能源化学(英文版)

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Electrochemical reduction of CO₂ in solid oxide electrolysis cells

Lixiao Zhang, Shiqing Hu, Xuefeng Zhu, Weishen Yang

2017, 26(4): 593-601. DOI: 10.1016/j.jechem.2017.04.004

摘要 ( 3062 )

The effort on electrochemical reduction of CO₂ to useful chemicals using the renewable energy to drive the process is growing fast recently. In this review, we introduce the recent progresses on the electrochemical reduction of CO₂ in solid oxide electrolysis cells (SOECs). At high temperature, only CO is produced with high current densities and Faradic efficiency while the reactor is complicated and a better sealing technique is urgently needed. The typical electrolytes such as zirconia-based oxides, ceria-based oxides and lanthanum gallates-based oxides, anodes and cathodes are introduced in this review, and the cathode materials, such as conventional metal-ceramics (cermets), mixed ionic and electronic conductors (MIECs) are discussed in detail. In the future, to gain more value-added products, the electrolyte, cathode and anode materials should be developed to allow SOECs to be operated at temperature range of 573- 873 K. At those temperatures, SOECs may combine the advantages of the low temperature system and the high temperature system to produce various products with high current densities.

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CO adsorption on a Pt(111) surface partially covered with FeO_x nanostructures

Yun Liu, Fan Yang, Yanxiao Ning, Qingfei Liu, Yi Zhang, Hao Chen, Xinhe Bao

2017, 26(4): 602-607. DOI: 10.1016/j.jechem.2017.02.006

摘要 ( 3592 )

The adsorption of CO on Pt group metals, as a most fundamental elementary reaction step, has been widely studied in catalysis and electrocatalysis. Particularly, the structures of CO on Pt(111) have been extensively investigated, owing to its importance to both fundamental and applied catalysis. Yet, much less is known regarding CO adsorption on a Pt(111) surface modulated by supported oxide nanostructures, which is of more relevance to technical catalysis. We thus investigated the coverage-dependent adsorption of CO on a Pt(111) surface partially covered by FeO_x nanostructures, which has been demonstrated as a remarkable catalyst for low-temperature CO oxidation. We found that, due to its strong chemisorption, the coverage-dependent structure of CO on bare Pt is not influenced by the presence of FeO_x. But, oxygen-terminated FeO_x nanostructures could modulate the diffusivity of CO at their vicinity, and thus affect the formation of ordered CO superstructures at low temperatures. Using scanning tunneling microscopy (STM), we inspected the diffusivity of CO, followed the phase transitions of CO domains, and resolved the molecular details of the coverage-dependent CO structures. Our results provide a full picture for CO adsorption on a Pt(111) surface modulated by oxide nanostructures and shed lights on the inter-adsorbate interaction on metal surfaces.

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Polyaniline-supported iron catalyst for selective synthesis of lower olefins from syngas

Bang Gu, Shun He, Wei Zhou, Jincan Kang, Kang Cheng, Qinghong Zhang, Ye Wang

2017, 26(4): 608-615. DOI: 10.1016/j.jechem.2017.04.009

摘要 ( 2878 )

Uniform iron nanoparticles dispersed on polyaniline have been used as catalysts for the direct conversion of synthesis gas into lower olefins. As compared to active carbon and N-doped active carbon, polyaniline as a support of Fe catalysts showed higher selectivity of lower olefins (C_2-4⁼). The C_2-4⁼ selectivity reached ～50% at a CO conversion of 79% over a 10wt% Fe/polyaniline catalyst without any promoters. The XRD, H₂-TPR, TEM and HRTEM studies revealed that the presence of nitrogen-containing groups in polyaniline structure could promote the dispersion and reduction of iron oxides, forming higher fraction of iron carbides with smaller mean sizes and narrower size distributions. The propylene-TPD result indicates that the use of polyaniline support facilitates the desorption of lower olefins, thus suppressing the consecutive hydrogenation to form undesirable lower paraffins.

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Highly efficient Fe/N/C catalyst using adenosine as C/N-source for APEFC

Huan Ren, Ying Wang, Xun Tang, Juntao Lu, Li Xiao, Lin Zhuang

2017, 26(4): 616-621. DOI: 10.1016/j.jechem.2017.05.001

摘要 ( 3033 )

An environmentally friendly precursor, adenosine, has been used as a dual source of C and N to synthesize nitrogen-doped carbon catalyst with/without Fe. A hydrothermal carbonization method has been used and water is the carbonization media. The morphology of samples with/without Fe component has been compared by HRTEM, and the result shows that Fe can promote the graphitization of carbon. Further electro-chemical test shows that the oxygen reduction reaction (ORR) catalytic activity of Fe-containing sample (C-FeN) is much higher than that of the Fe-free sample (C-N). Additionally, the intermediates of C-FeN formed during each synthetic procedure have been thoroughly characterized by multiple methods, and the function of each procedure has been discussed. The C-FeN sample exhibits high electro-catalytic stability and superior electro-catalytic activity toward ORR in alkaline media, with its half-wave potential 20 mV lower than that of commercial Pt/C (40 wt%). It is further incorporated into alkaline polymer electrolyte fuel cell (APEFC) as the cathode material and led to a power density of 100mW/cm².

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Lignin depolymerization for phenolic monomers production by sustainable processes

Javier Fernández-Rodríguez, Xabier Erdocia, Cristina Sánchez, María González Alriols, Jalel Labidi

2017, 26(4): 622-631. DOI: 10.1016/j.jechem.2017.02.007

摘要 ( 3466 )

Biomass wastes (almond shell and olive tree pruning) were used in this work as raw materials for the extraction of high purity lignin by different delignification methods. A pretreatment stage was carried out to remove the major hemicelluloses content in the solid feedstocks. Afterward, two sulfur-free pulping processes (soda and organosolv) were applied to extract the largest fraction of lignin. The extracted lignin contained in the liquors was isolated using selective precipitation methods to design a tailor-made technique for obtaining high-purity lignin (in all cases more 90% of purity was reached). Soda process allowed the extraction of more lignin (around 40%-47%) than organosolv process (lower than 20%) regardless of the lignocellulosic source employed.
Once the different lignin samples were isolated and characterized, they were depolymerized for the obtaining of small phenolic compounds. Three main streams were produced after the reaction: phenolic enriched oil, residual lignin and coke. After the purification of these fractions, their quantifications and characterization were conducted.
Once the different lignin samples were isolated and characterized, they were depolymerized for the obtaining of small phenolic compounds. Three main streams were produced after the reaction: phenolic enriched oil, residual lignin and coke. After the purification of these fractions, their quantifications and characterization were conducted.

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Fischer-Tropsch synthesis over iron catalysts with corncob-derived promoters

Lisheng Guo, Jian Sun, Jian Wei, Zhiyong Wen, Hengyong Xu, Qingjie Ge

2017, 26(4): 632-638. DOI: 10.1016/j.jechem.2017.03.017

摘要 ( 3088 )

A sustainable strategy for Fischer-Tropsch iron catalysts is successfully achieved by embedding of synergistic promoters from a renewable resource, corncob. The iron-based catalysts, named as “corncob-driven” catalysts, are composed of iron species supported on carbon as primary active components and various minerals (K, Mg, Ca, and Si, etc.) as promoters. The corncob-driven catalysts are facilely synthesized by a one-pot hydrothermal treatment under mild conditions. The characterization results indicate that the formation of iron carbides from humboldtine is clearly enhanced and the morphology of catalyst particles tends to be more regular microspheres after adding corncob. It is observed that the optimized corncob-driven catalyst exhibits a higher conversion than without promoters' catalyst in Fischer-Tropsch synthesis (ca. 73% vs. ca. 49%). More importantly, a synergistic effect exists in multiple promoters from corncob that can enhance heavy hydrocarbons selectivity and lower CO₂ selectivity, obviously different from the catalyst with promoters from chemicals. The proposed synthesis route of corncob-driven catalysts provides new strategies for the utilization of renewable resources and elimination of environmental pollutants from chemical promoters.

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Non-aqueous lithium bromine battery of high energy density with carbon coated membrane

Xiaoli Xi, Xianfeng Li, Chenhui Wang, Qinzhi Lai, Yuanhui Cheng, Pengcheng Xu, Huamin Zhang

2017, 26(4): 639-646. DOI: 10.1016/j.jechem.2017.04.013

摘要 ( 2804 )

Flow batteries with high energy density and long cycle life have been pursued to advance the progress of energy storage and grid application. Non-aqueous batteries with wide voltage windows represent a promising technology without the limitation of water electrolysis, but they suffer from low electrolyte concentration and unsatisfactory battery performance. Here, a non-aqueous lithium bromine rechargeable battery is proposed, which is based on Br₂/Br^- and Li⁺/Li as active redox pairs, with fast redox kinetics and good stability. The Li/Br battery combines the advantages of high output voltage (～3.1 V), electrolyte concentration (3.0 mol/L), maximum power density (29.1mW/cm²) and practical energy density (232.6Wh/kg). Additionally, the battery displays a columbic efficiency (CE) of 90.0%, a voltage efficiency (VE) of 88.0% and an energy efficiency (EE) of 80.0% at 1.0 mA/cm² after continuously running for more than 1000 cycles, which is by far the longest cycle life reported for non-aqueous flow batteries.

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Structures and oxygen storage/release capacities of Ce_xZr_1-xO₂: Effects of Zr content and preparation method

Zhiheng Ren, Peng Wang, Jiao Kong, Meijun Wang, Liping Chang

2017, 26(4): 647-654. DOI: 10.1016/j.jechem.2017.04.003

摘要 ( 3153 )

Ceria-zirconia solid solution has been prepared by the urea grind combustion and citric acid sol-gel methods for catalytic applications as oxygen storage/release materials in this study. The properties and oxygen storage/release capacities of samples with different Zr contents were characterized and evaluated by X-ray diffraction (XRD), N₂ adsorption, scanning electron microscopy (SEM), Raman spectroscopy, and insitu CO-CO₂ looping test. The results demonstrate that the samples prepared by two methods are all of excellent lattice [O] release/storage properties and maintain good long-term cycle stability. But the preparation method significantly impacts the homogeneity of samples related to their redox properties and the content of Zr over 20%, which greatly changed the properties of ceria-zirconia solid solutions and caused their changing of crystalline symmetry from cubic to tetragonal. The samples prepared by citric acid solgel method are of more homogeneous particle sizes and higher specific surface areas than that by urea grind combustion method, which is benefit to the oxygen release rather than oxygen storage. The bulk oxygen amount migrated to surface increases with the increasing Zr content, however, the amount of lattice oxygen migration decreases when Zr content is over 20%. When Zr content is 20%, the differences of storage/release capacities from two different preparation methods are reduced at high temperature in the long-term loop reaction.

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Recovering methane from quartz sand-bearing hydrate with gaseous CO₂

Shuanshi Fan, Xi Wang, Yanhong Wang, Xuemei Lang

2017, 26(4): 655-659. DOI: 10.1016/j.jechem.2017.04.014

摘要 ( 2987 )

The replacement method by CO₂ is regarded as a new approach to natural gas hydrate (NGH) exploitation method, by which methane production and carbon dioxide sequestration might be obtained simultaneously. In this study, CO₂ was used to recover CH₄ from hydrate reservoirs at different temperatures and pressures. During the CO₂-CH₄ recovery process, the pressure was selected from 2.1 to 3.4MPa, and the temperature ranged from 274.2 to 281.2 K. Calculating the fugacity differences between the gas phase and the hydrate phase for CO₂ and CH₄ at different conditions, it has found rising pressure was positive for hydrates formation process that was helpful for the improvement of CH₄ recovery rate. Rising temperature promoted the trend of CH₄ hydrate decomposition for the whole process of CO₂-CH₄ replacement. The highest recovery rate was 46.6 % at 3.4MPa 281.2 K for CO₂-CH₄ replacement reaction in this work.

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Removal of biomass tar by steam reforming over calcined scallop shell supported Cu catalysts

Malinee Kaewpanha, Surachai Karnjanakom, Guoqing Guan, Xiaogang Hao, Jingxuan Yang, Abuliti Abudula

2017, 26(4): 660-666. DOI: 10.1016/j.jechem.2017.03.012

摘要 ( 2588 )

In this study, the main purpose is to develop low-cost catalysts with high activity and stability for high quality syngas production via steam reforming of biomass tar in biomass gasification process. The calcined waste scallop shell (CS) supported copper (Cu) catalysts are prepared for steam reforming of biomass tar. The prepared Cu supported on CS catalysts exhibit higher catalytic activity than those on commercial CaO and Al₂O₃. Characterization results indicate that Cu/CS has a strong interaction between Cu and CaO in CS support, resulting in the formation of calcium copper oxide phase which could stabilize Cu species and provide new active sites for the tar reforming. In addition, the strong basicity of CS support and other inorganic elements contained in CS support could enhance the activity of Cu/CS. The addition of a small amount of Co is found to be able to stabilize the catalytic activity of Cu/CS catalysts, making them reusable after regeneration without any loss of their activities.

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Metal-organic framework derived hierarchical porous TiO₂ nanopills as a super stable anode for Na-ion batteries

Huan Li, Zhiguo Zhang, Xiao Huang, Tongbin Lan, Mingdeng Wei, Tingli Ma

2017, 26(4): 667-672. DOI: 10.1016/j.jechem.2017.02.008

摘要 ( 2660 )

Hierarchical porous TiO₂ nanopills were synthesized using a titanium metal-organic framework MIL- 125(Ti) as precursor. The as-synthesized TiO₂ nanopills owned a large specific surface area of 102 m²/g and unique porous structure. Furthermore, the obtained TiO₂ nanopills were applied as anode materials for Na-ion batteries for the first time. The as-synthesized TiO₂ nanopills achieved a high discharge capacity of 196.4 mAh/g at a current density of 0.1 A/g. A discharge capacity of 115.9 mAh/g was obtained at a high current density of 0.5 A/g and the capacity retention was remained as high as 90% even after 3000 cycles. The excellent electrochemical performance can be attributed to its unique hierarchical porous feature.

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Porous nanostructured ZnCo₂O₄ derived from MOF-74: High-performance anode materials for lithium ion batteries

Mengjuan Du, Dan He, Yongbing Lou, Jinxi Chen

2017, 26(4): 673-680. DOI: 10.1016/j.jechem.2017.02.001

摘要 ( 3484 )

Nanostructured metal oxides derived from metal organic frameworks have been shown to be promising materials for application in high energy density lithium ion batteries. In this work, porous nanostructured ZnCo₂O₄ and Co₃O₄ were synthesized by a facile and cost-effective approach via the calcination of MOF-74 precursors and tested as anode materials for lithium ion batteries. Compared with Co₃O₄, the electrochemical properties of the obtained porous nanostructured ZnCo₂O₄ exhibit higher specific capacity, more excellent cycling stability and better rate capability. It demonstrates a reversible capacity of 1243.2 mAh/g after 80 cycles at 100mA/g and an excellent rate performance with high average discharge specific capacities of 1586.8, 994.6, 759.6 and 509.2 mAh/g at 200, 400, 600 and 800 mA/g, respectively. The satisfactory electrochemical performances suggest that this porous nanostructured ZnCo₂O₄ is potentially promising for application as an efficient anode material for lithium ion batteries.

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Morphology and crystal-plane effects of Zr-doped CeO₂ nanocrystals on the epoxidation of styrene with tert-butylhydroperoxide as the oxidant

Jia Ren, Xin Liu, Ruihua Gao, Wei-Lin Dai

2017, 26(4): 681-687. DOI: 10.1016/j.jechem.2017.01.007

摘要 ( 2733 )

The morphology effect of Zr-doped CeO₂ was studied in terms of their activities in the selective oxidation of styrene to styrene oxide using tert-butyl hydroperoxide as the oxidant. In the present work, Zrdoped CeO₂ nanorods exhibited the highest catalytic performance (yield of styrene oxide and TOF value) followed by nanoparticles and nanocubes. For the Zr-doped CeO₂ nanorods, the apparent activation energy is 56.3 kJ/mol, which is much lower than the values of catalysts supported on nanoparticles and nanocubes (73.3 and 93.4 kJ/mol). The high resolution transmission electron microscopy results indicated that (1 0 0) and (1 1 0) crystal planes are predominantly exposed for Zr-doped CeO₂ nanorods while (1 0 0) and (1 1 1) for nanocubes, (1 1 1) for nanoparticles. The remarkably increased catalytic activity of the Zrdoped CeO₂ nanorods is mainly attributed to the higher percentage of Ce³⁺ species and more oxygen vacancies, which are associated with their exposed (1 0 0) and (1 1 0) crystal planes. Furthermore, recycling studies proved that the heterogeneous Zr-doped CeO₂ nanorods did not lose its initial high catalytic activity after five successive recycles.

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Effect of silicon precursor on silicon incorporation in SAPO-11 and their catalytic performance for hydroisomerization of n-octane on Pt-based catalysts

Zhichao Yang, Jilong Li, Yunqi Liu, Chenguang Liu

2017, 26(4): 688-694. DOI: 10.1016/j.jechem.2017.02.002

摘要 ( 2501 )

SAPO-11 molecular sieves were synthesized using silica sol, hydrophilic fumed silica, and tetraethyl orthosilicate (TEOS) as silicon precursors. Their physicochemical properties were characterized using XRD, SEM, nitrogen adsorption-desorption, Py-IR, NH₃-TPD, EDS, and ²⁷Al, ³¹P, ²⁹Si MAS NMR techniques. The catalytic performance was assessed in the hydroisomerization of n-octane. The results showed that the silicon precursors influenced the physicochemical properties and catalytic performance of SAPO-11. SAPO- 11 synthesized using hydrophilic fumed silica as silicon precursor showed higher silicon distribution and had more medium acid sites. SAPO-11 synthesized using TEOS as silicon precursor had more silicon content, but more silicon islands formed in its framework. The depolymerization of silicon precursors might affect the silicon content and distribution in SAPO-11. In the hydroisomerization of n-octane, the catalytic activity strongly depended on the number of medium acid sites instead of the number of total acid sites. SAPO-11 synthesized using hydrophilic fumed silica as silicon precursor exhibited higher catalytic activity than the other samples because it has more medium acid sites.

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Environment friendly hydrothermal synthesis of carbon-Co₃O₄ nanorods composite as an efficient catalyst for oxygen evolution reaction

Amol R. Jadhav, Harshad A. Bandal, Ashif H. Tamboli, Hern Kim

2017, 26(4): 695-702. DOI: 10.1016/j.jechem.2017.03.011

摘要 ( 2763 )

The design of cost-effective, highly active catalysts for hydrogen energy production is a vital element in the societal pursuit of sustainable energy. Water electrolysis is one of the most convenient processes to produce high purity hydrogen. Cobalt-based catalysts are well-known electrocatalysts for oxygen evolution reaction (OER). In this article, all these merits indicate that the present cobalt nanocomposite is a promising electrocatalyst for OER. C-Co₃O₄-nanorods catalyst with nanorod structure was synthesized by hydrothermal treatment of CoCl₂ ·6H₂O/dextrose/urea mixture at 180 ℃ for 18 h and then calcined at 400 ℃ for 3.5 h. The role of dextrose percentage in solution to achieve the uniform coating of carbon on the surface of Co₃O₄-nanorods has been demonstrated. The prepared materials were characterized by X-ray diffraction (XRD), X-ray photoelectron spectrum (XPS), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and Brunauer-Emmett-Teller instrument (BET). Due to its unique morphology, the C-Co₃O₄-nanorods catalyst exhibited better activity than Co₃O₄-microplates catalyst for OER in 1M KOH aqueous solution. The results showed a highly efficient, scalable, and low-cost method for developing highly active and stable OER electrocatalysts in alkaline solution.

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A rapid synthesis of high surface area PdRu nanosponges: Composition-dependent electrocatalytic activity for formic acid oxidation

Ehteram Hasheminejad, Reza Ojani, Jahan Bakhsh Raoof

2017, 26(4): 703-711. DOI: 10.1016/j.jechem.2017.02.009

摘要 ( 2865 )

Here, PdRu nanoparticle networks (NPNs) with various compositions were synthesized through an inexpensive method in water as a green solvent, at different ratios of the H₂PdCl₄ and RuCl₃ precursors. This is a fast, room temperature and surfactant free strategy which is able to form high surface area metal nanosponges with a three-dimensional (3D) porous structure. The structure of as-prepared nanosponges was characterized using the techniques of field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and cyclic voltammetry (CV). Then, the electrocatalytic activities of PdRu NPNs towards formic acid oxidation were examined by electrochemical measurements including CV, chronoamperometry, and electrochemical impedance spectroscopy (EIS). Based on studies, it was found that the current density of formic acid oxidation (FAO) is strongly dependent on the composition of PdRu NPNs. The best performance was realized for Pd₄Ru₁ NPNs compared to monometallic Pd counterpart and other bimetallic NPNs which might be ascribed to the role of Ru in the decrease of CO adsorption strength on the catalyst and consequently the priority of formic acid oxidation through the direct pathway. The Pd₄Ru₁ NPNs also showed the maximum current density and stability in chronoamperometric measurements. In addition, comparative studies were performed between as-prepared NPNs and CNTs-supported Pd nanoparticles (Pd NPs/CNTs). The present results demonstrated the unique structural advantages of NPNs compared to individual Pd NPs supported on the CNT which leads to the promising performance of NPNs as supportless catalysts for the oxidation of formic acid.

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Improving ORR activity of carbon nanotubes by hydrothermal carbon deposition method

Baobing Huang, Lu Peng, Fangfang Yang, Yuchuan Liu, Zailai Xie

2017, 26(4): 712-718. DOI: 10.1016/j.jechem.2017.03.016

摘要 ( 2800 )

Nitrogen doped carbons are an important family of materials with ideal activity for oxygen reduction reaction (ORR). It is always interesting to search functional carbons with high heteroatom contents and desirable structure for ORR. Within this study, the surface modification of carbon nanotubes (CNTs) via hydrothermal carbonization (HTC) technique in the presence of glucose and urea was reported, where the surface of CNTs is successfully coated by nitrogen containing hydrothermal carbon layers. The resulting composite combines both advantages of the outstanding electrical conductivity of CNTs and the effective ORR active sites provided by doped nitrogen in the HTC carbon layers. By controlling the ratio of glucose and urea, the nitrogen contents coated on the surface of CNTs can reach up to 1.7 wt%. The resulting materials show outstanding electrochemical activity towards ORR in alkaline electrolyte, making it one of the valuable metal-free electrode materials and a competent alternative to the state-of-the-art Pt/C catalyst.

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Direct synthesis of La-Mg-Ni-Co type hydrogen storage alloys from oxide mixtures

Alanur Binal Aybar, Mustafa Anik

2017, 26(4): 719-723. DOI: 10.1016/j.jechem.2017.02.010

摘要 ( 2625 )

(La_1-xMg_-x)₂(Ni_0.8Co_0.2)₇ (x=0.125, 0.25, 0.5) alloys were synthesized from the sintered mixture of La₂O₃ + NiO + CoO + MgO in the molten CaCl₂ electrolyte at 750 ℃ and the electrochemical hydrogen storage capacities of the synthesized alloys were measured. Non-hygroscopic LaNiO₃ phase formed during sintering (at 1200 ℃ for 2 h) as a result of the reaction of hygroscopic La₂O₃ with NiO. Another sinter product was Mg_0.4Ni_0.6O phase. Both mixed oxide sinter products facilitated the La-Ni and Mg-Ni phase formations. X-ray diffraction peaks indicated that the first stable phase appeared in the alloy structure was LaNi₅ which formed upon reduction of La₂NiO₄ phase. Increase in Mg content caused formation of La_1.5Mg_0.5Ni₇ phase in the alloy structure and the presence of this phase improved the hydrogen storage performance of the electrodes. It was observed that (La_1-xMg_-x)₂(Ni_0.8Co_0.2)₇ (x=0.125, 0.25, 0.5) alloys have promising discharge capacities change between 319mAh/g and 379mAh/g depending on the alloy Mg content.

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Water effect on band alignment of GaP: A theoretical insight into pyridinium catalyzed CO₂ reduction

Xue-Ting Fan, Mei Jia, Ming-Hsien Lee, Jun Cheng

2017, 26(4): 724-729. DOI: 10.1016/j.jechem.2017.03.002

摘要 ( 2745 )

GaP has been shown to have good photo-catalytic activity in pyridinium catalyzed CO₂ reduction. The photo-excited electrons in the conduction band of GaP should have a sufficient reduction potential to drive the reduction of pyridinium and CO₂. In this work, we have studied water adsorption on the GaP surface using density functional theory calculations, and its effect on the band alignment. Our calculations have shown that there are surface states present near the band edges due to unsaturated dangling bonds, and water adsorption can remove these states partially or almost completely depending on the adsorption states of water. More importantly, we have found that water adsorption has considerable effects on the band alignment, shifting up the band positions by up to 0.5 eV compared to the bare surface. The computed level of the conduction band with the adsorption of water is rather close to the reduction level of pyridinium ions, thus suggesting that photo-excited electrons are thermodynamically possible to reduce pyridinium to pyridinyl radicals that further help CO₂ reduction.

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Ultrathin free-standing electrospun carbon nanofibers web as the electrode of the vanadium flow batteries

Chi Xu, Xiaofei Yang, Xianfeng Li, Tao Liu, Huamin Zhang

2017, 26(4): 730-737. DOI: 10.1016/j.jechem.2017.03.005

摘要 ( 2606 )

Ultrathin free-standing electrospun carbon nanofiber web (ECNFW) used for the electrodes of the vanadium flow battery (VFB) has been fabricated by the electrospinning technique followed by the carbonization process in this study to reduce the ohmic polarization of the VFB. The microstructure, surface chemistry and electrochemical performance of ECNFW carbonized at various temperatures from 800 to 1400 ℃ have been investigated. The results show that ECNFW carbonized at 1100 ℃ exhibits the highest electrocatalytic activity toward the V²⁺/V³⁺ redox reaction, and its electrocatalytic activity decreases along with the increase of carbonization temperature due to the drooping of the surface functional groups. While for the VO²⁺/VO²⁺ redox couple, the electrocatalytic activity of ECNFW carbonized above 1100 ℃ barely changes as the carbonization temperature rises. It indicates that the surface functional groups could function as the reaction sites for the V²⁺/V³⁺ redox couple, but have not any catalytic effect for the VO²⁺/VO₂⁺ redox couple. And the single cell test result suggests that ECNFW carbonized at 1100 ℃ is a promising material as the VFB electrode and the VFB with ECNFW electrodes obtains a super low internal resistance of 250m cm².

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The adsorption and activation of formic acid on different anatase TiO₂ surfaces

Huaqing Dong, Zhenzhan Zhuang, Yongbing Gu, Jianrong Gao

2017, 26(4): 738-742. DOI: 10.1016/j.jechem.2017.03.009

摘要 ( 2465 )

Formic acid photodegradation is one of the most important reactions in organic pollution control, and helps to improve the hydrogen generation efficiency in titanium dioxide catalyzed water photodecomposition. Based on density functional theory and ReaxFF molecular dynamics, the adsorption, diffusion and activation of formic acid on the different anatase TiO₂ (1 0 1), (0 0 1), (0 1 0) surfaces are investigated. The result shows that the adsorption of COOH on anatase TiO₂ surface shrinks the energy gap between the dehydrogenation intermediate COOH and HCOO. On the anatase TiO₂ (101) surface, the formic acid breaks the O-H bond at the first step with activation energy 0.24 eV, and the consequent break of α-H become much easier with activation energy 0.77 eV. The dissociation of α-H is the determination step of the HCOOH decomposition.

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Improving photoreduction of CO₂ with water to CH₄ in a novel concentrated solar reactor

Sisi Han, Yinfei Chen, Stéphane Abanades, Zekai Zhang

2017, 26(4): 743-749. DOI: 10.1016/j.jechem.2017.03.006

摘要 ( 2594 )

CO₂ photoreduction is an attractive process which allows the storage of solar energy and synthesis of solar fuels. Many different photocatalytic systems have been developed, while the alternative photo-reactors are still insufficiently investigated. In this work, photoreduction of CO₂ with H₂O into CH₄ was investigated in a modified concentrating solar reactor, using TiO₂ and Pt/TiO₂ as the catalysts. The TiO₂ and Pt/TiO₂ samples were extensively characterized by different techniques including powder X-ray diffraction (XRD), N₂ adsorption/desorption and UV-vis absorption. The catalytic performance of the TiO₂ and Pt/TiO₂ samples in the gas phase was evaluated under unconcentrated and concentrated Xe-lamp light and nature solar light with different concentrating ratios. Various parameters of the reaction system and the catalysts were investigated and optimized to maximize the catalytic performance of CO₂ reduction system. Compared with the normal light irradiation, the TiO₂ and Pt/TiO₂ samples show higher photocatalytic activity (about 6-7 times) for reducing CO₂ into CH₄ under concentrated Xe-lamp light and nature solar light. In the range of experimental light intensity, it is found that the concentration of the light makes it suitable for the catalytic reaction, and increases the utilization efficiency of the TiO₂ and Pt/TiO₂ samples while does not decrease the quantum efficiency.

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Liquid phase synthesis of dendritic nickel carbide alloy with high conductivity for advanced energy storage

Mao-Cheng Liu, Yu-Mei Hu, Wen-Ya An, Ling-Bin Kong, Long Kang

2017, 26(4): 750-756. DOI: 10.1016/j.jechem.2017.03.019

摘要 ( 3023 )

Alloy materials have attracted increasing attentions because they possess superior electrical conductivity which can contribute to excellent electrochemical performance. Herein a dendritic Ni₃C alloy material has been prepared by the pyrolysis of nickel acetylacetonate employing oleylamine as a reductant and 1-octadecene or octadecane as the solvent. The current-voltage curves indicating that the electrical conductivity of Ni₃C is higher than that of nickel oxide. Electrochemical testing indicates that a high specific capacity of 390 C/g is found in alkaline electrolyte at 0.5 A/g, and deliver excellent rate characteristic as well as cycle life. The excellent electrochemical performance may be attributed to its high electrical conductivity and dendritic nanostructure that can promote diffusion of electrolyte ions. In addition, the AC//Ni₃C asymmetric supercapacitor has been assembled at a cell voltages between 0 and 1.6 V, achieving a maximum energy density of 37 Wh/kg (at a power density of 0.3995 kW/kg), and this manifests that the Ni₃C alloy is a promising electrode material for electrochemical energy storage.

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Annealing temperature dependent catalytic water oxidation activity of iron oxyhydroxide thin films

P. T. Babar, B. S. Pawar, A. C. Lokhande, M. G. Gang, J. S. Jang, M. P. Suryawanshi, S. M. Pawar, Jin Hyeok Kim

2017, 26(4): 757-761. DOI: 10.1016/j.jechem.2017.04.012

摘要 ( 2937 )

Nanostructured iron oxyhydroxide (FeOOH) thin films have been synthesized using an electrodeposition method on a nickel foam (NF) substrate and effect of air annealing temperature on the catalytic performance is studied. The as-deposited and annealed thin films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM) and linear sweep voltammetry (LSV) to determine their structural, morphological, compositional and electrochemical properties, respectively. The as-deposited nanostructured amorphous FeOOH thin film is converted into a polycrystalline Fe₂O₃ with hematite crystal structure at a high temperature. The FeOOH thin film acts as an efficient electrocatalyst for the oxygen evolution reaction (OER) in an alkaline 1M KOH electrolyte. The film annealed at 200 ℃ shows high catalytic activity with an onset overpotential of 240 mV with a smaller Tafel slope of 48mV/dec. Additionally, it needs an overpotential of 290 mV to the drive the current density of 10 mA/cm² and shows good stability in the 1M KOH electrolyte solution.

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Facile synthesis of nanoporous CuS nanospheres for high-performance supercapacitor electrodes

Hamid Heydari, Seyyed Ebrahim Moosavifard, Mohammad Shahraki, Saeed Elyasi

2017, 26(4): 762-767. DOI: 10.1016/j.jechem.2017.03.007

摘要 ( 2901 )

In recent years, development of high-performance supercapacitor electrode materials has stimulated a great deal of scientific research. The electrochemical performance of a supercapacitor strongly depends on its material structures. Herein, we report a simple strategy for high-performance supercapacitors by building pseudocapacitive CuS nanospheres with nanoporous structures, nanosized walls (<10 nm) and relatively large specific surface area of 65m²/g. This electrode demonstrates excellent electrochemical performance including a maximum specific capacitance of 814 F/g at 1 A/g, significant rate capability of 42% capacitance retention at an ultrafast rate of 50 A/g, and outstanding long-term cycling stability at various current densities. The remarkable electrochemical performance of as-prepared nanoporous CuS nanospheres electrode has been attributed to its unique structures that plays a key role in providing short ion and electron diffusion pathways, facilitated ion transport and more active sites for electrochemical reactions. This work sheds a new light on the metal sulfides design philosophy, and demonstrates that nanoporous CuS nanospheres electrode is a promising candidate for application in high-performance supercapacitors.

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Aromatization over nanosized Ga-containing ZSM-5 zeolites prepared by different methods: Effect of acidity of active Ga species on the catalytic performance

Yujun Fang, Xiaofang Su, Xuefeng Bai, Wei Wu, Gaoliang Wang, Linfei Xiao, Anran Yu

2017, 26(4): 768-775. DOI: 10.1016/j.jechem.2017.03.014

摘要 ( 3286 )

Nanosized Ga-containing ZSM-5 zeolites were prepared via isomorphous substitution and impregnation followed by characterized using various techniques. The catalytic performance of the zeolites for the aromatization of 1-hexene was investigated. The results indicate that isomorphous substitution promotes the incorporation of Ga heteroatoms into the framework along with the formation of extra-framework GaO⁺ species ([GaO⁺]^a) that have stronger interactions with the negative potential of the framework. In addition, based on the Py-IR results and catalytic performance, the [GaO⁺]^a species with stronger Lewis acid sites produced a better synergism with moderate Brønsted acid sites and thus improved the selectivity to aromatic compounds. However, the impregnation results in the formation of Ga₂O₃ phase and small amounts of GaO⁺ species that are mainly located on the external surface ([GaO⁺]^b), which contribute to weaker Lewis acid sites due to weaker interactions with the zeolite framework. During 1-hexene aromatization, the nanosized Ga isomorphously substituted ZSM-5 zeolite samples (Gax-NZ5) exhibited better catalytic performance compared to the impregnated samples, and the highest aromatic yield (i.e., 65.4wt%) was achieved over the Ga4.2-NZ5 sample, which contained with the highest Ga content.

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Direct amination of isobutylene over zeolite catalysts with various topologies and acidities

Shangyao Gao, Xiangxue Zhu, Xiujie Li, Yuzhong Wang, Sujuan Xie, Songwei Du, Fucun Chen, Peng Zeng, Shenglin Liu, Longya Xu

2017, 26(4): 776-782. DOI: 10.1016/j.jechem.2017.03.018

摘要 ( 2923 )

The atomically economic and green chemical reaction of direct amination of isobutylene to tertbutylamine, particularly under the relative mild reaction conditions available for future industrial use, was carried out over zeolite catalysts possessing different topological structures, from one dimensional to three dimensional pore system, and from small 8-member ring pore (MRP) to medium 10 MRP and further to large 12 MRP zeolites, to disclose the relationship between the zeolite properties/topologies and their amination performance systematically under the mild reaction conditions. It was discovered that the pore structure and the acidities of zeolite catalysts played crucial roles in the isobutylene amination process, and suitable pore diameter (larger than 0.5 nm or with large side pockets/cups in the outside surface) and a certain number of mid-strong acid sites are indispensable to catalyze the amination reaction, while too strong acid strength was not conducive to the process of isobutylene amination. Among them, zeolites with topologies of BEA, MFI, MEL, MWW and EUO exhibited good amination performance, with which the isobutylene conversion was higher than 12.61% (>46.42% of the equilibrium conversion) under the studied mild reaction conditions. Due to the good amination performance and the large adjustable Si/Al₂ ratio range, ZSM-5 was selected to further study the effect of acidity on the amination performance systematically under the mild reaction conditions, and the activity-acidity relationship in the amination process was disclosed: the amination activity (isobutylene conversion) had a linear correlation with the amount of mid-strong B acidity under the studied conditions over ZSM-5 catalyst, which can provide guidance for further developing high-efficient amination catalyst under mild reaction conditions available for future industrial use.

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Hydrothermal conversion of lignocellulosic biomass into high-value energy storage materials

Neriman Sinan, Ece Unur

2017, 26(4): 783-789. DOI: 10.1016/j.jechem.2017.04.011

摘要 ( 2865 )

Preparation of hierarchically porous, heteroatom-rich nanostructured carbons through green and scalable routes plays a key role for practical energy storage applications. In this work, naturally abundant lignocellulosic agricultural waste with high initial oxygen content, hazelnut shells, were hydrothermally carbonized and converted into nanostructured ‘hydrochar’. Environmentally benign ceramic/magnesium oxide (MgO) templating was used to introduce porosity into the hydrochar. Electrochemical performance of the resulting material (HM700) was investigated in aqueous solutions of 1M H₂SO₄, 6M KOH and 1M Na₂SO₄, using a three-electrode cell. HM700 achieved a high specific capacitance of 323.2 F/g in 1M H₂SO₄ (at 1 A/g, -0.3 to 0.9 V vs. Ag/AgCl) due to the contributions of oxygen heteroatoms (13.5wt%) to the total capacitance by pseudo-capacitive effect. Moreover, a maximum energy density of 11.1 Wh/kg and a maximum power density of 3686.2W/kg were attained for the symmetric supercapacitor employing HM700 as electrode material (1M Na₂SO₄, ΔE=2 V), making the device promising for green supercapacitor applications.

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Functionalized graphene oxide-reinforced electrospun carbon nanofibers as ultrathin supercapacitor electrode

W. K. Chee, H. N. Lim, Y. Andou, Z. Zainal, A. A. B. Hamra, I. Harrison, M. Altarawneh, Z. T. Jiang, N. M. Huang

2017, 26(4): 790-798. DOI: 10.1016/j.jechem.2017.04.007

摘要 ( 3169 )

Graphene oxide has been used widely as a starting precursor for applications that cater to the needs of tunable graphene. However, the hydrophilic characteristic limits their application, especially in a hydrophobic condition. Herein, a novel non-covalent surface modification approach towards graphene oxide was conducted via a UV-induced photo-polymerization technique that involves two major routes; a UV-sensitive initiator embedded via pi-pi interactions on the graphene planar rings, and the polymerization of hydrophobic polymeric chains along the surface. The functionalized graphene oxide successfully achieved the desired hydrophobicity as it displayed the characteristic of being readily dissolved in organic solvent. Upon its addition into a polymeric solution and subjected to an electrospinning process, non-woven random nanofibers embedded with graphene oxide sheets were obtained. The prepared polymeric nanofibers were subjected to two-step thermal treatments that eventually converted the polymeric chains into a carbon-rich conductive structure. A unique morphology was observed upon the addition of the functionalized graphene oxide, whereby the sheets were embedded and intercalated within the carbon nanofibers and formed a continuous structure. This reinforcement effectively enhanced the electrochemical performance of the carbon nanofibers by recording a specific capacitance of up to 140.10 F/g at the current density of 1 A/g, which was approximately three folds more than that of pristine nanofibers. It also retained the capacitance up to 96.2% after 1000 vigorous charge/discharge cycles. This functionalization technique opens up a new pathway in tuning the solubility nature of graphene oxide towards the synthesis of a graphene oxide-reinforced polymeric structure.

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Highly stable and selective Ru/NiFe₂O₄ catalysts for transfer hydrogenation of biomass-derived furfural to 2-methylfuran

Baowei Wang, Chuang Li, Bo He, Ji Qi, Changhai Liang

2017, 26(4): 799-807. DOI: 10.1016/j.jechem.2017.04.008

摘要 ( 2753 )

Spinel ferrites NiFe₂O₄ supported Ru catalysts have been prepared via a simple sol-gel route and applied for converting biomass-derived furfural to 2-methylfuran. The as-prepared catalysts were characterized by thermogravimetric analysis (TG), N₂ adsorption-desorption, X-ray diffraction (XRD), scanning electronic microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Results showed that the catalysts had well-dispersed Ru active sites and large surface area for calcination temperature ranging from 300 to 500 ℃. The conversion of biomass-derived furfural into 2-methylfuran was conducted over Ru/NiFe₂O₄ through catalytic transfer hydrogenation in liquid-phase with 2-propanol as the hydrogen source. A significantly enhanced activity and increased 2-methylfuran yield have been achieved in this study. Under mild conditions (180 ℃ and 2.1MPa N₂), the conversion of furfural exceeds 97% and 2-methylfuran yield was up to 83% over the catalyst containing 8 wt% Ru. After five repeated uses, the catalytic activity and the corresponding product yield remained almost unchanged. The excellent catalytic activity and recycling performance provide a broad prospects for various practical applications.

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Synergistic effect of combination of surfactant and oxide powder on enhancement of gas hydrates nucleation

Anatoliy N. Nesterov, Aleksey M. Reshetnikov, Andrey Yu. Manakov, Tatyana P. Adamova

2017, 26(4): 808-814. DOI: 10.1016/j.jechem.2017.04.001

摘要 ( 2500 )

In the present work we studied the induction periods of hydrate formation of natural gas in pure water, aqueous solutions of surfactants, and in the presence of surfactant together with aluminum oxide nanopowder, the activity of which as hydrate formation inducer was studied previously. Sodium dodecyl sulfate (SDS) or neonol AF-9-12 were used as the surfactants. It was demonstrated that the addition of either surfactants or aluminum oxide powder under our experimental conditions causes a decrease in the induction period of hydrate formation from ～105min for pure water to 30-35min for water with additives. In the case of the simultaneous presence of surfactants and aluminum oxide powder in the system, induction period decreased to ～20 min. So, the synergistic effect of the combination of surfactant and oxide powder on gas hydrate nucleation was demonstrated. Possible reasons of this effect have been discussed.

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Carbon-coated manganese dioxide nanoparticles and their enhanced electrochemical properties for zinc-ion battery applications

Saiful Islam, Muhammad Hilmy Alfaruqi, Jinju Song, Sungjin Kim, Duong Tung Pham, Jeonggeun Jo, Seokhun Kim, Vinod Mathew, Joseph Paul Baboo, Zhiliang Xiu, Jaekook Kim

2017, 26(4): 815-819. DOI: 10.1016/j.jechem.2017.04.002

摘要 ( 2873 )

In this study, we report the cost-effective and simple synthesis of carbon-coated α-MnO₂ nanoparticles (α-MnO₂@C) for use as cathodes of aqueous zinc-ion batteries (ZIBs) for the first time. α-MnO₂@C was prepared via a gel formation, using maleic acid (C₄H₄O₄) as the carbon source, followed by annealing at low temperature of 270 ℃. A uniform carbon network among the α-MnO₂ nanoparticles was observed by transmission electron microscopy. When tested in a zinc cell, the α-MnO₂@C exhibited a high initial discharge capacity of 272 mAh/g under 66 mA/g current density compared to 213mAh/g, at the same current density, displayed by the pristine sample. Further, α-MnO₂@C demonstrated superior cycleability compared to the pristine samples. This study may pave the way for the utilizing carbon-coated MnO₂ electrodes for aqueous ZIB applications and thereby contribute to realizing high performance eco-friendly batteries.

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