Hydrogen and oxygen production based on photocatalytic monolithic water splitting is considered to be one of the effective ways to produce sustainable and clean energy. The key challenge in this process is to develop new photocatalysts that can simultaneously produce H 2 and O 2 at a stoichiometric ratio of 2:1 without the use of any sacrificial agents. In order to solve this problem, highly efficient and ingenious photosystems in nature have been studied intensively. Herein, we prepared printable Z-type composite photocatalysts CdS@TiO 2 /Pt/ITO/WO 3 /Co 3 O 4 mimicking biological vegetative leaves in nature and constructed an “artificial leaf” device that completely decomposes water. We use an electron solid penetrating transporter ITO, which can rapidly transfer photogenerated electrons and photogenerated holes and reduce the compound rate of photogenerated carriers. Thus, the efficiency of photocatalytic total water dissolution is enhanced. This photocatalyst was able to produce both H 2 and O 2 in water with an H 2 production rate of 75.93 μmol g −1 h −1 and an O 2 production rate of 36.49 μmol g −1 h −1 . We designed the oxygen-producing photocatalyst WO 3 /Co 3 O 4 , which produced oxygen at a rate of 159.21 μmol g −1 h −1 6 times higher than that of WO 3 alone. Furthermore, the morphology, composition, and microstructures of the photocatalyst were characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and nitrogen adsorption–desorption.
ABSTRACT In order to avoid the formation of η phase (W 6 Co 6 C or W 3 Co 3 C) that adversely affects the sintering process and its products in the preparation process of ultra-fine WC-Co powder, a technical route of pre-reduction of WO 3 –Co 3 O 4 to WO 2 –Co and then deep reduction carbonization to WC-Co powder has been proposed. This study mainly investigates the influence of gas partial pressure on the pre-reduction process of WO 3 –Co 3 O 4 under a mixed atmosphere of H 2 –C 2 H 4 –Ar at 600 °C and establishes the kinetic equations of pre-reduction and carbon evolution. The results indicate that increasing the partial pressure of hydrogen is conducive to the rapid and complete conversion of WO 3 to WO 2 . High carbon content can be generated by the deposition of C 2 H 4 , and it hinders the diffusion of the reducing gas; WO 3 still cannot be completely reduced to WO 2 as the partial pressure of C 2 H 4 increases to 60%. For the carbon evolution of C 2 H 4 , the carbon amount is positively related to the H 2 partial pressure, but it shows the highest amount and evolution rate when the ethylene partial pressure is 20%. Based on the reduction rate curves of WO 3 and carbon evolution rate curves of C 2 H 4 , the rate equations of pre-reduction and carbon evolution of WO 3 –Co 3 O 4 system at 600 °C are established. The pre-reduction reaction belongs to the first-order reaction, and its equation is expressed as follows: r = − d w WO 3 d t = 9 ± 0.15 × 1 0 − 2 P H 2 0.44 P C 2 H 4 0.57 The carbon deposition rate equation of C 2 H 4 can be expressed as follows: r ' = d c C d t = r f − r b ≅ 7.35 × 1 0 − 2 × P C 2 H 4 0.31
In this work, a self-template in situ etching strategy was applied to fabricate a hollow shuttle-like WO 3 -Co 3 O 4 heterojunction. The morphology and nanostructure were investigated comprehensively by a series of techniques. Notably, the hollow shuttle-like WO 3 -Co 3 O 4 shows a large specific area and promising architecture, which can efficiently promote the gas adsorption-desorption process and provide more active sites in whole composites. Compared to other sensing devices, the WO 3 -Co 3 O 4 sample with hollow shuttle-like architecture shows the best gas sensing characterizations, and the response to 100 ppm acetone is as high as 52 under optimum working temperature. Moreover, it also presents good repeatability, high against moisture, fast response-recovery speed and long-term stability. The enhanced gas sensing characterizations can be ascribed to the synergistic effect of a unique hollow shuttle-like structure and the p-n heterojunction at the interface of WO 3 and Co 3 O 4 . These admirable properties make it an excellent candidate for constructing high-performance acetone sensors. In addition, the relative sensing mechanism of shuttle-like WO 3 -Co 3 O 4 composites-based sensors will be discussed in detail.
This article investigated the preparation of ultrafine W powder by fluidized bed hydrogen reduction, and the apparent activation energy was determined for various reduction stages by using temperature programmed reduction with hydrogen. The results demonstrate that the introduction of Co 3 O 4 significantly enhances the reduction process of WO 3 .High Co 3 O 4 content can lead to the formation of CoWO 4 in the initial stage and obtain products with high content of Co 3 W. An increase in the Co 3 O 4 content correlates with a gradual decrease in the particle size of the product. The apparent activation energy for the WO 3 → WO 2 and WO 2 → W processes decreases as the Co 3 O 4 content increases. It can be decreased from 105.59 kJ /mol to 78.72 kJ/mol for the WO 3 → WO 2 stage, and from 107.38 kJ/mol to 78.38 kJ/mol for the WO 2 → W stage, respectively.
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