Quantum‐Dot‐Mediated Controlled Synthesis of Dual Oxides of Molybdenum from MoS2: Quantification of Supercapacitor Efficacy

• Published in: Chemistry, an Asian journal an Asian journal, 2018-12, Vol.13 (24), p.3871-3884
• Main Authors: Mandal, Debasish, Routh, Parimal, Nandi, Arun K.
• Format: Article
• Language: English
• Subjects: Batteries; Chemistry; electrochemistry; Electrodes; Energy management; Flux density; Molybdenum; Molybdenum disulfide; Molybdenum oxides; Molybdenum trioxide; Nanoparticles; nanostructures; Power management; Quantum dots; Supercapacitors; Switches; Synthesis; synthesis design; Tubes
• ISSN: 1861-4728; 1861-471X
• DOI: 10.1002/asia.201801173

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 %. Belts and tubes: A method has been developed to synthesize both MoO3 microbelts and MoO2 hollow microtubular structures from MoS2 via quantum dot intermediates in a controlled manner. MoO2 exhibits an excellent pseudocapacitive response, whereas, in contrast, MoO3 shows mainly a battery‐type nature (see figure). The MoO2//graphite asymmetric supercapacitor has a very high energy density and delivers an ultrahigh power density.