Quantum-Dot-Mediated Controlled Synthesis of Dual Oxides of Molybdenum from MoS₂ : Quantification of Supercapacitor...

The versatile technological applications of molybdenum oxides requires the efficient synthesis of various stoichiometric molybdenum oxides. Thus, herein, a controlled method to synthesize both MoO₃ and MoO₂ from MoS₂ via quantum dot intermediates is reported. Microscopic, spectroscopic, and X-ray studies corroborate the formation of orthorhombic α-MoO₃ with a microbelt structure and monoclinic MoO₂ nanoparticles that self-assemble into hollow tubes. Quantitative investigations into charge-storage kinetics reveal that MoO₂ exhibits an excellent pseudocapacitive response up to a mass loading of 5 mg cm^-2 with an areal capacity of 327.2 mC cm^-2 at 5 mV s^-1 , with 41.9 % retention at 100 mV s^-1 . In contrast, above a mass loading of 0.5 mg cm^-2 , the charge-storage nature of MoO₃ electrodes switches from that of a supercapacitor to battery type. At a sweep rate of 50 mV s^-1 , 87.2 % of the total charge is contributed by a capacitive response in a 1 mg cm^-2 MoO₂ electrode. The charge-storage kinetics of MoO₃ and MoO₂ reflect on the respective asymmetric supercapacitors. A MoO₂ //graphite asymmetric supercapacitor holds an outstanding energy density of 341 mW h m^-2 at a power density of 4949 mW m^-2 and delivers an ultrahigh power density of 28140 mW m^-2 with an energy density 142 mW h m^-2 and energy efficiency of 87 %.