By combining ab initio calculations and experiments, we demonstrate how the band gap of the transition metal trichalcogenide TiS3 can be modified by inducing tensile or compressive strain. In addition, using our calculations, we predicted that the material would exhibit a transition from a direct to an indirect band gap upon application of a compressive strain in the direction of easy electrical transport. The ability to control the band gap and its nature could have a significant impact on the use of TiS3 for optical applications. We go on to verify our prediction via optical absorption experiments that demonstrate a band gap increase of up to 9% (from 0.99 to 1.08 eV) upon application of tensile stress along the easy transport direction.
We have demonstrated the improved performance of oxygen evolution reactions (OER) using Au/nickel phosphide (Ni12P5) core/shell nanoparticles (NPs) under basic conditions. NPs with a Ni12P5 shell and a Au core, both of which have well-defined crystal structures, have been prepared using solution-based synthetic routes. Compared with pure Ni12P5 NPs and Au-Ni12P5 oligomer-like NPs, the core/shell crystalline structure with Au shows an improved OER activity. It affords a current density of 10 mA/cm2 at a small overpotential of 0.34 V, in 1 M KOH aqueous solution at room temperature. This enhanced OER activity may relate to the strong structural and effective electronic coupling between the single-crystal core and the shell.
The development of photocatalysts that can effectively harvest visible light is essential for advances in high-efficiency solar-driven hydrogen generation. Herein, we synthesized water soluble CuInS2 (CIS) and Cu-In-Zn-S (CIZS) quantum dots (QDs) by using one-pot aqueous method. The CIZS QDs are well passivated by glutathione ligands and are highly stable in aqueous conditions. We subsequently applied these QDs as a light harvesting material for photocatalytic hydrogen generation. Unlike most small band gap materials that show extremely low efficiency, these new QDs display remarkable energy conversion efficiency in the visible and near-infrared regions. The external quantum efficiency at 650 nm is ～1.5%, which, to the best of our knowledge, is the highest value achieved until now in the near-infrared region.
Catalytic hydrogenation is an important process in the chemical industry. Traditional catalysts require the effective cleavage of hydrogen molecules on the metal-catalyst surface, which is difficult to achieve with non-noble metal catalysts. In this work, we report a new hydrogenation method based on water/proton reduction, which is completely different from the catalytic cleavage of hydrogen molecules. Active hydrogen species and photo-generated electrons can be directly applied to the hydrogenation process with Cu1.94S-Zn0.23Cd0.77S semiconductor heterojunction nanorods. Nitrobenzene, with a variety of substituent groups, can be efficiently reduced to the corresponding aniline without the addition of hydrogen gas. This is a novel and direct pathway for hydrogenation using non-noble metal catalysts.
Identification of atomic disorders and their subsequent control has proven to be a key issue in predicting, understanding, and enhancing the properties of newly emerging topological insulator materials. Here, we demonstrate direct evidence of the cation antisites in single-crystal SnBi2Te4 nanoplates grown by chemical vapor deposition, through a combination of sub-ångström-resolution imaging, quantitative image simulations, and density functional theory calculations. The results of these combined techniques revealed a recognizable amount of cation antisites between Bi and Sn, and energetic calculations revealed that such cation antisites have a low formation energy. The impact of the cation antisites was also investigated by electronic structure calculations together with transport measurement. The topological surface properties of the nanoplates were further probed by angle-dependent magnetotransport, and from the results, we observed a two-dimensional weak antilocalization effect associated with surface carriers. Our approach provides a pathway to identify the antisite defects in ternary chalcogenides and the application potential of SnBi2Te4 nanostructures in next-generation electronic and spintronic devices.
The development of an electrocatalyst based on abundant elements for the oxygen evolution reaction (OER) is important for water splitting associated with renewable energy sources. In this study, we develop an interconnected Ni(Fe)OxHy nanosheet array on a stainless steel mesh (SSNNi) as an integrated OER electrode, without using any polymer binder. Benefiting from the well-defined three-dimensional (3D) architecture with highly exposed surface area, intimate contact between the active species and conductive substrate improved electron and mass transport capacity, facilitated electrolyte penetration, and improved mechanical stability. The SSNNi electrode also has excellent OER performance, including low overpotential, a small Tafel slope, and long-term durability in the alkaline electrolyte, making it one of the most promising OER electrodes developed.
Because of the coupling between semiconducting and piezoelectric properties in wurtzite materials, strain-induced piezo-charges can tune the charge transport across the interface or junction, which is referred to as the piezotronic effect. For devices whose dimension is much smaller than the mean free path of carriers (such as a single atomic layer of MoS2), ballistic transport occurs. In this study, transport in the monolayer MoS2 piezotronic transistor is studied by presenting analytical solutions for two-dimensional (2D) MoS2. Furthermore, a numerical simulation for guiding future 2D piezotronic nanodevice design is presented.
A thermal emitter composed of a frequency-selective surface metamaterial layer and a hexagonal boron nitride-encapsulated graphene filament is demonstrated. The broadband thermal emission of the metamaterial (consisting of ring resonators) was tailored into two discrete bands, and the measured reflection and emission spectra agreed well with the simulation results. The high modulation frequencies that can be obtained in these devices, coupled with their operation in air, confirm their feasibility for use in applications such as gas sensing.
We report the investigation of the thermoelectric properties of large-scale solution-synthesized Bi2Te3 nanocomposites prepared from nanowires hotpressed into bulk pellets. A third element, Se, is introduced to tune the carrier concentration of the nanocomposites. Due to the Se doping, the thermoelectric figure of merit (ZT) of the nanocomposites is significantly enhanced due to the increased power factor and reduced thermal conductivity. We also find that thermal transport in our hot-pressed pellets is anisotropic, which results in different thermal conductivities along the in-plane and cross-plane directions. Theoretical calculations for both electronic and thermal transport are carried out to establish fundamental understanding of the material system and provide directions for further ZT optimization with adjustments to carrier concentration and mobility.
Recent studies have indicated that two-dimensional (2D) MoS2 exhibits low in-plane and inter-plane thermal conductivities. This poses a significant challenge to heat management in MoS2-based electronic devices. To address this challenge, we have designed MoS2-graphene interfaces that fully utilize graphene, a 2D material that exhibits very high thermal conductivity. First, we performed ab initio atomistic simulations to understand bonding and structural stability at the interfaces. The interfaces that we designed, which were connected via strong covalent bonds between Mo and C atoms, were energetically stable. We then performed molecular dynamics simulations to investigate interfacial thermal conductance in these materials. Surprisingly, the interfacial thermal conductance was high and comparable to those of covalently bonded graphene-metal interfaces. Importantly, each interfacial Mo–C bond served as an independent thermal channel, enabling modulation of the interfacial thermal conductance by controlling the Mo vacancy concentration at the interface. The present work provides a viable heat management strategy for MoS2-based electronic devices.
In this study, high-performance multilayer WSe2 field-effect transistor (FET) devices with carrier type control are demonstrated via thickness modulation and a remote oxygen plasma surface treatment. Carrier type control in multilayer WSe2 FET devices with Cr/Au contacts is initially demonstrated by modulating the WSe2 thickness. The carrier type evolves with increasing WSe2 channel thickness, being p-type, ambipolar, and n-type at thicknesses <3, ～4, and >5 nm, respectively. The thickness-dependent carrier type is attributed to changes in the bandgap of WSe2 as a function of the thickness and the carrier band offsets relative to the metal contacts. Furthermore, we present a strong hole carrier doping effect via remote oxygen plasma treatment. It non-degenerately converts n-type characteristics into p-type and enhances field-effect hole mobility by three orders of magnitude. This work demonstrates progress towards the realization of high-performance multilayer WSe2 FETs with carrier type control, potentially extendable to other transition metal dichalcogenides, for future electronic and optoelectronic applications.
An emerging method for effectively improving the catalytic activity of metal oxide hybrids involves the creation of metal oxide interfaces for facilitating the activation of reagents. Here, we demonstrate that bilayer vesicles formed from a hexavanadate cluster functionalized with two alkyl chains are highly efficient catalysts for the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) with H2O2 at room temperature, a widely used model reaction mimicking the activity of peroxidase in biological catalytic oxidation processes. Driven by hydrophobic interactions, the double-tailed hexavanadate-headed amphiphiles can self-assemble into bilayer vesicles and create hydrophobic domains that segregate the TMB chromogenic substrate. The reaction of TMB with H2O2 takes place at the interface of the hydrophilic and hydrophobic domains, where the reagents also make contact with the catalytic hexavanadate clusters, and it is approximately two times more efficient compared with the reactions carried out with the corresponding unassembled systems. Moreover, the assembled vesicular system possesses affinity for TMB comparable to that of reported noble metal mimic nanomaterials, as well as a higher maximum reaction rate.
Electrical and optical enhancements of single-layer semiconducting materials such as transition metal dichalcogenides have recently been studied to achieve sensitive properties via external treatments, such as the formation of organic/inorganic protecting layers on field-effect transistors (FETs), thermal annealing, and nano-dot doping of sensors and detectors. Here, we propose a new analytical approach to electrical and optical enhancement through a passivation process using atomic layer deposition (ALD), and demonstrate a synthesized MoS2 monolayer incorporated with Al atoms in an Al2O3 passivation layer. The incorporated Al atoms in the MoS2 monolayer are clearly observed by spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) and TEM-energy-dispersive X-ray spectroscopy results. We demonstrate that the chemically incorporated FETs exhibit highly enhanced mobilities of approximately 3.7 cm2·V?1·s?1, forty times greater than that of as-synthesized MoS2, with a three-fold improvement in the photoluminescence properties.
Rechargeable metal-iodine batteries are an emerging attractive electrochemical energy storage technology that combines metallic anodes with halogen cathodes. Such batteries using aqueous electrolytes represent a viable solution for the safety and cost issues associated with organic electrolytes. A hybrid-electrolyte battery architecture has been adopted in a lithium-iodine battery using a solid ceramic membrane that protects the metallic anode from contacting the aqueous electrolyte. Here we demonstrate an eco-friendly, low-cost zinc-iodine battery with an aqueous electrolyte, wherein active I2 is confined in a nanoporous carbon cloth substrate. The electrochemical reaction is confined in the nanopores as a single conversion reaction, thus avoiding the production of I3? intermediates. The cathode architecture fully utilizes the active I2, showing a capacity of 255 mAh·g?1 and low capacity cycling fading. The battery provides an energy density of ～ 151 Wh·kg?1 and exhibits an ultrastable cycle life of more than 1,500 cycles.
The luminescence of semiconductor quantum dots (QDs) can be adjusted using the piezotronic effect. An external mechanical force applied on the QD generates a piezoelectric potential, which alters the luminescence of the QD. A small mechanical force may induce a significant change on the emission spectrum. In the case of InN QDs, it is demonstrated that the unforced emission wavelength is more than doubled by a force of 1 μN. The strategy of using the piezotronic effect to tune the color of the emission leads to promising noncontact forcemeasurement applications in biological and medical sensors and force-sensitive displays. Several piezoelectric semiconductor materials have been investigated in terms of the tunability of the emission wavelength in the presence of an external applied force. It is found that CdS and CdSe demonstrate much higher tunability δλ/δF, which makes them suitable for micro/nano-newton force measurement applications.
Nanosized metal (Pt or Pd)-decorated TiO2 nanofibers (NFs) were synthesized by a wet impregnation method. CdSe quantum dots (QDs) were then anchored onto the metal-decorated TiO2 NFs. The photocatalytic performance of these catalysts was tested for activation and reduction of CO2 under UV-B light. Gas chromatographic analysis indicated the formation of methanol, formic acid, and methyl formate as the primary products. In the absence of CdSe QDs, Pd-decorated TiO2 NFs were found to exhibit enhanced performance compared to Pt-decorated TiO2 NFs for methanol production. However, in the presence of CdSe, Pt-decorated TiO2 NFs exhibited higher selectivity for methanol, typically producing ～90 ppmg?1·h?1 methanol. The CO2 photoreduction mechanism is proposed to take place via a hydrogenation pathway from first principles calculations, which complement the experimental observations.
One-dimension carbon self-doping g-C3N4 nanotubes (CNT) with abundant communicating pores were synthesized via thermal polymerization of saturated or supersaturated urea inside the framework of a melamine sponge for the first time. A ～16% improvement in photoelectric conversion efficiency (η) is observed for the devices fabricated with a binary hybrid composite of the obtained CNT and TiO2 compared to pure TiO2 device. The result of EIS analysis reveals that the interfacial resistance of the TiO2-dye|I3?/I? electrolyte interface of TiO2-CNT composite cell is much lower than that of pure TiO2 cell. In addition, the TiO2-CNT composite cell exhibits longer electron recombination time, shorter electron transport time, and higher charge collection efficiency than those of pure TiO2 cell. Systematic investigations reveal that the CNT boosts the light harvesting ability of the photovoltaic devices by enhancing not only the visible light absorption but also the charge separation and transfer.
This paper offers a comprehensive overview on the role of nanostructures in the development of advanced anode materials for application in both lithium and sodium-ion batteries. In particular, this review highlights the differences between the two chemistries, the critical effect of nanosize on the electrode performance, as well as the routes to exploit the inherent potential of nanostructures to achieve high specific energy at the anode, enhance the rate capability, and obtain a long cycle life. Furthermore, it gives an overview of nanostructured sodium- and lithium-based anode materials, and presents a critical analysis of the advantages and issues associated with the use of nanotechnology.
Hierarchical nano-architectures comprised of ultrathin ternary selenide (CoNiSe2) nanorods were directly grown on nickel foam (NF). The integrated CoNiSe2/NF functions as a robust electrocatalyst with an extremely high activity and stability for emerging renewable energy technologies, and electrochemical oxygen and hydrogen evolution reactions (OER and HER, respectively). The overpotentials required to deliver a current density of 100 mA·cm?2 are as low as 307 and 170 mV for the OER and HER, respectively; therefore, the obtained CoNiSe2 is among the most promising earth-abundant catalysts for water splitting. Furthermore, our synthetic sample validates a two-electrode electrolyzer for reducing the cell voltage in the full water splitting reaction to 1.591 V to achieve a current density of 10 mA·cm?2, which offers a novel, inexpensive, integrated selenide/NF electrode for electrocatalytic applications.
Iron oxides have attracted considerable interest as abundant materials for high-capacity Li-ion battery anodes. However, their fast capacity fading owing to poorly controlled reversibility of the conversion reactions greatly hinders their application. Here, a sandwich-structured nanocomposite of N-doped graphene and nearly monodisperse Fe3O4 nanoparticles were developed as high-performance Li-ion battery anode. N-doped graphene serves as a conducting framework for the self-assembled structure and controls Fe3O4 nucleation through the interaction of N dopants, surfactant molecules, and iron precursors. Fe3O4 nanoparticles were well dispersed with a uniform diameter of ~15 nm. The unique sandwich structure enables good electron conductivity and Li-ion accessibility and accommodates a large volume change. Hence, it delivers good cycling reversibility and rate performance with a capacity of ~1,227 mA·h·g–1 and 96.8% capacity retention over 1,000 cycles at a current density of 3 A·g–1. Our work provides an ideal structure design for conversion anodes or other electrode materials requiring a large volume change.
