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SPOTLIGHT
Interview with the Leader of Global Green Chemistry: Academician Chao-Jun Li
Office of Acta Physico-Chimica Sinica Editorial
2019, 35(9): 903-904  doi: 10.3866/PKU.WHXB201903058
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摘要:
PREFACE
C―H Activation
Chao-Jun LI
2019, 35(9): 905-905  doi: 10.3866/PKU.WHXB201903057
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通讯
基于双重碳氢活化的γ, δ-不饱和酰胺与炔烃的脱氢环化反应
王珍, 李恩, 和志奇, 陈杰安, 黄湧
2019, 35(9): 906-912  doi: 10.3866/PKU.WHXB201811038
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吡啶酮是一类重要的含氮杂环骨架,广泛存在于天然产物和药物分子中,是重要的化学转化中间体,其合成与修饰是现代医药学及化学领域的研究热点之一。杂环母核的官能团化修饰是该类化合物较为常见的衍生方式,但要求特定位点的反应基团预组装。相较而言,两个片段分子的直接偶联环化,是更为直接且具备较高实用性的合成类似杂环分子库的方式。近年来,过渡金属催化的丙烯酰胺与炔烃的氧化偶联制备吡啶酮类化合物取得了长足进展,关键活化步骤为过金属催化剂对酰胺βsp2碳氢键的活化。然而,通过对更加易得的烷基酰胺进行sp3碳氢键活化制备杂环骨架依然具有较高的挑战性。其原因主要在于较低的α-酸性使得酰胺的脱氢反应变得异常困难。本课题组最近报道了温和条件下,铱催化的酰胺、酸及酮的空气脱氢反应。反应中产生的烯丙基-铱中间体被认为提高了酰胺的α-酸性,从而加速了脱氢过程。在此基础上,我们报道一种铑(III)催化的γ, δ-不饱和酰胺与炔烃类化合物的脱氢环化新方法,制备一系列多取代的吡啶酮类化合物。催化循环历经酰胺导向铑(III)对底物β位点的sp3碳氢活化,进而脱氢生成共轭的双烯酰胺中间体,随后酰胺基团再次导向铑(III)对β位的sp2碳氢活化,进而与炔烃进行插入,环化获得吡啶酮。该反应对各种官能团具有较好的容忍性。γ-烯基结构不但促进第一步的酰胺脱氢,而且是杂环产物后修饰的重要位点。机理实验表明双烯酰胺的确为反应中间体之一。核磁实验显示酰胺脱氢迅速,而控制实验则表明炔烃的插入过程的选择性与其电性有密切的关系,有可能参与了该反应的速控步。
综述
双金属促进的均相碳氢键活化反应
胡媛媛, 王从洋
2019, 35(9): 913-922  doi: 10.3866/PKU.WHXB201809036
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近年来,过渡金属催化的碳氢键活化反应得到了快速的发展,已成为构建碳碳键及碳杂原子键的重要手段之一。利用双金属之间的协同效应,发展的双金属促进的碳氢键活化反应也引起了广泛的关注,并在均相催化领域里取得了良好的应用。双金属促进的碳氢键活化反应与单金属催化的碳氢键活化反应相比,能够表现出不同的化学选择性、区域选择性以及立体选择性,体现了其独特之处。本综述总结了各种双金属促进的碳氢键活化体系,同时依据实验和理论研究结果对可能的反应机理进行了探讨。
甲烷/甲醇光催化转化研究进展
张舒怡, 鲍静娴, 吴博, 钟良枢, 孙予罕
2019, 35(9): 923-939  doi: 10.3866/PKU.WHXB201810002
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在能源需求不断上涨及石油供应日益紧张的背景下,开展对煤、天然气或生物质等非油基资源(CO、CO2、CH3OH、CH4等)的高效利用显得尤为重要。C1小分子(CO、CO2、CH3OH、CH4等)经催化转化可得到燃料及多种化学品,一直受到学术界及工业界的广泛关注。甲烷/甲醇作为重要的C1平台分子,其催化转化在C1化学中占据重要地位。为了提高目标产物的选择性,需要有效地控制甲烷/甲醇中C―H键的活化。传统热催化作为甲烷/甲醇最常见的转化方法发展已久,但仍然面临着反应条件苛刻、能耗大、产率和选择性低等问题。光催化反应通过引入光能弥补反应中吉布斯自由能的上升,同时具有反应条件温和、操作简单、能耗低等特点,从而为甲烷/甲醇转化提供了新的途径。通过调节光的波长、强度以及催化剂的氧化能力可以实现甲烷/甲醇的选择性转化,减少副产物的生成。此外,光催化能够选择性活化甲醇的C―H键而非O―H键,从而实现甲醇的C―C偶联反应。本文主要围绕甲烷/甲醇的重整、氧化和偶联反应,总结近年来的光催化转化进展,并对进一步提高光催化性能做了展望。
过渡金属参与C―H键切断模式的理论研究进展
单春晖, 白若鹏, 蓝宇
2019, 35(9): 940-953  doi: 10.3866/PKU.WHXB201810052
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摘要:
过渡金属催化活化C―H键来构建新共价键因具有原子经济和合成简捷的特点,已成为合成化学中最为有效策略之一。本文中,我们总结了过渡金属参与的C―H键切断的理论研究进展,并系统性提出了C―H键切断的相关模式,包括:C―H键对金属的氧化加成、碱协助的去质子化、σ-复分解、Friedel-Crafts型亲电芳香取代、α-或β-氢消除以及夺氢活化等。理论计算表明,当使用还原性较强的零价金属催化剂时,反应可按照氧化加成模式进行。当使用金属羧酸盐作为催化剂时,通常以协同金属化-去质子化机理模式实现C―H键切断。当使用阳离子金属催化剂,富电子芳烃比缺电子芳烃优先反应时,C―H键切断则会经历碱协助的内部亲电取代模式。σ-复分解是协同金属化-去质子化机理的另一种模式。如果亲电体对芳烃进行加成时,则可按照Friedel-Crafts型亲电芳香取代方式活化C―H键。α-或β-氢消除也是比较常见的活化C―H键模式。此外,夺氢活化可通过自由基过程实现C―H键活化。本文通过对过渡金属参与的C―H键活化模式的论述旨在为实验提供理论指导。
C-H官能化构建硫醚
陈世豪, 王明, 姜雪峰
2019, 35(9): 954-967  doi: 10.3866/PKU.WHXB201810044
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硫醚作为一类重要的含硫功能分子,广泛存在于天然产物、药物及有机发光材料中。鉴于硫醚类化合物的重要性,近年来化学家们发展了一系列高效构建硫醚的方法。与传统的有机卤化物/有机硼酸与硫醇交叉偶联的合成方法相比,C―H官能化直接构建硫醚的策略因其步骤经济性、原子经济性备受合成化学家们关注,并取得重要进展。本文根据不同过渡金属进行分类,系统阐述了近年来过渡金属催化/参与C―H官能化或无过渡金属催化C―H官能化构建硫醚这一方向研究进展。
室温光驱动甲烷活化
母晓玥, 李路
2019, 35(9): 968-976  doi: 10.3866/PKU.WHXB201810007
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如何在较温和的条件下将甲烷转化为其它更有价值的有机衍生物,如醇、芳烃、长链烷烃和烯烃等,长期以来是催化、化学及化工领域的热点课题和难点课题之一。为了提高甲烷的转化效率,过去几十年里,研究人员不断开发新的催化剂和新的反应路径。与传统高温热催化方法相比,如果能利用自然界中丰富的太阳能驱动甲烷转化,将同时满足能源和环保两方面的要求,是各种新型非常规策略中比较令人期待的一种。本文从光催化材料的组成、结构及催化路线、催化机制等方面进行总结,对当前室温光活化甲烷分子的研究现状加以论述。
普通烷烃C―H键的活化官能化
赵梦迪, 陆文军
2019, 35(9): 977-988  doi: 10.3866/PKU.WHXB201811045
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普通烷烃C―H键是指不受杂原子和碳不饱和官能团影响的sp3C―H键,如甲烷、链烷烃和环烷烃的C―H键等。它们具有较大的键能和较小的酸碱性,因而呈现惰性,通常不易在温和条件下发生断裂。同时,除个别烷烃以外,普通烷烃往往具有不同性质和不同位置的C―H键,其反应选择性也是一个难点。近半个世纪以来,金属参与的惰性C―H键活化及官能化反应得到了重视与发展。其中,在没有官能团导向作用下,过渡金属催化剂对甲烷C―H键和普通烷烃一级C―H键进行选择性亲电活化和氧化加成,从而导致官能化反应发生是比较有效的。本文介绍了这些方法的研究进展,包含机理分析以及相关反应的建立。
多功能氧酰胺导向基在碳氢键活化反应中的研究进展
朱月路, 赵鑫阳, 吴谦, 陈颖, 赵劲
2019, 35(9): 989-1004  doi: 10.3866/PKU.WHXB201812016
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近年来,通过导向基团进行碳氢键活化构建C―C键及C―X键的方法得到了快速发展,已成为有机合成的重要手段之一。在碳氢键活化中,作为多功能导向基团之一的氧酰胺,由于其独特的性质,引起了科学家们的广泛关注。氧酰胺中O―N键的氧化性替代外部氧化剂,使反应处于氧化还原中性。加入化学计量的外部氧化剂,通常可以使O―N键得到保留。在不同的溶剂中,能够表现出不同的区域选择性和立体选择性;皆体现了氧酰胺作为导向基团的独特之处。本文综述了N-苯氧基酰胺作为底物进行碳氢键活化的研究进展,同时根据现有的实验和理论研究结果对不同反应的机理进行了探讨。
论文
单个金或银原子掺杂的氧化钒团簇上的甲烷活化反应
王丹, 丁迅雷, 廖珩璐, 戴佳钰
2019, 35(9): 1005-1013  doi: 10.3866/PKU.WHXB201809006
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运用密度泛函理论系统研究了甲烷在MV3Oyq (M = Au/Ag,y = 6–8,q = 0或±1)团簇上的吸附和活化。研究得到了吸附体系的微观几何构型、吸附能、电荷分布等性质,找到了5个可以明显活化甲烷分子的含Au团簇。在这些体系中,Au均吸附在基底团簇V3Oyq的O位置,而CH4均在Au原子上被活化。团簇电荷对活化能力有明显影响,阳离子团簇的活化能力最强,中性体系次之,阴离子团簇的活化能力很弱。测试计算表明引入D3色散矫正对于体系结构和能量的计算结果影响不大。本文作为单原子催化剂上甲烷吸附和活化反应的团簇模型研究,为进一步研究单原子催化剂上甲烷的活化机理提供了基础,也为合理设计低温下甲烷转化的单原子催化剂提供了有益的线索。
ARTICLE
Thermal Activation of Methane by Diatomic Vanadium Boride Cations
Qiang CHEN, Li-Xue JIANG, Hai-Fang LI, Jiao-Jiao CHEN, Yan-Xia ZHAO, Sheng-Gui HE
2019, 35(9): 1014-1020  doi: 10.3866/PKU.WHXB201811039
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摘要:
Methane activation by transition metal species has been extensively investigated over the past few decades. It is observed that ground-state monocations of bare 3d transition metals are inert toward CH4 at room temperature because of unfavorable thermodynamics. In contrast, many mono-ligated 3d transition metal cations, such as MO+ (M = Mn, Fe, Co, Cu, Zn), MH+ (M = Fe, Co), and NiX+ (X = H, CH3, F), as well as several bis-ligated 3d transition metal cations including OCrO+, Ni(H)(OH)+, and Fe(O)(OH)+ activate the C―H bond of methane under thermal collision conditions because of the pronounced ligand effects. In most of the above-mentioned examples, the 3d metal atoms are observed to cooperate with the attached ligands to activate the C―H bond. Compared to the extensive studies on active species comprising of middle and late 3d transition metals, the knowledge about the reactivity of early 3d transition metal species toward methane and the related C―H activation mechanisms are still very limited. Only two early 3d transition metal species HMO+ (M = Ti and V) are discovered so far to activate the C―H bond of methane via participation of their metal atoms. In this study, by performing mass spectrometric experiments and density functional theory calculations, we have identified that the diatomic vanadium boride cation (VB+) can activate methane to produce a dihydrogen molecule and carbon-boron species under thermal collision conditions. The strong electrostatic interaction makes the reaction preferentially proceed the V side. To generate experimentally observed product ions, a two-state reactivity scenario involving spin conversion from high-spin sextet to low-spin quartet is necessary at the entrance of the reaction. This result is consistent with the reported reactions of 3d transition metal species with CH4, in which the C―H bond cleavage generally occurs in the low-spin states, even if the ground states of the related active species are in the high-spin states. For VB+ + CH4, the insertion of the synergetic V―B unit (rather than a single V or B atom) into the H3C―H bond causes the initial C―H bond activation driven by the strong bond strengths of V―CH3 and B―H. The mechanisms of methane activation by VB+ discussed in this study may provide useful guidance to the future studies on methane activation by early transition metal systems.
DPPF-Mediated C―H Arylation of Arenes with Aryl Iodides for Synthesis of Biaryl Linkages
Qingbing WANG, Zhengwei GUO, Gong CHEN, Gang HE
2019, 35(9): 1021-1026  doi: 10.3866/PKU.WHXB201811044
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The broad existence of the biaryl linkage in bioactive organic molecules and functional materials makes it an attractive synthesis target via construction of aryl-aryl carbon bonds. Transition metal catalyzed cross-coupling reactions of two pre-functionalized aryl partners, e.g., Suzuki-Miyaura cross-coupling and Negishi cross-coupling reactions, are the main methods typically used for the construction of biaryl linkages. Since the end of the last century, transition metal catalyzed direct C-H arylation of unactivated arenes has emerged as a practical alternative to the well-established cross-coupling strategies. However, the use of transition metal catalysts and/or organometallic reagents would lead to problems, such as the disposal of waste from large-scale syntheses and the removal of heavy metal contaminants from pharmaceutical intermediates. In this regard, the base-promoted homolytic aromatic substitution (BHAS) reaction of aryl halides with unactivated arenes offers a simpler strategy for the synthesis of biaryl scaffolds, and avoids the use of transition metals. Although the BHAS reaction can proceed to a small extent without any additives, particularly at elevated temperatures, the addition of organic promoters would significantly accelerate the reaction rate and improve the overall efficiency of the process. Over the past ten years, a wide variety of N- and O-based organic promoters have been developed to promote the BHAS reaction in the presence of the tert-butoxide base. The mechanism of the BHAS reaction has been studied extensively, and is accepted as occurring via a radical chain process involving an aryl radical. However, the role and mode of initiation of most organic promoters studied remain controversial. The development of more and varied organic promoters will surely promote the mechanistic understanding and further development of the BHAS reaction. Herein, we report that 1, 1'-bis(diphenylphosphino)ferrocene (dppf, or DPPF) can act as a P-based promoter to facilitate the direct arylation of unactivated arenes with aryl iodides using potassium tert-butoxide as the base and electron donor. A broad range of aryl iodides and arenes reacted smoothly under the optimized reaction conditions, giving arylated products in good yields and with high regio-selectivity. Intramolecular C-H arylation also worked well following a sequence of single electron transfer (SET)/initiation, 5-exo-trig aryl radical addition, ring expansion, deprotonation, and re-aromatization/propagation. A mechanistic study indicated that the diphenylphosphino group of dppf played a vital role in the initiation step by enhancing the SET-inhibiting ability of the tert-butoxide anion. A primary kinetic isotope effect was observed in the parallel reactions between 4-methoxy-iodobenzene with benzene and deuterated benzene, implying that the deprotonation of the cyclohexadienyl radical intermediate by tert-butoxide was the rate-determining step in the radical chain pathway.
Influence of the Composition/Texture of Solid Acid WO3/TiO2-Supported Lithium-Manganese Catalysts on the Oxidative Coupling of Methane
Fei CHENG, Jian YANG, Liang YAN, Jun ZHAO, Huahua ZHAO, Huanling SONG, Lingjun CHOU
2019, 35(9): 1027-1036  doi: 10.3866/PKU.WHXB201902004
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摘要:
The selective oxidation of methane to basic petrochemicals (ethylene and ethane) is desirable and has attracted extensive research attention. The oxidative coupling of methane (OCM) is considered a promising one-step route for the production of C2 compounds (ethylene and ethane) from methane, and has been the focus of industrial and fundamental studies. It is widely accepted that the composition is a crucial factor governing the activity of a catalyst system. It was found that the phase structures, basicity, existing status and distribution of the active components, oxygen species, and chemical states of the catalyst were influenced by the composition and ratio, resulting in different catalytic performances for the OCM. In this study, a series of solid acid WO3/TiO2-supported lithium-manganese oxide catalysts for OCM were synthesized via the impregnation method. The impacts of diverse compositions, such as the individual contents (Li and Mn) and dual contents (Li-Mn), on the OCM were investigated in detail, using inductively coupled plasma optical emission spectrometry, X-ray diffraction, high-resolution transmission electron microscopy, CO2-temperature-programmed desorption, O2-temperature-programmed desorption, H2-temperature-programmed reduction, Raman spectroscopy, X-ray photoelectron spectroscopy, and CH4-temperature-programmed surface reaction. The addition of Li content to the catalyst not only led to the anatase-to-rutile crystal structure transformation of TiO2, and the reduction of the high-valence-state Mn species to low-valence-state Mn, but also increased the content of surface lattice oxygen and decreased the surface basicity. The observed effects on the structures and catalytic performance suggest that the Li content is helpful in suppressing the formation of completely oxidized CO2, and increases the C2 selectivity. Moreover, increasing the Li content of the catalyst facilitated the mobility of the lattice oxygen, which triggered the promotion of CH4 activation, thereby enhancing the OCM catalytic performance. The Mn content acted as the active sites for OCM; therefore, the performance of the catalyst was closely related to the Mn concentration and valence state. However, the WO3/TiO2-supported catalyst with excessive Mn content exhibited a high surface basicity, high valence state of Mn, and low abundant lattice oxygen, which was unfavorable for C2 selectivity. The Raman spectroscopy results revealed that MnTiO3 was formed due to the co-existence of Li and Mn on WO3/TiO2, and played an essential role in improving the low-temperature OCM performance. There was a synergic effect of the Li and Mn components on the OCM. The optimal performance (16.3% C2 yield) was achieved over the WO3/TiO2-supported lithium-manganese catalyst with n(Li) : n(Mn) = 2 : 1 at 750 ℃.

亮点
同分异构的胶体硫化镉半导体幻数团簇的可逆转化
刘忠范
2019, 35(5): 451-452  doi: 10.3866/PKU.WHXB201807016
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异原子占据Ag原子簇的中心核用于催化CO2生成碳碳键的反应
侯文华
2019, 35(5): 453-454  doi: 10.3866/PKU.WHXB201807017
[摘要]  (119) [HTML全文] (119) [PDF 659KB] (119)
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基于Au@PPy核壳结构纳米粒子自组装阵列的可程序化负微分电阻效应研究
韩布兴
2019, 35(5): 455-456  doi: 10.3866/PKU.WHXB201807063
[摘要]  (126) [HTML全文] (126) [PDF 597KB] (126)
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庄林
2019, 35(5): 457-458  doi: 10.3866/PKU.WHXB201807065
[摘要]  (173) [HTML全文] (173) [PDF 327KB] (173)
摘要:
电荷驱动水中氧化物纳米颗粒自组装的原位透射电子显微镜研究
吴凯
2019, 35(5): 459-460  doi: 10.3866/PKU.WHXB201807077
[摘要]  (129) [HTML全文] (129) [PDF 250KB] (129)
摘要:
综述
有机太阳能电池中基于苝二酰亚胺结构小分子受体进展
邓祎华, 彭爱东, 吴筱曦, 陈华杰, 黄辉
2019, 35(5): 461-471  doi: 10.3866/PKU.WHXB201806073
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摘要:
最近几年,有机太阳能电池中的非富勒烯小分子受体研究引起了人们的兴趣。其中,苝二酰亚胺(PDI)类分子因具有良好的电子传输能力,较强的电子亲和力,稳定的光、热、化学性能以及化学结构的可设计性带来的性能可调控性而得到广泛的关注。本文总结了近三年来在体异质结有机太阳能电池应用方面PDI小分子受体的研究进展,重点关注了PDI分子结构对其性能的影响,希望为以后PDI类受体分子的设计思路起到一定的启发作用。
碳基非贵金属氧还原电催化剂的活性位结构研究进展
杨晓冬, 陈驰, 周志有, 孙世刚
2019, 35(5): 472-485  doi: 10.3866/PKU.WHXB201806131
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摘要:
以热解型Fe/N/C为代表的碳基非贵金属材料被认为是当前最具潜力替代铂的非贵金属氧还原催化剂,其综合性能的进一步突破,对于推动质子交换膜燃料电池商业化应用具有重要意义。对热解型Fe/N/C催化剂活性位结构的深入认识是实现催化剂高活性位密度和高稳定性理性设计的关键。本文总结了热解型Fe/N/C活性位的研究进展,重点介绍了非晶态铁氮配位活性中心、氮掺杂和碳缺陷三类活性位构型。由于热解型Fe/N/C是非均相的,结构非常复杂,导致在活性位认识上还存在诸多争议,本文总结阐述了活性位结构的不同观点。最后,我们展望了Fe/N/C催化剂活性位研究的未来方向。
论文
正十二烷高温机理简化及验证
卢海涛, 刘富强, 王于蓝, 王成冬, 范雄杰, 刘存喜, 徐纲
2019, 35(5): 486-495  doi: 10.3866/PKU.WHXB201806081
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摘要:
由于详细化学反应机理在模拟燃烧室燃烧时,计算量极大,很难被广泛运用。为了满足工程设计要求,采用替代燃料的简化机理进行计算不失为一种行之有效的方法。本文基于误差传播的直接关系图法和敏感性分析法对正十二烷180组分1962步高温机理(温度大于1100 K)进行简化,获得40组分234步化学反应机理。在温度为1100–1650 K,压力为0.1–4 MPa条件下,采用简化机理及详细机理对不同当量比、压力下着火延迟时间进行模拟,模拟结果与实验数据吻合得较好。通过对不同压力及温度下火焰传播速度进行模拟,验证了简化机理能够正确地反映正十二烷的燃烧特性。利用C12H26/OH/H2O/CO2等重要组分随时间变化的数据,验证了简化机理能够准确描述燃烧过程反应物消耗、基团变化、生成物产生的过程,并表明该机理具有较高的模拟精度。利用该简化机理对本生灯进行数值分析,结果表明该机理能够准确地反映火焰区温度和组分浓度的变化。紧凑的正十二烷高温简化机理不仅能够正确体现其物理化学特性,而且能够用于三维数值模拟,具有较高的工程运用价值和应用前景。
固体氧化物燃料电池电化学阻抗谱差异化研究方法和分解
施王影, 贾川, 张永亮, 吕泽伟, 韩敏芳
2019, 35(5): 509-516  doi: 10.3866/PKU.WHXB201806071
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电化学阻抗谱技术(EIS)在固体氧化物燃料电池(SOFC)中已获得广泛应用。在EIS分析过程中,研究者能够清楚地获得燃料电池内部因纯离子(电子)导电引起的欧姆电阻和因电化学过程、扩散作用引起的极化阻抗的大小,但是对于极化阻抗的构成缺乏进一步解析。本文选用传统的Ni-YSZ阳极支撑电池,通过改变测试温度、阳极运行气氛和阴极运行气氛,设计了一套完整的阻抗差异分析(ADIS)实验。并基于弛豫时间分布法(DRT)和阻抗差异分析法,系统地分析并解释了阻抗谱中各频率段对应阻抗的物理或(电)化学含义,将该类型电池阻抗谱以6个RQ并联电路予以拟合,为之后燃料电池性能稳定性的研究奠定基础。
原位透射电子显微镜观察电荷驱动的氧化物纳米颗粒水中自组装
赵喆, 卢岳, 张振华, 隋曼龄
2019, 35(5): 539-545  doi: 10.3866/PKU.WHXB201806012
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摘要:
以四氧化三钴Co3O4纳米棒为研究对象,我们利用液体环境透射电子显微镜,原位观察了四氧化三钴纳米棒在水中的自组装过程。研究发现在电子束辐照的水环境下,四氧化三钴纳米棒的晶面存在互补式自组装现象。随着纳米棒之间的距离越来越近,纳米棒之间的相对运动速率逐渐增加,纳米棒之间的相互作用力逐渐增加。通过进一步分析纳米棒的形貌发现,纳米棒的暴露晶面大多数为{100}、{110}以及{111}晶面,而Co3O4属于极性氧化物,这些晶面往往会带有一定的电荷。在液体环境下,正是由于这些易暴露面都带有不同大小的电荷,在晶面电荷的驱动下,电荷属性相反的四氧化三钴纳米棒会互相吸引,形貌结构上进行互补,实现快速驱动的纳米棒之间自组装。
ARTICLE
Perylenediimide: Phosphonium-Based Binary Blended Small-Molecule Cathode Interlayer for Efficient Fullerene-Free Polymer Solar Cells with Open Circuit Voltage to 1.0 V
Monika GUPTA, Dong YAN, Fugang SHEN, Jianzhong XU, Chuanlang ZHAN
2019, 35(5): 496-502  doi: 10.3866/PKU.WHXB201805101
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摘要:
The fabrication of high-efficiency organic solar cells requires a cathode interlayer (CIF) having multiple properties such as forming an ohmic contact with the active layer, high electron conductivity, low-density traps, and hole blocking. These roles can be more completely fulfilled by using a suitable binary blended CIF rather than a single molecule based CIF. In this article, we present the roles by using binary blended PDINO (amino N-oxide perylene diimide) and QPhPBr (tetraphenylphosphonium bromide) as the CIF to fabricate fullerene-free polymer solar cells (PSCs) with PBDB-T:IDTBR, a new donor: acceptor combination, as the active layer. The high-lying lowest unoccupied molecular orbital of the acceptor and the low-lying highest occupied molecular orbital (HOMO) of the polymer with small driving force (the donor-acceptor HOMO-HOMO energy offset, ∆HOMO) for the hole transfer, both result in a high open circuit voltage (Voc). Moreover, our strategy to insert a dual mixed solution of CIF over the blended active layer better facilitates the role, which significantly improves charge extraction and collection, leading to the high Voc, short-circuit current density (Jsc), and fill factor (FF) observed in comparison to a single CIF material. It was observed that the power conversion efficiency (PCE) increases to 8.27%, with a high Voc of 1.0 V, using a binary mixture of CBL. Such tremendous improvements in Voc using well known polymer donors have not been reported till date in binary solar cell systems. This idea demonstrates that the minimum energy loss because of the small ∆HOMO of the D-A combination and the use of a dual mixed layer of CBL together present the future prospects of non-fullerene photovoltaic devices for researchers.
Bandgap Modulation of Dithienonaphthalene-Based Small-Molecule Acceptors for Nonfullerene Organic Solar Cells
Meiqi ZHANG, Yunlong MA, Qingdong ZHENG
2019, 35(5): 503-508  doi: 10.3866/PKU.WHXB201805151
[摘要]  (109) [HTML全文] (109) [PDF 1889KB] (109)
摘要:
By using photovoltaic technology, ambient solar light can be directly converted to electricity. The photovoltaic technology has been regarded as one of the most important and promising strategies to resolve the worldwide energy and pollution problems. As one type of photovoltaic technology, polymer solar cells have attracted increasing interest due to their advantages of solution processing capability, low-cost, feasibility to be fabricated on flexible substrates etc. Not until a few years ago, the fullerene derivatives had been dominated the organic photovoltaic field as the most promising acceptor materials for polymer solar cells. However, fullerene-based polymer solar cells have a power conversion efficiency bottleneck due to the relatively fixed energy levels as well as the fixed bandgaps of fullerene derivatives. Therefore, researchers started to develop nonfullerene acceptors which can be used as alternatives to replace the traditional fullerene derivatives. Compared to the fullerene derivatives, nonfullerene acceptors offer several advantages such as stronger light absorption, tunable bandgaps and frontier molecular orbital energy levels. For nonfullerene acceptors, a ladder-type fused ring is usually used as the central core which is an essential building block to tailor the bandgaps and energy levels. Although many fused ring systems have been explored for efficient nonfullerene acceptors, ladder-type angular-shape dithienonaphthalene is seldom reported as the donor unit for nonfullerene acceptors. Furthermore, the impact of thiophene bridge on the optical and photovoltaic properties of the dithienonaphthalene-based nonfullerene acceptors has never been reported. In this context, we report on the design and synthesis of a dithienonaphthalene-based small-molecule acceptor which contains thiophene bridges in between the acceptor terminals and the fused-ring donor core. Compared to the dithienonaphthalene-based small-molecule without the thiophene bridges, the resulting acceptor (DTNIT) exhibits a reduced bandgap of 1.52 eV which makes it more suitable to be blended with the benchmark large bandgap copolymer, poly[(2, 6-(4, 8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1, 2-b: 4, 5-b']dithiophene))-alt-(5, 5-(1', 3'-di-2-thienyl-5', 7'-bis(2-ethylhexyl)benzo[1', 2'-c:4', 5'-c']dithiophene-4, 8-dione)] (PBDB-T). The reduced band-gap of the resulting nonfullerene acceptor can be attributed to its extended π-conjugation in comparison with the dithienonaphthalene-based acceptor without the thiophene bridges. Inverted polymer solar cells with a device configuration of indium tin oxide/ZnO/PBDB-T:DTNIT/MoO3/Ag were fabricated and characterized. Polymer solar cells based on PBDB-T:DTNIT showed an open circuit voltage of 0.91 V, an enhanced short circuit current of 14.42 mA∙cm−2, and a moderate PCE of 7.05% which is comparable to the PCE of 7.12% for the inverted device based on PBDB-T:PC71BM. Our results not only provide a method to synthesize efficient nonfullerene acceptors with reduced bandgaps, but also offer a bandgap modulation strategy for nonfullerene acceptors.
Effect of Ink Solvents on Low-Pt Loading Proton Exchange Membrane Fuel Cell Performance
Wenhui CHEN, Shengli CHEN
2019, 35(5): 517-522  doi: 10.3866/PKU.WHXB201806011
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Owing to the scarcity of platinum, it is of high importance to develop electrodes with low platinum metal loading and to thereby improve the utilization of Pt for the commercialization of proton-exchange membrane fuel cells (PEMFCs). In comparison to conventional high-platinum electrodes, the thickness of the catalyst layer (CL) is thinner and the interatomic Pt spacing is larger for the low-Pt loading electrodes. The distribution of electrolyte ionomer and the electrode morphology, which are strongly influenced by the solvents used in the fabrication process, are therefore increasingly important factors for achieving high performance in the membrane electrode assembly (MEA). In this work, different solvents with various dielectric constants and evaporation rates were used to prepare the inks for low-Pt loading cathode (0.1 mg·cm-2) fabrication. First, the inks were fabricated by dispersing the catalyst and ionomer in different solvents which were then coated onto carbon paper to prepare the gas diffusion electrodes. The anode and cathode electrodes were then hot-pressed together with the Nafion membrane to produce the MEAs. The results showed a mixture of isopropanol-water (4:1) yielded the best-performing MEA during the single-cell tests compared to the other solvents tested. In order to elucidate the relationship between the performance of MEAs and the solvents, the structure and the surface morphology of the CL and the distribution of Nafion ionomer in the CL was characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A comparison of the SEM and TEM images of representative samples indicated that the best performing electrode had a much improved homogeneity in the surface morphology as well as the dispersion of catalyst and ionomer. This was because of the moderate evaporation rate and better dispersion, caused by the increased hydrogen bonding and high dielectric constant, respectively. The results from dynamic light scattering (DLS) showed that the size of the catalyst and ionomer aggregates are influenced by the solvents. It is suggested that larger aggregates might help the formation of holes in the CL for gas diffusion and water removal, with the optimum size found to be around 400–800 nm. In conclusion, the MEA fabricated from the isopropanol-water solvent exhibited a significantly increased power density (1.79 W·cm-2), and the utilization of Pt was increased to approximately 0.047 mg·W-1, which is among the best-performing fuel cells reported to date.
Molybdenum Carbide Prepared by a Salt Sealing Approach as an Electrocatalyst for Enhanced Hydrogen Evolution Reaction
Zhou LIN, Linfan SHEN, Ximing QU, Junming ZHANG, Yanxia JIANG, Shigang SUN
2019, 35(5): 523-530  doi: 10.3866/PKU.WHXB201806191
[摘要]  (160) [HTML全文] (160) [PDF 1571KB] (160)
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Molybdenum carbide is regarded as an excellent substitute for Pt-based catalysts in the hydrogen evolution reaction (HER), owing to its low cost, superior catalytic performance, and long-term stability. In this work, salt-sealed molybdenum carbide was prepared using sodium molybdate and 2, 6-diaminopyridine as the reactive raw materials, followed by continuous salt sealing and calcination of the precursor under an inert atmosphere. The morphology, composition and structure of salt-sealed molybdenum carbide were determined by scanning electron microscopy, transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The results indicate that salt-sealed molybdenum carbide has irregular morphology and includes nanoparticles and nanorods. A comparison of the TEM images of Mo2C with salt sealing (Mo2C/SS) and Mo2C without salt sealing (Mo2C) indicates that Mo2C/SS exhibits a smaller particle size. This suggests that salt sealing can efficiently avoid particle aggregation. The Brunauer-Emmett- Teller (BET) specific surface area of the catalysts was obtained from nitrogen adsorption/desorption isotherms. The increase in BET surface area from 2.55 to 8.14 m2·g−1 after salt sealing provides evidence for the formation of pores in the product. The results of XRD, EDS and XPS analyses show that Mo2C/SS has an orthorhombic crystal structure with molybdenum oxides on the surface, which may originate from surface oxidation. Considering the results of XPS and the turnover frequency (TOF) calculation, we can conclude that the formation of pores via salt sealing contributes to the exposure of more active sites, while simultaneously enlarging the contact area with oxygen. Therefore, higher molybdenum oxide content is generated on the surface, resulting in a lower proportion of active centers (molybdenum carbides) on the catalyst surface. Furthermore, the pseudocapacitance generated by the faradaic reaction of molybdenum oxides is superimposed on the double-layer capacitance of Mo2C catalysts, which increases the double layer capacitance. Since the effect of pseudo-capacitance on Mo2C/SS is more significant, the TOF number declines after salt sealing. Compared with Mo2C, Mo2C/SS exhibits three features that promote HER mass activity: (1) the generation of large quantities of pores via salt sealing leads to an increase in the BET surface area and exposure of more active sites, which is beneficial for improving HER performance; (2) the porous structure and enlarged surface area pave the way for effective mass and charge transfer; (3) the decrease of the Tafel slope from 145 to 88 mV·dec−1. In summary, salt-sealed Mo2C exhibited enhanced HER activity with an overpotential of 175 mV to achieve a current density of 10 mA·cm−2. The Tafel slope for HER on salt-sealed Mo2C is 88 mV·dec−1. This can be considered as the proof of the Volmer-Heyrovsky mechanism with electrochemical desorption as the rate-determining step.
Reactivities of VO1–4+ Toward n-CmH2m+2 (m = 3, 5, 7) as Functions of Oxygen Content and Carbon Chain Length
Yue ZHAO, Jiatong CUI, Jichuang HU, Jiabi MA
2019, 35(5): 531-538  doi: 10.3866/PKU.WHXB201805231
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Vanadium oxides are one of the most important heterogeneous catalysts that are widely used to oxidize hydrocarbon molecules into value-added chemicals. In order to reveal the mechanisms and the nature of active sites, numerous experimental and theoretical studies have been reported on the reactivities of gas-phase vanadium oxide clusters toward small molecules. However, there has been very limited research on the chemical reactivity changes associated with the oxygen contents of vanadium oxides and the carbon chain lengths of alkanes. In this work, the reactions of vanadium oxide ions VO1−4+ with alkanes (n-CmH2m+2, m = 3, 5, 7) were systematically investigated by time-of-flight mass spectrometry and the reactions of VO1−3+ with pentane were further studied by density functional theory calculations. Experimental results show that in the reactions of VO+, VO3+, and VO4+ with n-C5H12, in addition to the major adsorption processes, the activation of the C―H and C―C bonds of n-C5H12 was observed. The activation of both the bonds was observed experimentally during the reaction of VO2+ with n-C5H12 with large branching ratios. Among the vanadium oxide cations studied, VO2+ shows the strongest oxidizability and the generation of lighter alkanes and alkenes dominates the reactions; VO+ is more reactive than VO3+. VO4+ pocesses only one η2-O2 unit. Due to the weak bond between VO2+ and η2-O2, the η2-O2 unit is released in VO4+/n-C5H12 system leading to the formation of VO2+; thus VO4+ cations reflect some reactivity of VO2+. Although the oxidation states in the vanadium oxide clusters increase from +Ⅲ in VO+ to +Ⅴ in VO2+ and +Ⅳ in VO3+, the reactivity does not gradually increase. Moreover, the reactivity of the mononuclear vanadium oxide cations also does not exhibit a gradually increasing trend with the increase in oxygen content. Based on the observed reactivity trend, the adsorption channels gradually become weak as the carbon chain lengths increase; meanwhile, the dehydrogenation and C―C bond activation channels gradually become obvious and some oxygen transfer products appear. Therefore, much lighter fragments of alkanes/alkenes will be obtained if linear alkanes with more carbon atoms were reacted with VO1−4+. The theoretical results are generally consistent with those obtained from the experiments. The various reaction channels and versatile reactivity of the mononuclear vanadium oxide cations investigated in this study not only offer new insights into gas-phase reactions but also shed light on the processes occurring on the surfaces of the corresponding condensed-phase catalysts.
Single-Molecule Study on the Folding of OmpT in Tween-20 Micelles
Peixuan BU, Chenhui HE, Xinsheng ZHAO
2019, 35(5): 546-554  doi: 10.3866/PKU.WHXB201806072
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摘要:
The cell envelope of gram-negative bacteria consists of the outer membrane (OM), inner membrane (IM), and periplasm. The β-barrel outer membrane proteins (OMPs) embedded in the OM perform diverse and significant functions such as signaling, transporting, and proteolysis. The OMPs of gram-negative bacteria share similar folding pathways with that of mitochondria and chloroplasts. Therefore, the study of the OMP folding mechanism not only provides insights into antimicrobial drug design but also helps elucidate mitochondrial and chloroplast biogenesis. Most knowledge about OMP folding was obtained from ensemble experiments where OMPs were usually at micromolar concentrations and prone to aggregate, which is different from the physiological environment in the cells. Unlike ensemble techniques, single-molecule detection (SMD) can measure OMPs from nano- to picomolar concentrations and prevent aggregation. In this work, we investigated the folding of OmpT, one of the OMPs, in Tween-20 and n-dodecyl β-d-maltopyranoside (DDM) micelles by SMD. We prepared monodisperse OmpT and observed both unfolded and folded OmpT in Tween-20 and DDM micelles under different urea concentrations by single-molecule fluorescence resonance energy transfer (FRET). The folded OmpT in Tween-20 is structurally similar to the native OmpT folded in DDM but exhibits weaker resistance to urea. In contrast, OmpA barely folds and OmpC hardly folds in Tween-20 micelles. We confirmed that folded OmpT forms complexes with detergent micelles and estimated the number of bound Tween-20 and DDM molecules per OmpT by fluorescence correlation spectroscopy. We compared the enzymatic activity of OmpT folded in two detergents with a fluorescent peptide as substrate, and found that the folded form of OmpT in Tween-20 possesses weaker enzymatic activity than that in DDM. We also investigated the folding properties of OmpT, OmpA, and OmpC in the presence of the β-barrel assembly machine (BAM) complex. OmpT folds efficiently in liposome even without the BAM complex; OmpA only folds with the help of the BAM complex; and OmpC does not fold with or without the BAM complex. Based on the comparison of the folding of OmpT, OmpA, and OmpC in detergent micelles and in the presence of the BAM complex, we propose that OmpT has stronger folding tendency than OmpA and OmpC, which supports the idea that the exact role of the BAM complex is dependent on the distinct folding properties of individual OMPs. Since Tween-20 is a widely used reagent to block nonspecific adsorption in SMD experiments, our results also remind people to exercise caution to prevent possible wrong interpretations caused by the interaction between proteins and Tween-20.

编委会

发布时间:


《物理化学学报》第4届编委会

(按拼音排序)

名誉主编

唐有祺

北京大学

顾问编委

包信和

中国科学院大连化学物理研究所

段雪

北京化工大学

付贤智

福州大学

侯建国

中国科学技术大学

黄维

南京工业大学

LIEBER Charles M.

Harvard University

田中群

厦门大学

万立骏

中国科学院化学研究所

吴云东

北京大学

谢晓亮

Harvard University, 北京大学

杨伟涛

 Duke University

姚建年

中国科学院化学研究所

赵新生

北京大学

主编

刘忠范

北京大学

副主编

韩布兴

中国科学院化学研究所

刘鸣华

国家纳米科学中心

申文杰

中国科学院大连化学物理研究所

吴凯

北京大学

杨金龙

中国科学技术大学

庄林

武汉大学

迟力峰

苏州大学

编委

曹勇

复旦大学

陈经广

University of Delaware

陈军

南开大学

崔屹

Stanford University

邓风

中国科学院武汉物理与数学研究所

邓友全

中国科学院兰州化学物理研究所

樊卫斌

中国科学院山西煤炭化学研究所

房喻

陕西师范大学

付红兵

中国科学院化学研究所

傅强

中国科学院大连化学物理研究所

高毅勤

北京大学

郭林

北京航空航天大学

郝京诚

山东大学

侯文华

南京大学

金荣超

Carnegie Mellon University

来鲁华

北京大学

李朝军

McGill University

李隽

清华大学

李象远

四川大学

梁万珍

厦门大学

刘海超

北京大学

刘洪来

华东理工大学

刘述斌

University of North Carolina

刘义

武汉大学

刘志敏

中国科学院化学研究所

罗小民

中国科学院上海药物研究所

马晶

南京大学

孟庆波

中国科学院物理研究所

邵翔

中国科学技术大学

孙俊奇

吉林大学

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湖南大学

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国家纳米科学中心

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河南师范大学

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中国科学院长春应用化学研究所

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福州大学

王永锋

北京大学

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重庆大学

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中国科学院物理研究所

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华东师范大学

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复旦大学

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National University of Singapore

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国家自然科学基金委员会

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武汉理工大学

尉志武

清华大学

占肖卫

北京大学

张东辉

中国科学院大连化学物理研究所

张浩力

兰州大学

张锦

北京大学

章俊良

上海交通大学

周永贵

中国科学院大连化学物理研究所

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发布时间: 2018-05-02


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发布日期:2009-06-24 浏览: