Coal is the single most important fuel for power generation today. Nowadays, most coal is consumed by means of “burning coal in air” and pollutants such as NOx, SOx, CO2, PM2.5 etc. are inevitably ...formed and mixed with excessive amount of inner gases, so the pollutant emission reduction system is complicated and the cost is high. IGCC is promising because coal is gasified before utilization. However, the coal gasifier mostly operates in gas environments, so special equipments are needed for the purification of the raw gas and CO2 emission reduction. Coal and supercritical water gasification process is another promising way to convert coal efficiently and cleanly to H2 and pure CO2. The gasification process is referred to as “boiling coal in water” and pollutants containing S and N deposit as solid residual and can be discharged from the gasifier. A novel thermodynamics cycle power generation system was proposed by us in State Key Laboratory of Multiphase Flow in Power Engineering (SKLMFPE) of Xi'an jiaotong University (XJTU), which is based on coal and supercritical water gasification and multi-staged steam turbine reheated by hydrogen combustion. It is characterized by its high coal-electricity efficiency, zero net CO2 emission and no pollutants. A series of experimental devices from quartz tube system to a pilot scale have been established to realize the complete gasification of coal in SKLMFPE. It proved the prospects of coal and supercritical water gasification process and the novel thermodynamics cycle power generation system.
•A novel thermodynamics cycle power generation system is proposed.•The novel cycle is based on coal and supercritical water gasification.•The novel cycle has multi-staged steam turbine reheated by hydrogen combustion.•The novel cycle has high coal-electricity efficiency and no pollutants.•Developments of coal and supercritical water gasification in SKLMFPE are reviewed.
Ag3PO4 has been reported to be an excellent photocatalyst for O2 evolution from aqueous solution, which makes it a promising candidate for designing a Z-scheme water-splitting system. In this work, ...in order to further improve the photocatalytic activity, a series of SrTiO3/Ag3PO4 composite photocatalysts was constructed by introducing SrTiO3 (with a less positive valence band minimum) to Ag3PO4 and was synthesized by two consecutive hydrothermal processes. The obtained photocatalysts were systematically characterized by XRD, SEM, BET, UV–vis, etc., showing that SrTiO3/Ag3PO4 composites were formed by coating SrTiO3 onto a Ag3PO4 polyhedron. Photocatalytic O2 evolution results demonstrated that a small amount of SrTiO3 brought about significant enhancement of photocatalytic activity of Ag3PO4 and that the apparent quantum yield at 420 nm reached 16.2% with a molar ratio of SrTiO3 to Ag3PO4 equal to 1/20, which led to the fact that SrTiO3 could serve as cocatalyst for water oxidation providing both accelerated electron–hole separation by band gap alignment and more active sites by enlarged surface area.
<正>ABO3-based photocatalysts for water splitting were systematically reviewed in this manuscript. Crystal structure and chemical composition characteristics of ABO3 materials were briefly ...introduced to guide the modification of ABOrbased photocatalysts.The ABO3-based photocatalysts were then reviewed in detail and divided into four groups based on the employed modification strategies,i.e.,chemical component adjustment,micro-/nano-structure adjustment,local lattice structure adjustment,and application of the modification strategy of ABO3 photocatalysts in designing AxBy0z photocatalysts.In this section,the recent research works on ABOrbased photocatalysts in our group were presented.Finally, application of ABO3 photocatalysts in Z-scheme systems for overall water splitting was introduced.This review summarized the development of ABOrbased photoaitalysts and showed the values and possible direction of future research,thereby ottering a guide for photocatalytic water splitting.
Efficient charge separation is of crucial importance for the improvement of photocatalytic activity for solar hydrogen evolution. Here we report efficient photo-generated charge separation by ...twin-induced one-dimensional homojunctions with type-II staggered band alignment, using a ternary chalcogenate, i.e. Cd0.5Zn0.5S nanorod as a model material. The quantum efficiency of solar hydrogen evolution over this photocatalyst, without noble metal loading, reaches 62%. Unlike traditional heterojunctions, doping or combination of additional elements are not needed for the formation of this junction, which permits us to tune the band structures of semiconductors to the specific application in a more precise way. Our results highlight the power of forming long-range ordered homojunctions at the nanoscale for photocatalytic and photoelectrochemical applications.
Heat transfer under convective boundary condition is common in heat exchangers. This paper presented the experimental results of air flow and heat transfer through three stainless steel foam filled ...tubes under convection boundary condition. The air flow velocity inside the tube is relatively high, which varied from 7.0 to 26.0m/s. The stainless steel foam filled tubes, manufactured using high-temperature metallic sintering technique, are of different pore densities (10, 30 and 70 PPI) but have the same porosity of 0.93.
The air pressure drop through the stainless steel foam filled tubes was measured. It was found that the inertial drag is the dominant part of the pressure drop at higher velocity. The pressure drop experimental data under high velocity were compared to the predictions by the correlations obtained under relatively low velocity and great discrepancies have been found. A new correlation for the pressure drop through metal foams under high velocity was presented. The effect of the boundary condition on the heat transfer performance was addressed by the comparison of Nusselt number obtained in the present study with that obtained under constant heat flux boundary condition in the published investigation. It was found that the Nusselt number obtained under convective boundary condition is much lower than that obtained under constant heat flux boundary condition. A new correlation for Nusselt number under convective boundary condition was developed.
•The pressure drop through metal foams under relatively high velocity was studied.•A correlation for friction factor in metal foams under high velocity was obtained.•The effect of boundary condition on heat transfer performance was displayed.•A correlation for Nusselt number under convection boundary condition was developed.
We report on a novel heterojunction WO3/BiVO4 photoanode for photoelectrochemical water splitting. The heterojunction films are prepared by solvothermal deposition of a WO3 nanorod-array film onto ...fluorine-doped tin oxide (FTO) coated glass, with subsequent deposition of a low bandgap, 2.4 eV, visible light responding BiVO4 layer by spin-coating. The heterojunction structure offers enhanced photoconversion efficiency and increased photocorrosion stability. Compared to planar WO3/BiVO4 heterojunction films, the nanorod-array films show significantly improved photoelectrochemical properties due, we believe, to the high surface area and improved separation of the photogenerated charge at the WO3/BiVO4 interface. Synthesis details are discussed, with film morphologies and structures characterized by field emission scanning electron microscopy and X-ray diffraction.
A look at the use of semiconductor-based photocatalytic hydrogen generation as an alternative energy source is presented. Issues that still need to be examined include chemical composition and ...electronic properties.
With the intense interest in inorganic cesium lead halide perovskites and their nanostructures for optoelectronic applications, high-quality crystalline nanomaterials with controllable morphologies ...and growth directions are desirable. Here, we report a vapor-phase epitaxial growth of horizontal single-crystal CsPbX3 (X = Cl, Br, I) nanowires (NWs) and microwires (MWs) with controlled crystallographic orientations on the (001) plane of phlogopite and muscovite mica. Moreover, single NWs, Y-shaped branches, interconnected NW or MW networks with 6-fold symmetry, and, eventually, highly dense epitaxial network of CsPbBr3 with nearly continuous coverage were controllably obtained by varying the growth time. Detailed structural study revealed that the CsPbBr3 wires grow along the 001 directions and have the (100) facets exposed. The incommensurate heteroepitaxial lattice match between the CsPbBr3 and mica crystal structures and the growth mechanism of these horizontal wires due to asymmetric lattice mismatch were proposed. Furthermore, the photoluminescence waveguiding and good performance from the photodetector device fabricated with these CsPbBr3 networks demonstrated that these well-connected CsPbBr3 NWs could serve as straightforward platforms for fundamental studies and optoelectronic applications.
Supercritical water gasification (SCWG) of coal is a promising technology for clean coal utilization. In this paper, hydrogen production by catalytic gasification of coal in supercritical water (SCW) ...was carried out in a micro batch reactor with various alkaline catalysts: Na sub(2)CO sub(3), K sub(2)CO sub(3), Ca(OH) sub(2), NaOH and KOH. H sub(2) yield in relation to the alkaline catalyst was in the following order: K sub(2)CO sub(3) approximately KOH approximately NaOH > Na sub(2)CO sub(3) > Ca(OH) sub(2). Then, hydrogen production by catalytic gasification of coal with K sub(2)CO sub(3) was systematically investigated in supercritical water. The influences of the main operating parameters including feed concentration, catalyst loading and reaction temperature on the gasification characteristics of coal were investigated. The experimental results showed that carbon gasification efficiency (CE, mass of carbon in gaseous product/mass of carbon in coal 100%) and H sub(2) yield increased with increasing catalyst loading, increasing temperature, and decreasing coal concentration. In particular, coal was completely gasified at 700 degree C when the weight ratio of K sub(2)CO sub(3) to coal was 1, and it was encouraging that raw coal was converted into white residual. At last, a reaction mechanism based on oxygen transfer and intermediate hybrid mechanism was proposed to understand coal gasification in supercritical water.
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