Electrocatalytically Active Graphene–Porphyrin MOF Composite for Oxygen Reduction Reaction

Pyridine-functionalized graphene (reduced graphene oxide) can be used as a building block in the assembly of metal organic framework (MOF). By reacting the pyridine-functionalized graphene with iron–porphyrin, a graphene–metalloporphyrin MOF with enhanced catalytic activity for oxygen reduction reactions (ORR) is synthesized. The structure and electrochemical property of the hybrid MOF are investigated as a function of the weight percentage of the functionalized graphene added to the iron–porphyrin framework. The results show that the addition of pyridine-functionalized graphene changes the crystallization process of iron–porphyrin in the MOF, increases its porosity, and enhances the electrochemical charge transfer rate of iron–porphyrin. The graphene–metalloporphyrin hybrid shows facile 4-electron ORR and can be used as a promising Pt-free cathode in alkaline Direct Methanol Fuel Cell

Degradation of Two-Dimensional CH₃NH₃PbI₃ Perovskite and CH₃NH₃PbI₃/Graphene Heterostructure

Hybrid organic–inorganic metal halide perovskites have been considered as promising materials for boosting the performance of photovoltaics and optoelectronics. Reduced-dimensional condiments and tunable properties render two-dimensional (2D) perovskite as novel building blocks for constructing micro-/nanoscale devices in high-performance optoelectronic applications. However, the stability is still one major obstacle for long-term practical use. Herein, we provide microscale insights into the degradation kinetics of 2D CH₃NH₃PbI₃ (MAPbI₃) perovskite and CH₃NH₃PbI₃/graphene heterostructures. It is found that the degradation is mainly caused by cation evaporation, which consequently affects the microstructure, light–matter interaction, and the photoluminescence quantum yield efficiency of the 2D perovskite. Interestingly, the encapsulation of perovskite by monolayer graphene can largely preserve the structure of the perovskite nanosheet and maintain reasonable optical properties upon exposure to high temperature and humidity. The heterostructure consisting of perovskite and another 2D impermeable material affords new possibilities to construct high-performance and stable perovskite-based optoelectronic devices

Electrochemical Delamination of CVD-Grown Graphene Film: Toward the Recyclable Use of Copper Catalyst

The separation of chemical vapor deposited (CVD) graphene from the metallic catalyst it is grown on, followed by a subsequent transfer to a dielectric substrate, is currently the adopted method for device fabrication. Most transfer techniques use a chemical etching method to dissolve the metal catalysts, thus imposing high material cost in large-scale fabrication. Here, we demonstrate a highly efficient, nondestructive electrochemical route for the delamination of CVD graphene film from metal surfaces. The electrochemically delaminated graphene films are continuous over 95% of the surface and exhibit increasingly better electronic quality after several growth cycles on the reused copper catalyst, due to the suppression of quasi-periodical nanoripples induced by copper step edges. The electrochemical delamination process affords the advantages of high efficiency, low-cost recyclability, and minimal use of etching chemicals

Additional file 1: of Efficiency Enhancement of Perovskite Solar Cells by Pumping Away the Solvent of Precursor Film Before Annealing

J-V curves of both the reference and modified devices measured in dark condition. J-V curves and photovoltaic parameters of a modified MAPbI3 − x Cl x -based device scanned in both forward and reverse directions. Device stability of both reference and modified devices measured in air (humidity: ~40 %, temperature: ~20 °C)

Using the Graphene Moiré Pattern for the Trapping of C₆₀ and Homoepitaxy of Graphene

The graphene Moiré superstructure offers a complex landscape of humps and valleys to molecules adsorbing and diffusing on it. Using C₆₀ molecules as the classic hard sphere analogue, we examine its assembly and layered growth on this corrugated landscape. At the monolayer level, the cohesive interactions of C₆₀ molecules adsorbing on the Moiré lattice freeze the molecular rotation of C₆₀ trapped in the valley sites, resulting in molecular alignment of all similarly trapped C₆₀ molecules at room temperature. The hierarchy of adsorption potential well on the Moiré lattice causes diffusion-limited dendritic growth of C₆₀ films, as opposed to isotropic growth observed on a smooth surface like graphite. Due to the strong binding energy of the C₆₀ film, part of the dentritic C₆₀ films polymerize at 850 K and act as solid carbon sources for graphene homoepitaxy. Our findings point to the possibility of using periodically corrugated graphene in molecular spintronics due to its ability to trap and align organic molecules at room temperature

Solvothermal Growth of Bismuth Chalcogenide Nanoplatelets by the Oriented Attachment Mechanism: An in Situ PXRD Study

Ultrathin two-dimensional bismuth chalcogenide materials have received substantial research attention due to their potential applications in electronics and optoelectronics. While solvothermal synthesis is considered to be one of the most promising methods for large-scale production of such materials, the mechanisms that govern the crystallization during solvothermal treatment are still poorly understood. In this work, the solvothermal syntheses of Bi₂Se_<i>x</i>Te_3–<i>x</i> (<i>x</i> = 0–3) hexagonal nanoplatelets were monitored by synchrotron-based in situ powder X-ray diffraction, which enabled investigation of crystallization curves, lattice parameters, and crystal size evolution under a variety of synthesis conditions. On the basis of the crystallization curves and crystal size evolution, a general 3-step crystallization process has been deduced: (1) An induction period for the dissolution of the precursor and nucleation of Bi₂Se_<i>x</i>Te_3–<i>x</i>, followed by (2) rapid growth of planar crystals through the oriented attachment, and finally (3) a diffusion-controlled slow growth step consuming the remaining precursor from the solution. Oriented attachment is very effective for the growth of binary composites, resulting in a high yield of large planar crystals; however, it is much less effective for the growth of ternary composites due to lattice mismatch of the nuclei formed at the induction period, producing much smaller crystals accompanied by a limited yield of large planar crystals. Additionally, three intermediate phases (Bi₂TeO₅, Bi₂SeO₅, and Na₂SeO₃) were observed that played an important role in controlling the phase separation as well as the composition of the final ternary compounds

Graphene–Bi₂Te₃ Heterostructure as Saturable Absorber for Short Pulse Generation

Rapid progresses have been achieved in the photonic applications of two-dimensional materials such as graphene, transition metal dichalcogenides, and topological insulators. The strong light–matter interactions and large optical nonlinearities in these atomically thin layered materials make them promising saturable absorbers for pulsed laser applications. Either Q-switching or mode-locking pulses with particular output characteristics can be achieved by using different saturable absorbers. However, it remains still very challenging to produce saturable absorbers with tunable optical properties, in particular, carrier dynamics, saturation intensity as well as modulation depth, to suit for self-starting, high energy or ultrafast pulse laser generation. Here we report a new type of saturable absorber which is a van der Waals heterostructure consisting of graphene and Bi₂Te₃. The synergetic integration of these two materials by epitaxial growth affords tunable optical properties, that is, both the photocarrier dynamics and the nonlinear optical modulation are variable by tuning the coverage of Bi₂Te₃ on graphene. We further fabricated graphene–Bi₂Te₃ saturable absorbers and incorporated them into a 1.5 μm fiber laser to demonstrate both Q-switching and mode-locking pulse generation. This work provides a new insight for tailoring two-dimensional heterostructures so as to develop desired photonic applications

Mechanically-Assisted Electrochemical Production of Graphene Oxide

Graphene oxide (GO) is promising for a variety of applications due to its excellent dispersibility and processability. However, current chemical oxidation routes have several drawbacks, including the use of explosive oxidizing agents, residual metal ions contaminations, and the creation of irreparable hole defects on the GO sheet. The electrochemical exfoliation and oxidation of graphite is a potentially greener approach without the need for extensive purification steps. Most reported electrochemical methods employ a single preformed bulk graphite as electrode, which limits their scalability, reproducibility, and degree of oxidation. Herein, we reported a novel mechanically assisted electrochemical method to produce graphene oxide directly from graphite flakes. The electrochemically derived graphene oxide (EGO) shows a good degree of oxidation but with less physical defects than chemically derived graphene oxide (CGO). EGO has good dispersibility in water and various solvents and, in particular, displays better long-term stability in ethanol when compared with CGO. Notably, unlike conventional CGO, EGO can undergo facile thermal conversion at 200 °C in air to conductive thermally processed EGO, which is highly desirable for heat/chemical-sensitive applications

Two-Dimensional CH₃NH₃PbI₃ Perovskite: Synthesis and Optoelectronic Application

Hybrid organic–inorganic perovskite materials have received substantial research attention due to their impressively high performance in photovoltaic devices. As one of the oldest functional materials, it is intriguing to explore the optoelectronic properties in perovskite after reducing it into a few atomic layers in which two-dimensional (2D) confinement may get involved. In this work, we report a combined solution process and vapor-phase conversion method to synthesize 2D hybrid organic–inorganic perovskite (<i>i.e.</i>, CH₃NH₃PbI₃) nanocrystals as thin as a single unit cell (∼1.3 nm). High-quality 2D perovskite crystals have triangle and hexagonal shapes, exhibiting tunable photoluminescence while the thickness or composition is changed. Due to the high quantum efficiency and excellent photoelectric properties in 2D perovskites, a high-performance photodetector was demonstrated, in which the current can be enhanced significantly by shining 405 and 532 nm lasers, showing photoresponsivities of 22 and 12 AW^–1 with a voltage bias of 1 V, respectively. The excellent optoelectronic properties make 2D perovskites building blocks to construct 2D heterostructures for wider optoelectronic applications

Giant Plasmene Nanosheets, Nanoribbons, and Origami

We introduce <i>Plasmene</i> in analogy to grapheneas free-standing, one-particle-thick, superlattice sheets of nanoparticles (“meta-atoms”) from the “plasmonic periodic table”, which has implications in many important research disciplines. Here, we report on a general bottom-up self-assembly approach to fabricate giant plasmene nanosheets (<i>i.e.</i>, plasmene with nanoscale thickness but with macroscopic lateral dimensions) as thin as ∼40 nm and as wide as ∼3 mm, corresponding to an aspect ratio of ∼75 000. In conjunction with top–down lithography, such robust giant nanosheets could be milled into one-dimensional nanoribbons and folded into three-dimensional origami. Both experimental and theoretical studies reveal that our giant plasmene nanosheets are analogues of graphene from the plasmonic nanoparticle family, simultaneously possessing unique structural features and plasmon propagation functionalities