Inorganic thermoelectric materials: A review

Thermoelectric generator, which converts heat into electrical energy, has great potential to power portable devices. Nevertheless, the efficiency of a thermoelectric generator suffers due to inefficient thermoelectric material performance. In the last two decades, the performance of inorganic thermoelectric materials has been significantly advanced through rigorous efforts and novel techniques. In this review, major issues and recent advancements that are associated with the efficiency of inorganic thermoelectric materials are encapsulated. In addition, miscellaneous optimization strategies, such as band engineering, energy filtering, modulation doping, and low dimensional materials to improve the performance of inorganic thermoelectric materials are reported. The methodological reviews and analyses showed that all these techniques have significantly enhanced the Seebeck coefficient, electrical conductivity, and reduced the thermal conductivity, consequently, improved ZT value to 2.42, 2.6, and 1.85 for near-room, medium, and high temperature inorganic thermoelectric material, respectively. Moreover, this review also focuses on the performance of silicon nanowires and their common fabrication techniques, which have the potential for thermoelectric power generation. Finally, the key outcomes along with future directions from this review are discussed at the end of this article.     

Chemical looping gasification of cotton stalk with bimetallic Cu/Ni/olivine as oxygen carrier

Bimetallic Cu/Ni/olivine oxygen carriers (OCs) were prepared using olivine as support material for chemical looping gasification (CLG). The cyclic redox behaviors and oxygen carrying capacity (R_o) of OCs were evaluated by thermo-gravimetric analysis. The effect of Cu/Ni ratio, gasification temperature, steam to biomass ratio (S/B), oxygen carrier to biomass ratio (OC/B) on CLG of cotton stalk has been studied in a fixed bed. The OCs characterized using BET surface area, scanning electron microscopy (SEM), X-ray diffraction (XRD), temperature-programmed reduction (TPR) to investigate the physicochemical property of OCs during CLG. Result shows that the sintering problem of OC was progressively alleviated with the increasing Cu/Ni ratio. The olivine behaves as suitable OC support with oxygen carrying capacity of 1.07%. The redox reactivity of all of the OCs kept well during multiple redox cycles. The R_o of OCs progressively increased with the Cu/Ni ratio. By comparing the product gas concentration, carbon conversion, H₂ + CO yield and gas yield over the invested OCs, the Cu9/Ni6/O was found to demonstrate better comprehensive CLG performance due to the synergistic effect of Cu and Ni. The maximum gas yield, H₂ + CO yield and carbon conversion with Cu9/Ni6/O can be obtained at the S/B of 0.8 and OC/B of 2. Compared to theoretical value, 65% of lattice oxygen has been supplied by Cu9/Ni6/O during actual CLG process. The OC displayed better reactivity due to basic crystalline phase being preserved well during multiple CLG cycles.     

Synthesis and experimental study of novel double perovskite Ba2NixCo2−xO6 as promising oxygen carrier materials for CO2 capture application

Novel oxygen-deficient double-perovskite type oxide Ba₂Ni_xCo_2−xO₆ was applied to produce O₂/CO₂ mixed stream gas for oxyfuel combustion application. A series of different Co concentration substituted Ba₂Ni_xCo_2−xO₆ was synthesized by an EDTA-citrate sol-gel combustion method. The oxygen carriers, Ba₂Ni_0.25Co_1.75O_6, Ba₂Ni_0.45Co_1.55O₆, Ba₂Ni_0.65Co_1.35O₆ and Ba₂Ni_0.85Co_1.15O₆ were c\characterized by scanning electron microscopy and cyclic oxygen adsorption/desorption experiments. The results showed that the capacity of provided O₂ was improved by the partial substitution of Ni by Co. In addition, the synthesized perovskites exhibit good regeneration ability. The optimal degree of Co substitution was x = 0.25 for Ba₂Ni_xCo_2−xO₆ with consideration of oxygen desorption ability. Therefore, Ba₂Ni_0.25Co_1.75O₆ was selected to examine the influence of the operating parameters on the oxygen release performance. It was found that the desorption temperature and CO₂ partial pressure are the two main operating parameters for the oxygen desorption performance. Further, the proposed novel double perovskite Ba₂Ni_0.25Co_1.75O₆ provided excellent performance, the O₂ production of Ba₂Ni_0.25Co_1.75O₆ can still reach 120 mg/g after 10 cycles.     

粘性土起动流速影响因素试验研究

由于粘性土颗粒间粘结力的作用,使得其具有较强的抗冲性和较高的起动流速,这对河势的演变造成一定的影响。为此,通过粘性土起动试验,分析了淤积固结过程中粘性土的物理参量变化情况,建立了干密度、粘粒含量(粒径)与起动流速之间的关系。结果表明,粘性土的粘聚力随含水率的增大而减小,相同含水率条件下,粘粒含量越高粘聚力越大;起动流速随干密度、粘粒含量的增大而增大,粘性土起动流速受中值粒径的影响,实质上与粘粒含量对起动流速的作用相同。在此基础上分析了粘性土起动流速影响因素,提出了起动流速经验公式。研究结果为进一步分析粘性土层对河势演变的影响奠定了基础。     

Effect of surface properties controlled by Ce addition on CO2 methanation over Ni/Ce/Al2O3 catalyst

Ce-promoted Ni/Al₂O₃ catalysts with Ce contents of 0, 5, 10, 15, and 20 wt% were investigated for CO₂ methanation. Ni/15Ce/Al₂O₃ showed good selectivity and catalytic performance in CO₂ methanation and remained stable at 350 °C for 80 h with minor fluctuations. Interactions between Ni and the Ce/Al₂O₃ support was characterized using X-ray diffraction, temperature-programmed reduction of H₂, temperature-programmed desorption of CO₂, X-ray photoelectron spectroscopy, Raman spectroscopy, and thermogravimetric analysis. Addition of Ce did not increase the catalytic surface area, which can significantly enhance the heterogeneous catalytic activity. However, XPS analysis showed that the Ce on the Ni/Al₂O₃ catalyst changed the surface electron states of Ni, Ce, and O. Additionally, CO₂ adsorption/desorption was confirmed to be related to the amount of Ce present on Ni/Al₂O₃ by TGA and CO₂-TPD. The Ce addition thus played an important role in determining the CO₂ adsorption, desorption, and conversion.     

The recent development on MgH2 system by 16 wt% nickel addition and particle size reduction through ball milling: A noticeable hydrogen capacity up to 5 wt% at low temperature and pressure

The addition of nickel as catalyst and particle size reduction through milling process is considered as the best approach for MgH₂ properties to be thermodynamically and kinetically more favorable. The recent development in MgH₂ is done by adding Ni (14–16 wt%) and particle size reduction through simple mechanical milling at a large sample of 100 g. The research sequences are easy to adopt for the implementation and sustainable research of MgH₂. Starting from the moisture test to the milling process, continue with particle size distribution (PSD) for the milled sample and final moisture test after PSD. Some critical finding from our research includes high capacity storage of Mg₈₄:Ni₁₆ above 5 wt% H₂ within 20 min at 573 K, the effect of moisture content on system performance and the different effect of carbon (C) in the system at specific temperature and pressure that may have.     

Role of molecular oxygen on the synthesis of Ni(OH)2/TiO2 photocatalysts and its effect on solar hydrogen production activity

Molecular oxygen performs a vital role in the photocatalytic activity of anatase TiO₂, but there is a little experimental insight into the role of molecular oxygen on the synthesis of TiO₂ based photocatalysts. Herein, we have shown that Ni(OH)₂/TiO₂ prepared in the presence and absence of molecular oxygen results in significantly varied hydrogen production activity. The sample synthesized in the presence of O₂ and N₂ produced 6624 μmol/h/g and 4468 μmol/h/g of hydrogen under direct solar light exposure. Additionally, the samples prepared in the presence of light irradiation produced 8289 μmol/h/g of hydrogen, a 72 fold jump in hydrogen production compared to TiO₂. XPS, FTIR, Raman, and ESR measurements were carried out to investigate the underlined mechanism for such variation in the photocatalytic activity. Our results suggest that the presence of molecular oxygen during Ni(OH)₂/TiO₂ synthesis causes the formation of terminal OH and reduced the oxygen vacancies on the surface of TiO₂, which can significantly alter the H₂ production. Also, the reusability of the photocatalysts is greatly affected by the synthesis conditions, namely the presence of light and molecular oxygen.     

Exploiting array manipulation habits to optimize garbage collection and type flow analysis

A widespread practice to implement a flexible array is to consider the storage area into two parts: the used area, which is already available for read/write operations, and the supply area, which is used in case of enlargement of the array. The main purpose of the supply area is to avoid as much as possible the reallocation of the whole storage area in case of enlargement. As the supply area is not used by the application, the main idea of the paper is to convey the information to the garbage collector, making it possible to avoid completely the marking of the supply area. We also present a simple method to analyze the types of objects, which are stored in an array as well as the possible presence of NULL values within the array. This allows us to better specialize the work of the garbage collector when marking the used area, and also, by transitivity, to improve overall results for type analysis of all expressions of the source code. After introducing several abstract data types, which represent the main arrays concerned by our technique (i.e., zero or variable indexing, circular arrays and hash maps), we measure its impact during the bootstrap of two compilers whose libraries are equipped with these abstract data types. We then measure, on various software products we have not written, the frequency of certain habits of manipulation of arrays, to assess the validity of our approach. Copyright © 2014 John Wiley & Sons, Ltd.     

Application of amaranth protein isolate and hydrolysate on a reduced salt fish restructured product: antioxidant properties,textural and microbiological effects

This work evaluates amaranth protein ingredients [isolate (I) and alcalase‐hydrolysate (H)] acting as antioxidants and binders in restructured fish products. Gel products were obtained after thermal treatment (40 °C, 30 min; 90 °C, 30 min) of different formulations from fish muscle pastes, where salt (2%) was partially or totally replaced by I or H. Antioxidant activity was assessed by conjugated dienes and thiobarbituric acid‐reactive substances (TBARs) measurements during the chilled storage. Textural properties, water‐holding capacity, colour and microbiological quality were evaluated. Reduced‐salt content products containing 2% w/w of I or H partially inhibited lipid oxidation especially at the level of the decomposition of hydroperoxides into secondary products, due to about 50% and 60% of inhibition of TBARs, respectively, was registered. Also, these products showed acceptable microbiological quality and technological characteristics with only minimal changes in properties as gel hardness and colour parameters compared with control products (2% w/w salt).