•Co3O4-MnCo2O4 was synthesized by a two-step method, different from previously reported.•The methyl groups of ZIF-67 were oxidized to carboxyl groups with MnO2 loaded.•After annealing, Co3O4-MnCo2O4 ...was obtained with an average diameter of 20–50 nm.•Co3O4-MnCo2O4 exhibited excellent rate performance and outstanding cycle capacity.•The two-step method can be used to prepare other mixed transition-metal oxides.
Spinel Co3O4-MnCo2O4 was synthesized by a two-step method, with a post annealing step after loading MnO2 on the surface of Co-MOF (ZIF-67). For the first step, the methyl (-CH3) groups of ZIF-67 were oxidized to carboxyl (-COOH) groups, with MnO2 uniformly loaded on ZIF-67. Benefiting from this step, the uniform distribution of spinel Co3O4-MnCo2O4 was achieved after calcination. Based on the stable framework of Co-MOF, a nanoparticle spinel Co3O4-MnCo2O4 was obtained with an average diameter of 20–50 nm. This nano-sized characteristic not only shortens the diffusion lengths of lithium ion, but also alleviates the volume expansion of material during the Li+ insertion/extraction process. The as-synthesized spinel Co3O4-MnCo2O4 exhibited superior rate stability and cycle stability with high energy density and power density. Even at 5000 mA g−1, a specific capacity of 614 mA h g−1 can be maintained. In view of the remarkable performance of spinel Co3O4-MnCo2O4, it can be concluded that spinel Co3O4-MnCo2O4 has a potential to be an anode material in LIBs. Further, this two-step method can be used to prepare other mixed transition-metal oxides in various fields.
Layered 2D materials, such as graphene, transition metal dichalcogenides, transition metal oxides, black phosphorus, graphitic carbon nitride, hexagonal boron nitride, and MXenes, have attracted ...intensive attention over the past decades owing to their unique properties and wide applications in electronics, catalysis, energy storage, biomedicine, etc. Further reducing the lateral size of layered 2D materials down to less than 10 nm allows for preparing a new class of nanostructures, namely, nanodots derived from layered materials. Nanodots derived from layered materials not only can exhibit the intriguing properties of nanodots due to the size confinement originating from the ultrasmall size, but also can inherit some unique properties of ultrathin layered 2D materials, making them promising candidates in a wide range of applications, especially in biomedicine and catalysis. Here, a comprehensive summary on the materials categories, advantages, synthesis methods, and potential applications of these nanodots derived from layered materials is provided. Finally, personal insights about the challenges and future directions in this promising research field are also given.
Nanodots derived from layered materials not only exhibit the intriguing properties of traditional nanodots due to the size confinement effect, but also inherit some unique properties of layered materials, making them promising candidates in various applications. The state‐of‐the‐art progress on the preparation and applications of nanodots derived from layered materials is reviewed.
Transition metal oxides (TMOs) have attracted considerable attention due to their variety of chromogenic properties. Among them, vanadium pentoxide (V2O5) has gained significant interest in respect ...of multichromism associated with orange, green and blue colors. Herein, we report a simple and easy method for the fabrication of Mo doped V2O5 thick films, leading to improved cyclability. Molybdenum doped vanadium pentoxide powders were synthesized from one single polyol route through the precipitation of an intermediate precursor: molybdenum doped vanadium ethyleneglycolate (Mo doped VEG). The as-synthesized Mo-doped V2O5 exhibits improved electrochromic performance in terms of capacity, cycling stability, and color contrast compared to single-component V2O5 in lithium as well as sodium based electrolyte. The improvement in EC performances lies in films of higher porosity as well as higher diffusion coefficients. To conclude, an electrochromic device combining Mo-V2O5 to WO3.2H2O, via a PMMA-lithium based electrolyte membrane exhibits simultaneously reversible color change from yellow to green for Mo-V2O5 and from blue to yellow white for WO3.2H2O with a cycling stability up to 10 000 cycles.
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High-entropy materials (HEMs) exhibit extensive application potential owing to their unique structural characteristics. Structure regulation is an effective strategy for enhancing material ...performance. However, the fabrication of HEMs by integrating five metal elements into a single crystalline phase remains a grand challenge, not to mention their structure regulation. Herein, an amorphous-to-crystalline transformation route is proposed to simultaneously achieve the synthesis and structure regulation of high-entropy metal oxides (HEMOs). Through a facile hydrothermal technique, five metal sources are uniformly integrated into amorphous carbon spheres, which are transformed to crystalline HEMOs after calcination. Importantly, by controlling ion diffusion and oxidation rates, HEMOs with different structures can be controllably achieved. As an example, HEMO of the five first-row transition metals CrMnFeCoNiO is synthesized through the amorphous-to-crystalline transformation route, and structure regulation from solid spheres to core-shell spheres, and then to hollow spheres, is successfully realized. Among the structures, the core-shell CrMnFeCoNiO exhibits enhanced lithium storage performance due to the component and structural advantages. Our work expands the synthesis methods for HEMs and provides a rational route for structure regulation, which brings them great potential as high-performance materials in energy storage and conversion.
A universal amorphous-to-crystalline transformation strategy is developed, and the synthesis and structure regulation of high entropy metal oxide is simultaneously achieved with the structure controlled from solid, to core-shell, to hollow spheres.
Owing to the special electronic structure and earth-abundance, spinel structure-based oxides (AB2O4, A = Ni, Cu and B= Co, Fe) have considerable attractive for photo/electro/catalysis. In this work, ...AB2O4 thin films were synthesized via the spray pyrolysis method on FTO substrates and annealed at 550 °C for 1 h. The structural, morphology, optical and photoelectrochemical properties were studied. The crystalline results show that the thin films have a cubic spinel structure, and the morphology results show a fine grainy surface. The photoelectrochemical measurements in terms of photocurrent density, Incident Photon-to-Current Efficiency (IPCE) and applied bias photon-to-current efficiency (ABPE) were investigated for all samples under neutral pH condition. The results of photocurrent density were (109, 41, 28, 25) μA/cm2 and the IPCE results at 530 nm were 3.05% > 1.52% > 1.42% > 1.32% for CuCo2O4, NiCo2O4, CuFe2O4 and NiFe2O4 respectively under AM 1.5G (100 mW/cm−2) and applied bias −0.5 V. The band structure including the conduction/valence band was determined by Mott-Schottky plot revealing the ability of hydrogen production from neutral water.
•The structural study of (Cu, Ni) (Fe, Co)2O4 photocathode is a spinel structure.•The photocathodes reveal possibility to produce H2 and O2 under pH-neutral water.•They have demonstrated a significant charge trap surface.•The highest photocurrent was obtained by CuCo2O4 and then NiCo2O4.•The stability of the photocathodes is not efficient for practical application.
One dimensional (1D) transition metal oxide nano-structured materials have high possibilities in the field of sensor applications. In the current work, we have investigated gas sensing response of ...the less explored hexagonal-Molybdenum Oxide (h-MoO3) for ammonia (NH3) gas. We have synthesized h-MoO3 nano-rods by facile chemical bath technique (CBT). To fabricate sensors, thin films were deposited on glass substrates using spin coating technique. Change in resistance of the film on NH3 exposure was recorded with time. The gas sensing response was measured at different concentration levels of NH3 ranging from 5 ppm to 100 ppm at 200 °C. We observed comparatively high sensing percentage for low to high concentration of NH3 gas at moderate operating temperature. h-MoO3 nano-structured rods based ammonia sensors lend a promising prospective in industrial applications like fertilizer, refrigeration industries etc.
The essential requirement to harness well-known renewable energy sources like wind energy, solar energy,
etc
. as a component of an overall plan to guarantee global power sustainability will require ...highly efficient, high power and energy density batteries to collect the derived electrical power and balance out variations in both supply and demand. Owing to the continuous exhaustion of fossil fuels, and ever increasing ecological problems associated with global warming, there is a critical requirement for searching for an alternative energy storage technology for a better and sustainable future. Electrochemical energy storage technology could be a solution for a sustainable source of clean energy. Sodium-ion battery (SIB) technology having a complementary energy storage mechanism to the lithium-ion battery (LIB) has been attracting significant attention from the scientific community due to its abundant resources, low cost, and high energy densities. Layered transition metal oxide (TMO) based materials for SIBs could be a potential candidate for SIBs among all other cathode materials. In this paper, we discussed the latest improvement in the various structures of the layered oxide materials for SIBs. Moreover, their synthesis, overall electrochemical performance, and several challenges associated with SIBs are comprehensively discussed with a stance on future possibilities. Many articles discussed the improvement of cathode materials for SIBs, and most of them have pondered the use of Na
x
MO
2
(a class of TMOs) as a possible positive electrode material for SIBs. The different phases of layered TMOs (Na
x
MO
2
; TM = Co, Mn, Ti, Ni, Fe, Cr, Al, V, and a combination of multiple elements) show good cycling capacity, structural stability, and Na
+
ion conductivity, which make them promising cathode material for SIBs. This review discusses and summarizes the electrochemical redox reaction, structural transformations, significant challenges, and future prospects to improve for Na
x
MO
2
. Moreover, this review highlights the recent advancement of several layered TMO cathode materials for SIBs. It is expected that this review will encourage further development of layered TMOs for SIBs.
Na
+
ion intercalated layered metal oxides have tremendous applications as the cathode materials for SIBs owing to their superior electrochemical performance compared to other types of cathode materials.
A band better than the Beatles? Tungsten oxide doping by hafnium induces a shift of the valence and conduction bands towards higher energies without losing the visible light absorption properties of ...the material and introducing impurity states in the gap. The new band edges position with respect to the redox potentials for both H2 and O2 evolution is suitable for efficient water splitting.
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