太阳能光催化制氢反应体系及其材料研究进展

光催化制氢是利用太阳能获取氢能的重要途径,是当前研究热点。长期以来,人们致力于各种新型可见光光催化制氢材料的研究并取得较大进展。反应体系的设计和选择是实现高效光催化制氢和能否走向工业化的核心问题之一,因此,近年来研究者开始对光催化制氢反应体系加大研究。光催化制氢主要有非均相光催化制氢(HPC)和光电催化制氢(PEC),不同的体系具有各自的优缺点和应用范围。重点介绍光催化制氢半反应、光催化完全分解水和光电催化分解水3种主要反应体系,分析各种反应体系的特点,阐述各个体系涉及的光催化材料的发展进程,并展望太阳能光催化制氢研究前景,其中,新型高效的PEC-PV(光伏)耦合光化学转化系统有望为光解水制氢实现工业化提供一种重要的发展途径。     

Hydrothermal synthesis of carbonate-free submicron-sized barium titanate from an amorphous precursor: Synthesis and characterization

In this paper, the amorphous barium titanate precursor was prepared by the peroxo-hydroxide method and post-treated by various drying procedures, such as: room temperature drying, room temperature vacuum drying and vacuum drying at 50 °C. The objective in the latter two treatments was to increase the Ti-O-Ba bonds of the precursor. The post-treated precursors were compared with the untreated (i.e., ‘wet’) precursor. Also, a barium titanate precursor was prepared by an alkoxide route. Afterwards, the precursors were hydrothermally treated at 200 °C in a 10 M NaOH solution. Vacuum drying of the precursor seemingly promoted the formation of Ti-O-Ti bonds in the hydrothermal end-product. The low Ba:Ti ratio (0.66) of the alkoxide-route prepared precursor lead to a multi-phase hydrothermal product with BaTiO₃ as the main phase. In contrast, phase pure BaTiO₃, i.e. without BaCO₃ contamination, was obtained for the precursor which was dried at room temperature. Cube-shaped and highly crystalline BaTiO₃ particles were observed by electron microscopy for the hydrothermally treated peroxo-hydroxide-route prepared precursor.     

Thermodynamic Analysis of Thermal Efficiency of HTR-10 Hydrogen Production System

This paper presents thermodynamic analysis of the thermal efficiency of the 10 MW high temperature gas cooled reactor (HTR-10) hydrogen production system. The global reaction for the equilibrium reaction model is introduced. An analytical expression for the thermal efficiency is developed using the global reaction. For the specified temperature and pressure the thermal efficiency can be computed with the solution of the equilibrium. The investigation provides a more realistic limit for the efficiency of the nuclear hydrogen production system. The influence of the temperature, latent heat, steam-to-carbon ratio and pressure on the thermal efficiency is analyzed. Varying the temperature there is a maximum thermal efficiency for the specified pressure and steam-to-carbon ratio. The latent heat influences the thermal efficiency significantly, especially at the high temperature condition. Also varying the steam-to-carbon ratio there is a maximum thermal efficiency for the specified pressure and temperature. The process should be operated with high steam-to-carbon ratio to obtain maximum thermal efficiency when the reforming temperature is low and pressure is high. The maximum value is 68.9% within the range of the pressure greater than 1 MPa and steam-to-carbon ratio greater than 2. Comparison of theoretical results to experimental data is carried out.     

Synthesis of porous silicon nitride using silica/carbon composite derived from phenol–resorcinol–formaldehyde gel

Mesoporous silicon nitride (Si₃N₄), which is one of the most promising structural materials for applications in high-temperature filtration, was synthesized from the carbothermal reduction and nitridation of a pyrolyzed silica-containing phenol-resorcinol-formaldehyde (PRF) gel. The PRF gel was synthesized by combining sol–gel and polymerization of phenol, resorcinol and formaldehyde using sodium carbonate as a catalyst. Silica was incorporated into the gel by addition of 3-aminopropyl trimethoxysilane (APTMS) as a silica precursor. After aging and being freeze-dried, the silica/PRF composite was pyrolyzed under nitrogen gas to convert it into porous silica/carbon composite. The combination of phenol-formaldehyde (PF) and resorcinol-formaldehyde (RF) gels into PRF gel, allows further enhancement in porosity of the silica/carbon composite via pre-calcination in the range of 400–500 °C, since carbon derived from PF gel and that from RF gel have different thermal stability. The final product obtained after final calcination to remove residual carbon has a surface area as high as 194 m²/g, which is significantly much higher than the conventional Si₃N₄ granules. Specific surface area of the product is affected by molar ratio of phenol-to-resorcinol, molar ratio of silica-to-carbon, and the pre-calcination temperature.     

Resource potential for wind-hydrogen power in Ukraine

The paper provides an assessment of the current wind energy potential in Ukraine, and discusses developmental prospects for wind-hydrogen power generation in the country. Hydrogen utilization is a highly promising option for Ukraine's energy system, environment, and business. In Ukraine, an optimal way towards clean zero-carbon energy production is through the development of the wind-hydrogen sector. In order to make it possible, the energy potential of industrial hydrogen production and use has to be studied thoroughly.Ukraine possesses huge resources for wind energy supply. At the beginning of 2020, the total installed capacity of Ukrainian wind farms was 1.17 GW. Wind power generation in Ukraine has significant advantages in comparison to the use of traditional sources such as thermal and nuclear energy.In this work, an assessment of the wind resource potential in Ukraine is made via the geographical approach suggested by the authors, and according to the «Methodical guidelines for the assessment of average annual power generation by a wind turbine based on the long-term wind speed observation data». The paper analyses the long-term dynamics of average annual wind speed at 40 Ukrainian weather stations that provide valid data. The parameter for the vertical wind profile model is calculated based on the data reanalysis for 10 m and 50 m altitudes. The capacity factor (CF) for modern wind turbine generators is determined. The CF spatial distribution for an average 3 MW wind turbine and the power generation potential for the wind power plants across the territory of Ukraine are mapped.Based on the wind energy potential assessment, the equivalent possible production of water electrolysis-derived green hydrogen is estimated. The potential average annual production of green hydrogen across the territory of Ukraine is mapped.It is concluded that Ukraine can potentially establish wind power plants with a total capacity of 688 GW on its territory. The average annual electricity production of this system is supposed to reach up to 2174 bln kWh. Thus, it can provide an average annual production of 483 billion Nm³ (43 million tons) of green hydrogen by electrolysis. The social efficiency of investments in wind-hydrogen electricity is presented.     

CoPtx‐loaded Zn0.5Cd0.5S nanocomposites for enhanced visible light photocatalytic H2 production

Zn_0.5Cd_0.5S solid solution, modified with bimetallic CoPt_x nanoparticles, has been prepared using a two‐step organic solution method. The photocatalytic H₂ production rate of CoPt_x–Zn_0.5Cd_0.5S nanocomposites with different composition and percentage of CoPt_x was investigated. The results showed that the 1 wt% CoPt₃–Zn_0.5Cd_0.5S sample had the best activity which was 4.7 times higher than that of pure Zn_0.5Cd_0.5S and 1.2 times higher than that of Pt–Zn_0.5Cd_0.5S for photocatalytic H₂ production. The transient photocurrent response of the Zn_0.5Cd_0.5S showed an obvious increase in the current density after CoPt_x loading. Electrochemical impedance spectra measurements showed that the CoPt_x–Zn_0.5Cd_0.5S nanocomposites with x = 2 and 3 had lower charge transfer resistance R_t than that of Pt–Zn_0.5Cd_0.5S. The enhanced catalytic properties of the CoPt_x–Zn_0.5Cd_0.5S nanocomposites are attributed to their better accumulation ability for photoexcited electrons and higher rate for charge separation and transportation. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental investigation of a multi‐stage air‐steam gasification process for hydrogen enriched gas production

To achieve hydrogen‐rich and low‐tar producer gas, multi‐stage air‐blown and air‐steam gasification processes were studied in this research. Results showed that the tar content from multi‐stage air‐blown and air‐steam gasification were lower, compared to the average value of that from downdraft gasification. In the cases of air supplies of 80, 100 l min^?1 and 100, 100 l min^?1 with steam, hydrogen yields were increased by 40.71 and 41.62%, respectively, compared to that without steam. These were about 1.6 times of hydrogen flow rate of the base case (S/B = 0). However, it was found that too much steam added to the process was disadvantageous. The equilibrium model was also applied to predict the hydrogen production and the composition of producer gas obtained from the multi‐stage air‐blown and air‐steam gasification processes. The predicted result showed a better match for the case of multi‐stage air‐blown gasification process. Copyright © 2010 John Wiley & Sons, Ltd.     

Estimation of electrolytic hydrogen production potential in Venezuela from renewable energies

An initial estimation of the potential for hydrogen (H₂) production in Venezuela is made, obtained by water electrolysis using electricity from renewable sources, taking advantage of the great potential of the country for solar, wind and mini hydro energies. For the first two, its potential maps is obtained from insolation and wind speed maps, respectively, prepared from satellite data, and for mini-hydro, the potential is obtained from documentary information. To calculate the amount of H₂ to produce is used the Higher Heating Value, considering the electrolytic system overall efficiency of 75%, including power requirements of the electrolyzer, auxiliary equipment, and system losses. In addition, in the calculation of usable renewable potential are excluded land areas under special administration, marine, lake and urban areas, and other limitations are considered concerning energy conversion efficiencies and useful areas available for the location of the different renewable technologies.