Pr-doped oxygen-vacancy-induced porous NiMoO4 cathode and MoS2-modified CNT anode for constructing ultra-high-performance supercapacitors

Abstract

In this study, the sol–gel method was used to prepare NiMoO₄ electrode materials doped with different concentrations of the rare earth element Pr. The microstructure and phase structure of the samples were thoroughly studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The results showed that the prepared materials were porous nanospheres. Due to their porous spherical shape, these structures showed a large specific surface area, providing more surface area for charge storage and release, which helped in increasing the reaction rate of the electrode, thereby improving the energy storage performance of the capacitor. Since the ionic radius of Pr differed from that of the original metal in NiMoO₄, the size mismatch could result in the removal of oxygen atoms from the crystal lattice, forming oxygen vacancies. The electronic structure of the material was changed, and the number of active sites increased, which affected the electrochemical properties of the material. The electrochemical performance of the rare earth Pr-doped NiMoO₄ electrode material (Pr–NiMoO₄) was further tested. The experimental results showed that the Pr–NiMoO₄ electrode exhibited excellent electrochemical performance with 0.7% Pr doping, achieving a specific capacity of 2078 F g⁻¹ at a current density of 1 Å g⁻¹. Even at a current density of 5 Å g⁻¹ and 10 000 charge and discharge cycles, the material retained 98.8% of its capacitance, showing better electrochemical stability than undoped NiMoO₄. An asymmetric supercapacitor was constructed using 0.7% Pr–NiMoO₄ material (Pr–NiMoO₄) as the positive electrode material and MoS₂@C as the negative electrode material, showing a high energy density of 73.5 W h kg⁻¹. After 10 000 charge and discharge cycles, the capacitance retention rate of the capacitor could still be maintained at 91.9%. This study successfully proposes an effective strategy for the preparation of rare earth-doped bimetallic oxide electrode materials.