Black phosphorus (BP), a promising two-dimensional layer material, has attracted increasing attention due to its high carrier mobility, thickness-dependent tunable bandgap, in-plane anisotropy, and other advantageous characteristics. Because of these excellent characteristics, BP has been considered for applications in optics, electronics, optoelectronics, sensors, and energy storage. However, early studies found that BP has high chemical activity due to the lone pair electrons of P atoms on the surface and edges, resulting in rapid degradation under ambient conditions and limiting many applications. Recently, these thorny issues have been alleviated through superior physical and chemical passivation techniques, and passivated BP can be used in various devices under ambient and water conditions with excellent performance over a long period. This review, highlights the critical problems addressed in solving the serious instability of BP in a harsh environment by effective passivation technology. These unique strategies can provide more researchers with a fundamental study of the fascinating properties of BP. Finally, we found that passivated BP not only showed good stability under ambient conditions but also exhibited excellent performance compared with the original BP. Therefore, it is anticipated that this overview can contribute to the application of BP.

Van der Waals (vdW) heterojunctions based on two-dimensional (2D) atomic crystals have been extensively studied in recent years. Herein, we show that both vertical and lateral vdW heterojunctions can be realized with layered molecular crystals using a two-step physical vapor transport (PVT) process. Both types of heterojunctions show clean and sharp interfaces without phase mixing under atomic force microscopy (AFM). They also exhibit a strong interfacial built-in electric field similar to that of their inorganic counterparts. These heterojunctions have greater potential for device applications than individual materials. The lateral heterojunction (LHJ) devices show rectifying characteristics due to the asymmetric energy barrier for holes at the interface, while the vertical heterojunction (VHJ) devices behave like metal–insulator–semiconductor tunnel junctions, with pronounced negative differential conductance (NDC). Our work extends the concept of vdW heterojunctions to molecular materials, which can be generalized to other layered organic semiconductors (OSCs) to obtain new device functionalities.

Two-dimensional transition-metal dichalcogenides (WS₂ and SnS₂) have recently joined the family of energy storage materials (for lithium-ion batteries and supercapacitors) as a result of their favorable ion intercalation. So far, challenges in the synthesis of phase-pure WS₂, restacking between WS₂ nanosheets, low electronic conductivity, and the brittle nature of WS₂, severely limit its use Li-ion battery application. Herein, we develop a facile low temperature solution sulfuration process to improve battery performance dramatically. The sulfuration process is demonstrated to be effective in converting WO₃ impurities to WS₂, and in repairing the sulfur vacancies, to improve cyclability and rate capability. Lithium-ion battery measurements demonstrate that the stable capacity of the WS₂ anode could be enhanced by 48.4% via sulfuration reprocessing, i.e., from 381.7 to 566.8 mAh/g at a relatively high current density of 0.8 A/g after 50 cycles. We further show that the sulfuration process can be readily extended to other dichalcogenides, and may provide a class of versatile electrode materials for lithium-ion batteries with improved electrochemical characteristics.

Chemical reduction of graphene oxide represents an important route towards large-scale production of graphene sheets for many applications. Thus far, gas-phase reactions have been demonstrated to efficiently reduce graphene oxide, but a molecular understanding of the reaction processes is largely lacking. Here, using molecular dynamics simulations, we compare the reduction of graphene oxide in different environments. We find that NH₃ affords more efficient reduction of hydroxyl and epoxide groups than H₂ and vacuum annealing partly due to lower energy barriers. Various reduction paths of oxygen groups in NH₃ and H₂ are quantitatively identified. Furthermore, we show that with the combination of vacancies and oxygen groups, pyridinic- or pyrrolic-like nitrogen can readily be incorporated into graphene. All of these nitrogen configurations lead to n-doping of the graphene. Our results are consistent with many previous experiments and provide insights towards doping engineering of graphene.