Oxygen-Vacancy-Tunable Electrochemical Properties of Electrodeposited Molybdenum Oxide Films

Abstract

Molybdenum oxides have been widely studied in recent years, owing to their electrochromic properties, electrocatalytic activities for hydrogen evolution reactions (HERs) and excellent energy storage performance. These characteristics strongly depend on the valence states of Mo in the oxides such as IV, V, and VI, which can be efficiently altered through oxygen deficiencies within the oxides. Here, we present a colloidal electrodeposition method to introduce oxygen vacancies in such Mo oxide films. We prepared uniform MoO x films and investigated their electrochemical characteristics under different valence states IV, V, and VI. In this paper, we demonstrate that MoO 2+x films, where Mo in valence states IV and V, can be used for high-performance supercapacitor electrodes. Due to their high conductivity, they exhibit an areal capacitance of 89 mF cm −2 at 1 mA cm −2 and negligible capacitance loss within 600 cycles. Additionally, we demonstrate that, in a complementary electrochromic device configuration, the introduction of an MoO 2+x counter electrode remarkably lowers the activation potential of WO 3 from −2 to −0.5 V and achieves a fully bleached state at 0.5 V. These properties make the MoO 2+x film an ideal counter electrode to store ions for an electrochromic device. Furthermore, MoO 3−y films, where Mo in the valence states V and VI, are obtained by annealing the electrodeposited MoO 2+x film under 200 °C for 24 h. Such films exhibit an excellent catalytic for the HER with an overpotential of 201 mV. Furthermore, we show that MoO 3 films, where Mo at its highest oxidation state (VI), can be obtained via annealing the MoO 2+x film at 300 °C for 6 h, and the resulting films exhibit battery characteristics. Our research provides a new and facile strategy to fabricate substoichiometric molybdenum oxide nanofilms and reveals the effect of different valences on the electrochemical performance of molybdenum oxide films, which opens new doorways for future research in the electrochemical applications of transition metal oxides.

Electrochromic Battery Displays with Energy Retrieval Functions Using Solution‐Processable Colloidal Vanadium Oxide Nanoparticles

“…To analyze the phase composition of the as-synthesized vanadium oxide nanoparticles, the colloidal suspension was dried at room temperature and characterized by the powder X-ray diffraction (XRD) measurement. The high-resolution TEM image, inset in Figure 1e, shows clear lattice fringes of 1.91 and 2.92 Å correspond to the and (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) planes, respectively. 00-028-1433) phase.…”

“…[6,7] The electrochromic battery exhibits self-coloration behaviors and eliminates the external voltage requirement for triggering the coloration process. [11][12][13][14][15] Among the TMOs, vanadium oxide is considered the most promising material for electrochromic displays because of its multicolor behaviors. [8][9][10] The lower charged/bleached potential indicates a lower energy consumption during the bleaching process.…”

“…[11][12][13][14][15] Among the TMOs, vanadium oxide is considered the most promising material for electrochromic displays because of its multicolor behaviors. Transition metal oxides (TMOs) have shown excellent electrochromic properties due to their remarkable multivalence states and the corresponding color evolutions.…”

Nanostructured MoO3 for Efficient Energy and Environmental Catalysis

“…In this way, 2D α-MoO 3 nanosheets were fabricated and exhibited a considerable HER performance with low overpotential of 142 mV, to achieve 10 mA/cm 2 current density [61]. Zhang et al also found that MoO 3−y (valence state of V and VI) can be used for efficient electrocatalytic hydrogen evolution [62]. Second, the morphology is another key factor.…”

Carbon Transition‐metal Oxide Electrodes: Understanding the Role of Surface Engineering for High Energy Density Supercapacitors

“…During the deposition, electrical energy is supplied to provide a strong driving force for the redox reaction that ensures uniform growth and large surface area of TMO on the conductive substrate such as stainless steel, Ni foam, carbon cloth, ITO coated glass, etc. [53][54][55][56] Furthermore, it also features the advantage of doping TMO with other metals. [57] A conductive substrate as the working electrode is used and the deposition conditions, such as scan rate, number of cycles, electrolyte concentration, and pH, are used as controlling parameters to achieve high surface area and uniform deposition.…”