In‐Plane Black Phosphorus/Dicobalt Phosphide Heterostructure for Efficient Electrocatalysis

Heterostructures composed of two‐dimensional black phosphorus (2D BP) with unique physical/chemical properties are of great interest. Herein, we report a simple solvothermal method to synthesize in‐plane BP/Co₂P heterostructures for electrocatalysis. By using the reactive edge defects of the BP nanosheets as the initial sites, Co₂P nanocrystals are selectively grown on the BP edges to form the in‐plane BP/Co₂P heterostructures. Owing to disposition on the original defects of BP, Co₂P improves the conductivity and offers more active electrocatalytic sites, so that the BP/Co₂P nanosheets exhibit better and more stable electrocatalytic activities in the hydrogen evolution and oxygen evolution reactions. Our work not only extends the application of BP to electrochemistry, but also provides a new idea to improve the performance of BP by utilization of defects. Furthermore, this strategy can be extended to produce other BP heterostructures to expand the corresponding applications.     

Ultra‐Long Crystalline Red Phosphorus Nanowires from Amorphous Red Phosphorus Thin Films

Heating red phosphorus in sealed ampoules in the presence of a Sn/SnI₄ catalyst mixture has provided bulk black phosphorus at much lower pressures than those required for allotropic conversion by anvil cells. Herein we report the growth of ultra‐long 1D red phosphorus nanowires (>1 mm) selectively onto a wafer substrate from red phosphorus powder and a thin film of red phosphorus in the present of a Sn/SnI₄ catalyst. Raman spectra and X‐ray diffraction characterization suggested the formation of crystalline red phosphorus nanowires. FET devices constructed with the red phosphorus nanowires displayed a typical I–V curve similar to that of black phosphorus and a similar mobility reaching 300 cm² V^?1 s with an I_on/I_off ratio approaching 10². A significant response to infrared light was observed from the FET device.     

Layered Black Phosphorus: Strongly Anisotropic Magnetic,Electronic, and Electron‐Transfer Properties

Layered elemental materials, such as black phosphorus, exhibit unique properties originating from their highly anisotropic layered structure. The results presented herein demonstrate an anomalous anisotropy for the electrical, magnetic, and electrochemical properties of black phosphorus. It is shown that heterogeneous electron transfer from black phosphorus to outer‐ and inner‐sphere molecular probes is highly anisotropic. The electron‐transfer rates differ at the basal and edge planes. These unusual properties were interpreted by means of calculations, manifesting the metallic character of the edge planes as compared to the semiconducting properties of the basal plane. This indicates that black phosphorus belongs to a group of materials known as topological insulators. Consequently, these effects render the magnetic properties highly anisotropic, as both diamagnetic and paramagnetic behavior can be observed depending on the orientation in the magnetic field.     

Free-Standing Black Phosphorus Foils for Energy Storage and Catalysis

Few-layered black phosphorus (BP) is a two-dimensional material that has attracted intensive attention for applications in energy storage and catalysis due to its large surface area and good electrical and thermal conductivity. Herein, a comparable study of BP electrochemical exfoliation in various solutions of tetrabutylammonium salts (TBAX; X is PF₆⁻, BF₄⁻, and ClO₄⁻) in DMSO is reported. Based on morphological and structural analyses, it is shown that TBAPF₆/DMSO medium was specifically appropriate for the production of high-quality BP nanosheets with micrometer lateral size and a thickness of about 2.4 nm. TBAPF₆/DMSO-processed, few-layered BP exhibits enhanced hydrogen evolution reaction (HER) catalytic activity compared with that of samples exfoliated with the assistance of BF₄⁻ and ClO₄⁻ ions. Finally, the fabrication of flexible, free-standing BP films and their performance in an all-solid-state supercapacitor device are demonstrated.     

Topochemical Synthesis of Two‐Dimensional Transition‐Metal Phosphides Using Phosphorene Templates

Transition‐metal phosphides (TMPs) have emerged as a fascinating class of narrow‐gap semiconductors and electrocatalysts. However, they are intrinsic nonlayered materials that cannot be delaminated into two‐dimensional (2D) sheets. Here, we demonstrate a general bottom‐up topochemical strategy to synthesize a series of 2D TMPs (e.g. Co₂P, Ni₁₂P₅, and Co_xFe_2?xP) by using phosphorene sheets as the phosphorus precursors and 2D templates. Notably, 2D Co₂P is a p‐type semiconductor, with a hole mobility of 20.8 cm² V^?1 s^?1 at 300 K in field‐effect transistors. It also behaves as a promising electrocatalyst for the oxygen evolution reaction (OER), thanks to the charge‐transport modulation and improved surface exposure. In particular, iron‐doped Co₂P (i.e. Co_1.5Fe_0.5P) delivers a low overpotential of only 278 mV at a current density of 10 mA cm^?2 that outperforms the commercial Ir/C benchmark (304 mV).     

Unravelling the Correlation between Charge Mobility and Cocrystallization in Rod–Rod Block Copolymers for High‐Performance Field‐Effect Transistors

Cocrystallization involving two or more components aggregating into cocrystals allows the preparation of materials with markedly improved charge mobility. This approach however, is little explored in all‐conjugated block copolymers (BCPs). Herein, we report the first investigation into the correlation between cocrystals and charge mobility in a series of new all‐conjugated BCPs: poly(3‐butylthiophene)‐b‐poly(3‐hexylselenophene) (P3BT‐b‐P3HS) for high‐performance field‐effect transistors. These rationally synthesized rod–rod BCPs self‐assemble into cocrystals with high charge mobilities. Upon one‐step thermal annealing, their charge mobilities decrease slightly despite their increased crystallinities. After two‐step thermal annealing, P3BT‐b‐P3HS (P3BT/P3HS=2:1) and (1:1) cocrystals disappear and phase separation occurs, leading to greatly decreased charge mobilities. In contrast, P3BT‐b‐P3HS (1:2) retains its cocrystalline structure and its charge mobility.     

Light‐Induced Ambient Degradation of Few‐Layer Black Phosphorus: Mechanism and Protection

The environmental instability of single‐ or few‐layer black phosphorus (BP) has become a major hurdle for BP‐based devices. The degradation mechanism remains unclear and finding ways to protect BP from degradation is still highly challenging. Based on ab initio electronic structure calculations and molecular dynamics simulations, a three‐step picture on the ambient degradation of BP is provided: generation of superoxide under light, dissociation of the superoxide, and eventual breakdown under the action of water. The well‐matched band gap and band‐edge positions for the redox potential accelerates the degradation of thinner BP. Furthermore, it was found that the formation of P‐O‐P bonds can greatly stabilize the BP framework. A possible protection strategy using a fully oxidized BP layer as the native capping is thus proposed. Such a fully oxidization layer can resist corrosion from water and leave the BP underneath intact with simultaneous high hole mobility.     

Stable Confinement of Black Phosphorus Quantum Dots on Black Tin Oxide Nanotubes: A Robust,Double‐Active Electrocatalyst toward Efficient Nitrogen Fixation

A conceptually new, metal‐free electrocatalyst, black phosphorus (BP) is presented, which is further downsized to quantum dots (QDs) for larger surface areas, and thus, more active sites than the bulk form. However, BP QDs are prone to agglomeration, which inevitably results in the loss of active sites. Besides, their poor conductivity is not favorable for charge transport during electrolysis. To solve these problems, an electrochemically active, electrically conductive matrix, black tin oxide (SnO_2?x) nanotubes, is employed for the first time. Through facile self‐assembly, BP QDs are stably confined on the SnO_2?x nanotubes due to Sn‐P coordination, resulting in a robust, double‐active electrocatalyst. Benefiting from their synergistic superiority, the BP@SnO_2?x nanotubes deliver impressively high ammonia yield and Faradaic efficiency, which represent a successful attempt toward advanced hybrid electrocatalysts for ambient nitrogen fixation.     

Enhanced Cytosolic Delivery and Release of CRISPR/Cas9 by Black Phosphorus Nanosheets for Genome Editing

A biodegradable two‐dimensional (2D) delivery platform based on loading black phosphorus nanosheets (BPs) with Cas9 ribonucleoprotein engineered with three nuclear localization signals (NLSs) at C terminus (Cas9N3) is successfully established. The Cas9N3‐BPs enter cells effectively via membrane penetration and endocytosis pathways, followed by a BPs biodegradation‐associated endosomal escape and cytosolic releases of the loaded Cas9N3 complexes. The Cas9N3‐BPs thus provide efficient genome editing and gene silencing in vitro and in vivo at a relatively low dose as compared with other nanoparticle‐based delivery platforms. This biodegradable 2D delivery platform offers a versatile cytosolic delivery approach for CRISPR/Cas9 ribonucleoprotein and other bioactive macromolecules for biomedical applications.     

Identifying the Crystalline Orientation of Black Phosphorus Using Angle‐Resolved Polarized Raman Spectroscopy

An optical anisotropic nature of black phosphorus (BP) is revealed by angle‐resolved polarized Raman spectroscopy (ARPRS), and for the first time, an all‐optical method was realized to identify the crystal orientation of BP sheets, that is, the zigzag and armchair directions. We found that Raman intensities of A_g¹, B_2g, and A_g² modes of BP not only depend on the polarization angle α, but also relate to the sample rotation angle θ. Furthermore, their intensities reach the local maximum or minimum values when the crystalline orientation is along with the polarization direction of scattered light (e_s). Combining with the angle‐resolved conductance, it is confirmed that A_g² mode intensity achieves a relative larger (or smaller) local maximum under parallel polarization configuration when armchair (or zigzag) direction is parallel to e_s. Therefore, ARPRS can be used as a rapid, precise, and nondestructive method to identify the crystalline orientation of BP layers.     

A High‐Pressure Polymorph of Phosphorus Nitride Imide

Phosphorus nitride imide, PN(NH), is of great scientific importance because it is isosteric with silica (SiO₂). Accordingly, a varied structural diversity could be expected. However, only one polymorph of PN(NH) has been reported thus far. Herein, we report on the synthesis and structural investigation of the first high‐pressure polymorph of phosphorus nitride imide, β‐PN(NH); the compound has been synthesized using the multianvil technique. By adding catalytic amounts of NH₄Cl as a mineralizer, it became possible to grow single crystals of β‐PN(NH), which allowed the first complete structural elucidation of a highly condensed phosphorus nitride from single‐crystal X‐ray diffraction data. The structure was confirmed by FTIR and ³¹P and ¹H solid‐state NMR spectroscopy. We are confident that high‐pressure/high‐temperature reactions could lead to new polymorphs of PN(NH) containing five‐fold‐ or even six‐fold‐coordinated phosphorus atoms and thus rivalling or even surpassing the structural variety of SiO₂.     

Two‐Dimensional Haeckelite NbS2: A Diamagnetic High‐Mobility Semiconductor with Nb4+ Ions

In all known Group 5 transition‐metal dichalcogenide monolayers (MLs), the metal centers carry a spin, and their ground‐state phases are either metallic or semiconducting with indirect band gaps. Here, on grounds of first‐principles calculations, we report that the Haeckelite polytypes 1 S ‐NbX₂ (X=S, Se, Te) are diamagnetic direct‐band‐gap semiconductors even though the Nb atoms are in the 4+ oxidation state. In contrast, 1 S ‐VX₂ MLs are antiferromagnetically coupled indirect‐band‐gap semiconductors. The 1 S phases are thermodynamically and dynamically stable but of slightly higher energy than their 1 H and 1 T ML counterparts. 1 S ‐NbX₂ MLs are excellent candidates for optoelectronic applications owing to their small band gaps (between 0.5 and 1 eV). Moreover, 1 S ‐NbS₂ shows a particularly high hole mobility of 2.68×10³ cm² V⁻¹ s⁻¹, which is significantly higher than that of MoS₂ and comparable to that of WSe₂.     

A High‐Pressure Polymorph of Phosphorus Oxonitride with the Coesite Structure

The chemical and physical properties of phosphorus oxonitride (PON) closely resemble those of silica, to which it is isosteric. A new high‐pressure phase of PON is reported herein. This polymorph, synthesized by using the multianvil technique, crystallizes in the coesite structure. This represents the first occurrence of this very dense network structure outside of SiO₂. Phase‐pure coesite PON (coe‐PON) can be synthesized in bulk at pressures above 15 GPa. This compound was thoroughly characterized by means of powder X‐ray diffraction, DFT calculations, and FTIR and MAS NMR spectroscopy, as well as temperature‐dependent diffraction. These results represent a major step towards the exploration of the phase diagram of PON at very high pressures and the possibly synthesis of a stishovite‐type PON containing hexacoordinate phosphorus.     

A Black Phosphorus–Graphite Composite Anode for Li‐/Na‐/K‐Ion Batteries

Black phosphorus (BP) is a desirable anode material for alkali metal ion storage owing to its high electronic/ionic conductivity and theoretical capacity. In‐depth understanding of the redox reactions between BP and the alkali metal ions is key to reveal the potential and limitations of BP, and thus to guide the design of BP‐based composites for high‐performance alkali metal ion batteries. Comparative studies of the electrochemical reactions of Li⁺, Na⁺, and K⁺ with BP were performed. Ex situ X‐ray absorption near‐edge spectroscopy combined with theoretical calculation reveal the lowest utilization of BP for K⁺ storage than for Na⁺ and Li⁺, which is ascribed to the highest formation energy and the lowest ion diffusion coefficient of the final potassiation product K₃P, compared with Li₃P and Na₃P. As a result, restricting the formation of K₃P by limiting the discharge voltage achieves a gravimetric capacity of 1300 mAh g^?1 which retains at 600 mAh g^?1 after 50 cycles at 0.25 A g^?1.     

High‐Pressure Phase Transformations in TiPO4: A Route to Pentacoordinated Phosphorus

Titanium(III) phosphate, TiPO₄ , is a typical example of an oxyphosphorus compound containing covalent P?O bonds. Single‐crystal X‐ray diffraction studies of TiPO₄ reveal complex and unexpected structural and chemical behavior as a function of pressure at room temperature. A series of phase transitions lead to the high‐pressure phase V, which is stable above 46 GPa and features an unusual oxygen coordination of the phosphorus atoms. TiPO₄‐V is the first inorganic phosphorus‐containing compound that exhibits fivefold coordination with oxygen. Up to the highest studied pressure of 56 GPa, TiPO₄‐V coexists with TiPO₄‐IV, which is less dense and might be kinetically stabilized. Above a pressure of about 6 GPa, TiPO₄‐II is found to be an incommensurately modulated phase whereas a lock‐in transition at about 7 GPa leads to TiPO₄‐III with a fourfold superstructure compared to the structure of TiPO₄‐I at ambient conditions. TiPO₄‐II and TiPO₄‐III are similar to the corresponding low‐temperature incommensurate and commensurate magnetic phases and reflect the strong pressure dependence of the spin‐Peierls interactions.     

An A‐D‐A′‐D‐A Conjugated Molecule Entailing Diazapentalene Unit for an n‐Type Organic Semiconductor

Conjugated molecules with low lying LUMO levels are demanding for the development of air stable n‐type organic semiconductors. In this paper, we report a new A‐D‐A′‐D‐A conjugated molecule ( DAPDCV ) entailing diazapentalene (DAP) and dicyanovinylene groups as electron accepting units. Both theoretical and electrochemical studies manifest that the incorporation of DAP unit in the conjugated molecule can effectively lower the LUMO energy level. Accordingly, thin film of DAPDCV shows n‐type semiconducting behavior with electron mobility up to 0.16 cm²?V^?1?s^?1 after thermal annealing under N₂ atmosphere. Moreover, thin film of DAPDCV also shows stable n‐type transporting property in air with mobility reaching 0.078 cm²?V^?1?s^?1.     

A Conjugated Polymer Containing Arylazopyrazole Units in the Side Chains for Field‐Effect Transistors Optically Tunable by Near Infra‐Red Light

Optically tunable field‐effect transistors (FETs) with near infra‐red (NIR) light show promising applications in various areas. Now, arylazopyrazole groups are incorporated in the side chains of a semiconducting donor–acceptor (D‐A) polymer. The cis–trans interconversion of the arylazopyrazole can be controlled by 980 nm and 808 nm NIR light irradiation, by utilizing NaYF₄:Yb,Tm upconversion nanoparticles and the photothermal effect of conjugated D‐A polymers, respectively. This reversible transformation affects the interchain packing of the polymer thin film, which in turn reversibly tunes the semiconducting properties of the FETs by the successive 980 nm and 808 nm light irradiation. The resultant FETs display fast response to NIR light, good resistance to photofatigue, and stability in storage for up to 120 days. These unique features will be useful in future memory and bioelectronic wearable devices.     

A General Method for Growing Two‐Dimensional Crystals of Organic Semiconductors by “Solution Epitaxy”

Two‐dimensional (2D) crystals of organic semiconductors (2DCOS) have attracted attention for large‐area and low‐cost flexible optoelectronics. However, growing large 2DCOS in controllable ways and transferring them onto technologically important substrates, remain key challenges. Herein we report a facile, general, and effective method to grow 2DCOS up to centimeter size which can be transferred to any substrate efficiently. The method named “solution epitaxy” involves two steps. The first is to self‐assemble micrometer‐sized 2DCOS on water surface. The second is epitaxial growth of them into millimeter or centimeter sized 2DCOS with thickness of several molecular layers. The general applicability of this method for the growth of 2DCOS is demonstrated by nine organic semiconductors with different molecular structures. Organic field‐effect transistors (OFETs) based on the 2DCOS demonstrated high performance, confirming the high quality of the 2DCOS.