A-Novel-CdS-Nanorod with Stacking Fault Structures: Preparation and Properties of Visible-Light-Driven Photocatalytic Hydrogen Production from Water Splitting

AbstractIn the present study, CdS nanorod particles with the stacking fault structures were hydrothermally synthesized through a dissolution-recrystallization approach in concentrated ammonia solvent, for the first time. It was clear that concentrated ammonia solution contained a large number of hydroxyl ions and large numbers of ammonia. Comprehensive characteristics were performed to investigate the influence of stacking fault structures on the photocatalytic activity and stability of CdS nanorod particles. Transmission electron microscopy (TEM) images revealed that the CdS catalyst included many nanorods with stacking fault structures. Stacking fault structures were obviously observed within CdS nanorods with the length ranging from 70 to 200nm and diameter ranging from 20 to 65nm, respectively. It revealed that the formation of CdS nanorod particles with stacking faults was contributed to the dissolution-recrystallization process. There were many structural units for cubic phase changing to hexagonal phase in the CdS crystals in the process of hydrothermal resulting in forming a large number of stacking fault structures. Photo-generated electrons and holes migrating directionally along the nanorods direction and the stacking fault structures in some nanorods could promote the separation of photo-generated electrons and holes, which enhanced the activity of visible-light-driven photocatalytic hydrogen production. Through the photocatalytic hydrogen production experiments, CdS nanorod particles with the stacking fault structures showed much higher photocatalytic activity than CdS patticles prepared by the conventional hydrothermal method using the water as the hydrothermal solvent

A NUMERICAL SIMULATION OF POOL BOILING USING CAS MODEL

ABSTRACT This paper presents a new numerical model, called the CAS model, for boiling heat transfer. The CAS model is based on the cellular automata technique that is integrated into the popular-SIMPLER algorithm for CFD problems. In the model, the cellular automata technique deals with the microscopic nonlinear dynamic interactions of bubbles while the traditional CFD algorithm is used to determine macroscopic system parameters such as pressure and temperature. The popular SIMPLER algorithm is employed for the CFD treatment. The model is then employed to simulate a pool boiling process. The computational results show that the CAS model can reproduce most of the basic features of boiling and capture the fundamental characteristics of boiling phenomena. The heat transfer coefficient predicted by the CAS model is in excellent agreement with the experimental data and existing empirical correlations

Structural and Photoelectrochemical Properties of Cu-Doped CdS Thin Films Prepared by Ultrasonic Spray Pyrolysis

Cu-doped CdS thin films of variable doping levels have been deposited on indium tin oxide-coated glass substrate by simple and cost-effective ultrasonic spray pyrolysis. The influences of doping concentration and annealing treatment on the structure and photoelectrochemical properties of the films were investigated. The deposited films were characterized by XRD, SEM, and UV-Vis spectra. Moreover, the films were investigated by electrochemical and photoelectrochemical measurements with regard to splitting water for solar energy conversion. The results showed that the Cu impurity can cause a structural change and red shift of absorption edge. It was found that the photocurrent can be improved by the Cu-doping process for the unannealed films under the weak illumination. The unannealed 5 at.% Cu-doped sample obtained the maximum IPCE, which achieved about 45% at 0.3 V versus SCE potential under 420 nm wavelength photoirradiation. In addition, the p-type CdS was formed with a doping of 4 at.%~10 at.% Cu after 450°C 2 h annealed in vacuum

Effect of Heating Method on Hydrogen Production by Biomass Gasification in Supercritical Water

The glucose as a test sample of biomass is gasified in supercritical water with different heating methods driven by renewable solar energy. The performance comparisons of hydrogen production of glucose gasification are investigated. The relations between temperature raising speed of reactant fluid, variation of volume fraction, combustion enthalpy, and chemical exergy of H2 of the product gases with reactant solution concentration are presented, respectively. The results show that the energy quality of product gases with preheating process is higher than that with no preheating unit for hydrogen production. Hydrogen production quantity and gasification rate of glucose decrease obviously with the increase of concentration of material in no preheating system

Effect of Heating Method on Hydrogen Production by Biomass Gasification in Supercritical Water

The glucose as a test sample of biomass is gasified in supercritical water with different heating methods driven by renewable solar energy. The performance comparisons of hydrogen production of glucose gasification are investigated. The relations between temperature raising speed of reactant fluid, variation of volume fraction, combustion enthalpy, and chemical exergy of H 2 of the product gases with reactant solution concentration are presented, respectively. The results show that the energy quality of product gases with preheating process is higher than that with no preheating unit for hydrogen production. Hydrogen production quantity and gasification rate of glucose decrease obviously with the increase of concentration of material in no preheating system

Solar light-driven photocatalytic hydrogen evolution over ZnIn2S4 loaded with transition-metal sulfides

A series of Pt-loaded MS/ZnIn2S4 (MS = transition-metal sulfide: Ag2S, SnS, CoS, CuS, NiS, and MnS) photocatalysts was investigated to show various photocatalytic activities depending on different transition-metal sulfides. Thereinto, CoS, NiS, or MnS-loading lowered down the photocatalytic activity of ZnIn2S4, while Ag2S, SnS, or CuS loading enhanced the photocatalytic activity. After loading 1.0 wt.% CuS together with 1.0 wt.% Pt on ZnIn2S4, the activity for H2 evolution was increased by up to 1.6 times, compared to the ZnIn2S4 only loaded with 1.0 wt.% Pt. Here, transition-metal sulfides such as CuS, together with Pt, acted as the dual co-catalysts for the improved photocatalytic performance. This study indicated that the application of transition-metal sulfides as effective co-catalysts opened up a new way to design and prepare high-efficiency and low-cost photocatalysts for solar-hydrogen conversion

Hydrogen Production by Supercritical Water Gasification of Biomass with Homogeneous and Heterogeneous Catalyst

Biomass gasification in supercritical water is a clean and efficient way to convert biomass to hydrogen-rich gaseous products. Appropriate catalyst can lower the reaction temperature to guarantee the technological and economic feasibility. This paper selects Ca(OH)2, Na2CO3, K2CO3, NaOH, KOH, LiOH, and ZnCl2 as typical homogeneous catalysts and three kinds of Raney-Ni, dolomite, and olivine as typical heterogeneous catalysts. The catalyst effects are investigated in the process of biomass gasification in supercritical water with the temperature of 400°C, pressure of 22∼24 MPa, and residence time of 20 min. The experimental results show that Raney-Ni has the best hydrogen selectivity and hydrogen yield. The mixture of NaOH with Raney-Ni was investigated in order to research the synergistic effect of different catalysts. The experimental results show that Raney-Ni and NaOH have a synergistic effect in the biomass gasification in supercritical water

experimentalinvestigationofparticlevelocitydistributionsinwindblownsandmovement

With the PDPA (Phase Doppler Particle Analyzer) measurement technology, the probability distributions of particle impact and lift-off velocities on bed surface and the particle velocity distributions at different heights are detected in a wind tunnel. The results show that the probability distribution of impact and lift-off velocities of sand grains can be expressed by a log-normal function, and that of impact and lift-off angles complies with an exponential function. The mean impact angle is between 28 degrees and 39 degrees, and the mean lift-off angle ranges from 30 degrees to 44 degrees. The mean lift-off velocity is 0.81-0.9 times the mean impact velocity. The proportion of backward-impacting particles is 0.05-0.11, and that of backward-entrained particles ranges from 0.04 to 0.13. The probability distribution of particle horizontal velocity at 4 mm height is positive skew, the horizontal velocity of particles at 20 mm height varies widely, and the variation of the particle horizontal velocity at 80 mm height is less than that at 20 mm height. The probability distribution of particle vertical velocity at different heights can be described as a normal function

A study on current overshoot during start-ups and optimal start-up strategy of proton exchange membrane fuel cells

Current overshoot resulting from a sudden decrease in the cell voltage during start-up process could cause performance fluctuation and reduced durability in proton exchange membrane (PEM) fuel cells. In this study, transient responses of local current densities and high frequency resistance (HFR) of the cell are measured in situ. The experimental results show that when the cell starts up under potentiostatic mode, both the magnitude of current overshoot and the fluctuation of HFR decrease with the increase of anode humidity. A dimensionless current overshoot is defined to describe the magnitude of current overshoot during start-ups. Experimental results show that dimensionless current overshoots are very different at different locations along the flow direction under different anode humidification. When unsaturated hydrogen is fed into the cell, dimensionless current overshoot increases along the flow direction; while as anode gas is fully- or over-humidified, the dimensionless current overshoot decreases along the flow direction. Further experimental results show that the magnitudes of current overshoot are significantly reduced when a linear start-up strategy is used, indicating that the linear start-up strategy is effective in alleviating current density overshoots in PEM fuel cells during start-ups. •Current overshoots occur in the entire cell during startups.•Patterns of local current overshoot are very different under different humidification.•Current overshoot increases along the channel with under-humidified condition.•Current overshoot decreases along the channel with fully-humidified condition.•The linear startup mode is effective in reducing current overshoot during startup