Tailoring Mo5+/Mn2+ defect states in MoS2 nanoflowers to enhance pseudocapacitive supercapacitor performance

Manganese-doped molybdenum disulfide (MoS 2 ) nanoflowers (MoS 2 :Mn x , x = 0, 0.3, 0.5, 0.7, and 1 nominal mol%) were synthesized via a one-step hydrothermal route and evaluated as electrode materials for all-in-one supercapacitor devices. Scanning and transmission electron microscopy imaging revealed a hierarchical, flower-like morphology composed of self-assembled nanosheets that was preserved across all doping levels, while energy-dispersive X-ray spectroscopy elemental mapping confirmed a homogeneous distribution of Mo, S, and Mn throughout the particles. Electron paramagnetic resonance spectroscopy identified a Mo 5+ defect signal at g = 1.93 in the undoped sample, which persists in the doped sample, overlapping with the characteristic six-line Mn 2+ hyperfine sextet, providing complementary, site-sensitive evidence for the site-specific incorporation of Mn into the MoS 2 lattice. Nitrogen adsorption–desorption analysis showed that the specific surface area and pore volume remain largely unchanged below 1% Mn, but nearly double at 1% Mn, consistent with greater electrolyte access to the electrode surface. Electrochemical testing showed that Mn doping markedly enhances charge-storage performance: the MoS 2 :Mn0.7 electrode achieved the highest specific capacitance (493.7 F/g at 10 mV/s), energy density (34.16 Wh/kg), and power density (1242 W/kg) among the series, along with a cycling stability of 70% capacitance retention after 10000 cycles, compared to 83.3 F/g, 5.78 Wh/kg, and 210 W/kg for the undoped MoS 2 based device. Dunn’s kinetic analysis showed that the capacitive (surface-limited) contribution of MoS 2 :Mn0.7 is much higher than that of undoped MoS 2 across the whole scan-rate range (e.g., 84% vs. 15% at 10 mV/s), indicating that Mn doping shifts the charge-storage kinetics from diffusion-limited toward faster, surface-limited behavior. These results establish Mn doping and the associated Mo 5+ / Mn 2+ defect states as an effective strategy for tailoring the charge-storage mechanism and improving the electrochemical performance of MoS 2 -based supercapacitor electrodes.