Journal of Energy Chemistry
ISSN 1003-9953
     
能源化学(英文)

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Tang and coworkers in their Article on pages 564-574 report that two-dimensional (2-D) BiVO4 nanosheets–graphene (GR) composites can be easily synthesized via a facile wet chemistry process. The as synthesized composites exhibit higher photocatalytic activities than the pristine BiVO4 nanosheets toward the degradation of dyes under visible light irradiation. This work provides a simple strategy for fabricating the sheet-on-sheet composites of 2-D semiconductor–2-D GR and their potential application as active visible light photocatalysts in purifying polluted water resources.


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2014 Vol.23 No.5, Published: 2014-09-24
REVIEW | COMMUNICATIONS | ARTICLES |
 
 
REVIEW
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Lithium manganese spinel materials for high-rate electrochemical applications
Anna V. Potapenko, Sviatoslav A. Kirillov
2014 Vol. 23 (5): 543-558 [Abstract] ( 433 ) [HTML 1KB] [PDF] ( 42 )

In order to successively compete with supercapacitors, an ability of fast discharge is a must for lithium-ion batteries. From this point of view, stoichiometric and substituted lithium manganese spinels as cathode materials are one of the most prospective candidates, especially in their nanosized form. In this article, an overview of the most recent data regarding physico-chemical and electrochemical properties of lithium manganese spinels, especially, LiMn2O4 and LiNi0.5Mn1.5O4, synthesized by means of various methods is presented, with special emphasis of their use in high-rate electrochemical applications. In particular, specific capacities and rate capabilities of spinel materials are analyzed. It is suggested that reduced specific capacity is determined primarily by the aggregation of material particles, whereas good high-rate capability is governed not only by the size of crystallites but also by the perfectness of crystals. The most technologically advantageous solutions are described, existing gaps in the knowledge of spinel materials are outlined, and the ways of their filling are suggested, in a hope to be helpful in keeping lithium batteries afloat in the struggle for a worthy place among electrochemical energy systems of the 21st century.

COMMUNICATIONS
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Unique ZnS nanobuns decorated with reduced graphene oxide as an efficient and low-cost counter electrode for dye-sensitized solar cells
Jie Yin, Jie Wang, Huaiyong Li, Huiyan Ma, Wenzhi Li, Xin Shao
2014 Vol. 23 (5): 559-563 [Abstract] ( 298 ) [HTML 1KB] [PDF] ( 40 )

Unique ZnS nanobuns decorated with reduced graphene oxide (RGO) was synthesized and found to exhibit a synergetic effect as a highly efficient and low-cost counter electrode (CE) in dye-sensitized solar cells (DSCs). Using this ZnS-RGO CE, a power conversion efficiency (PCE) of 7.03% was achieved. This value was 53% and 41% higher than those of pure ZnS and RGO CEs, respectively. The ZnS-RGO nanocomposite is indeed an efficient and cost-effective Pt-like alternative for iodine reduction reaction.

ARTICLES
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Synthesis of BiVO4 nanosheets-graphene composites toward improved visible light photoactivity
Qianqian Yu, Zi-Rong Tang, Yi-Jun Xu
2014 Vol. 23 (5): 564-574 [Abstract] ( 396 ) [HTML 1KB] [PDF] ( 44 )

Two-dimensional (2-D) BiVO4 nanosheets-graphene (GR) composites with different weight addition ratios of GR have been prepared via a facile wet chemistry process. X-ray diffraction (XRD), Raman spectra, X-ray photoelectron spectra (XPS), UV-vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption, transient photocurrent response and photoluminescence (PL) spectra were employed to determine the properties of the samples. It is found that BiVO4 nanosheets could pave well on the surface of graphene sheets. BiVO4 nanosheets-GR composites with a proper addition amount of GR exhibited higher photocatalytic activity than bare BiVO4 nanosheets toward liquid-phase degradation of rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. The enhancement of photocatalytic activities of BiVO4 nanosheets-GR composites can be attributed to the effective separation of photoexcited electron-hole pairs. This work not only provides a simple strategy for fabricating specific 2-D semiconductor-2-D GR composites, but also opens a new window of such 2-D semiconductor-2-D GR composites as visible light photocatalysts toward an improved visible light photoactivity in purifying polluted water resources.

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Microstructure evolution and oxidation states of Co in perovskite-type oxide Ba1.0Co0.7Fe0.2Nb0.1O3-δ annealed in CO2 atmosphere
Chengzhang Wu, He Wang, Xingxing Zhang, Yuwen Zhang, Weizhong Ding, Chenghua Sun
2014 Vol. 23 (5): 575-581 [Abstract] ( 309 ) [HTML 1KB] [PDF] ( 38 )

Ba1.0Co0.7Fe0.2Nb0.1O3-δ (BCFN) oxide with perovskite cubic structure was synthesized by solid state reaction method. CO2 corrosion of BCFN membrane was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance infrared Fourier-transformed spectroscopy (DRIFT) and X-ray absorption fine structure spectroscopy (XAFS). Cobalt (Co) K-edge absorption spectra of BCFN annealed in CO2 reveal that the oxidation states of Co in all the samples were larger than +3 and they decreased with the increase of calcination time. At 800℃, 1% CO2 introduced into He could speed up the reduction of Co cations in comparison with pure He. In addition, sulfate ions in the bulk of BCFN membrane preferred to migrate to the surface under CO2 calcination and form monoclinic Ba(CO3)0.9(SO4)0.1 besides orthorhombic witherite. Moreover, SEM results indicate that the nucleation and growth of carbonates grains started at the grain boundary of the membrane.

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Effect of silica nanoparticles/poly(vinylidene fluoride-hexafluoropropylene) coated layers on the performance of polypropylene separator for lithium-ion batteries
Hongyu Liu, Zehui Dai, Jun Xu, Baohua Guo, Xiangming He
2014 Vol. 23 (5): 582-586 [Abstract] ( 254 ) [HTML 1KB] [PDF] ( 82 )

In an effort to reduce thermal shrinkage and improve electrochemical performance of porous polypropylene (PP) separators for lithium-ion batteries, a new composite separator is developed by introducing ceramic coated layers on both sides of PP separator through a dip-coating process. The coated layers are comprised of heat-resistant and hydrophilic silica nanoparticles and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) binders. Highly porous honeycomb structure is formed and the thickness of the layer is only about 700 nm. In comparison to the pristine PP separator, the composite separator shows significant reduction in thermal shrinkage and improvement in liquid electrolyte uptake and ionic conduction, which play an important role in improving cell performance such as discharge capacity, C-rate capability, cycle performance and coulombic efficiency.

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Unique catalysis of Ni-Al hydrotalcite derived catalyst in CO2 methanation: cooperative effect between Ni nanoparticles and a basic support
Lei He, Qingquan Lin, Yu Liu, Yanqiang Huang
2014 Vol. 23 (5): 587-592 [Abstract] ( 306 ) [HTML 1KB] [PDF] ( 44 )

Ni-Al hydrotalcite derived catalyst (Ni-Al2O3-HT) exhibited a narrow Ni particle-size distribution with an average particle size of 4.0 nm. Methanation of CO2 over this catalyst initiated at 225℃ and reached 82.5% CO2 conversion with 99.5% CH4 selectivity at 350℃, which was much better than its impregnated counterpart. Characterizations by means of CO2 microcalorimetry and 27Al NMR indicated that large amount of strong basic sites existed on Ni-Al2O3-HT, originated from the formation of Ni-O-Al structure. The existence of strong basic sites facilitated the activation of CO2 and consequently promoted the activity. The combination of highly dispersed Ni with strong basic support led to its unique and high efficiency for this reaction.

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Improved catalytic performance of Ni catalysts for steam methane reforming in a micro-channel reactor
Bozhao Chu, Nian Zhang, Xuli Zhai, Xin Chen, Yi Cheng
2014 Vol. 23 (5): 593-600 [Abstract] ( 311 ) [HTML 1KB] [PDF] ( 96 )

Milliseconds process to produce hydrogen by steam methane reforming (SMR) reaction, based on Ni catalyst rather than noble catalyst such as Pd, Rh or Ru, in micro-channel reactors has been paid more and more attentions in recent years. This work aimed to further improve the catalytic performance of nickel-based catalyst by the introduction of additives, i.e., MgO and FeO, prepared by impregnation method on the micro-channels made of metal-ceramic complex substrate. The prepared catalysts were tested in the same micro-channel reactor by switching the catalyst plates. The results showed that among the tested catalysts Ni-Mg catalyst had the highest activity, especially under harsh conditions, i.e., at high space velocity and/or low reaction temperature. Moreover, the catalyst activity and selectivity were stable during the 12 h on stream test even when the ratio of steam to carbon (S/C) was as low as 1.0. The addition of MgO promoted the active Ni species to have a good dispersion on the substrate, leading to a better catalytic performance for SMR reaction.

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Effects of thermal activation conditions on the microstructure regulation of corncob-derived activated carbon for hydrogen storage
Dabin Wang, Zhen Geng, Cunman Zhang, Xiangyang Zhou, Xupeng Liu
2014 Vol. 23 (5): 601-608 [Abstract] ( 293 ) [HTML 1KB] [PDF] ( 91 )

Activated carbons derived from corncob (CACs) were prepared by pyrolysis carbonization and KOH activation. Through modifying activation conditions, samples with large pore volume and ultrahigh BET specific surface area could be obtained. The sample achieved the highest hydrogen uptake capacity of 5.80 wt% at 40 bar and -196℃. The as-obtained samples were characterized by N2-sorption, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Besides, thermogravimetric analysis was also employed to investigate the activation behavior of CACs. Detailed investigation on the activation parameters reveals that moderate activation temperature and heating rate are favorable for preparing CACs with high surface area, large pore volume and optimal pore size distribution. Meanwhile, the micropore volume between 0.65 nm and 0.85 nm along with BET surface area and total pore volume has great effects on hydrogen uptake capacities. The present results indicate that CACs are the most promising materials for hydrogen storage application.

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Selective oxidation of ethane to aldehydes over SBA-15 supported molybdenum catalyst
Jianmei Li, Jian Liu, Liwei Ren, Qinglong Liu, Zhen Zhao, Yongsheng Chen, Pengyu Zhu, Yuechang Wei, Aijun Duan, Guiyuan Jiang
2014 Vol. 23 (5): 609-616 [Abstract] ( 289 ) [HTML 1KB] [PDF] ( 41 )

SBA-15 supported Mo catalysts (Moy/SBA-15) were prepared by an ultrasonic assisted incipient-wetness impregnation method. The physical and chemical properties of the catalysts were characterized by means of N2-adsorption-desorption, XRD, TEM, UV-Vis, Raman, XANES and H2-TPR. The results showed that a trace amount of MoO3 was produced on high Mo content samples. Turn-over frequency (TOF) and product selectivity are dependent on the molybdenum content. Both Mo0.75/SBA-15 and Mo1.75/SBA-15 catalysts give the higher catalytic activity and the selectivity to the total aldehydes for the selective oxidation of C2H6. At the reaction temperature of 625℃, the maximum yield of aldehydes reached 4.2% over Mo0.75/SBA-15 catalyst. The improvement of the activity and selectivity was related with the state of MoOx species.

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Differences between Zn/HZSM-5 and Zn/HZSM-11 zeolite catalysts in alkylation of benzene with dimethyl ether
Hui Liu, Huijuan Wei, Wenjie Xin, Chao Song, Sujuan Xie, Zhenni Liu, Shenglin Liu, Longya Xu
2014 Vol. 23 (5): 617-624 [Abstract] ( 316 ) [HTML 1KB] [PDF] ( 42 )

HZSM-11 zeolite supported Zn catalysts with different Zn contents (xZn/HZSM-11A) were prepared. In the alkylation of benzene with dimethyl ether (DME) in a fixed bed reactor, the catalyst with Zn content of 6 wt% (6Zn/HZSM-11A) showed appropriate performance. Focus was put on the comparison between 6Zn/HZSM-5 and 6Zn/HZSM-11 with the same crystal size of 600--800 nm, and also with the similar BET surface area, micropore volume, Si/Al2 molar ratio, and acidity. In the alkylation of benzene with DME, the 6Zn/HZSM-11 showed better activity and stability, and especially enhanced the conversion of benzene and selectivities to xylene and trimethylbenzene, compared with the 6Zn/HZSM-5. This was mainly related to the higher adsorption capacity and adsorption-desorption rates to the three adsorbates (benzene, m-xylene and 1,3,5-trimethylbenzene) over the 6Zn/HZSM-11 in comparison with the 6Zn/HZSM-5.

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High CO methanation activity on zirconia-supported molybdenum sulfide catalyst
Zhenhua Li, Ye Tian, Jia He, Baowei Wang, Xinbin Ma
2014 Vol. 23 (5): 625-632 [Abstract] ( 324 ) [HTML 1KB] [PDF] ( 39 )

In this study, different methods were used to prepare MoO3/ZrO2 catalysts for sulfur resistant methanation reaction. It was found that MoO3/ZrO2 catalyst prepared by one-step co-precipitation method achieved high methanation performance. CO conversion could reach up to 90% on 25 wt% MoO3/ZrO2 catalyst, much higher than that on the conventional 25 wt% MoO3/Al2O3 catalyst. The Mo-based catalysts were characterized by XRF, XRD, Raman, BET, TEM and H2-TPR etc. It was found that MoO3 particles were highly dispersed on ZrO2 support for 25 wt% MoO3/ZrO2 catalyst prepared at 65-85 ℃ because of its relatively larger pore size, which contributed to a high CO conversion. Meanwhile, when MoO3 loading exceeded the monolayer coverage, the formed crystalline MoO3 and ZrMo2O8 might block the micropores of the catalyst and make the methanation activity declined. These results are useful for preparing highly efficient catalyst for CO methanation process.

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Effect of Ni loadings on the activity and coke formation of MgO-modified Ni/Al2O3 nanocatalyst in dry reforming of methane
Zahra Alipour, Mehran Rezaei, Fereshteh Meshkani
2014 Vol. 23 (5): 633-638 [Abstract] ( 304 ) [HTML 1KB] [PDF] ( 39 )

MgO-modified Ni/Al2O3 catalysts with different Ni loadings were prepared and employed in dry reforming of methane (DRM). The effect of Ni loadings on the activity and coke formation of Ni/MgO-Al2O3 catalysts were investigated. The synthesized catalysts were characterized by XRD, N2 adsorption-desorption, SEM, TPO and TPR techniques. The obtained results showed that increasing nickel loading decreased the BET surface area and increased the catalytic activity and amount of deposited carbon. In addition, the effect of gas hourly space velocity (GHSV) and feed ratio were studied.

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Kinetic behaviour of commercial catalysts for methane reforming in ethanol steam reforming process
Jorge Vicente, Javier Ereña, Martin Olazar, Pedro L. Benito, Javier Bilbao, Ana G. Gayubo
2014 Vol. 23 (5): 639-644 [Abstract] ( 326 ) [HTML 1KB] [PDF] ( 87 )

Ethanol steam reforming has been studied in a fluidized bed (in order to ensure bed isothermicity) on commercial catalysts for methane reforming. The results allow analyzing the effect of temperature (in 300-700 ℃ range), and both metal and support nature on the reaction indices (ethanol conversion, yields and selectivities to H2 and byproducts (CO2, CO, CH4 and C2H4O)). Special attention has been paid to catalysts' stability by comparing the evolution of the reaction indices with time on stream at 500 ℃ (minimum CO formation) and 700 ℃ (minimum deactivation by coke deposition). Although they provide a slightly lower H2 yield, the results evidence a good behaviour of Ni based catalysts, indicating that they are an interesting alternative of more expensive Rh based ones.

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Catalytic performance of cement clinker supported nickel catalyst in glycerol dry reforming
Hua Chyn Lee, Kah Weng Siew, Maksudur R. Khan, Sim Yee Chin, Jolius Gimbun, Chin Kui Cheng
2014 Vol. 23 (5): 645-656 [Abstract] ( 325 ) [HTML 1KB] [PDF] ( 40 )

The paper reports the development of cement clinker-supported nickel (with metal loadings of 5 wt%, 10 wt%, 15 wt% and 20 wt%) catalysts for glycerol dry (CO2) reforming reaction. XRF results showed that CaO constituted 62.0% of cement clinker. The physicochemical characterization of the catalysts revealed 32-folds increment of BET surface area (SmBET) with the addition of nickel metal into the cement clinker, which was also corroborated by FESEM images. Significantly, XRD results suggested different types of Ni oxides formation with Ni loading, whilst Ca3SiO5 and Ca2Al0.67Mn0.33FeO5 were the main crystallite species for pure cement clinker. Temperature-programmed reduction analysis yielded three domains of H2 reduction peaks, viz. centered at approximately 750 K referred to as type-I peaks, another peaks at 820 K denoted as type-II peaks and the highest reduction peaks, type-III recorded at above 1000 K. 20 wt% Ni was found to be the best loading with the highest XmG and H2 yield, whilst the lowest methanation activity. Syngas with lower H2/CO ratios (0.6 to 1.5) were readily produced from glycerol dry reforming at CO2-to-Glycerol feed ratio (CGR) of unity. Nonetheless, carbon deposit comprised of whisker type (Cmv) and graphitic-like type (Cmc) species were found to be in majority on 20 wt%Ni/CC catalysts.

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Facile synthesis and performance of polypyrrole-coated sulfur nanocomposite as cathode materials for lithium/sulfur batteries
Guanghui Yuan, Haodong Wang
2014 Vol. 23 (5): 657-661 [Abstract] ( 357 ) [HTML 1KB] [PDF] ( 37 )

In situ chemical oxidation polymerization of pyrrole on the surface of sulfur particles was carried out to synthesize a sulfur/polypyrrole (S/PPy) nanocomposite with core-shell structure. The composite was characterized by elemental analysis, X-ray diffraction, scanning/transmission electron microscopy, and electrochemical measurements. XRD and FTIR results showed that sulfur well dispersed in the core-shell structure and PPy structure was successfully obtained via in situ oxidative polymerization of pyrrole on the surface of sulfur particles. TEM observation revealed that PPy was formed and fixed to the surface of sulfur nanoparticle after polymerization, developing a well-defined core-shell structure and the thickness of PPy coating layer was in the range of 20-30 nm. In the composite, PPy worked as a conducting matrix as well as a coating agent, which confined the active materials within the electrode. Consequently, the as prepared S/PPy composite cathode exhibited good cycling and rate performances for rechargeable lithium/sulfur batteries. The resulting cell containing S/PPy composite cathode yields a discharge capacity of 1039 mAh·g-1 at the initial cycle and retains 59% of this value over 50 cycles at 0.1 C rate. At 1 C rate, the S/PPy composite showed good cycle stability, and the discharge capacity was 475 mAh·g-1 after 50 cycles.

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Preparation of activated carbon with high surface area for high-capacity methane storage
Bingsi Liu, Wenshuo Wang, Na Wang, (Peter) Chak Tong Au
2014 Vol. 23 (5): 662-668 [Abstract] ( 346 ) [HTML 1KB] [PDF] ( 47 )

Activated carbon (AC) was fabricated from corncob, which is cheap and abundant. Experimental parameters such as particle size of corncob, KOH/char weight ratio, and activation temperature and time were optimized to generate AC, which shows high methane sorption capacity. AC has high specific surface area (3227 m2/g), with pore volume and pore size distribution equal to 1.829 cm3/g and ca. 1.7-2.2 nm, respectively. Under the condition of 2 ℃ and less than 7.8 MPa, methane sorption in the presence of water (Rw = 1.4) was as high as 43.7 wt% methane per unit mass of dry AC. The result is significantly higher than those of coconut-derived AC (32 wt%) and ordered mesoporous carbon (41.2 wt%, Rw = 4.07) under the same condition. The physical properties and amorphous chaotic structure of AC were characterized by N2 adsorption isotherms, XRD, SEM and HRTEM. Hence, the corncob-derived AC can be considered as a competitive methane-storage material for vehicles, which are run by natural gas.

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Formation mechanism of methane during coal evolution: A density functional theory study
Lina Zhang, Lixia Ling, Senpeng Zhao, Riguang Zhang, Baojun Wang
2014 Vol. 23 (5): 669-678 [Abstract] ( 364 ) [HTML 1KB] [PDF] ( 42 )

The formation mechanism of methane (CH4) during coal evolution has been investigated by density functional theory (DFT) of quantum chemistry. Thermogenic gas, which is generated during the thermal evolution of medium rank coal, is the main source of coalbed methane (CBM). Ethylbenzene (A) and 6,7-dimethyl-5,6,7,8-tetrahydro-1-hydroxynaphthalene (B) have been used as model compounds to study the pyrolysis mechanism of highly volatile bituminous coal (R), according to the similarity of bond orders and bond lengths. All possible paths are designed for each model. It can be concluded that the activation energies for H-assisted paths are lower than others in the process of methane formation; an H radical attacking on β-C to yield CH4 is the dominant path for the formation of CH4 from highly volatile bituminous coal. In addition, the calculated results also reveal that the positions on which H radical attacks and to which intramolecular H migrates have effects on methyl cleavage.

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(Started in 1992)
?¨Renamed from JNGC in 2013??

ISSN 2095-4956
CN 21-1585/O4

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Xinhe Bao
Alexis T. Bell


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Journal of Energy Chemistry

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