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ISSN / EISSN : 1613-6810 / 1613-6829
Published by: Wiley (10.1002)
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Xiaoyan Liu, Sheng Ye, Guojun Lan, Panpan Su, Xiaoli Zhang, Cameron Alexander Hurd Price, ,
Published: 12 July 2021
Small; doi:10.1002/smll.202101271

Abstract:
Nitrogen-doped nanocarbons are widely used as supports for metal-heterogeneous catalytic conversions. When nitrogen-doped nanocarbon supports are used to disperse metallic nanoparticles (MNPs), the nitrogen dopant can enhance MNPs electron density to reach higher catalytic activity and promote MNPs stability through anchoring effects. However, the precise identification of active nitrogen species between N-dopants and reactants is rarely reported. Herein, a proof-of-concept study on the active N species for levulinic acid hydrogenation is reported. A double-shell structured carbon catalyst (DSC) is designed with selectively locating ultrafine Ru NPs only on inner carbon shell, specifically, different N species on the external carbon shell. Through the design of such a nanostructure, it is demonstrated that the alkaline pyridinic N species on the outer shell serves as an anchor point for the spontaneous binding of the acidic reactant. The pyridinic N content can be modulated from 7.4 to 29.2 mg gcat−1 by selecting different precursors. Finally, the Ru-DSC-CTS (using chitosan as the precursor) catalyst achieves a 99% conversion of levulinic acid under 70 °C and 4 MPa hydrogen pressure for 1 h. This work sheds light on the design of nanoreactors at the atomic scale and investigates heterogeneous catalysis at the molecular level.
Dong Liang, Chong Dong, Lei Cai, Zhenhuang Su, Jiaqing Zang, Chenyue Wang, Xuechun Wang, Yatao Zou, Yajuan Li, Li Chen, et al.
Published: 12 July 2021
Small; doi:10.1002/smll.202100972

Abstract:
Quasi-2D perovskites are enchanting alternative materials for solar cells due to their intrinsic stability. The manipulation of crystal orientation of quasi-2D perovskites is indispensable to target efficient devices, however, the origin of orientation during the film fabrication process still lacks in-depth understanding and convincing evidence yet, which hinders further boosting the performance of photovoltaic devices. Herein, the crystallizing processes during spin-coating and annealing are probed by in situ grazing-incidence wide-angle X-ray scattering (GIWAXS), and the incident-angle-dependent GIWAXS is conducted to unveil the phase distribution in the films. It is found that undesirable lead iodide sol–gel formed intermediate phase would disturb oriented crystalline growth, resulting in random crystal orientation in poor quasi-2D films. A general strategy is developed via simple additive agent incorporation to suppress the formation of the intermediate phase. Accordingly, highly oriented perovskite films with reduced trap density and higher carrier mobility are obtained, which enables the demonstration of optimized quasi-2D perovskite solar cells with a power conversion efficiency of 15.2% as well as improved stability. This work paves a promising way to manipulate the quasi-2D perovskites nucleation and crystallization processes via tuning nucleation stage.
Yanze Wei, Fenghua Zhang, Jingjing Wei,
Published: 12 July 2021
Small; doi:10.1002/smll.202102047

Abstract:
Mixed-dimensional heterostructures (MDHs), which combine nanomaterials of different dimensionalities deliver on the promise to bypass intrinsic limitations of a given low-dimensional material. Here, a strategy to engineer MDHs between two low-dimensional materials by curvature-complementary self-assembly is described. CdSe nanotubes rolled from 2D nanosheets and 1D CdSe nanorods, with negative and positive curvatures, respectively, are selected to illustrate complementary curvature self-assembly. The assembly process, optical, and photoelectrical properties of the CdSe MDHs are thoroughly investigated. Several remarkable features of CdSe MDHs, including increased light absorption, efficient charge separation, and appropriate bandgap structure are confirmed. The MDHs significantly alleviate the sluggish kinetics of electron transfer in the quantum sized CdSe subunits (onset potential of 0.21 V vs RHE for MDHs; 0.4 V lower than their low-dimensional building blocks), while the spatial nano-confinement effect in the CdSe MDHs also assists the interfacial reaction kinetics to render them ideal photocatalysts for benzylamine oxidation (conversion > 99% in 4 h with a two times higher rate than simple mixtures). The results highlight opportunities for building MDHs from low-dimensional building blocks with curvature-complementary features and expand the application spectrum of low dimensional materials in artificial photosynthesis.
Huangang Shi, , Xiaomin Xu, Yangli Pan, Guangming Yang, Ran Ran,
Published: 12 July 2021
Small; doi:10.1002/smll.202101872

Abstract:
Here a new strategy is unveiled to develop superior cathodes for protonic ceramic fuel cells (PCFCs) by the formation of Ruddlesden–Popper (RP)-single perovskite (SP) nanocomposites. Materials with the nominal compositions of LaSrxCo1.5Fe1.5O10−δ (LSCFx, x = 2.0, 2.5, 2.6, 2.7, 2.8, and 3.0) are designed specifically. RP-SP nanocomposites (x = 2.5, 2.6, 2.7, and 2.8), SP oxide (x = 2.0), and RP oxide (x = 3.0) are obtained through a facile one-pot synthesis. A synergy is created between RP and SP in the nanocomposites, resulting in more favorable oxygen reduction activity compared to pure RP and SP oxides. More importantly, such synergy effectively enhances the proton conductivity of nanocomposites, consequently significantly improving the cathodic performance of PCFCs. Specifically, the area-specific resistance of LSCF2.7 is only 40% of LSCF2.0 on BaZr0.1Ce0.7Y0.2O3−δ (BZCY172) electrolyte at 600 °C. Additionally, such synergy brings about a reduced thermal expansion coefficient of the nanocomposite, making it better compatible with BZCY172 electrolyte. Therefore, an anode-supported PCFC with LSCF2.7 cathode and BZCY172 electrolyte brings an attractive peak power output of 391 mW cm−2 and excellent durability at 600 °C.
Lulu Chai, Junqing Pan, Yue Hu, , Maochun Hong
Published: 10 July 2021
Small; doi:10.1002/smll.202100607

Abstract:
Multiporous metal-organic frameworks (MOFs) have emerged as a subclass of highly crystalline inorganic-organic materials, which are endowed with high surface areas, tunable pores, and fascinating nanostructures. Heterostructured MOF-on-MOF composites are recently becoming a research hotspot in the field of chemistry and materials science, which focus on the assembly of two or more different homogeneous or heterogeneous MOFs with various structures and morphologies. Compared with one single MOF, the dual MOF-on-MOF composites exhibit unprecedented tunability, hierarchical nanostructure, synergistic effect, and enhanced performance. Due to the difference of inorganic metals and organic ligands, the lattice parameters in a, b, and c directions in the single crystal cells could bring about subtle or large structural difference. It will result in the composite material with distinct growth methods to obtain secondary MOF grown from the initial MOF. In this review, the authors wish to mainly outline the latest synthetic strategies of heterostructured MOF-on-MOFs and their derivatives, including ordered epitaxial growth, random epitaxial growth, etc., which show the tutorial guidelines for the further development of various MOF-on-MOFs.
Xue Wang, Yanan Liu, Huili Li, Tian Lv, Jun Wan, Keyi Dong, Zilin Chen,
Published: 9 July 2021
Small; doi:10.1002/smll.202102054

Abstract:
Supercapacitors with high power density and an ultralong cyclic lifetime have been intensively investigated. However, the crucial challenge of their rapid self-discharge process is often neglected in most cases. A heterogeneous interface formed between two layers of polymer electrolytes is designed, in which a polyanion and a polycation are added into a common matrix of polymer electrolyte, respectively. By using the heterogeneous polymer electrolyte (HPE) as the separator simultaneously, the resultant supercapacitors exhibit comparable electrochemical performance to that of devices based on traditional polymer electrolytes. The HPE-based supercapacitors using both electric double-layer capacitive and pseudocapacitive electrodes show at least one time longer self-discharge time than that of devices based on homogenous polymer electrolyte, especially for the electrode in an electrolyte containing polyanion served as a positive pole during the charging process. Because of the same polymer matrix used, the heterojunction structure of the HPE exhibits excellent stability without obvious phase separation during thousands of charge/discharge and repeated bending cycles. This novel strategy by interface engineering of electrolyte to suppress the self-discharge behavior of supercapacitors is very meaningful to promote their practical applications.
Seunghyun Rhee, Dongju Jung, Dahin Kim, Doh C. Lee, Changhee Lee,
Published: 9 July 2021
Small; doi:10.1002/smll.202101204

Abstract:
Due to their anisotropic structure, quantum rods (QRs) feature unique properties that differ from quantum dots, such as suppression of non-radiative Auger recombination and linearly polarized light emission. Despite many potential advantages, the progress of QR-based light-emitting diodes (QR-LEDs) is left behind due to the difficulty in aligning QRs. In this study, polarized electroluminescence emission is reported in high-performance QR-LEDs by employing the Langmuir-Blodgett (LB) technique. The adoption of the LB technique successfully produces a highly dense and smooth QR film with a high degree of alignment. As a result, the aligned QR films exhibit polarized photoluminescence emission with a degree of linear polarization of 2.1. Advantageous features of the LB technique, such as nondestructiveness, precise thickness control, and the nonnecessity of an additional matrix material, allow to fabricate QR-LEDs with the same procedure as the standard spin coating-based scheme. The device is fabricated via the LB technique, which shows excellent device performance, such as the low turn-on voltage of 1.8 V, peak luminance of 56 287 cd m−2, and peak external quantum efficiency (EQE) of 10.33%. Furthermore, these devices clearly exhibit an indication of polarized electroluminescence emission, which opens new opportunities for QRs in display technologies.
Wentao Deng, Jun Chen, Li Yang, Xinxing Liang, Shouyi Yin, Xinglan Deng, Guoqiang Zou, Hongshuai Hou,
Published: 9 July 2021
Small; doi:10.1002/smll.202101058

Abstract:
The sodium-ion battery (SIB) has attracted ever growing attention as a promising alternative of the lithium-ion battery (LIB). Constructing appropriate anode materials is critical for speeding up the application of SIB. This review aims at guiding anode design from the material's perspective, and specifically focusing on solid solution metal chalcogenide anode. The sodium ion storage mechanisms of a solid solution metal chalcogenide anode is overviewed on basis of the elements it is composed of, and discusses how the solid solution character alters the electrochemical performances through diffusion and surface-controlled processes. In addition, by classifying solid solution metal chalcogenide as cation and anion, their recent applications are updated, and understanding the roles of guest elements in improving the electrochemical behaviors of a solid solution metal chalcogenide is carried out. After that, discussion of possible strategies to further optimize these anode materials in the future, flowing from crystal structure design to morphology control and finally to the intimacy improvement between conductive matrix and solid solution metal chalcogenide are also provided.
Bingxing Zhang, Baohua Zhang, Yinzhu Jiang, Tianyi Ma, Hongge Pan,
Published: 9 July 2021
Small; doi:10.1002/smll.202101443

Abstract:
The multi-electron reduction of CO2 to hydrocarbons or alcohols is highly attractive in a sustainable energy economy, and the rational design of electrocatalysts is vital to achieve these reactions efficiently. Single-atom electrocatalysts are promising candidates due to their well-defined coordination configurations and unique electronic structures, which are critical for delivering high activity and selectivity and may accelerate the explorations of the activity origin at atomic level as well. Although much effort has been devoted to multi-electron reduction of CO2 on single-atom electrocatalysts, there are still no reviews focusing on this emerging field and constructive perspectives are also urgent to be addressed. Herein recent advances in how to design efficient single-atom electrocatalysts for multi-electron reduction of CO2, with emphasis on strategies in regulating the interactions between active sites and key reaction intermediates, are summarized. Such interactions are crucial in designing active sites for optimizing the multi-electron reduction steps and maximizing the catalytic performance. Different design strategies including regulation of metal centers, single-atom alloys, non-metal single-atom catalysts, and tandem catalysts, are discussed accordingly. Finally, current challenges and future opportunities for deep electroreduction of CO2 are proposed.
Tokuhisa Kawawaki, Ayano Ebina, Yasunaga Hosokawa, Shuhei Ozaki, Daiki Suzuki, Sakiat Hossain, Yuichi Negishi
Published: 8 July 2021
by 10.1002
Small, Volume 17; doi:10.1002/smll.202170138

Abstract:
In article number 2005328, Yuichi Negishi and co-workers describe recent progress in the field of thiolate (SR)-protected metal nanoclusters in three areas: synthesis, understanding, and application. The challenges that must be overcome for further development in this field and the possibilities that SR-protected metal NCs can contribute to solving the problems facing modern society are also discussed in this review.
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