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2016, Vol. 25, No. 2　Online: 2016-03-15


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Nanostructure in Energy Conversion

Tailor-made nanostructured materials can be applied for solving the pressing challenges associated with energy conversion and storage. The review puts different research fields into perspective, namely (photo) thermal synthesis of renewable fuels over heterogeneous catalysts, the fabrication of stable and active electrocatalysts and electrode materials for water splitting, and the direct conversion of sunlight in photovoltaics and photoelectrodes. Differing challenges, but also common benefits associated with applications of nanostructured materials in those different fields are discussed. It will be shown that well-controlled catalytically active sites are often the main challenge, and that a multitude of elementary steps have to be considered.

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Preface

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Preface to the Special Issue on Nanoconcepts in Energy Chemistry and Catalysis Dangsheng Su, Gabriele Centi 2016, 25(2): 0-0.  摘要 ( 3808 )   PDF(1KB) ( 0 )   The demand for a sustainable development of our society requires a fundamental turn in the current approach to energy production and use, which requires developing new concepts and technologies for catalysis in energy chemistry and environmental protection. Realize this challenge requires new materials, new technologies and new processes that can bring about a revolutionary change in our daily life. The title of this special JEC issue remarks that we need to operate at the nano-scale and introduce new concepts in materials design to change from an evolutionary to a revolutionary change in this area. For this reason, we indicated “Nanoconcepts in Energy Chemistry and Catalysis”, to remark the idea of the need to manipulate the fundamental steps in energy conversion and storage and in catalysis at the level of nanostructured materials and their composite. This issue collects 22 contributions, including one highlight, four reviews, one communication and 16 full papers covering all the important applications of nanoconcepts in energy chemistry and catalysis. All the papers were written by international leading experts and specialists in the field of energy chemistry and catalysis including electrocatalysis for oxygen reduction reaction, electrode design for battery, nanocatalysts for Fisher-Tropsch synthesis, photocatalyst for hydrogen production, and materials for CO2 capture. The first paper highlighted the recent work of Bao's group on the direct, non-oxidative conversion of methane to ethylene, aromatics, and hydrogen, an excellent example how nanoconcepts in catalysis can lead to breakthrough in the use of natural gas. The following four reviews, written by international well-known experts in the field, address the application of nanomaterials and ionic liquid in energy conversion and catalysis. These reviews provide a unique opportunity for the readers to be updated on the latest developments and new opportunities offered by using the advanced nanoconcepts discussed in these reviews. Finally, one communication and 16 full articles report the newest results using nanostructured and materials in a various applications from oxygen reduction reaction, water splitting, hydrogen peroxide production, CO2 capture, as electrode materials and some other energy- and catalysis-related process. We believe that this special issue dedicated to the use of nanoconcepts in energy chemistry represents a unique opportunity for young and experienced researches in the field of sustainable energy to have an updated view on this exciting topic that we are convinced is an enabling factor for the future of our society. We thus invite all to have this special issue as a privileged component of your bookshelf.

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A new horizontal in C1 chemistry: Highly selective conversion of syngas to light olefins by a novel OX-ZEO process Ye Wang 2016, 25(2): 169-170.  DOI: 10.1016/j.jechem.2016.03.001 摘要 ( 4241 )   The most challenging goal of C1 chemistry is the control of C-C coupling to produce chemicals or fuels from C1 feedstocks, in particular syngas (H2 /CO), which can be derived from various carbon resources such as coal, natural gas or shale gas, and biomass. Light olefins including ethylene, propylene and butenes (C2=-C4=) are important building-block chemicals, which are currently produced from naphtha. The synthesis of light olefins from syngas is a promising alternative. Fischer-Tropsch (FT) synthesis, which has a history of more than 90 years, is currently the major process for the direct conversion of syngas to hydrocarbons including light olefins, but the C2 =-C4= selectivity is limited because of the FT mechanism, which involves the C-C coupling of CHx(x=1-3) intermediates formed via CO dissociation on metal (typically Fe, Co or Ru) surfaces [1]. The C-C coupling on open metal surfaces is uncontrollable, leading to wide distribution of hydrocarbon products following the Anderson-Schulz-Flory (ASF) distribution. The maximum selectivity of C2-C4 hydrocarbons (including paraffins and olefins) is 58% [1]. Light olefins may also be produced from syngas via a two-process route, i.e., methanol synthesis and methanol to olefins (MTO), but this indirect route is water- and energyintensive.

Communication

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A nano-engineered graphene/carbon nitride hybrid for photocatalytic hydrogen evolution Xiaobo Li, Yao Zheng, Anthony F. Masters, Thomas Maschmeyer 2016, 25(2): 225-227.  DOI: 10.1016/j.jechem.2015.12.002 摘要 ( 5291 )   A metal-free photocatalytic hydrogen evolution system was successfully fabricated using heteroatom doped graphene materials as electron-transfer co-catalysts and carbon nitride as a semiconductor. The catalytic role of graphene is significantly dependent on the heteroatom dopant of the graphene, such as O, S, B, N doped/undoped graphene co-catalysts, and N-graphene shows the best catalytic hydrogen evolution rate.

Articles

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Water oxidation electrocatalysis with iron oxide nanoparticles prepared via laser ablation Erica Pizzolato, Stefano Scaramuzza, Francesco Carraro, Alessia Sartori, Stefano Agnoli, Vincenzo Amendola, Marcella Bonchio, Andrea Sartorel 2016, 25(2): 246-250.  DOI: 10.1016/j.jechem.2015.12.004 摘要 ( 4566 )   Iron oxide nanoparticles (FeOx NPs, 5-30 nm size) prepared via laser ablation in liquid were supported onto Indium Tin Oxide conductive glass slides by magnetophoretic deposition (MD) technique. The resulting FeOx@ITO electrodes are characterized by a low amount of iron coverage of 16-50 nmol/cm2, and show electrocatalytic activity towards water oxidation in neutral phosphate buffer pH 7 with 0.58 V overpotential and quantitative Faradaic efficiency towards oxygen production. XPS analysis on the oxygen region of the FeOx films reveals a substantial hydration of the surface after catalysis, recognized as a crucial step to access reactivity.

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Atomic layer deposition of ultrathin layered TiO2 on Pt/C cathode catalyst for extended durability in polymer electrolyte fuel cells Sangho Chung, Myounghoon Choun, Beomgyun Jeong, Jae Kwang Lee, Jaeyoung Lee 2016, 25(2): 258-264.  DOI: 10.1016/j.jechem.2016.01.010 摘要 ( 4806 )   This study shows the preparation of a TiO2 coated Pt/C (TiO2/Pt/C) by atomic layer deposition (ALD), and the examination of the possibility for TiO2/Pt/C to be used as a durable cathode catalyst in polymer electrolyte fuel cells (PEFCs). Cyclic voltammetry results revealed that TiO2/Pt/C catalyst which has 2 nm protective layer showed similar activity for the oxygen reduction reaction compared to Pt/C catalysts and they also had good durability. TiO2/Pt/C prepared by 10 ALD cycles degraded 70% after 20 0 0 Accelerated degradation test, while Pt/C corroded 92% in the same conditions. TiO2 ultrathin layer by ALD is able to achieve a good balance between the durability and activity, leading to TiO2/Pt/C as a promising cathode catalyst for PEFCs. The mechanism of the TiO2 protective layer used to prevent the degradation of Pt/C is discussed.

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Design of Fe3-xO4 raspberry decorated graphene nanocomposites with high performances in lithium-ion battery Olivier Gerber, Sylvie Bégin-Colin, Benoit P. Pichon, Elodie Barraud, Sébastien Lemonnier, Cuong Pham-Huu, Barbara Daffos, Patrice Simon, Jeremy Come, Dominique Bégin 2016, 25(2): 272-277.  DOI: 10.1016/j.jechem.2016.01.021 摘要 ( 4864 )   Fe3-xO4 raspberry shaped nanostructures/graphene nanocomposites were synthesized by a one-step polyol-solvothermal method to be tested as electrode materials for Li-ion battery (LIB). Indeed, Fe3-xO4 raspberry shaped nanostructures consist of original oriented aggregates of Fe3-xO4 magnetite nanocrystals, ensuring a low oxidation state of magnetite and a hollow and porous structure, which has been easily combined with graphene sheets. The resulting nanocomposite powder displays a very homogeneous spatial distribution of Fe3-xO4 nanostructures at the surface of the graphene sheets. These original nanostructures and their strong interaction with the graphene sheets resulted in very small capacity fading upon Li+ ion intercalation. Reversible capacity, as high as 660 mAh/g, makes this material promising for anode in Li-ion batteries application.

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Synthesis-structure correlations of manganese-cobalt mixed metal oxide nanoparticles Manuel Gliech, Arno Bergmann, Camillo Spöri, Peter Strasser 2016, 25(2): 278-281.  DOI: 10.1016/j.jechem.2016.01.002 摘要 ( 5395 )   Mixed metal oxides in the nanoscale are of great interest for many aspects of energy related research topics as water splitting, fuel cells and battery technology. The development of scalable, cost-efficient and robust synthetic routes toward well-defined solid state structures is a major objective in this field. While monometallic oxides have been studied in much detail, reliable synthetic recipes targeting specific crystal structures of mixed metal oxide nanoparticles are largely missing. Yet, in order to meet the requirements for a broad range of technical implementation it is necessary to tailor the properties of mixed metal oxides to the particular purpose. Here, we present a study on the impact of the nature of the gas environment on the resulting crystal structure during a post-synthesis thermal heat treatment of manganese-cobalt oxide nanoparticles. We monitor the evolution of the crystal phase structure as the gas atmosphere is altered from pure nitrogen to synthetic air and pure oxygen. The particle size and homogeneity of the resulting nanoparticles increase with oxygen content, while the crystal structure gradually changes from rocksalt-like to pure spinel. We find the composition of the particles to be independent of the gas atmosphere. The manganese-cobalt oxide nanoparticles exhibited promising electrocatalytic activity regarding oxygen evolution in alkaline electrolyte. These findings offer new synthesis pathways for the direct preparation of versatile utilizable mixed metal oxides.

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Promoting effect of nitrogen doping on carbon nanotub e-supporte d RuO2 applied in the electrocatalytic oxygen evolution reaction Kunpeng Xie, Wei Xia, Justus Masa, Fengkai Yang, Philipp Weide, Wolfgang Schuhmann, Martin Muhler 2016, 25(2): 282-288.  DOI: 10.1016/j.jechem.2016.01.023 摘要 ( 5749 )   RuO2 nanoparticles supported on multi-walled carbon nanotubes (CNTs) functionalized with oxygen (OCNTs) and nitrogen (NCNTs) were employed for the oxygen evolution reaction (OER) in 0.1 M KOH. The catalysts were synthesized by metal-organic chemical vapor deposition using ruthenium carbonyl (Ru3(CO)12 ) as Ru precursor. The obtained RuO2/OCNT and RuO2/NCNT composites were characterized using TEM, H2-TPR, XRD and XPS in order probe structure-activity correlations, particularly, the effect of the different surface functional groups on the electrochemical OER performance. The electrocatalytic activity and stability of the catalysts with mean RuO2 particle sizes of 13-14 nm was evaluated by linear sweep voltammetry, cyclic voltammetry, and chronopotentiometry, showing that the generation of nitrogen-containing functional groups on CNTs was beneficial for both OER activity and stability. In the presence of RuO2, carbon corrosion was found to be significantly less severe.

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Effect of initial nickel particle size on stability of nickel catalysts for aqueous phase reforming Tomas van Haasterecht, Marten Swart, Krijn P. de Jong, Johannes Hendrik Bitter 2016, 25(2): 289-296.  DOI: 10.1016/j.jechem.2016.01.006 摘要 ( 5864 )   The deactivation behavior by crystallite growth of nickel nanoparticles on various supports (carbon nanofibers, zirconia, SiC, α-Al2O3 and γ-Al2O3 ) was investigated in the aqueous phase reforming of ethylene glycol. Supported Ni catalysts of ~10 wt% were prepared by impregnation of carbon nanofibers (CNF), ZrO2, SiC, γ-Al2O3 and α-Al2O3. The extent of the Ni nanoparticle growth on various support materials follows the order CNF ~ ZrO2 > SiC > γ-Al2O3 >> α-Al2O3 which sequence, however, was determined by the initial Ni particle size. Based on the observed nickel leaching and the specific growth characteristics; the particle size distribution and the effect of loading on the growth rate, Ostwald ripening is suggested to be the main mechanism contributing to nickel particle growth. Remarkably, initially smaller Ni particles (~12 nm) supported on α-Al2O3 were found to outgrow Ni particles with initially larger size (~20 nm). It is put forward that the higher susceptibility with respect to oxidation of the smaller Ni nanoparticles and differences in initial particle size distribution are responsible for this behavior.

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Role of size and pretreatment of Pd particles on their behaviour in the direct synthesis of H2O2 Salvatore Abate, Katia Barbera, Gabriele Centi, Gianfranco Giorgianni, Siglinda Perathoner 2016, 25(2): 297-305.  DOI: 10.1016/j.jechem.2016.01.008 摘要 ( 4459 )   Two families of catalysts, based on Pd nanoparticles supported on ceramic asymmetric tubular alumina membranes, are studies in the direct synthesis of H2O2. They are prepared by depositing Pd in two ways: (i) reduction with N 2 H 4 in an ultrasonic bath and (ii) by impregnation-deposition. The first preparation leads to larger particles, with average size of around 11 nm, while the second preparation leads to smaller particles, with average size around 4 nm. The catalytic membranes were tested as prepared, after thermal treatment in air and after further pre-reduction with H2 in mild (100℃) conditions. Samples were characterized by TEM, CO-chemisorption monitored by DRIFTS method and TPR, while catalytic tests have been performed in a semi-batch recirculation membrane reactor. Experimental catalytic results were analysed using two kinetics models to derive the reaction constants for the parallel and consecutive reactions of the kinetic network. Smaller particles of Pd show lower selectivity due to the higher rate of parallel combustion, even if the better dispersion of Pd and thus higher metal surface area in the sample lead to a productivity in H2O2similar or even higher than the sample with the larger Pd particles. Independently on the presence of smaller or larger Pd nanoparticles, an oxidation treatment leads to a significant enhancement in the productivity, although the catalyst progressively reduces during the catalytic process. The inhibition of the parallel combustion reaction (to water) induced from the calcination treatment remains after the in-situ reduction of the oxidized Pd species formed during the pre-treatment. This is likely due to the elimination of defect sites which dissociatively activate oxygen, and tentatively attributed to Pd sites able to give three-and four-fold coordination of CO.

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Selective synthesis of carbon monoxide via formates in reverse water-gas shift reaction over alumina-supported gold catalyst Nobuhiro Ishito, Kenji Hara, Kiyotaka Nakajima, Atsushi Fukuoka 2016, 25(2): 306-310.  DOI: 10.1016/j.jechem.2015.12.005 摘要 ( 4399 )   Thermal decomposition of formic acid on SiO2, CeO2 and γ-Al2O3 was studied as an elementary step of reverse water-gas shit reaction (RWGS) over supported Au catalysts. γ-Al2O3 showed the highest CO selectivity among the tested oxides in the decomposition of formic acid. Infrared spectroscopy showed the formation of four formate species on γ-Al2O3 : three η1-type and one μ2-type species, and these formates decomposed to CO at 473 K or higher. Au-loaded γ-Al2O3 samples were prepared by a depositionprecipitation method and used as catalysts for RWGS. The supported Au catalyst gave CO with high selectivity over 99% from CO2 and H2, which is attributed to the formation of formates on Au and subsequent decomposition to CO on γ-Al2O3.

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Fabrication of K-promoted iron/carbon nanotubes composite catalysts for the Fischer-Tropsch synthesis of lower olefins Xuezhi Duan, Di Wang, Gang Qian, John C. Walmsley, Anders Holmen, De Chen, Xinggui Zhou 2016, 25(2): 311-317.  DOI: 10.1016/j.jechem.2016.01.003 摘要 ( 4971 )   K-promoted iron/carbon nanotubes composite (i.e., FeK-OX) was prepared by a redox reaction between carbon nanotubes and K2FeO4 followed by thermal treatments on a purpose as the Fischer-Tropsch catalyst for the direct conversion of syngas to lower olefins. Its catalytic behaviors were compared with those of the other two Fe-IM and FeK-IM catalysts prepared by impregnation method followed by thermal treatments. The novel FeK-OX composite catalyst is found to exhibit higher hydrocarbon selectivity, lower olefins selectivity and chain growth probability as well as better stability. The catalyst structureperformance relationship has been established using multiple techniques including XRD, Raman, TEM and EDS elemental mapping. In addition, effects of additional potassium into the FeK-OX composite catalyst on the FTO performance were also investigated and discussed. Additional potassium promoters further endow the catalysts with higher yield of lower olefins. These results demonstrated that the introduction method of promoters and iron species plays a crucial role in the design and fabrication of highly active, selective and stable iron-based composite catalysts for the FTO reaction.

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Tuning of textural properties of germanosilicate zeolites ITH and IWW by acidic leaching Valeryia I. Kasneryk, Mariya V. Shamzhy, Maksym V. Opanasenko, Jiří Čejka 2016, 25(2): 318-326.  DOI: 10.1016/j.jechem.2015.12.003 摘要 ( 5870 )   The possibility to adjust textural properties of ITH and IWW zeolites by the variation of conditions (e.g. temperature, pH, duration) of acidic leaching was shown. While the growth of the temperature of acid treatment caused the increasing amount of leached Ge atoms and enhancing volumes of both micro and mesopores at 80℃, the mesopore volume in ITH (Si/Ge = 3.4 and 5.8) and IWW (Si/Ge = 3.3) zeolites changed with the duration of the treatment (pH = 2; T= 80℃) as follows: 96 h < 1 h < 24 h. Independently on the chemical composition and zeolite topology, the treatment of germanosilicate zeolites at pH = 2-7 resulted in development of both micro and mesoporosity accompanied by the extraction of substantial amount of Ge atoms, while the increasing acidity up to pH = 0 resulted in some reduction of Ge extraction and in the development of mesopores at maintained value of micropore volume when compared with initial germanosilicates. The higher activity (i.e. number of reactant molecules converted per active site) of germanosilicate with modified micro-mesoporous channel system in comparison with parent IWW zeolite in esterification of levulinic acid was attributed to enhanced accessibility of active sites.

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Impact of solvents and surfactants on the self-assembly of nanostructured amine functionalized silica spheres for CO2 capture Edith Berger, Maximilian W. Hahn, Thomas Przybilla, Benjamin Winter, Erdmann Spiecker, Andreas Jentys, Johannes A. Lercher 2016, 25(2): 327-335.  DOI: 10.1016/j.jechem.2016.02.005 摘要 ( 4852 )   Macroscopic SiO2 spheres with a homogeneous amine distribution were synthesized by a one-step emulsion based synthesis approach in a flow column reactor. The CO2 adsorption capacity of the nanostructured amine-functionalized silica spheres was studied in absence and presence of H2O. The structural properties were adjusted by varying solvents and surfactants during the synthesis and, at constant amine loadings, were found to be the main factor for influencing the CO2 sorption capacities. Under water-free conditions CO2 is bound to the amino groups via the formation of carbamates, which require two neighboring amino groups to adsorb one CO2 molecule. At constant amine concentrations sorbents with lower surface area allow to establish a higher amine density on the surface, which enhances the CO2 uptake capacities under dry conditions. In presence of H2O the CO2 adsorption changes to 1:1 stoichiometry due to stabilization of carbamates by protonation of H2O and formation of further species such as bicarbonates, which should in principle double the adsorption capacities. Low concentrations of physisorbed H2O (0.3 mmol/g) did not impair the adsorption capacity of the adsorbents for CO2, while at higher water uptakes (0.6 and 1.1 mmol/g) the CO2 uptake is reduced, which could be attributed to capillary condensation of H2O or formation of bulky reaction products blocking inner pores and access to active sites.

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Novel layer-by-layer assembly of rGO-hybridised ZnO sandwich thin films for the improvement of photo-catalysed hydrogen production Swe Jyan Teh, Chin Wei Lai, Sharifah Bee Abd. Hamid 2016, 25(2): 336-344.  DOI: 10.1016/j.jechem.2016.01.009 摘要 ( 4874 )   Metal oxide semiconductor materials such as ZnO have tremendous potential as light absorbers for photocatalysed electrodes in the electrochemical reduction of water. Promoters such as rGO have been added to reduce the recombination losses of charge carriers and improve its photoelectrochemical activity. In this study, the effect of layer ordering on the charge transfer properties of rGO-hybridised ZnO sandwich thin films for the photo-catalysed electrochemical reduction of water was investigated. rGO-hybridised ZnO sandwich thin films were prepared via a facile electrode position technique using a layer-by-layer approach. The thin films were analysed using FESEM, XRD, Raman, PL, UV-vis, EIS and CV techniques to investigate its morphological, optical and electrochemical properties. The FESEM images show the formation of distinct layers of rGO and ZnO nanorods/flakes via the layer-by-layer method. XRD confirmed the wurtzite structure of ZnO. PL spectroscopy revealed a reduction of photoemission intensity in the visible region (580 nm) when rGO was incorporated into the ZnO thin film. Among the six thin films prepared, ZnO/rGO showed superior performance compared to the other thin films (0.964 mA/cm) due to the presence of graphene edges which participate as heterogenous electrocatalysts in the photocatalysed electrolysis of water. rGO also acts as electron acceptor, forming an n-p heterojunction which improves the activity of ZnO to oxidise water molecules to O2. EIS revealed that the application of rGO as back contact (rGO/ZnO, rGO/ZnO/rGO) reduces the charge transfer resistance of a semiconductor thin film. Alternatively, rGO as front contact (ZnO/rGO, rGO/ZnO/rGO) improves the photo-catalysed electrolysis of water through the participation of the rGO edges in the chemical activation of water. The findings from this study indicate that the layer ordering significantly affects the thin film's electrostatic properties and this understanding can be further advantageous for tunable applications.