Hybrid Materials Based on Carbon Nanotubes and Graphene: Synthesis, Interfacial Processes, and Applications in Chemical Sensing

Development of hybrid nanostructures based on two or more building blocks can significantly expand the complexity and functionality of nanomaterials. For the specific objective of advanced sensing materials, single-walled carbon nanotubes and graphene have been recognized as ideal platforms, because of their unique physical and chemical properties. Other functional building blocks include polymers, metal and metal oxide nanostructures, and each of them has the potential to offer unique advances in the hybrid systems. In any case of constructing hybrid nanostructures, challenges exist in the controlling of composition, morphology and structure of different nanoscale building blocks, as well as the precise placement of these building blocks in the final assembly. Both objectives require systematical exploration of the synthetic conditions. Furthermore, there has been an increasing recognition of the fundamental importance of interface within the nanohybrid systems, which also requires detailed investigation. We have successfully developed several innovative synthetic strategies to regulate the assembly of nanoscale building blocks and to control the morphology of the hybrid systems based on graphitic carbon nanomaterials. We demonstrate the importance of surface chemistry of each building block in these approaches. Moreover, interfacial processes in the hybrid system have been carefully investigated to elucidate their impacts on the functions of the hybrid products. Specifically, we explored the synthesis and characterization of hybrid nanomaterials based on single-walled carbon nanotubes and graphene, with other building blocks including conducting polymers, metal, metal oxide and ceramic nanostructures. We demonstrated the development of core/shell morphology for polyaniline and titanium dioxide functionalized single-walled carbon nanotubes, and we showed a bottom-up synthesis of metal nanostructures that involves directed assembly and nanowelding of metal nanoparticles on the graphitic surfaces. Through electrical, electrochemical and spectroscopic characterizations, we further investigated their surface chemistry, interfacial interaction/processes, as well as their fundamental influence on the performance of the hybrid systems. We showed improved or even synergic properties for each hybrid system. Their chemical sensitivities, material stabilities, and charge separation efficiency were superior to individual components. These properties hold great promise in the real-world sensor applications, and can potentially benefit other research fields such as catalysis and green energy

Towards barrier free contact to MoS2 using graphene electrodes

The two-dimensional (2D) layered semiconductors such as MoS2 have attracted tremendous interest as a new class of electronic materials. However, there is considerable challenge in making reliable contacts to these atomically thin materials. Here we present a new strategy by using graphene as back electrodes to achieve Ohmic contact to MoS2. With a finite density of states, the Fermi level of graphene can be readily modified by gate potential to ensure a nearly perfect band alignment with MoS2. We demonstrate, for the first time, a transparent contact can be made to MoS2 with essentially zero contact barrier and linear output behaviour at cryogenic temperatures (down to 1.9 K) for both monolayer and multilayer MoS2. Benefiting from the barrier-free transparent contacts, we show that a metal-insulator-transition (MIT) can be observed in a two-terminal MoS2 device, a phenomenon that could be easily masked by Schottky barrier and only seen in four-terminal devices in conventional metal-contacted MoS2 system. With further passivation y born nitride encapsulation, we demonstrate a record high extrinsic (two-terminal) field effect mobility over 1300 cm2/Vs in MoS2

Wafer-scale growth of large arrays of perovskite microplate crystals for functional electronics and optoelectronics

Methylammonium lead iodide perovskite has attracted intensive interest for its diverse optoelectronic applications. However, most studies to date have been limited to bulk thin films that are difficult to implement for integrated device arrays because of their incompatibility with typical lithography processes. We report the first patterned growth of regular arrays of perovskite microplate crystals for functional electronics and optoelectronics. We show that large arrays of lead iodide microplates can be grown from an aqueous solution through a seeded growth process and can be further intercalated with methylammonium iodide to produce perovskite crystals. Structural and optical characterizations demonstrate that the resulting materials display excellent crystalline quality and optical properties. We further show that perovskite crystals can be selectively grown on prepatterned electrode arrays to create independently addressable photodetector arrays and functional field effect transistors. The ability to grow perovskite microplates and to precisely place them at specific locations offers a new material platform for the fundamental investigation of the electronic and optical properties of perovskite materials and opens a pathway for integrated electronic and optoelectronic systems.Comment: 8 pages, 4 figure

Boosting the performance of single-atom catalysts via external electric field polarization

Single-atom catalysts represent a unique catalytic system with high atomic utilization and tunable reaction pathway. Despite current successes in their optimization and tailoring through structural and synthetic innovations, there is a lack of dynamic modulation approach for the single-atom catalysis. Inspired by the electrostatic interaction within specific natural enzymes, here we show the performance of model single-atom catalysts anchored on two-dimensional atomic crystals can be systematically and efficiently tuned by oriented external electric fields. Superior electrocatalytic performance have been achieved in single-atom catalysts under electrostatic modulations. Theoretical investigations suggest a universal “onsite electrostatic polarization” mechanism, in which electrostatic fields significantly polarize charge distributions at the single-atom sites and alter the kinetics of the rate determining steps, leading to boosted reaction performances. Such field-induced on-site polarization offers a unique strategy for simulating the catalytic processes in natural enzyme systems with quantitative, precise and dynamic external electric fields

Single-atom tailoring of platinum nanocatalysts for high-performance multifunctional electrocatalysis

Platinum-based nanocatalysts play a crucial role in various electrocatalytic systems that are important for renewable, clean energy conversion, storage and utilization. However, the scarcity and high cost of Pt seriously limit the practical application of these catalysts. Decorating Pt catalysts with other transition metals offers an effective pathway to tailor their catalytic properties, but often at the sacrifice of the electrochemical active surface area (ECSA). Here we report a single-atom tailoring strategy to boost the activity of Pt nanocatalysts with minimal loss in surface active sites. By starting with PtNi alloy nanowires and using a partial electrochemical dealloying approach, we create single-nickel-atom-modified Pt nanowires with an optimum combination of specific activity and ECSA for the hydrogen evolution, methanol oxidation and ethanol oxidation reactions. The single-atom tailoring approach offers an effective strategy to optimize the activity of surface Pt atoms and enhance the mass activity for diverse reactions, opening a general pathway to the design of highly efficient and durable precious metal-based catalysts

Single-atom tailoring of platinum nanocatalysts for high-performance multifunctional electrocatalysis

Platinum-based nanocatalysts play a crucial role in various electrocatalytic systems that are important for renewable, clean energy conversion, storage and utilization. However, the scarcity and high cost of Pt seriously limit the practical application of these catalysts. Decorating Pt catalysts with other transition metals offers an effective pathway to tailor their catalytic properties, but often at the sacrifice of the electrochemical active surface area (ECSA). Here we report a single-atom tailoring strategy to boost the activity of Pt nanocatalysts with minimal loss in surface active sites. By starting with PtNi alloy nanowires and using a partial electrochemical dealloying approach, we create single-nickel-atom-modified Pt nanowires with an optimum combination of specific activity and ECSA for the hydrogen evolution, methanol oxidation and ethanol oxidation reactions. The single-atom tailoring approach offers an effective strategy to optimize the activity of surface Pt atoms and enhance the mass activity for diverse reactions, opening a general pathway to the design of highly efficient and durable precious metal-based catalysts