Exfoliation Of Black Phosphorus Research Articles

Inducing Directional Charge Delocalization in 3D-Printable Micro-Supercapacitors Based on Strongly Coupled Black Phosphorus and ReS2 Nanocomposites.

The growing interest in so-called interface coupling strategies arises from their potential to enhance the performance of active electrode materials. Nevertheless, designing a robust coupled interface in nanocomposites for stable electrochemical processes remains a challenge. In this study, an epitaxial growth strategy is proposed by synthesizing sulfide rhenium (ReS2) on exfoliated black phosphorus (E-BP) nanosheets, creating an abundance of robust interfacial linkages. Through spectroscopic analysis using X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, the authors investigate the interfacial environment. The well-developed coupled interface and structural stability contribute to the impressive performance of the 3D-printed E-BP@ReS2-based micro-supercapacitor, achieving a specific capacitance of 47.3 mF cm-2 at 0.1mA cm-2 and demonstrating excellent long-term cyclability (89.2% over 2000 cycles). Furthermore, density functional theory calculations unveil the positive impact of the strongly coupled interface in the E-BP@ReS2 nanocomposite on the adsorption of H+ ions, showcasing a significantly reduced adsorption energy of -2.17eV. The strong coupling effect facilitates directional charge delocalization at the interface, enhancing the electrochemical performance of electrodes and resulting in the successful construction of advanced micro-supercapacitors.

One-Step Electrochemical Synthesis of AlO x -Passivated Twisted-Phosphorene Nanosheets for Potentially Stable Energy Storage Devices.

Black phosphorus (BP), a promising 2D material for electronics, energy storage, catalysis, and sensing, has sparked a research boom. However, exfoliated thin-layered BP is unstable and can easily be degraded under environmental conditions, severely limiting its practical applications. In this context, a simple and cost-effective method has been proposed that involves electrochemically exfoliating BP and simultaneously electrochemically depositing aluminum oxide (AlO x ) for passivation of the exfoliated BP. The ambient stability of the exfoliated BP is studied using a time-dependent atomic force microscope (AFM). The AlO x capping layer significantly improves the environmental stability of BP compared to uncapped BP. The thermal stability of the resulting BP is evaluated using power-dependent Raman spectroscopy. The results show that the AlO x -passivated BP has increased thermal stability, with only a slight shift in peak position toward higher Raman power intensity. These properties can make the material suitable for stable energy storage devices. Interestingly, the electrochemical exfoliation and passivation processes resulted in the BP with a twist angle (9.86°), which is expected to exhibit unique electronic properties similar to those of graphene with a twist angle.

Interface-Coupling of NiFe-LDH on Exfoliated Black Phosphorus for the High-Performance Electrocatalytic Oxygen Evolution Reaction.

Electrochemical oxygen evolution reaction (OER) always plays an important role in many electrochemical energy storage and conversion systems. Owing to the slow kinetics mainly brought from multiple proton-coupled electron transfer steps, the design and exploit low-cost, highly active, durable OER electrocatalysts are of significant importance. Although the black phosphorus (BP) shows good electrocatalytic OER performance, it still faces the problems of poor intrinsic activity and low stability due to its instability under ambient conditions. The NiFe-LDH was assembled onto the surfaces of exfoliated BP (EBP) nanoflakes to realize the interfacial coupling between them, achieving an effective improvement in electrocatalytic activity and stability. Benefitting from the interfacial P-O bonding, the NiFe-LDH@EBP hybrid shows high OER activity with a low overpotential of ∼240 mV@10 mA cm−2 toward OER under alkaline conditions, as well as the good stability. Density functional theory (DFT) calculations proved that the interface-coupling of NiFe-LDH on BP promotes charge transfer kinetics and balances the adsorption/desorption of reaction intermediates, ultimately imparting excellent OER electrocatalytic activity.

Exfoliation of black phosphorus in isopropanol-water cosolvents

Black phosphorous (BP) has been gaining in popularity in the past decade in the 2D materials community because of the interesting properties of phosphorene, the graphene-type monolayered product obtained by the exfoliation of BP. Not all exfoliations are created equal: the properties – and hence, the usability – of phosphorene flakes can be fine-tuned by the optimization of the process parameters. Moreover, phosphorene processing is inherently sensitive to oxidation issues. Here we report on the liquid phase exfoliation of BP in isopropanol–water cosolvents. The efficiency of the exfoliation was monitored by AFM, DLS, and Raman spectroscopy. Our main findings are that (i) the solvent composition affects the size of the flakes, and that (ii) the extent of oxidation suffered by phosphorene during exfoliation is independent of the isopropanol:water ratio. We achieved optimal results using 30% isopropanol solvent that yielded mostly monolayers and bilayers measuring over 110 nm in diameter.

Covalent carbene modification of 2D black phosphorus

Black phosphorus (BP) has attracted an ever-growing interest due to its unique anisotropic two-dimensional structure, impressive photoelectronic properties and attractive application potential. However, the tools for bandgap engineering and passivation via covalent modification of BP nanosheets remain limited to diazonium salt and nucleophilic addition methods, so that developing new modification strategies for BP nanosheets is crucial to explore its physical and chemical properties and enrich the toolbox for functionalization. Herein, we report the covalent modification of liquid-phase exfoliated BP nanosheets based on a rational analysis of BP structure. The modification of BP is achieved via carbene, a highly reactive organic mediate. The carbene modification improves the solubility and stability of BP nanosheets. Detailed microscopic and spectroscopic characterizations including infrared spectra, Raman spectra, X-ray photoelectron spectra, SEM and TEM were conducted to provide insights for the reaction. The proof of the existence of covalent bonds between BP nanosheets and organic moieties confirms the successful modification. Moreover, theoretical calculations were conducted to unveil the reaction mechanism of the two different types of bonds and the chemical property of two-dimensional BP.

Coupled intramolecular/heterointerfacial electron transfer in polyelectrolyte-shielded Iso-type black phosphorus hetero-structure boosts oxygen reduction kinetics

Searching new structured black phosphorus (BP) and exploring intriguing functions and applications have become a hot topic so far. Here, we introduce a novel Iso-type black phosphorus heterostructure guided by first principle calculation, which features unique heterointerface and electronic coupling interaction via stacking assembly of exfoliated black phosphorus (EBP) and amine-functionalized EBP (N-EBP). Inspired by the theoretical results, we constructed the Iso-type heterostructure comprising of ultrathin exfoliated few-layered EBP and N-EBP, both of which were derived from identical bulk BP. The purposive amine-functionalization not only creates positively-charged P atoms on N-EBP as effective active sites via N-induced intramolecular electron transfer (IET) but also endows N-EBP with lower work function relative to EBP, while the unique EBP/N-EBP Iso-type heterostructure engenders directional heterointerfacial electron transfer (HET). The coupled IET/HET effects optimize the charge redistribution to afford favorable O2 adsorption. In this case, our unique strategy for the first time exploits the inherent catalytic capability of BP toward the oxygen reduction reaction (ORR) and enables the first use of BP as metal-free ORR catalysts for Zn-air cells. The newly-designed heterostructure facilitates a 4-e− transfer ORR relative to inactive EBP or N-EBP. Importantly, the polymer-shielded heterostructure acts as efficient air electrodes to endow a primary Zn-air cell with high stability, large capacity and high energy density—superior to the commercial Pt/C-enabled cell. This study as the first report on metal-free BP-based ORR catalysts and air electrodes not only extends BP’s application scopes but also renders new insight toward design of electronically-coupled superstructures for energy-related applications.

2D Heterostructure of Amorphous CoFeB Coating Black Phosphorus Nanosheets with Optimal Oxygen Intermediate Absorption for Improved Electrocatalytic Water Oxidation.

The oxygen evolution reaction (OER) plays a paramount role in a variety of electrochemical energy conversion devices, and the exploration of highly active, stable, and low-cost electrocatalysts is one of the most important topics in this field. The exfoliated black phosphorus (EBP) nanosheet with a two-dimensional (2D) layered structure has high carrier mobility but is limited by excessive oxygen-containing intermediate absorption and fast deterioration in air. We here report the fabrication of nanohybrids of amorphous CoFeB nanosheets on EBP nanosheets (EBP/CoFeB). The 2D/2D heterostructure, thanks to the electronic interactions and oxygen affinity difference between EBP and CoFeB nanosheets, is capable of balancing the oxygen-containing intermediate absorption to an optimal status for facilitating the OER process. While the crystalline EBP contributes to the improved conductivity, the amorphous coating protects EBP and thus ensures the catalytic stability. The EBP/CoFeB electrocatalyst shows excellent OER performance with an ultralow overpotential of 227 mV at 10 mA cm-2 with an ultrasmall Tafel slope of 36.7 mV dec-1 with excellent stability. This study may inspire more researches to develop heterostructured nanohybrid electrocatalysts for a diversity of electrochemical reactions.

Liquid‐Based Exfoliation of Black Phosphorus into Phosphorene and Its Application for Energy Storage Devices

Black phosphorus (BP) as a rising star among 2D materials has attracted attention for a wide range of applications due to its fascinating properties. The key point for the real application of phosphorene depends on its exfoliation technique to produce high‐quality nanosheets. In recent years, tremendous efforts have been made in the preparation and energy storage application of phosphorene and phosphorene‐based hybrid electrodes. Herein, the state‐of‐the‐art liquid‐based exfoliation and characterization of phosphorene fabricated by sonication, anodic and cathodic electrochemical exfoliation, and bipolar electrochemical exfoliation in diverse solutions and conditions are discussed. In addition, the electrochemical properties and storage mechanism of phosphorene‐based electrodes for rechargeable batteries and supercapacitors are discussed. Finally, the challenges and opportunities of phosphorene nanosheets in terms of exfoliation and energy storage applications are addressed.

Robust Carbon-Stabilization of Few-Layer Black Phosphorus for Superior Oxygen Evolution Reaction

Few-layer exfoliated black phosphorus (Ex-BP) has attracted tremendous attention owing to its promising applications, including in electrocatalysis. However, it remains a challenge to directly use few-layer Ex-BP as oxygen-involved electrocatalyst because it is quite difficult to restrain structural degradation caused by spontaneous oxidation and keep it stable. Here, a robust carbon-stabilization strategy has been implemented to prepare carbon-coated Ex-BP/N-doped graphene nanosheet (Ex-BP/NGS@C) nanostructures at room temperature, which exhibit superior oxygen evolution reaction (OER) activity under alkaline conditions. Specifically, the as-synthesized Ex-BP/NGS@C hybrid presents a low overpotential of 257 mV at a current density of 10 mA cm−2 with a small Tafel slope of 52 mV dec−1 and shows high durability after long-term testing.

Interface and valence modulation on scalable phosphorene/phosphide lamellae for efficient water electrolysis

The quest for high-efficiency and earth-abundant electrocatalysts replacing precious metals for water splitting is actively pursued for the future of hydrogen economy to wean us off the dependency on fossil fuel. Herein, a moderate catalyst is constructed via the in-situ formation of well-defined CoP nanodots on electrochemical exfoliated black phosphorus (EEBP) nanosheets for overall water splitting. The electro-exfoliation process ensures a high-yield (~85%) preparation of BP nanosheets from bulk BP, prompting the large-scale chemosynthesis of CoP/EEBP heterostructures. It is demonstrated that the Co3+/Co2+ and phosphide state ratios can be elegantly tuned in the CoP/EEBP heterostructure to modulate electron donating/accepting characteristics. As for hydrogen and oxygen evolution reaction (HER/OER), CoP/EEBP heterostructure reveals remarkable electrocatalytic capacity with ultralow overpotentials of only 118 mV and 315 mV at 10 mA cm−2 (η10) in alkaline media, respectively. Coupled with CoP/EEBP heterostructure for both anode and cathode, the overall water splitting is attested stably with voltage of 1.666 V at η10, which is among the best list of BP-based water-splitting electrocatalysts. The basis of the promising electrocatalytic activity is investigated using density functional theory (DFT) calculations. The results indicate that the CoP-BP interface coupling could be able to benefit the electron-transfer and accelerate the adsorption/dissociation of water. The research provides primary comprehension for the electrocatalytic fulfilment of black phosphorus revisited through valence modulation and interface engineering.

Ultrathin Black Phosphorus-on-Nitrogen Doped Graphene for Efficient Overall Water Splitting: Dual Modulation Roles of Directional Interfacial Charge Transfer.

Few-layered exfoliated black phosphorus (EBP) has attracted surging interest for electronics, optoelectronics, and catalysis. As compared to excellent progress in electronic and optoelectronic applications, very few reports are available for electrocatalysis by metal-free EBPs. Herein, we couple solution-processable ultrathin EBP nanosheets with higher Fermi level of N-doped graphene (NG) into a new metal-free 2D/2D heterostructure (EBP@NG) with well-designed interfaces and unique electronic configuration, as efficient and durable bifunctional catalysts toward hydrogen evolution and oxygen evolution reactions (HER/OER) for overall water splitting in alkaline media. By rational interface engineering, the synergy of EBP and NG is fully exploited, which not only improves the stability of EBP, but also effectively modulates electronic structures of each component to boost their intrinsic activities. Specifically, due to the lower Fermi level of EBP relative to NG, their electronic interaction induces directional interfacial electron transfer, which not only enriches the electron density over EBP and optimizes H adsorption/desorption to promote HER, but also introduces abundant positively charged carbon sites on NG and provides favorable formation of key OER intermediates (OOH*) to improve OER energetics. Thus, despite that pure EBP or NG alone has poor or negligible activity, EBP@NG achieves remarkably enhanced bifunctional HER/OER activities, along with an excellent durability. This endows an optimized electrolyzer using EBP@NG as anode and cathode with a low cell voltage of 1.54 V at 10 mA cm-2, which is smaller than that of the costly integrated Pt/C@RuO2 couple (1.60 V).

Modelling strategies for the covalent functionalization of 2D phosphorene.

This paper is a comparative outline of the potential acid-base adducts formed by an unsaturated main group or transition metal species and P atoms of phosphorene (Pn), which derives from black phosphorus exfoliation. Various possibilities of attaining a realistic covalent functionalization of the 2D material have been examined via DFT solid state calculations. The distribution of neighbor P atoms at one side of the sheet and the reciprocal directionalities of their lone pairs must be clearly understood to foreshadow the best possible acceptor reactants. Amongst the latter, the main group BH3 or I2 species have been examined for their intrinsic acidity, which favors the periodic mono-hapto anchoring at Pn atoms. The corresponding adducts are systematically compared with other molecular P donors from a phosphine to white phosphorus, P4. Significant variations emerge from the comparison of the band gaps in the adducts and the naked phosphorene with a possible electronic interpretation being offered. Then, the Pn covalent functionalization has been analyzed in relation to unsaturated metal fragments, which, by carrying one, two or three vacant σ hybrids, may interact with a different number of adjacent P atoms. For the modelling, the concept of isolobal analogy is important for predicting the possible sets of external coligands at the metal, which may allow the anchoring at phosphorene with a variety of hapticities. Structural, electronic, spectroscopic and energy parameters underline the most relevant pros and cons of some new products at the 2D framework, which have never been experimentally characterized but appear to be reasonably stable.

Stabilizing ultra-thin black phosphorus with in-situ-grown 1 nm-Al2O3 barrier

Exfoliated black phosphorus is a 2D semiconductor with promising properties for electronics, spintronics, and optoelectronics. Nevertheless, its rapid degradation in air renders its integration and use in devices particularly challenging—even more so for smaller thicknesses for which the degradation rate is tremendously enhanced. In order to effectively protect the thinnest flakes, we present here an approach based on an in-situ dielectric capping to avoid all contact with air. Optical microscopy, Raman spectroscopy, and atomic force microscopy studies confirm that 1 nm of Al2O3 efficiently passivates exfoliated black phosphorus (below 5 layers) on Si/SiO2 substrates. Such an ultrathin and transparent passivation layer can act as a tunnel barrier allowing for black phosphorus devices processing without passivation layer removal.

Efficient and Fast Synthesis of Few‐Layer Black Phosphorus via Microwave‐Assisted Liquid‐Phase Exfoliation

AbstractHigh‐quality, few‐layer black‐phosphorus (BP) flakes are prepared in a common organic solvent with very short processing times using microwave‐assisted liquid‐phase exfoliation. A comprehensive range of analysis, combined with density‐functional theory calculations, confirms that the product prepared using the microwave technique is few‐layer BP with small‐ and large‐area flakes. The suspended exfoliated BP sheets show excellent stability, while samples dispersed onto silicon from the suspensions exhibit low oxidation levels after several days in ambient conditions. This straightforward synthesis method is facile, efficient, and extremely fast, and does not involve use of any surfactant or ultrasonication steps and will facilitate future development of phosphorene research.

2D black phosphorous nanosheets as a hole transporting material in perovskite solar cells

We demonstrate for the first-time liquid exfoliated few layers of 2D Black phosphorus (BP) nanosheets as a hole transporting material (HTM) for perovskite based solar cells. The photoelectron spectroscopy in air (PESA) measurements confirm the low laying valence band level of BP nanosheets (−5.2 eV) favourable for hole injection from CH3NH3PbI3 (MAPbI3). Our results show that ∼25% improvement in power conversion efficiency (PCE) of η = 16.4% for BP nanosheets + Spiro-OMeTAD as an HTM as compared to spiro-OMeTAD (η = 13.1%). When BP nanosheets are exclusively utilised as an HTM, a PCE of η = 7.88% is noted, an improvement over the 4% PCE values observed for HTM free devices. Photoluminescence (PL) quenching of MAPbI3 and impedance measurements further confirm the charge extraction ability of BP nanosheets. The structural and optical characterization of liquid exfoliated BP nanosheets is discussed in detail with the aid of transmission electron microscopy, Raman spectroscopy, absorption spectroscopy and photo-electron spectroscopy.

Platinum-functionalized black phosphorus hydrogen sensors

Black phosphorus (BP), especially in its two-dimensional (2D) form, is an intriguing material because it exhibits higher chemical sensing ability as compared to other thin-film and 2D materials. However, its implementation into hydrogen sensors has been limited due to its insensitivity toward hydrogen. We functionalized exfoliated BP flakes with Pt nanoparticles to improve their hydrogen sensing efficiency. Pt-functionalized BP sensors with back-gated field-effect transistor configuration exhibited a fast response/decay, excellent reproducibility, and high sensitivities (over 50%) at room temperature. Langmuir isotherm model was employed to analyze the Pt-catalyzed BP sensors. Furthermore, the activation energy of hydrogen adsorption on Pt-decorated BP was evaluated, which is equal to the change in work function resulting from hydrogen adsorption on the Pt(111) surface. These results demonstrate that Pt-catalyzed BP exhibits a great potential for next-generation hydrogen sensors.

(Invited) Solution Exfoilated Black Phosphorus and Its Applications

Black phosphorus (BP), has recently attracted much attention all over the world and demonstrated great potential in novel nanoelectronics owing to its direct and narrow bandgap. Regarding to the scale production of BP and its related electronic devices, solution exfoliation reveals superior advances when compared with mechanical exfoliation. Remarkably, liquid-phase exfoliated BP flakes and quantum dots (QDs) exhibit exciting properties in solar cells, electronic, and optical devices. The exfoliation of BP in diverse solvents have been demonstrated. The solution exfoliated BP flakes can be an effective electron transport layer in organic photovoltaics (OPVs). The BP QDs can be incorporated in the active layer of OPV to enhance its power conversion efficiencies. In addition, the BP flakes exhibit nonlinear optical properties which can be an excellent saturable absorber for high energy pulse generation in fiber laser.

(Invited) Solution Exfoilated Black Phosphorus and Its Applications

Black phosphorus (BP), has recently attracted much attention all over the world and shown great potential in novel nanoelectronics owing to its direct and narrow bandgap. Regarding to the scale production of BP and its related electronic devices, solution exfoliation reveals superior advances when compared with mechanical exfoliation. Remarkably, liquid-phase exfoliated BP flakes and quantum dots (QDs) exhibit exciting properties in solar cells, electronic, and optical devices. The exfoliation of BP in diverse solvents have been demonstrated. The solution exfoilated BP flakes can be an effective electron transport layer in organic photovotaics (OPVs). The BP QDs can be incorporated in the active layer of OPV to enhance its power conversion efficiencies. In addition, the BP flakes exhibit nonlinear opical properties which can be an excellent saturable absorber for high energy pulse generation in fiber laser.

Raman Sensitive Degradation and Etching Dynamics of Exfoliated Black Phosphorus

Layered black phosphorus has drawn much attention due to the existence of a band gap compared to the widely known graphene. However, environmental stability of black phosphorus is still a major issue, which hinders the realization of practical device applications. Here, we spatially Raman map exfoliated black phosphorus using confocal fast-scanning technique at different time intervals. We observe a Raman intensity modulation for , B2g, and modes. This Raman modulation is found to be caused by optical interference, which gives insights into the oxidation mechanism. Finally, we examine the fabrication compatible PMMA coating as a viable passivation layer. Our measurements indicate that PMMA passivated black phosphorus thin film flakes can stay pristine for a period of 19 days when left in a dark environment, allowing sufficient time for further nanofabrication processing. Our results shed light on black phosphorus degradation which can aid future passivation methods.

Rapid and Large-Area Characterization of Exfoliated Black Phosphorus Using Third-Harmonic Generation Microscopy.

Black phosphorus (BP) is a layered semiconductor that recently has been the subject of intense research due to its novel electrical and optical properties, which compare favorably to those of graphene and the transition metal dichalcogenides. In particular, BP has a direct bandgap that is thickness-dependent and highly anisotropic, making BP an interesting material for nanoscale optical and optoelectronic applications. Here, we present a study of the anisotropic third-harmonic generation (THG) in exfoliated BP using a fast scanning multiphoton characterization method. We find that the anisotropic THG arises directly from the crystal structure of BP. We calculate the effective third-order susceptibility of BP to be ∼1.64 × 10-19 m2 V-2. Further, we demonstrate that multiphoton microscopy can be used for rapid, large-area characterization indexing of the crystallographic orientations of many exfoliated BP flakes from one set of multiphoton images. This method is therefore beneficial for samples of areas ∼1 cm2 in future investigations of the properties and growth of BP.