Formation of hexagonal-molybdenum trioxide (h-MoO₃) nanostructures and their pseudocapacitive behavior

Abstract

The crystallographic structure and morphology of redox active transition metal oxides have a pronounced effect on their electrochemical properties. In this work, h-MoO3 nanostructures with three distinct morphologies, i.e., pyramidal nanorod, prismatic nanorod and hexagonal nanoplate, were synthesized by a facile solvothermal method. The morphologies of h-MoO3 nanostructures were tailored by a controlled amount of hexamethylenetetramine. An enhanced specific capacitance about 230 F g(-1) at an applied current density of 0.25 A g(-1) was achieved in h-MoO3 pyramidal nanorods. Electrochemical studies confirmed that the h-MoO3 pyramidal nanorods exhibit superior charge-storage ability. This improved performance can be ascribed to the coexistence of its well exposed crystallographic planes with abundant active sites, i.e., hexagonal window (HW), trigonal cavity (TC) and four-coordinated square window (SW). The mechanism of charge-storage is likely facilitated by the vehicle mechanism of proton transportation due to the availability of the vehicles, i.e., NH4(+) and H2O. The promising, distinct and unexploited features of h-MoO3 nanostructures reveal a strong candidate for pseudocapacitive electrode materials.

Flexible Transparent Molybdenum Trioxide Nanopaper for Energy Storage

“…The device also exhibits excellent cycling performance (Figure c). It retains 96.5% of its initial capacitance after 20 000 cycles, which is much better than the previous reported values . The energy density of the symmetric device was calculated to be 22.89 Wh kg −1 at an average power density of 686.84 W kg −1 , which is about three times higher than carbon nanofiber supercapacitors, 20 times higher than H‐TiO 2 /MnO 2 , K y MoO 3‐ x , and H x MoO y supercapacitors, and 200 times higher than activated carbon cloth, TiN and H‐ZnO/MnO 2 supercapacitors .…”

“…The excellent specific capacitance can be ascribed to the efficient ion diffusion in the thin nanobelts (with thickness about 50–70 nm) and the 3D structure, as well as the reduced distance of electron transport from ultrathin nanopaper electrode to current collector . Moreover, ultrathin MoO 3 NB nanopaper electrode shows outstanding cycling stability with a capacitance retention rate of 99.1% over 20 000 cycles, which is the best cycling performance for a MoO 3 ‐based energy storage system (Figure d and Table S1, Supporting Information) …”

Fabrication of a Single‐Atom Platinum Catalyst for the Hydrogen Evolution Reaction: A New Protocol by Utilization of HxMoO3−x with Plasmon Resonance

“…Additionally, according to our reported method, the intensities of the surface plasmonic bands can be tuned in situ by illuminating the sample for different amounts of time under a xenon lamp with a power of 300 mW cm −2 ; this further causes an increase in the degree of H + intercalation, which leads to stronger plasmonic bands that result from higher concentrations of free electrons (see Figure S1). It is known that the open‐channel structure of h‐MoO 3 nanorods can accept intercalated ions and can also favor transportation of ions, as reported in the literature . The dissolution of CO 2 in water has an acidifying effect, which helps in the formation of hexagonal molybdenum oxide under high‐temperature and high‐pressure conditions.…”

“…It can be observed that the pure H x MoO 3− x sample is mostly formed from nanorods with amorphous edges. Usually, hexagonal molybdenum oxide is a metastable phase, which is favorable for its transformation into 2D molybdenum oxide . Besides, the amorphous structure is known to possess high HER activity, primarily as a result of more active sites .…”

Design of Mixed‐Metal Silver Decamolybdate Nanostructures for High Specific Energies at High Power Density

“…[4,5] At present, supercapacitors are the important class of the alternative energy-storage devices due to their fast charging/ discharging rate, high rate of reversibility, and ultralong cycling stability compared to batteries. Binary transition metal oxides, e.g., RuO 2 , [6] MnO 2 , [7] Nb 2 O 5 , [8] Co 3 O 4 , [9] MoO 3 , [10] etc., have been studied as prospective negative or positive supercapacitor (pseudocapacitor) electrode materials hitherto. In the pseudocapacitors' perspective, Trasatti and coworkers [6] stated that the specific capacitance obtained in oxide-based systems (i.e., RuO 2 -distorted rutile structure) is the sum of the inner (diffusion controlled, i α v 1/2 ) and outer (surface controlled, i α v) active sites available on the material.…”