Publications by authors named "Xinliang Feng"

418 Publications

Ultrathin tin monosulfide nanosheets with the exposed (001) plane for efficient electrocatalytic conversion of CO into formate.

Chem Sci 2020 Mar 23;11(15):3952-3958. Epub 2020 Mar 23.

Center for Advancing Electronics Dresden (cfaed) and Department of Chemistry and Food Chemistry, Technische Universität Dresden Mommsenstraße 4 01062 Dresden Germany

Current Sn-based materials are ideal catalysts developed to drive the electrochemical conversion of CO to formate, but competing proton reduction to hydrogen is an ever-present drain on catalytic selectivity. Herein, we report a reliable electrochemical exfoliation route, with the assistance of alternating voltage, for large-scale preparation of two-dimensional (2D) ultrathin tin monosulfide nanosheets (SnS NSs), which feature a large lateral size of 1.0 μm with a thickness of ∼5.0 nm. Systematic electrochemical studies demonstrated that the achieved SnS NSs exhibited an outstanding electrocatalytic activity towards the CO reduction reaction (CORR) to the formate product, as evidenced by a considerable faradaic efficiency (F.E.) of 82.1%, a high partial current density of 18.9 mA cm at -1.1 V, and a low Tafel slope of 180 mV dec. Further, using an electrode prepared from the resulting SnS NSs by the particle transfer method, a remarkably high formate F.E. over 91% was achieved in a wide potential window. Such high performance renders the SnS NSs among the best reported tin sulfide-based CORR electrocatalysts. Theoretical calculations coupled with comprehensive experimental studies demonstrated that the synergistic effect between the ultrathin layered architecture and dominantly exposed (001) plane of SnS NSs accounted for the uniquely efficient catalytic activity for the CORR.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c9sc06548bDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8152678PMC
March 2020

Hexa--benzocoronene with two extra K-regions in an -configuration.

Chem Sci 2020 Oct 23;11(47):12816-12821. Epub 2020 Oct 23.

Max Planck Institute for Polymer Research Ackermannweg 10 55128 Mainz Germany

There are three possible isomers for hexa--hexabenzocoronene (HBC) with two extra K-regions, but only two of them have been reported, namely with the - and -configurations. Herein, we describe the synthesis of HBC with two extra K-regions in the -configuration, forming a longer zigzag edge compared with the other two isomers. The structure of was validated by laser desorption/ionization time-of-flight mass analysis and nuclear magnetic resonance spectra, as well as Raman and infrared spectroscopies supported by density functional theory calculations. The optical properties of were investigated by UV/vis absorption and ultrafast transient absorption spectroscopy. Together with the analysis of aromaticity, the influence of the zigzag edge on the π-conjugation pathway and HOMO-LUMO gaps of the three isomers were investigated.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0sc04649cDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8163021PMC
October 2020

Ultrathin two-dimensional conjugated metal-organic framework single-crystalline nanosheets enabled by surfactant-assisted synthesis.

Chem Sci 2020 Apr 21;11(29):7665-7671. Epub 2020 Apr 21.

Center for Advancing Electronics Dresden (cfaed) and Faculty of Chemistry and Food Chemistry, Technische Universität Dresden 01062 Dresden Germany

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have recently emerged for potential applications in (opto-)electronics, chemiresistive sensing, and energy storage and conversion, due to their excellent electrical conductivity, abundant active sites, and intrinsic porous structures. However, developing ultrathin 2D c-MOF nanosheets (NSs) for facile solution processing and integration into devices remains a great challenge, mostly due to unscalable synthesis, low yield, limited lateral size and low crystallinity. Here, we report a surfactant-assisted solution synthesis toward ultrathin 2D c-MOF NSs, including HHB-Cu (HHB = hexahydroxybenzene), HHB-Ni and HHTP-Cu (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene). For the first time, we achieve single-crystalline HHB-Cu(Ni) NSs featured with a thickness of 4-5 nm (∼8-10 layers) and a lateral size of 0.25-0.65 μm, as well as single-crystalline HHTP-Cu NSs with a thickness of ∼5.1 ± 2.6 nm (∼10 layers) and a lateral size of 0.002-0.02 μm. Benefiting from the ultrathin feature, the synthetic NSs allow fast ion diffusion and high utilization of active sites. As a proof of concept, when serving as a cathode material for Li-ion storage, HHB-Cu NSs deliver a remarkable rate capability (charge within 3 min) and long-term cycling stability (90% capacity retention after 1000 cycles), superior to the corresponding bulk materials and other reported MOF cathodes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0sc01408gDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8159486PMC
April 2020

Multiscale Modeling Strategy of 2D Covalent Organic Frameworks Confined at an Air-Water Interface.

ACS Appl Mater Interfaces 2021 Jun 26;13(22):26411-26420. Epub 2021 May 26.

Institute for Materials Science and Max Bergmann Center of Biomaterials, Technische Universität Dresden, 01062 Dresden, Germany.

Two-dimensional covalent organic frameworks (2D COFs) have attracted attention as versatile active materials in many applications. Recent advances have demonstrated the synthesis of monolayer 2D COF via an air-water interface. However, the interfacial 2D polymerization mechanism has been elusive. In this work, we have used a multiscale modeling strategy to study dimethylmethylene-bridged triphenylamine building blocks confined at the air-water interface to form a 2D COF via Schiff-base reaction. A synergy between the computational investigations and experiments allowed the synthesis of a 2D-COF with one of the linkers considered. Our simulations complement the experimental characterization and show the preference of the building blocks to be at the interface with a favorable orientation for the polymerization. The air-water interface is shown to be a key factor to stabilize a flat conformation when a dimer molecule is considered. The structural and electronic properties of the monolayer COFs based on the two monomers are calculated and show a semiconducting nature with direct bandgaps. Our strategy provides a first step toward the polymerization of 2D COFs at air-water interfaces capturing the initial steps of the synthesis up to the prediction of electronic properties of the 2D material.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acsami.1c05967DOI Listing
June 2021

Surface-Modified Phthalocyanine-Based Two-Dimensional Conjugated Metal-Organic Framework Films for Polarity-Selective Chemiresistive Sensing.

Angew Chem Int Ed Engl 2021 May 25. Epub 2021 May 25.

Technische Universitat Dresden, Department of Chemistry and Food Chemistry, Mommsenstrasse 4, 01062, Dresden, GERMANY.

Two-dimensional conjugated metal-organic frameworks (2D c -MOFs) are emerging as new-generation electroactive materials for chemiresistive sensors. However, selective sensing with fast response/recovery remains a challenge. Here, we report for the first time phthalocyanine-based Ni 2 [MPc(NH) 8 ] 2D c -MOF films as active layers for polarity-selective chemiresisitors toward water and volatile organic compounds (VOCs). We demonstrate that surface-hydrophobic-modification by grafting aliphatic alkyl chains on 2D c -MOF films reduces the amount of diffused analytes into the MOF backbone, thus resulting in a considerably accelerated recovery progress (from ~ 50 to ~ 10 s) during humidity sensing. Toward VOCs, the sensors deliver a polarity-selective response among alcohols while no signal is recorded for the low-polar aprotic hydrocarbons. Typically, the octadecyltrimethoxysilane-modified Ni 2 [MPc(NH) 8 ] based sensor displays high-performance methanol sensing with fast response (36 s)/recovery (13 s) and a detection limit as low as 10 ppm, which surpass the reported chemiresistors based on MOFs, conducting polymers, metal disulfides, and black phosphorus at room temperature.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.202104461DOI Listing
May 2021

Interfacial Covalent Bonds Regulated Electron-Deficient 2D Black Phosphorus for Electrocatalytic Oxygen Reactions.

Adv Mater 2021 May 3;33(20):e2008752. Epub 2021 May 3.

Center for Advancing Electronics Dresden (cfaed) & Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Mommsenstrasse 4, Dresden, 01062, Germany.

Developing resource-abundant and sustainable metal-free bifunctional oxygen electrocatalysts is essential for the practical application of zinc-air batteries (ZABs). 2D black phosphorus (BP) with fully exposed atoms and active lone pair electrons can be promising for oxygen electrocatalysts, which, however, suffers from low catalytic activity and poor electrochemical stability. Herein, guided by density functional theory (DFT) calculations, an efficient metal-free electrocatalyst is demonstrated via covalently bonding BP nanosheets with graphitic carbon nitride (denoted BP-CN-c). The polarized PN covalent bonds in BP-CN-c can efficiently regulate the electron transfer from BP to graphitic carbon nitride and significantly promote the OOH* adsorption on phosphorus atoms. Impressively, the oxygen evolution reaction performance of BP-CN-c (overpotential of 350 mV at 10 mA cm , 90% retention after 10 h operation) represents the state-of-the-art among the reported BP-based metal-free catalysts. Additionally, BP-CN-c exhibits a small half-wave overpotential of 390 mV for oxygen reduction reaction, representing the first bifunctional BP-based metal-free oxygen catalyst. Moreover, ZABs are assembled incorporating BP-CN-c cathodes, delivering a substantially higher peak power density (168.3 mW cm ) than the Pt/C+RuO -based ZABs (101.3 mW cm ). The acquired insights into interfacial covalent bonds pave the way for the rational design of new and affordable metal-free catalysts.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.202008752DOI Listing
May 2021

Persistent peri-Heptacene: Synthesis and In Situ Characterization.

Angew Chem Int Ed Engl 2021 Jun 12;60(25):13853-13858. Epub 2021 May 12.

Center for Advancing Electronics Dresden (cfaed) & Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Mommsenstrasse 4, 01062, Dresden, Germany.

n-peri-Acenes (n-PAs) have gained interest as model systems of zigzag-edged graphene nanoribbons for potential applications in nanoelectronics and spintronics. However, the synthesis of n-PAs larger than peri-tetracene remains challenging because of their intrinsic open-shell character and high reactivity. Presented here is the synthesis of a hitherto unknown n-PA, that is, peri-heptacene (7-PA), in which the reactive zigzag edges are kinetically protected with eight 4-tBu-C H groups. The formation of 7-PA is validated by high-resolution mass spectrometry and in situ FT-Raman spectroscopy. 7-PA displays a narrow optical energy gap of 1.01 eV and exhibits persistent stability (t ≈25 min) under inert conditions. Moreover, electron-spin resonance measurements and theoretical studies reveal that 7-PA exhibits an open-shell feature and a significant tetraradical character. This strategy could be considered a modular approach for the construction of next-generation (3 N+1)-PAs (where N≥3).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.202102757DOI Listing
June 2021

A Two-Dimensional Polyimide-Graphene Heterostructure with Ultra-fast Interlayer Charge Transfer.

Angew Chem Int Ed Engl 2021 Jun 11;60(25):13859-13864. Epub 2021 May 11.

Faculty of Chemistry and Food Chemistry & Center for Advancing Electronics Dresden, Technische Universität Dresden, 01062, Dresden, Germany.

Two-dimensional polymers (2DPs) are a class of atomically/molecularly thin crystalline organic 2D materials. They are intriguing candidates for the development of unprecedented organic-inorganic 2D van der Waals heterostructures (vdWHs) with exotic physicochemical properties. In this work, we demonstrate the on-water surface synthesis of large-area (cm ), monolayer 2D polyimide (2DPI) with 3.1-nm lattice. Such 2DPI comprises metal-free porphyrin and perylene units linked by imide bonds. We further achieve a scalable synthesis of 2DPI-graphene (2DPI-G) vdWHs via a face-to-face co-assembly of graphene and 2DPI on the water surface. Remarkably, femtosecond transient absorption spectroscopy reveals an ultra-fast interlayer charge transfer (ca. 60 fs) in the resultant 2DPI-G vdWH upon protonation by acid, which is equivalent to that of the fastest reports among inorganic 2D vdWHs. Such large interlayer electronic coupling is ascribed to the interlayer cation-π interaction between 2DP and graphene.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.202102984DOI Listing
June 2021

Microengineered Hollow Graphene Tube Systems Generate Conductive Hydrogels with Extremely Low Filler Concentration.

Nano Lett 2021 04 16;21(8):3690-3697. Epub 2021 Mar 16.

Institute for Molecular Systems Engineering (IMSE), Heidelberg University, Im Neuenheimer Feld 253, 69120 Heidelberg, Germany.

The fabrication of electrically conductive hydrogels is challenging as the introduction of an electrically conductive filler often changes mechanical hydrogel matrix properties. Here, we present an approach for the preparation of hydrogel composites with outstanding electrical conductivity at extremely low filler loadings (0.34 S m, 0.16 vol %). Exfoliated graphene and polyacrylamide are microengineered to 3D composites such that conductive graphene pathways pervade the hydrogel matrix similar to an artificial nervous system. This makes it possible to combine both the exceptional conductivity of exfoliated graphene and the adaptable mechanical properties of polyacrylamide. The demonstrated approach is highly versatile regarding porosity, filler material, as well as hydrogel system. The important difference to other approaches is that we keep the original properties of the matrix, while ensuring conductivity through graphene-coated microchannels. This novel approach of generating conductive hydrogels is very promising, with particular applications in the fields of bioelectronics and biohybrid robotics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.nanolett.0c04375DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8155331PMC
April 2021

Sulfur-Doped Nanographenes Containing Multiple Subhelicenes.

Org Lett 2021 Mar 2;23(6):2069-2073. Epub 2021 Mar 2.

Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Hong Kong 999077, China.

In this work, we describe the synthesis and characterization of three novel sulfur-doped nanographenes (NGs) () containing multiple subhelicenes, including carbo[4]helicenes, thieno[4]helicenes, carbo[5]helicenes, and thieno[5]helicenes. Density functional theory calculations reveal that the helicene substructures in possess dihedral angles from 15° to 34°. The optical energy gaps of are estimated to be 2.67, 2.45, and 2.30 eV, respectively. These three sulfur-doped NGs show enlarged energy gaps compared to those of their pristine carbon analogues.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.orglett.1c00232DOI Listing
March 2021

Making large single crystals of 2D MOFs.

Nat Mater 2021 02;20(2):122-123

Center for Advancing Electronics Dresden (CfAED), Dresden, Germany.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41563-020-00912-1DOI Listing
February 2021

Defective Nanographenes Containing Seven-Five-Seven (7-5-7)-Membered Rings.

J Am Chem Soc 2021 Feb 27;143(5):2353-2360. Epub 2021 Jan 27.

Department of Chemistry and State Key Laboratory of Synthetic Chemistry, The University of Hong Kong, Pokfulam Road, 999077 Hong Kong, P. R. China.

Defects have been observed in graphene and are expected to play a key role in its optical, electronic, and magnetic properties. However, because most of the studies focused on the structural characterization, the implications of topological defects on the physicochemical properties of graphene remain poorly understood. Here, we demonstrate a bottom-up synthesis of three novel nanographenes (-) with well-defined defects in which seven-five-seven (7-5-7)-membered rings were introduced to their sp carbon frameworks. From the X-ray crystallographic analysis, compound adopts a nearly planar structure. Compound , with an additional five-membered ring compared to , possesses a slightly saddle-shaped geometry. Compound , which can be regarded as the "head-to-head" fusion of with two bonds, features two saddles connected together. The resultant defective nanographenes - were well-investigated by UV-vis absorption, cyclic voltammetry, and time-resolved absorption spectra and further corroborated by density functional theory (DFT) calculations. Detailed experimental and theoretical investigations elucidate that these three nanographenes - exhibit an anti-aromatic character in their ground states and display a high stability under ambient conditions, which contrast with the reported unstable biradicaloid nanographenes that contain heptagons. Our work reported herein offers insights into the understanding of structure-related properties and enables the control of the electronic structures of expanded nanographenes with atomically precise defects.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jacs.0c12116DOI Listing
February 2021

Ambient-Stable Two-Dimensional Titanium Carbide (MXene) Enabled by Iodine Etching.

Angew Chem Int Ed Engl 2021 Apr 10;60(16):8689-8693. Epub 2021 Mar 10.

Center for Advancing Electronics Dresden (cfaed), Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Mommsenstrasse 4, 01062, Dresden, Germany.

MXene (e.g., Ti C ) represents an important class of two-dimensional (2D) materials owing to its unique metallic conductivity and tunable surface chemistry. However, the mainstream synthetic methods rely on the chemical etching of MAX powders (e.g., Ti AlC ) using hazardous HF or alike, leading to MXene sheets with fluorine termination and poor ambient stability in colloidal dispersions. Here, we demonstrate a fluoride-free, iodine (I ) assisted etching route for preparing 2D MXene (Ti C T , T=O, OH) with oxygen-rich terminal groups and intact lattice structure. More than 71 % of sheets are thinner than 5 nm with an average size of 1.8 μm. They present excellent thin-film conductivity of 1250 S cm and great ambient stability in water for at least 2 weeks. 2D MXene sheets with abundant oxygen surface groups are excellent electrode materials for supercapacitors, delivering a high gravimetric capacitance of 293 F g at a scan rate of 1 mV s , superior to those made from fluoride-based etchants (<290 F g at 1 mV s ). Our strategy provides a promising pathway for the facile and sustainable production of highly stable MXene materials.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.202015627DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8048443PMC
April 2021

Two-dimensional conjugated metal-organic frameworks (2D -MOFs): chemistry and function for MOFtronics.

Chem Soc Rev 2021 Mar;50(4):2764-2793

Center for Advancing Electronics Dresden (cfaed) & Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, 01062 Dresden, Germany.

The 21st century has seen a reinvention of how modern electronics impact our daily lives; silicon-electronics and organic electronics are currently at the core of modern electronics. Recent advances have demonstrated that conductive metal-organic frameworks (MOFs), as another unique class of electronic materials, are emerging to provide additional possibility for multifunctional electronic devices that brings us "MOFtronics". Typically, two-dimensional conjugated MOFs (2D c-MOFs) are a novel class of layer-stacked MOFs with in-plane extended π-conjugation that exhibit unique properties such as intrinsic porosity, crystallinity, stability, and electrical conductivity as well as tailorable band gaps. Benefiting from their unique features and high conductivity, 2D c-MOFs have displayed great potential for multiple high-performance (opto)electronic, magnetic, and energy devices. In this review article, we introduce the chemical and synthetic methodologies of 2D c-MOFs, intrinsic influences on their electronic structures and charge transport properties, as well as multifunctional applications of this class of materials for MOFtronics and potential power sources for MOFtronics. We highlight the benefits and limitations of thus-far developed 2D c-MOFs from synthesis to function and offer our perspectives in regard to the challenges to be addressed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0cs01160fDOI Listing
March 2021

Synthesis and characterization of [7]triangulene.

Nanoscale 2021 Jan;13(3):1624-1628

[email protected] Laboratory, Empa - Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland.

Triangulene and its π-extended homologues constitute non-Kekulé polyradical frameworks with high-spin ground states, and are anticipated to be key components of organic spintronic devices. We report a combined in-solution and on-surface synthesis of the hitherto largest triangulene homologue, [7]triangulene (C78H24), consisting of twenty-eight benzenoid rings fused in a triangular fashion. We employ low-temperature scanning tunneling microscopy to confirm the chemical structure of individual molecules adsorbed on a Cu(111) surface. While neutral [7]triangulene in the gas phase is predicted to have an open-shell septet ground state; our scanning tunneling spectroscopy measurements, in combination with density functional theory calculations, reveal chemisorption of [7]triangulene on Cu(111) together with considerable charge transfer, resulting in a closed-shell state. Furthermore, substantial hybridization between the molecular orbitals of [7]triangulene is observed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0nr08181gDOI Listing
January 2021

Carbon materials for ion-intercalation involved rechargeable battery technologies.

Chem Soc Rev 2021 Feb 21;50(4):2388-2443. Epub 2020 Dec 21.

Department of Chemistry and Food Chemistry & Center for Advancing Electronics Dresden (cfaed), Technische Universität Dresden, 01062 Dresden, Germany.

The ever-increasing energy demand motivates the pursuit of inexpensive, safe, scalable, and high-performance rechargeable batteries. Carbon materials have been intensively investigated as electrode materials for various batteries on account of their resource abundance, low cost, nontoxicity, and diverse electrochemistry. Taking use of the reversible donor-type cation intercalation/de-intercalation (including Li, Na, and K) at low redox potentials, carbon materials can serve as ideal anodes for 'Rocking-Chair' alkali metal-ion batteries. Meanwhile, acceptor-type intercalation of anions into graphitic carbon materials has also been revealed to be a facile, reversible process at high redox potentials. Based on anion-intercalation graphitic carbon materials, a number of dual-ion battery and Al-ion battery technologies are experiencing booming development. In this review, we summarize the significant advances of carbon materials in terms of the porous structure, chemical composition, and interlayer spacing control. Fundamental mechanisms of carbon materials as the cation host and anion host are further revisited by elaborating the electrochemistry, intercalant effect, and intercalation form. Subsequently, the recent progress in the development of novel carbon nanostructures and carbon-derived energy storage devices is presented with particular emphasis on correlating the structures with electrochemical properties as well as assessing the device configuration, electrochemical reaction, and performance metric. Finally, perspectives on the remaining challenges are provided, which will accelerate the development of new carbon material concepts and carbon-derived battery technologies towards commercial implementation.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0cs00187bDOI Listing
February 2021

High-Mobility Semiconducting Two-Dimensional Conjugated Covalent Organic Frameworks with -Type Doping.

J Am Chem Soc 2020 Dec 17;142(52):21622-21627. Epub 2020 Dec 17.

Center for Advancing Electronics Dresden (cfaed) and Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, Mommsenstrasse 4, 01062 Dresden, Germany.

Two-dimensional conjugated covalent organic frameworks (2D -COFs) are emerging as a unique class of semiconducting 2D conjugated polymers for (opto)electronics and energy storage. Doping is one of the common, reliable strategies to control the charge carrier transport properties, but the precise mechanism underlying COF doping has remained largely unexplored. Here we demonstrate molecular iodine doping of a metal-phthalocyanine-based pyrazine-linked 2D -COF. The resultant 2D -COF maintains its structural integrity and displays enhanced conductivity by 3 orders of magnitude, which is the result of elevated carrier concentrations. Remarkably, Hall effect measurements reveal enhanced carrier mobility reaching ∼22 cm V s for , which represents a record value for 2D -COFs in both the direct-current and alternating-current limits. This unique transport phenomenon with largely increased mobility upon doping can be traced to increased scattering time for free charge carriers, indicating that scattering mechanisms limiting the mobility are mitigated by doping. Our work provides a guideline on how to assess doping effects in COFs and highlights the potential of 2D -COFs to display high conductivities and mobilities toward novel (opto)electronic devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jacs.0c10482DOI Listing
December 2020

Introduction to 'Chemistry of 2D materials: graphene and beyond'.

Nanoscale 2020 Dec;12(48):24309-24310

ISIS, University of Strasbourg & CNRS, France.

View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0nr90263bDOI Listing
December 2020

Facile assembly of layer-interlocked graphene heterostructures as flexible electrodes for Li-ion batteries.

Faraday Discuss 2021 Apr 8;227:321-331. Epub 2020 Dec 8.

Center for Advancing Electronics Dresden (cfaed), Department of Chemistry and Food Chemistry, Technische Universität Dresden, 01062 Dresden, Germany.

Flexible electrodes with robust mechanical properties and high electrochemical performance are of significance for the practical implementation of flexible batteries. Here we demonstrate a general and straightforward co-assembly approach to prepare flexible electrodes, where electrochemically exfoliated graphene (EG) is exploited as the film former/conducting matrix and different binary metal oxides (LiTiO, LiCoO, LiMnO, LiFePO) are incorporated. The resultant EG-metal oxide hybrids exhibit a unique layer-interlocked structure, where the metal oxide is conformably wrapped by the highly flexible graphene. Due to numerous contact interphases generated between EG and the intercalated material, the hybrid films show high flexibility and can endure rolling, bending, folding and even twisting. When serving as the anode for Li-ion batteries, the freestanding EG-LiTiO hybrid presents a characteristic flat discharge plateau at 1.55 V (vs. Li/Li), indicating transformation of LiTiO to LiTiO. Small polarization, high rate capability and excellent cycling stability against mechanical bending are also demonstrated for the prepared EG-LiTiO hybrid. Finally, full cells composed of EG-LiTiO and EG-LiFePO hybrids show impressive cycling (98% capacity retention after 100 cycles at 1C) and rate performance (84% capacity retained at 2.5C). The straightforward co-assembly approach based on EG can be extended to other two-dimensional layered materials for constructing highly efficient flexible energy storage devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/c9fd00120dDOI Listing
April 2021

Designer spin order in diradical nanographenes.

Nat Commun 2020 Nov 27;11(1):6076. Epub 2020 Nov 27.

Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Shenyang National Laboratory for Materials Science, School of Physics and Astronomy, Shanghai Jiao Tong University, 200240, Shanghai, China.

The magnetic properties of carbon materials are at present the focus of intense research effort in physics, chemistry and materials science due to their potential applications in spintronics and quantum computing. Although the presence of spins in open-shell nanographenes has recently been confirmed, the ability to control magnetic coupling sign has remained elusive but highly desirable. Here, we demonstrate an effective approach of engineering magnetic ground states in atomically precise open-shell bipartite/nonbipartite nanographenes using combined scanning probe techniques and mean-field Hubbard model calculations. The magnetic coupling sign between two spins was controlled via breaking bipartite lattice symmetry of nanographenes. In addition, the exchange-interaction strength between two spins has been widely tuned by finely tailoring their spin density overlap, realizing a large exchange-interaction strength of 42 meV. Our demonstrated method provides ample opportunities for designer above-room-temperature magnetic phases and functionalities in graphene nanomaterials.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-020-19834-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7695855PMC
November 2020

Multilayer stabilization for fabricating high-loading single-atom catalysts.

Nat Commun 2020 Nov 18;11(1):5892. Epub 2020 Nov 18.

Max Planck Institute for Polymer Research, 55128, Mainz, Germany.

Metal single-atom catalysts (M-SACs) have emerged as an attractive concept for promoting heterogeneous reactions, but the synthesis of high-loading M-SACs remains a challenge. Here, we report a multilayer stabilization strategy for constructing M-SACs in nitrogen-, sulfur- and fluorine-co-doped graphitized carbons (M = Fe, Co, Ru, Ir and Pt). Metal precursors are embedded into perfluorotetradecanoic acid multilayers and are further coated with polypyrrole prior to pyrolysis. Aggregation of the metals is thus efficiently inhibited to achieve M-SACs with a high metal loading (~16 wt%). Fe-SAC serves as an efficient oxygen reduction catalyst with half-wave potentials of 0.91 and 0.82 V (versus reversible hydrogen electrode) in alkaline and acid solutions, respectively. Moreover, as an air electrode in zinc-air batteries, Fe-SAC demonstrates a large peak power density of 247.7 mW cm and superior long-term stability Our versatile method paves an effective way to develop high-loading M-SACs for various applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41467-020-19599-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7674447PMC
November 2020

Thiophene-Bridged Donor-Acceptor sp -Carbon-Linked 2D Conjugated Polymers as Photocathodes for Water Reduction.

Adv Mater 2021 Jan 16;33(1):e2006274. Epub 2020 Nov 16.

Center for Advancing Electronics Dresden (cfaed) and Faculty of Chemistry and Food Chemistry, Chair of Molecular Functional Materials, Technische Universität Dresden, Mommsenstraße 4, Dresden, 01069, Germany.

Photoelectrochemical (PEC) water reduction, converting solar energy into environmentally friendly hydrogen fuel, requires delicate design and synthesis of semiconductors with appropriate bandgaps, suitable energy levels of the frontier orbitals, and high intrinsic charge mobility. In this work, the synthesis of a novel bithiophene-bridged donor-acceptor-based 2D sp -carbon-linked conjugated polymer (2D CCP) is demonstrated. The Knoevenagel polymerization between the electron-accepting building block 2,3,8,9,14,15-hexa(4-formylphenyl) diquinoxalino[2,3-a:2',3'-c]phenazine (HATN-6CHO) and the first electron-donating linker 2,2'-([2,2'-bithiophene]-5,5'-diyl)diacetonitrile (ThDAN) provides the 2D CCP-HATNThDAN (2D CCP-Th). Compared with the corresponding biphenyl-bridged 2D CCP-HATN-BDAN (2D CCP-BD), the bithiophene-based 2D CCP-Th exhibits a wide light-harvesting range (up to 674 nm), a optical energy gap (2.04 eV), and highest energy occupied molecular orbital-lowest unoccupied molecular orbital distributions for facilitated charge transfer, which make 2D CCP-Th a promising candidate for PEC water reduction. As a result, 2D CCP-Th presents a superb H -evolution photocurrent density up to ≈7.9 µA cm at 0 V versus reversible hydrogen electrode, which is superior to the reported 2D covalent organic frameworks and most carbon nitride materials (0.09-6.0 µA cm ). Density functional theory calculations identify the thiophene units and cyano substituents at the vinylene linkage as active sites for the evolution of H .
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.202006274DOI Listing
January 2021

A High-Rate Two-Dimensional Polyarylimide Covalent Organic Framework Anode for Aqueous Zn-Ion Energy Storage Devices.

J Am Chem Soc 2020 Nov 9;142(46):19570-19578. Epub 2020 Nov 9.

Center for Advancing Electronics Dresden (cfaed) & Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, 01062 Dresden, Germany.

Rechargeable aqueous Zn-ion energy storage devices are promising candidates for next-generation energy storage technologies. However, the lack of highly reversible Zn-storage anode materials with low potential windows remains a primary concern. Here, we report a two-dimensional polyarylimide covalent organic framework (PI-COF) anode with high-kinetics Zn-storage capability. The well-organized pore channels of PI-COF allow the high accessibility of the build-in redox-active carbonyl groups and efficient ion diffusion with a low energy barrier. The constructed PI-COF anode exhibits a specific capacity (332 C g or 92 mAh g at 0.7 A g), a high rate capability (79.8% at 7 A g), and a long cycle life (85% over 4000 cycles). Raman investigation and first-principle calculations clarify the two-step Zn-storage mechanism, in which imide carbonyl groups reversibly form negatively charged enolates. Dendrite-free full Zn-ion devices are fabricated by coupling PI-COF anodes with MnO cathodes, delivering excellent energy densities (23.9 ∼ 66.5 Wh kg) and supercapacitor-level power densities (133 ∼ 4782 W kg). This study demonstrates the feasibility of covalent organic framework as Zn-storage anodes and shows a promising prospect for constructing reliable aqueous energy storage devices.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jacs.0c07992DOI Listing
November 2020

One-Pot Synthesis of Boron-Doped Polycyclic Aromatic Hydrocarbons via 1,4-Boron Migration.

Angew Chem Int Ed Engl 2021 Feb 9;60(6):2833-2838. Epub 2020 Dec 9.

Center for Advancing Electronics Dresden (cfaed) & Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, 01062, Dresden, Germany.

Herein, we demonstrate a novel one-pot synthetic method towards a series of boron-doped polycyclic aromatic hydrocarbons (B-PAHs, 1 a-1 o), including hitherto unknown B-doped zethrene derivatives, from ortho-aryl substituted diarylalkynes with high atom efficiency and broad substrate scopes. A reaction mechanism is proposed based on the experimental investigation together with the theoretical calculations, which involves a unique 1,4-boron migration process. The resultant benchtop-stable B-PAHs are thoroughly investigated by X-ray crystallography, cyclic voltammetry, UV/Vis absorption, and fluorescence spectroscopies. The blue and green organic light-emitting diode (OLED) devices based on 1 f and 1 k are further fabricated, demonstrating the promising application potential of B-PAHs in organic optoelectronics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.202011237DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7898796PMC
February 2021

A Curved Graphene Nanoribbon with Multi-Edge Structure and High Intrinsic Charge Carrier Mobility.

J Am Chem Soc 2020 Oct 20;142(43):18293-18298. Epub 2020 Oct 20.

School of Chemistry and Chemical Engineering, Frontiers Science Center for Transformative Molecules, Shanghai Key Laboratory of Electrical Insulation and Thermal Ageing, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China.

Structurally well-defined graphene nanoribbons (GNRs) have emerged as highly promising materials for the next-generation nanoelectronics. The electronic properties of GNRs critically depend on their edge topologies. Here, we demonstrate the efficient synthesis of a curved GNR () with a combined cove, zigzag, and armchair edge structure, through bottom-up synthesis. The curvature of the is elucidated by the corresponding model compounds tetrabenzo[]perylene () and diphenanthrene-fused tetrabenzo[]perylene (), the structures of which are unambiguously confirmed by the X-ray single-crystal analysis. The resultant multi-edged exhibits a well-resolved absorption at the near-infrared (NIR) region with a maximum peak at 850 nm, corresponding to a narrow optical energy gap of ∼1.22 eV. Employing THz spectroscopy, we disclose a long scattering time of ∼60 fs, corresponding to a record intrinsic charge carrier mobility of ∼600 cm V s for photogenerated charge carriers in .
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1021/jacs.0c07013DOI Listing
October 2020

Vibrational signature of the graphene nanoribbon edge structure from high-resolution electron energy-loss spectroscopy.

Nanoscale 2020 Oct;12(38):19681-19688

Dipartimento di Scienze Fisiche, Informatiche e Matematiche (FIM), Università degli Studi di Modena e Reggio Emilia, 41125, Modena, Italy. and Centro S3, Istituto Nanoscienze CNR-NANO, 41125, Modena, Italy.

Bottom-up approaches exploiting on-surface synthesis reactions allow atomic-scale precision in the fabrication of graphene nanoribbons (GNRs); this is essential for their technological applications since their unique electronic and optical properties are largely controlled by the specific edge structure. By means of a combined experimental-theoretical investigation of some prototype GNRs, we show here that high-resolution electron energy-loss spectroscopy (HREELS) can be successfully employed to fingerprint the details of the GNR edge structure. In particular, we demonstrate how the features of HREEL vibrational spectra - mainly dictated by edge CH out-of-plane modes - are unambiguously related to the GNR edge structure. Moreover, we single out those modes which are localized at the GNR termini and show how their relative intensity can be related to the average GNR length.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1039/d0nr05763kDOI Listing
October 2020

Synthesis of Vinylene-Linked Two-Dimensional Conjugated Polymers via the Horner-Wadsworth-Emmons Reaction.

Angew Chem Int Ed Engl 2020 Dec 22;59(52):23620-23625. Epub 2020 Oct 22.

Chair of Molecular Functional Materials, Center for Advancing Electronics Dresden (cfaed) and Faculty of Chemistry and Food Chemistry, Technische Universität Dresden, 01062, Dresden, Germany.

In this work, we demonstrate the first synthesis of vinylene-linked 2D CPs, namely, 2D poly(phenylenequinoxalinevinylene)s 2D-PPQV1 and 2D-PPQV2, via the Horner-Wadsworth-Emmons (HWE) reaction of C -symmetric 1,4-bis(diethylphosphonomethyl)benzene or 4,4'-bis(diethylphosphonomethyl)biphenyl with C -symmetric 2,3,8,9,14,15-hexa(4-formylphenyl)diquinoxalino[2,3-a:2',3'-c]phenazine as monomers. Density functional theory (DFT) simulations unveil the crucial role of the initial reversible C-C single bond formation for the synthesis of crystalline 2D CPs. Powder X-ray diffraction (PXRD) studies and nitrogen adsorption-desorption measurements demonstrate the formation of proclaimed crystalline, dual-pore structures with surface areas of up to 440 m  g . More importantly, the optoelectronic properties of the obtained 2D-PPQV1 (E =2.2 eV) and 2D-PPQV2 (E =2.2 eV) are compared with those of cyano-vinylene-linked 2D-CN-PPQV1 (E =2.4 eV) produced by the Knoevenagel reaction and imine-linked 2D COF analog (2D-C=N-PPQV1, E =2.3 eV), unambiguously proving the superior conjugation of the vinylene-linked 2D CPs using the HWE reaction.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/anie.202010398DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7814668PMC
December 2020

On-surface Synthesis of a Chiral Graphene Nanoribbon with Mixed Edge Structure.

Chem Asian J 2020 Nov 12;15(22):3807-3811. Epub 2020 Oct 12.

Department of Chemistry, Johannes Gutenberg-University, 55099, Mainz, Germany.

Chiral graphene nanoribbons represent an important class of graphene nanomaterials with varying combinations of armchair and zigzag edges conferring them unique structure-dependent electronic properties. Here, we describe the on-surface synthesis of an unprecedented cove-edge chiral GNR with a benzo-fused backbone on a Au(111) surface using 2,6-dibromo-1,5-diphenylnaphthalene as precursor. The initial precursor self-assembly and the formation of the chiral GNRs upon annealing are revealed, along with a relatively small electronic bandgap of approximately 1.6 eV, by scanning tunnelling microscopy and spectroscopy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/asia.202001008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7756733PMC
November 2020

Near-atomic-scale observation of grain boundaries in a layer-stacked two-dimensional polymer.

Sci Adv 2020 Aug 14;6(33):eabb5976. Epub 2020 Aug 14.

Central Facility of Electron Microscopy, Electron Microscopy Group of Materials Science, Universität Ulm, 89081 Ulm, Germany.

Two-dimensional (2D) polymers hold great promise in the rational materials design tailored for next-generation applications. However, little is known about the grain boundaries in 2D polymers, not to mention their formation mechanisms and potential influences on the material's functionalities. Using aberration-corrected high-resolution transmission electron microscopy, we present a direct observation of the grain boundaries in a layer-stacked 2D polyimine with a resolution of 2.3 Å, shedding light on their formation mechanisms. We found that the polyimine growth followed a "birth-and-spread" mechanism. Antiphase boundaries implemented a self-correction to the missing-linker and missing-node defects, and tilt boundaries were formed via grain coalescence. Notably, we identified grain boundary reconstructions featuring closed rings at tilt boundaries. Quantum mechanical calculations revealed that boundary reconstruction is energetically allowed and can be generalized into different 2D polymer systems. We envisage that these results may open up the opportunity for future investigations on defect-property correlations in 2D polymers.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1126/sciadv.abb5976DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7428334PMC
August 2020

Polymer-Based Batteries-Flexible and Thin Energy Storage Systems.

Adv Mater 2020 Oct 23;32(39):e2000587. Epub 2020 Aug 23.

Laboratory of Organic and Macromolecular Chemistry (IOMC), Friedrich Schiller University Jena, Humboldtstr. 10, Jena, 07743, Germany.

Batteries have become an integral part of everyday life-from small coin cells to batteries for mobile phones, as well as batteries for electric vehicles and an increasing number of stationary energy storage applications. There is a large variety of standardized battery sizes (e.g., the familiar AA-battery or AAA-battery). Interestingly, all these battery systems are based on a huge number of different cell chemistries depending on the application and the corresponding requirements. There is not one single battery type fulfilling all demands for all imaginable applications. One battery class that has been gaining significant interest in recent years is polymer-based batteries. These batteries utilize organic materials as the active parts within the electrodes without utilizing metals (and their compounds) as the redox-active materials. Such polymer-based batteries feature a number of interesting properties, like high power densities and flexible batteries fabrication, among many more.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/adma.202000587DOI Listing
October 2020