Science, 12 MAY 2023, VOL 380, ISSUE 6645
《科学》2023年5月12日，第380卷，6645期
天文学Astronomy
Optical polarization from colliding stellar stream shocks in a tidal disruption event
潮汐破坏事件中碰撞恒星流冲击产生的光学偏振
▲ 作者：I. LIODAKIS, K. I. I. KOLJONEN, D. BLINOV, E. LINDFORS, K. D. ALEXANDER, T. HOVATTA, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.abj9570
▲ 摘要：
当一个超大质量黑洞撕裂一颗经过的恒星时，就会发生潮汐破坏事件（TDE）。部分恒星物质落入黑洞，形成吸积盘，在某些情况下会发射相对论性喷流。
研究组对一场TDE（AT 2020mot）进行了偏振光测量。结果发现峰值线性偏振度为25±4%，与高度偏振的同步辐射一致，这通常可从相对论性喷流中观察到。然而，该射电观测在光学峰值后长达8个月的时间里，并没有探测到预期来自相对论性喷流的相应射电发射。
研究组认为，当恒星物质流与其自身发生碰撞时，线性偏振光发射由吸积盘形成过程中发生的冲击引发。
▲ Abstract：
A tidal disruption event (TDE) occurs when a supermassive black hole rips apart a passing star. Part of the stellar material falls toward the black hole, forming an accretion disk that in some cases launches a relativistic jet. We performed optical polarimetry observations of a TDE, AT 2020mot. We find a peak linear polarization degree of 25 ± 4%, consistent with highly polarized synchrotron radiation, as is typically observed from relativistic jets. However, our radio observations, taken up to 8 months after the optical peak, do not detect the corresponding radio emission expected from a relativistic jet. We suggest that the linearly polarized optical emission instead arises from shocks that occur during accretion disk formation, as the stream of stellar material collides with itself.
材料科学Materials Science
Restructuring of titanium oxide overlayers over nickel nanoparticles during catalysis
催化过程中镍纳米颗粒上氧化钛覆层的重构
▲ 作者：MATTEO MONAI, KELLIE JENKINSON, ANGELA E. M. MELCHERTS, JAAP N. LOUWEN, ECE A. IRMAK, SANDRA VAN AERT, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.adf6984
▲ 摘要：
还原性载体可通过在还原时形成低氧化物覆层来影响金属催化剂的性能，这一过程被称为金属-载体强相互作用（SMSI）。
动态原位电子显微镜结合振动光谱探测表明，镍/二氧化钛催化剂在400℃还原过程中形成的薄TiOx覆层，在二氧化碳加氢条件下被完全去除。相反，在600℃还原后，暴露于二氧化碳加氢反应条件下仅导致镍部分再暴露，形成与TiOx接触的界面位点，并通过提供碳物种库来促进碳-碳偶联。
该发现挑战了对SMSI的传统理解，并呼吁在单颗粒水平上对纳米催化剂进行更详细的动态原位研究，以重新审视结构-活性关系的静态模型。
▲ Abstract：
Reducible supports can affect the performance of metal catalysts by the formation of suboxide overlayers upon reduction, a process referred to as the strong metal–support interaction (SMSI). A combination of operando electron microscopy and vibrational spectroscopy revealed that thin TiOxoverlayers formed on nickel/titanium dioxide catalysts during 400°C reduction were completely removed under carbon dioxide hydrogenation conditions. Conversely, after 600°C reduction, exposure to carbon dioxide hydrogenation reaction conditions led to only partial reexposure of nickel, forming interfacial sites in contact with TiOx and favoring carbon–carbon coupling by providing a carbon species reservoir. Our findings challenge the conventional understanding of SMSIs and call for more-detailed operando investigations of nanocatalysts at the single-particle level to revisit static models of structure-activity relationships.
Three-dimensional inhomogeneity of zeolite structure and composition revealed by electron ptychography
电子叠层成像术揭示沸石结构和组成的三维非均质性
▲ 作者：HUI ZHANG, GUANXING LI, JIAXING ZHANG, DALIANG ZHANG, ZHEN CHEN, XIAONA LIU, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.adg3183
▲ 摘要：
结构和组成的非均质性在沸石中很常见，并极大地影响了它们的性能。厚度限制的横向分辨率、缺乏纵向分辨率，以及电子量限制的聚焦限制了传统透射电子显微镜（TEM）对沸石的局部结构研究。
研究组证明了一种基于四维扫描TEM（4D-STEM）数据的多层叠层成像术可克服这些限制。从约40纳米厚的MFI沸石上获得的图像显示出约0.85埃的横向分辨率，能够识别单个框架氧（O）原子并精确确定吸附分子的方向。
此外，约6.6纳米的纵向分辨率实现了氧空位以及共生MFI和MEL沸石相边界的三维分布探测。4D-STEM叠层成像术可普遍应用于具有类似高电子束灵敏度的其他材料。
▲ Abstract：
Structural and compositional inhomogeneity is common in zeolites and considerably affects their properties. Thickness-limited lateral resolution, lack of depth resolution, and electron dose-constrained focusing limit local structural studies of zeolites in conventional transmission electron microscopy (TEM). We demonstrate that a multislice ptychography method based on four-dimensional scanning TEM (4D-STEM) data can overcome these limitations. Images obtained from a ~40-nanometer-thick MFI zeolite exhibited a lateral resolution of ~0.85 angstrom that enabled the identification of individual framework oxygen (O) atoms and the precise determination of the orientations of adsorbed molecules. Furthermore, a depth resolution of ~6.6 nanometers allowed probing of the three-dimensional distribution of O vacancies, as well as the phase boundaries in intergrown MFI and MEL zeolites. The 4D-STEM ptychography can be generally applied to other materials with similar high electron-beam sensitivity.
Fluoropolymer ferroelectrics: Multifunctional platform for polar-structured energy conversion
含氟聚合物铁电体：极性结构能量转换的多功能平台
▲ 作者：XIAOSHI QIAN, XIN CHEN, LEI ZHU, AND Q. M. ZHANG
▲ 链接：
https://www.science.org/doi/10.1126/science.adg0902
▲ 摘要：
铁电材料是目前应用最广泛的材料体系之一，并不断产生具有更高效率的优化功能。基于聚偏氟乙烯（PVDF）的聚合物铁电材料的进展，为要求便携、轻便、可穿戴和耐用的应用提供了弯曲、高效耦合和多功能的材料平台。
研究组重点介绍了含氟聚合物铁电体的最新进展、其能量交叉耦合效应和新兴技术，包括可穿戴、高效机电致动器和传感器、电热制冷和介电器件。
这些进展表明，通过简单的缺陷偏置，极化场相互作用的分子和纳米结构操控可增强物理效应，助力新兴沉浸式虚拟世界和可持续未来的智能系统实现多感官和多功能可穿戴设备。
▲ Abstract：
Ferroelectric materials are currently some of the most widely applied material systems and are constantly generating improved functions with higher efficiencies. Advancements in poly(vinylidene fluoride) (PVDF)–based polymer ferroelectrics provide flexural, coupling-efficient, and multifunctional material platforms for applications that demand portable, lightweight, wearable, and durable features. We highlight the recent advances in fluoropolymer ferroelectrics, their energetic cross-coupling effects, and emerging technologies, including wearable, highly efficient electromechanical actuators and sensors, electrocaloric refrigeration, and dielectric devices. These developments reveal that the molecular and nanostructure manipulations of the polarization-field interactions, through facile defect biasing, could introduce enhancements in the physical effects that would enable the realization of multisensory and multifunctional wearables for the emerging immersive virtual world and smart systems for a sustainable future.
化学Chemistry
Regio-controllable [2+2] benzannulation with two adjacent C(sp3)–H bonds
具有两个相邻C(sp3)-H键的区域可控[2+2]苯环化
▲ 作者：SJI-MIN YANG, YU-KUN LIN, TAO SHENG, LIANG HU, XIN-PEI CAI, AND JIN-QUAN YU
▲ 链接：
https://www.science.org/doi/10.1126/science.adg5282
▲ 摘要：
在不饱和碳化合物之间的传统环加成反应中，区域控制往往颇具挑战性。现代药物化学对苯并环丁烯（BCB）支架的关注日益增加，这表明需要一种可替代、更具选择性的途径来获得富含C（sp3）特征的各种刚性碳环。
研究组报道了羧酸中钯催化的两个相邻亚甲基单元的双C-H活化（通过双齿酰胺-吡啶酮配体实现），通过仅涉及σ键（两个C-H键和两个芳基卤素键）的[2+2]环加成形式实现BCB的区域可控合成。
广泛的环状和无环脂肪酸以及二卤代杂芳烃是相容的，可生成存在于药物分子和生物活性天然产物中的不同官能化BCB和异质BCB。
▲ Abstract：
Regiocontrol in traditional cycloaddition reactions between unsaturated carbon compounds is often challenging. The increasing focus in modern medicinal chemistry on benzocyclobutene (BCB) scaffolds indicates the need for alternative, more selective routes to diverse rigid carbocycles rich in C(sp3) character. Here, we report a palladium-catalyzed double C–H activation of two adjacent methylene units in carboxylic acids, enabled by bidentate amide-pyridone ligands, to achieve a regio-controllable synthesis of BCBs through a formal [2+2] cycloaddition involving σ bonds only (two C–H bonds and two aryl–halogen bonds). A wide range of cyclic and acyclic aliphatic acids, as well as dihaloheteroarenes, are compatible, generating diversely functionalized BCBs and hetero-BCBs present in drug molecules and bioactive natural products.
La- and Mn-doped cobalt spinel oxygen evolution catalyst for proton exchange membrane electrolysis
镧和锰掺杂钴尖晶石析氧催化剂助力质子交换膜电解
▲ 作者：LINA CHONG, GUOPING GAO, JIANGUO WEN, HAIXIA LI, HAIPING XU, ZACH GREEN, ET AL.
▲ 链接：
https://www.science.org/doi/10.1126/science.ade1499
▲ 摘要：
在质子交换膜水电解槽（PEMWE）中发现地球上丰富的电催化剂来取代铱进行析氧反应（OER）是降低绿色制氢成本的关键一步。
研究组报道了由嵌入在电纺聚合物纤维中的沸石咪唑盐框架制备、共掺杂镧（La）和锰（Mn）的纳米纤维钴尖晶石催化剂。该催化剂在10 mA/cm2时具有353 mV的低过电位，且在酸性电解液中OER低降解超过360小时。
阳极含有该催化剂的PEMWE在2.47 V时（Nafion 115膜）电流密度为2000 mA/cm2，在3.00 V时（Nafion 212膜）电流密度为4000 mA/cm2，并且在加速应力测试中降解率很低。
▲ Abstract：
Discovery of earth-abundant electrocatalysts to replace iridium for the oxygen evolution reaction (OER) in a proton exchange membrane water electrolyzer (PEMWE) represents a critical step in reducing the cost for green hydrogen production. We report a nanofibrous cobalt spinel catalyst codoped with lanthanum (La) and manganese (Mn) prepared from a zeolitic imidazolate framework embedded in electrospun polymer fiber. The catalyst demonstrated a low overpotential of 353 millivolts at 10 milliamperes per square centimeter and a low degradation for OER over 360 hours in acidic electrolyte. A PEMWE containing this catalyst at the anode demonstrated a current density of 2000 milliamperes per square centimeter at 2.47 volts (Nafion 115 membrane) or 4000 milliamperes per square centimeter at 3.00 volts (Nafion 212 membrane) and low degradation in an accelerated stress test.
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