogen is incorporated into MnO₂ to form the N+MnO₂@TiC/C electrode with a specific capacity of 371.1 F g⁻¹ or 103 mAh g⁻¹ rendering it very attractive to high-performance supercapacitors. After nitrogen doping, the cyclic stability of the electrode is improved greatly, and 91% retention of the gravimetric capacity is accomplished after 50,000 cycles. The mechanism is investigated by analyzing the pseudocapacitances of the composite electrodes with and without N doping. Nitrogen doping not only changes the elemental composition of the electrode and enhances the conductivity, but also increases the active sites on MnO₂. As a result, the pseudocapacitance contribution increases from 66.4% to 76.3% at 1 mV s⁻¹. The supercapacitor constructed with N+MnO₂@TiC/C as the positive electrode and nickel foam coated with activated carbon (AC) as the negative electrode shows excellent power density of 5400 W kg⁻¹ at 23.9 Wh kg⁻¹. Owing to the excellent electrochemical characteristics and cycling stability, the materials and associated design concept have large potential in energy storage applications.