High-throughput Synthesis of Solution-Processable van der Waals Heterostructures through Electrochemistry.

Two-dimensional van der Waals heterostructures (2D vdWHs) have recently gained widespread attention because of their abundant and exotic properties, which open up many new possibilities for next-generation nanoelectronics. However, practical applications remain challenging due to the lack of high-throughput techniques for fabricating high-quality vdWHs. Here, we demonstrate a general electrochemical strategy to prepare solution-processable high-quality vdWHs, in which electrostatic forces drive the stacking of electrochemically exfoliated individual assemblies with intact structures and clean interfaces into vdWHs with strong interlayer interactions. Thanks to the excellent combination of strong light absorption, interfacial charge transfer, and decent charge transport properties in individual layers, thin-film photodetectors based on graphene/In2 Se3 vdWHs exhibit great promise for near-infrared (NIR) photodetection, owing to a high responsivity (267 mA W-1 ), fast rise (72 ms) and decay (426 ms) times under NIR illumination. This approach enables various hybrid systems, including graphene/In2 Se3 , graphene/MoS2 and graphene/MoSe2 vdWHs, providing a broad avenue for exploring emerging electronic, photonic, and exotic quantum phenomena.

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

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 (Li4Ti5O12, LiCoO2, Li2MnO4, LiFePO4) 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-Li4Ti5O12 hybrid presents a characteristic flat discharge plateau at 1.55 V (vs. Li/Li+), indicating transformation of Li4Ti5O12 to Li7Ti5O12. Small polarization, high rate capability and excellent cycling stability against mechanical bending are also demonstrated for the prepared EG-Li4Ti5O12 hybrid. Finally, full cells composed of EG-Li4Ti5O12 and EG-LiFePO4 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.

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

MXene (e.g., Ti3 C2 ) 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., Ti3 AlC2 ) 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 (I2 ) assisted etching route for preparing 2D MXene (Ti3 C2 Tx , 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-1 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-1 at a scan rate of 1 mV s-1 , superior to those made from fluoride-based etchants (<290 F g-1 at 1 mV s-1 ). Our strategy provides a promising pathway for the facile and sustainable production of highly stable MXene materials.

Carbon-Supported Copper Nanomaterials: Recyclable Catalysts for Huisgen [3+2] Cycloaddition Reactions.

Highly disperse copper nanoparticles immobilized on carbon nanomaterials (CNMs; graphene/carbon nanotubes) were prepared and used as a recyclable and reusable catalyst to achieve Cu(I) -catalyzed [3+2] cycloaddition click chemistry. Carbon nanomaterials with immobilized N-heterocyclic carbene (NHC)-Cu complexes prepared from an imidazolium-based carbene and Cu(I) show excellent stability including high efficiency at low catalyst loading. The catalytic performance evaluated in solution and in bulk shows that both types of Cu-CNMs can function as an effective recyclable catalysts (more than 10 cycles) for click reactions without decomposition and the use of external additives.

Hybrid Aeromaterials for Enhanced and Rapid Volumetric Photothermal Response.

Conversion of light into heat is essential for a broad range of technologies such as solar thermal heating, catalysis and desalination. Three-dimensional (3D) carbon nanomaterial-based aerogels have been shown to hold great promise as photothermal transducer materials. However, until now, their light-to-heat conversion is limited by near-surface absorption, resulting in a strong heat localization only at the illuminated surface region, while most of the aerogel volume remains unused. We present a fabrication concept for highly porous (>99.9%) photothermal hybrid aeromaterials, which enable an ultrarapid and volumetric photothermal response with an enhancement by a factor of around 2.5 compared to the pristine variant. The hybrid aeromaterial is based on strongly light-scattering framework structures composed of interconnected hollow silicon dioxide (SiO2) microtubes, which are functionalized with extremely low amounts (in order of a few µg cm-3) of reduced graphene oxide (rGO) nanosheets, acting as photothermal agents. Tailoring the density of rGO within the framework structure enables us to control both light scattering and light absorption and thus the volumetric photothermal response. We further show that by rapid and repeatable gas activation, these transducer materials expand the field of photothermal applications, like untethered light-powered and light-controlled microfluidic pumps and soft pneumatic actuators.

Electrochemical Exfoliation to Produce High-Quality Black Phosphorus.

To obtain high-quality two-dimensional (2D) materials from the bulky crystals, delamination under an externally controlled stimulus is crucial. Electrochemical exfoliation of layered materials requires simple instrumentation yet offers high-quality exfoliated 2D materials with high yields and features straightforward upscalability; therefore, it represents a key technology for advancing fundamental studies and industrial applications. Moreover, the solution processability of functionalized 2D materials enables the fabrication of (opto)electronic and energy devices via different printing technologies such as inkjet printing and 3D printing. This paper presents the electrochemical exfoliation protocol for the synthesis of black phosphorus (BP), one of the most promising emerging 2D materials, from its bulk crystals in a step-by-step manner, namely, cathodic electrochemical exfoliation of BP in the presence of N(C4H9)4∙HSO4 in propylene carbonate, dispersion preparation by sonication and subsequent centrifugation for the separation of flakes, and morphological characterization by scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM).

Scalable one-step production of electrochemically exfoliated graphene decorated with transition metal oxides for high-performance supercapacitors.

Graphene and related materials have been widely studied due to their superior properties in a wide range of applications. However, large-scale production remains a critical challenge to enable commercial acceptance. Here, we present a facile, scalable, one-step electrochemical method for producing hybrid transition metal oxide (V, Fe, Ti, or Mn)/graphene materials (TMO-EGs) as active materials for supercapacitors. Therein, we have designed and developed a continuous flow reactor with a high production rate (>4 g h-1) of TMO-EGs, where the TMO accounts for 36 weight%. TMO-EG flakes demonstrate a moderate lateral size of up to 5 µm and a specific surface area of 64 m2 g-1. Notably, TMO-EGs present a capacitance of up to 188 F g-1 as single electrodes in 4 M LiCl. The most promising material, MnOx-EG, has been used for the large-scale production of thin-film supercapacitor devices (40 × 40 × 0.25 mm) in a commercial pilot line. Using 1 M Na2SO4 as the electrolyte, the as-fabricated devices deliver a capacitance of 52 mF cm-2, with 83% capacitance retention after 6000 charge-discharge cycles, comparable to recent reports of similar devices. The simplicity, scalability, and versatility of our method are highly promising to promote the commercial applications of graphene-based materials and can be further developed for the upscalable production of other 2D materials, such as transition metal dichalcogenides and MXenes.

Molecularly Engineered Black Phosphorus Heterostructures with Improved Ambient Stability and Enhanced Charge Carrier Mobility.

Overcoming the intrinsic instability and preserving unique electronic properties are key challenges for the practical applications of black phosphorus (BP) under ambient conditions. Here, it is demonstrated that molecular heterostructures of BP and hexaazatriphenylene derivatives (BP/HATs) enable improved environmental stability and charge transport properties. The strong interfacial coupling and charge transfer between the HATs and the BP lattice decrease the surface electron density and protect BP sheets from oxidation, resulting in an excellent ambient lifetime of up to 21 d. Importantly, HATs increase the charge scattering time of BP, contributing to an improved carrier mobility of 97 cm2 V-1 s-1 , almost three times of the pristine BP films, based on noninvasive THz spectroscopic studies. The film mobility is an order of magnitude larger than previously reported values in exfoliated 2D materials. The strategy opens up new avenues for versatile applications of BP sheets and provides an effective method for tuning the physicochemical properties of other air-sensitive 2D semiconductors.

Ultrafast Electrochemical Synthesis of Defect-Free In2 Se3 Flakes for Large-Area Optoelectronics.

Because of its thickness-dependent direct bandgap and exceptional optoelectronic properties, indium(III) selenide (In2 Se3 ) has emerged as an important semiconductor for electronics and optoelectronics. However, the scalable synthesis of defect-free In2 Se3 flakes remains a significant barrier for its practical applications. Here, a facile electrochemical strategy is presented for the ultrafast delamination of bulk layered In2 Se3 crystals in nonaqueous media, resulting in high-yield (83%) production of defect-free In2 Se3 flakes with large lateral size (up to 26 µm). The intercalation of tetrahexylammonium (THA+ ) ions mainly creates stage-3 intercalated compounds in which every three layers of In2 Se3 are occupied by one layer of THA molecules. The subsequent exfoliation leads to a majority of trilayer In2 Se3 nanosheets. As a proof of concept, solution-processed, large-area (400 µm × 20 µm) thin-film photodetectors embedded with the exfoliated In2 Se3 flakes reveal ultrafast response time with a rise and decay of 41 and 39 ms, respectively, and efficient responsivity (1 mA W-1 ). Such performance surpasses most of the state-of-the-art thin-film photodetectors based on transition metal dichalcogenides.

Click chemistry promoted by graphene supported copper nanomaterials.

A facile and robust approach is provided for the synthesis of highly dispersed copper nanoparticles immobilized onto graphene nanosheets, useful as a recyclable and reusable heterogeneous catalyst with excellent catalytic activity to achieve Cu(I)-catalyzed [3+2] cycloaddition 'click' chemistry.