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Conversion reaction-based transition metal oxides have been considered as advanced anode materials for lithium batteries because of their high storage capacities; however, the initial lithiation/de...

Noble-metal-decorated metal oxide sensors have shown promising gas-sensing properties. However, the optimal dispersion of metal particles on a semiconductor is still challenging for most sensing ma...

A BiVO

A well-defined WO3/Bi2S3 composite comprised of single-crystalline Bi2S3 nanowire (Bi2S3NW) layers on top of the WO3 nanoparticles (WO3NP) was synthesized via an in situ hydrothermal reaction. The ...

A pinhole-free BiVO4 electrode was successfully synthesized using an ultrasonic-assisted synthetic method on a conductive substrate. The pinhole-free BiVO4 electrode showed highly improved photoelectrochemical activity for both sulfite oxidation and water oxidation. The blocking recombination processes were examined to clarify the enhanced photoelectrochemical performances.

Photoelectrochemical (PEC) water splitting to its constituents, hydrogen and oxygen, is a promising approach to producing chemical fuels. The preparation of metal oxides on a conductive substrate with a well-defined structure has been an important issue for improving the efficiency of PEC water splitting. In this study, we have developed a facile synthetic process for the manufacture of WO 3 nanocrystals with full coverage on a fluorine-doped tin oxide (FTO) substrate. The preparation of WO 3 as a continuous film on the FTO substrate is indispensable to study charge separation processes in its composite structure. Typically, various ratios of WO 3 /BiVO 4 composite structures were prepared with the WO 3 held constant to investigate charge separation processes in WO 3 and BiVO 4 for efficient PEC water oxidation. The photocurrent initially drops and then rises with growing BiVO 4 molar ratios. We attribute this initial decrease in photocurrent to electron-hole recombination at the semiconductor-semiconductor interface. On the other hand, an improved photocurrent is attributed to enhanced charge separation of BiVO 4 on the WO 3 electrode. Our work reveals the important relationship between WO 3 and BiVO 4 in water oxidation reaction.

The addition of water initiates the phase transition of hexagonal CoO to Co(OH)2 nanocrystals. Inducing the phase transition of h-CoO on various substrates results in efficient chemical bonding between Co(OH)2 and the substrate. The efficient deposition of Co(OH)2 is widely applicable for electrochemical and photoelectrochemical water oxidation reactions.

The preparation of metal oxides on a conductive substrate has been an important issue for improving photoelectrochemical water splitting efficiency. In this work, a facile synthetic process is reported for single-crystalline WO3 microplates with variable thicknesses grown directly on a fluorine-doped tin oxide substrate followed by an annealing procedure. The WO3 microplate electrode showed an improved photocurrent under 1 sun irradiation (1.9 mA/cm2 at 0.6 V vs Ag/AgCl, 100 mW/cm2) for water oxidation, including a significant enhancement in the visible light region compared to either a nanoparticle or a bulk film electrode. The enhanced water oxidation activity originates from both the single crystallinity with an optimum thickness and the oxygen-deficient characteristic of the WO3 microplates. To improve the photochemical stability, FeOOH electrocatalysts were deposited on the surfaces of the WO3 microplates. The resulting WO3/FeOOH composite electrode showed enhanced stability for water oxidation react...

A nanoscale sensing material was prepared in a facile manner via the phase transition of wurtzite CoO to spinel Co3O4, as a new gas sensor preparation platform. The combination of a h-CoO → β-Co(OH)2 phase transition followed by thermal oxidation led to the spontaneous deposition of Co3O4 on interdigitated electrodes. The prepared Co3O4 nanoplates exhibited good contact adhesion with the sensor substrate, which obviated the need for conventional film forming processes, and were shown to be suitable for direct gas sensing. Compared to other Co3O4 sensors, the phase-transitioned Co3O4 nanoplates showed very high sensitivity to acetone gas (12.5 for 1 ppm acetone) in the range 20–1000 ppb at an operating temperature of 200 ℃ and enhanced selectivity. The improved performance of the Co3O4 nanoplates was attributed to typical crystal facets with mainly exposed (111) planes as well as an enlarged surface area during phase transition. Therefore, it was concluded that phase transition methods can be applied to promising sensing substances to develop a variety of related ultrasensitive acetone sensors.

A pinhole-free BiVO4 electrode was successfully synthesized using an ultrasonic-assisted synthetic method on a conductive substrate. The pinhole-free BiVO4 electrode showed highly improved photoelectrochemical activity for both sulfite oxidation and water oxidation. The blocking recombination processes were examined to clarify the enhanced photoelectrochemical performances.

The present study numerically investigates two-dimensional laminar fluid flow and heat transfer past a circular cylinder near a moving wall. Numerical simulations to calculate the fluid flow and heat transfer past a circular cylinder are performed for different Reynolds numbers varying in the range of 60–200 and a fixed Prandtl numbers of 0.7 (air) in the range of 0.1 ⩽ G/D ⩽ 4, where G/D is the ratio of the gap between the cylinder and a moving wall, G and the cylinder diameter, D . The flow and thermal fields become the steady state below the critical gap ratios of 0.8, 0.4 and 0.2 for the Reynolds numbers of 60, 80 and 100, respectively. As the gap ratio decreases, the magnitude of lift coefficient for all Reynolds numbers increased significantly with diminishing G/D due to the ground effect. The cases of Reynolds numbers of 60, 80 and 100 revealed the sharp slope of drag coefficient in the range of the gap ratio where the flow transfers from the unsteady state to the steady state. As the Reynolds number decreases, the variation of Nusselt is much significant and increases considerably with decreasing G / D .

The present study numerically investigates two-dimensional laminar force convection heat transfer past two rotating circular cylinders in a side-by-side arrangement at a various range of absolute rotational speeds (| α | ⩽ 2) for four different gap spacings ( g ∗) of 3, 1.5, 0.7 and 0.2 at Reynolds number of 100, and a fixed Prandtl numbers of 0.7 (air). As | α | increases, the thermal field became stabilized and eventually steady beyond the critical rotational speed depending on the gap spacing. In general, as | α | increases, because the vertical motion of flow in the region of gap is strongly inhibited, the inner isotherms are early merged and shorter than the outer isotherms in the free-stream sides elongating further downstream. As | α | increases, because the rotating fluid near the cylinders surrounded much space where the steady conduction mode is predominant to the heat transfer, the behavior of the time- and surface-averaged Nusselt number has the decaying pattern with increasing | α | for all gap spacings considered in this study.