Ultrathin Nanostructures Research Articles

Three-dimensionally reconfigurable focusing of laser by mechanically tunable metalens doublet with built-in holograms for alignment

Abstract Metalenses have potential to replace various bulky conventional optical elements with ultrathin nanostructure arrays. In particular, active metalenses with reconfigurable focusing capability have attracted considerable interest from the academic and industrial communities. However, their tuning range is currently restricted by limited material properties and fabrication difficulties. Here, a hybrid optical system capable of three-dimensional relocation of a focal spot is proposed and experimentally demonstrated. The system comprises a mechanically actuated passive metalens doublet that can be easily fabricated with commonly available materials and processes. An incident laser can be focused to a desired point in three-dimensional space simply by rotating two metalenses or changing their separation. In addition, exploiting the polarization-multiplexing capability of metasurfaces, a hologram is incorporated to the metalenses to guide rotational and positional alignment of two metasurfaces. The ease of fabrication and alignment provided by this approach could widen its application to many practical fields.

Tunable Plasmonic Perfect Absorber for Hot Electron Photodetection in Gold-Coated Silicon Nanopillars

Infrared detection technology has important applications in laser ranging, imaging, night vision, and other fields. Furthermore, recent studies have proven that hot carriers which are generated by surface plasmon decay can be exploited for photodetection to get beyond semiconductors’ bandgap restriction. In this study, silicon nanopillars (NPs) and gold film at the top and bottom of silicon nanopillars were designed to generate surface plasmon resonance and Fabry–Perot resonance to achieve perfect absorption. The absorption was calculated using the Finite Difference Time Domain (FDTD) method, and factors’ effects on resonance wavelength and absorption were examined. Here we demonstrate how this perfect absorber can be used to achieve near-unity optical absorption using ultrathin plasmonic nanostructures with thicknesses of 15 nm, smaller than the hot electron diffusion length. Further study revealed that the resonance wavelength can be redshifted to the mid-infrared band (e.g., 3.75 μm) by increasing the value of the structure parameters. These results demonstrate a success in the study of polarization insensitivity, detection band adjustable, and efficient perfect absorption infrared photodetectors.

Ni-based ultrathin nanostructures for overall electrochemical water splitting

We outline the synthesis approaches of Ni-utNSs toward improvement in morphology, active structures, efficiency, and stability as well as their electrocatalytic mechanism in order to achieve clean H2 production through overall water splitting.

Facile synthesis of large-size Pd nanosheets-assembled nanofilms with enhanced electrocatalytic performance

Ultrathin metal nanostructures have received extensive attention in the field of electrocatalysis owing to their large surface area and high electron/mass transfer efficiency. Here, large-size Pd nanosheets-assembled nanofilms were synthesized with a facile strategy. The structural advantages endowed Pd nanofilms with outstanding electrocatalytic performance toward ethanol oxidation, including larger electrochemical active surface areas, excellent mass activity, better CO anti-poisoning ability and stability. This work may provide a novel idea for the design and synthesis of high-efficient electrocatalysts.

Transition metal tuned g-C3N4 induce highly efficient photocatalytic of ammonia borane to hydrogen evolution and mechanism investigation

Ammonia borane (AB) aqueous solution can produce high purity hydrogen by catalytic hydrolysis reaction under the action of catalyst. Herein, through hydrogen bonding self-assembly method, g-C3N4 atomic thin nanosheets with the thickness of 1.71 nm were prepared, and transition metal alloy nanoparticles were successfully deposited on its surface by in-situ liquid phase reduction. The TOF values of the prepared CuNiCo/g-C3N4 nanosheets hydrolyzed AB with/without light irradiation are 45.1 and 28.2 respectively, and their activity even exceeds that of some noble metal catalysts. Besides, after five cycles of hydrogen production experiments, the catalytic hydrogen production decreased by less than 2 %, indicating that CuNiCo/CNS has good reusability. By forming an ultra-thin nanostructure, photogenerated electron-hole pairs can transmit faster, and the deposition of the transition metal alloy changes the orbital hybrid mode of g-C3N4, thereby changing the band structure. Cu, Ni and Co are partly involved in the composition of the valence band of g-C3N4, among which the influence of 3d orbital of Co metal is the most severe, indicating that charge polarization occurs in Co as a local electron aggregation center. In addition, the alloy effect of metal catalysis coupled with Schottky junction of photocatalytic semiconductor system and LSPR (Localized Surface Plasmon Resonance) effect of Cu metal jointly improved the synergetic activity of CuNiCo/CNS catalyst.

Ultrathin CoOOH/Co(OH)2 hybrid nanosheets for high-performance anodes of lithium-ion batteries

CoOOH and Co(OH)2 have great potential in lithium-ion battery anodes due to their high theoretical specific capacities. But they suffer from large volume change during the cycle and hence display fast capacity fading. Carbon coated ultrathin two-dimensional porous nanostructure engineering can be conducive to improving cycling stability of both CoOOH and Co(OH)2, but it is a huge challenge. Herein, a tetraethyl orthosilicate (TEOS) assisted synthesis of carbon coated ultrathin porous CoOOH/Co(OH)2 hybrid nanosheets (COH@C NSs) has been proposed and achieved successfully. This original idea using the TEOS as the reactant not only constructs the ultrathin two-dimensional nanosheets as a structure directing reagent but also forms a porous structure as a precursor of SiO2 pore templates. As a result, the COH@C NSs integrate the advantages of ultrathin two-dimensional nanosheets, porous structure and carbon coating, and hence have significantly improved structural stability and electrochemical kinetics during the cycle, delivering 845.3 mA h g−1 in 350th cycle at 200 mA g−1 and 696.2 mA h g−1 in 400th cycle at 1000 mA g−1. This work gives a unique insight for engineering ultrathin two-dimensional porous nanostructure of high-capacity CoOOH/Co(OH)2 hybrid electrode.

Ultrathin Two-Dimensional Fe-Co Bimetallic Oxide Nanosheets for Separator Modification of Lithium-Sulfur Batteries.

The shuttle effect is understood to be the most significant issue that needs to be solved to improve the performance of lithium-sulfur batteries. In this study, ultrathin two-dimensional Fe-Co bimetallic oxide nanosheets were prepared using graphene as a template, which could rapidly catalyze the conversion of polysulfides and inhibit the shuttle effect. Additionally, such ultrathin nanostructures based on graphene provided sufficient active sites and fast diffusion pathways for lithium ions. Taking into account the aforementioned benefits, the ultrathin two-dimensional Fe-Co bimetallic oxide nanosheets modified separator assembled lithium-sulfur batteries delivered an incredible capacity of 1044.2 mAh g-1 at 1 C and retained an excellent reversible capacity of 859.4 mAh g-1 after 100 cycles. Even under high loading, it still achieved high area capacity and good cycle stability (92.6% capacity retention).

Design and fabrication of MOF-derived leaf-like Zn-Co-S nanosheet arrays decorated with Ni-Zn-P ultrathin nanostructure for hybrid supercapacitors

Transitional Metal phosphides and sulfides are considered a promising electrode material in energy storage sources due to their high electronic conductivity, rich valences and high electrochemical activity, and excellent stability. Here, we report porous Ni-Zn-P/Zn-Co-S hybrid nanostructures on nickel foam as a novel free-binder electrode achieved via a facile three-step immersion procedure, a sulfurization process, followed by an electrodeposition approach consisting of leaf-like Zn-Co-S nanosheet arrays covered with ultrathin Ni-Zn-P nanosheets. The unique multicomponent heterostructure of Ni-Zn-P/Zn-Co-S can possess the large accessible surface area, more active sites, promotes free diffusion of electrolytes, shortens the path of electron transfer in electrochemical reaction process, and the synergistic effect from both components, leading to better electrochemical performances. The Ni-Zn-P/Zn-Co-S electrode demonstrates outstanding electrochemical performance, including ultrahigh specific capacitance of 2803 F g−1 at 1.0 A g−1, favourable rate capability, and supreme stability with 91.3% capacitance retention after 3000 cycles.More importantly, a prototype hybrid asymmetric supercapacitor is assembled based on Ni-Zn-P/Zn-Co-S as the battery-type electrode and rGO as the capacitive-type electrode. The fabricated device has a capacitance of 94.51 F g−1 at 2.3 A g−1 and demonstrates an energy density of 30.6 Wh kg−1 at a power density of 1742 W kg−1 with a remarkably long cycle life. This work delivers a simple and innovative strategy to develop advanced binder-free electrodes as a next-generation energy storage system.

Deep eutectic solvent induced ultrathin Co4N/N-doped carbon nanosheets self-supporting electrode for boosting hydrogen evolution integrated with biomass electrooxidation

Metal nitrides are considered promising catalysts for the hydrogen evolution reaction integrated with electrooxidation reaction of biomass due to their metal-like properties. However, the synthesis of metal nitrides involves multi-step reactions and requires continuous reactions under a large amount of NH3 atmosphere. Herein, we exploit deep eutectic solvent (DES) to induce in-situ synthesize N-doped carbon (NC) composite Co4N ultrathin nanosheets self-supporting electrode on carbon cloth (Co4N/NC@CC) without additional input NH3 atmosphere. XAFS spectra showed that the strong interaction between Co4N and NC accelerated the electron transport at the interface, and the ultrathin nanostructure of Co4N/NC is beneficial to increasing the catalytic active sites, thereby effectively improving the catalytic performance of Co4N/NC@CC. During the HER process, Co4N/NC@CC only needs 62, 98, and 60 mV overpotentials to reach a current density of 10 mA/cm2 in alkaline, neutral, and acidic electrolytes. When Co4N/NC@CC is used to produce 2,5-furandicarboxylic acid (FDCA) and hydrogen fuel synchronously in alkaline electrolytes, only a low voltage of 1.38 V is required at 10 mA/cm2, and the conversion rate of 5-hydroxymethylfurfural (HMF) is close to 100 % and the selectivity of FDCA is 98.6 %.

Reciprocal polariton-induced transparency in alpha-molybdenum trioxide-graphene heteronanostructures

An ultrathin heterogeneous nanostructure consisting of periodic orthorhombic-phase molybdenum trioxide (α-MoO3), graphene nanoribbons, and a dielectric spacer layer has been proposed. Coupling between a hyperbolic phonon polariton from α-MoO3 and a surface plasmon polariton from graphene leads to the presence of reciprocal polariton-induced transparency (RPoIT). The near-field coupling is further evaluated by combining the current distribution values of the multipole decomposition. The RPoIT can be controlled by changing the structural parameters and tuning the chemical potential of graphene. Effects of the incidence angle and polarization angle have been investigated thoroughly from the finite-difference time-domain calculations. The potential applications in the refractive index sensor and mid-infrared (MIR) absorbers have also been investigated. This research provides a clear understanding and practical guidance for the realization of tunable RPoIT, which is desirable from the development of nano-devices and multifunctional hybrid polarization devices in the MIR region.

In situ/operando structural tracking of Ni-Fe LDH

Deciphering <i>in situ</i> structure of layer double hydroxides (LDHs) and their corresponding mechanism of oxygen evolution reaction (OER) is essential to further development of LDH-based OER catalysts. In this issue of <i>Chem Catalysis</i>, Ko et al. demonstrated a scalable synthesis of ultrathin Ni-Fe LDH nanostructure, its chemical oxidation process, and its catalytic mechanism by <i>in situ/operando</i> spectroscopies, paving a solid pathway to potential practical application of LDH-based catalysts.

Ultrathin metal organic framework nanosheets with rich defects for enhanced fluoride removal

Herein, we present a defluoridation approach based on ultrathin two-dimensional metal organic framework (MOF, viz., Ce-DCPBA) nanosheets. The nanosized layers and ultimately exposed metal defects of Ce-DCPBA enable the high-capacity adsorption of fluoride in a wide pH window. Attributed to tailored ligand exchange at metal defects and boron-fluoride complexation, Ce-DCPBA exhibits exceptional selectivity for fluoride with a partition coefficient up to 18.805 L g−1, even in the matrixes with ultrahigh salinity (8 mol/L of nitrate). Negligible interference from other anions, superior adsorption ability and favorable reusability promotes the practical application of Ce-DCPBA for the selective and efficient removal of fluoride from complex environmental samples. These findings furnish a promising strategy for the anesis of fluoride contamination, and illuminate the application potentials and superiorities of ultrathin MOFs-based nanostructures for environmental remediation.

One-pot electrochemical synthesis of ultrathin trimetallic Mn-Sn-Co oxide coral-like nanostructure as free-standing active electrode material for energy storage applications

The present study proposes a facile and controllable approach for the design and fabrication of an ultrathin binder-free trimetallic oxide nanostructure on nickel foam as an efficient hybrid supercapacitor. The morphological and physicochemical characteristics of the as-prepared Mn-Sn-Co-1 oxide (MSCO-1) electrode were validated using various techniques. The integrated MSCO-1 electrode displayed a high area-specific capacitance of 4.15 F cm−2 at 1 A g−1, good rate capability, and excellent cycling stability of 92.9 % capacitance retention after 3000 CD cycles in a three-electrode system. Its superior electrochemical performance is related to the distinctive coral-like morphology with a hierarchical porous network structure and synergistic effects of the multi-component metal oxides, effectively improving the electroactive sites and assisting the ease penetration of both electrolyte ions and electrons. Likewise, the corresponding asymmetric supercapacitor (ASC) was successfully fabricated by assembling MSCO-1 and activated carbon (AC) as cathode and anode, respectively, exhibiting a high energy density of 39.6 Wh kg−1 at 800 W kg−1 along with superior cycling stability. Moreover, the asymmetric supercapacitor suggests a good state of health with a small leakage current and low self-discharge, which can maintain 1.2 V of its initial voltage (1.6 V) after eight hours of self-discharge test. We also demonstrated the illumination of a yellow LED indicator for more than 480 s. These exciting results render that the MSCO-1 nanostructure could be a promising electrode in developing energy storage systems for feasible applications.

PtO2-decorated MoS2 ultrathin nanostructures for enhanced NH3 gas sensing properties

Recently, transition metal dichalcogenides (TMDs) have attracted much attention due to their high surface-to-volume ratio, various active edge sites, and adjustable bandgaps. However, in general, TMDs still exhibit low gas response and incomplete recovery. Surface modification is an effective way to facilitate the adsorption and desorption processes, thus enhancing the TMD gas sensor's sensing performance. In this study, a PtO2-decorated MoS2 nanostructure gas sensor was fabricated using a chemical reduction process. The result showed that the as-obtained nanostructures consist of accumulated ultrathin MoS2 nanosheets decorated with spherical PtO2 nanoparticles. The gas response of the as-obtained PtO2-decorated MoS2 gas sensor toward NH3 is remarkably high, with 450% upon 500 ppm NH3, which is almost 20 times higher than that of the pristine MoS2 nanostructure gas sensor in their optimal working conditions. The enhancement in gas sensing properties was attributed to the catalytic spillover effect of PtO2 nanoparticles as well as the formation of p-p heterojunction on the MoS2 surface.

Microwave selective heating ultrafast construction of coral-like TiO2-MXene /graphene hybrid architectures for high-performance lithium-ion battery

Graphene and MXenes, both as an emerging two-dimensional (2D) material, have become the predominant choice of electrochemical energy electrode materials owing to large surface-area-to-volume ratio and high electrical conductivity. However, severe restacking of such 2D ultrathin nanostructures largely lowers active surfaces and thus constrains their applications. Herein, we develop a microwave selective heating strategy that is highly efficient for ultrafast and scalable fabrication of novel coral-like porous MXene/graphene composite with high-quality graphene and well-dispersed TiO2 nanocrystals. The MXene not only works as a source material but also serves as an excellent microwave absorbent, which leads to that reduction of graphene oxides can be completed within only 10 s under microwave irradiation at a much lower applied power of 200 W than the reported value of 1000 W. Especially the coral-like TiO2-MXene/graphene material with large porosity delivers much higher capacity (356 mAh g−1 at 50 mA g−1) and much better rate capability than those for pure graphene, MXene and other MXene/graphene composites. That is attributed to the composites avoids restacking, assures structural stability, and provides high specific surface area and excellent electrons/ions conductivity. This work provides a new route to large-scale and low-cost production of high-performance electrode materials for lithium-ion battery.

Tunable Infrared Detection, Radiative Cooling and Infrared-Laser Compatible Camouflage Based on a Multifunctional Nanostructure with Phase-Change Material.

The nanostructure composed of nanomaterials and subwavelength units offers flexible design freedom and outstanding advantages over conventional devices. In this paper, a multifunctional nanostructure with phase-change material (PCM) is proposed to achieve tunable infrared detection, radiation cooling and infrared (IR)-laser compatible camouflage. The structure is very simple and is modified from the classic metal–dielectric–metal (MIM) multilayer film structure. We innovatively composed the top layer of metals with slits, and introduced a non-volatile PCM Ge2Sb2Te5 (GST) for selective absorption/radiation regulation. According to the simulation results, wide-angle and polarization-insensitive dual-band infrared detection is realized in the four-layer structure. The transformation from infrared detection to infrared stealth is realized in the five-layer structure, and laser stealth is realized in the atmospheric window by electromagnetic absorption. Moreover, better radiation cooling is realized in the non-atmospheric window. The proposed device can achieve more than a 50% laser absorption rate at 10.6 μm while ensuring an average infrared emissivity below 20%. Compared with previous works, our proposed multifunctional nanostructures can realize multiple applications with a compact structure only by changing the temperature. Such ultra-thin, integratable and multifunctional nanostructures have great application prospects extending to various fields such as electromagnetic shielding, optical communication and sensing.

Anchoring ZnIn2S4 nanosheets on ultrathin boron carbon nitride layers for improved photo-redox catalysis

Ultrathin boron carbon nitride (BCN) nanosheets as fascinating candidates for advanced photocatalysis have aroused broad attention due to their highly stable physicochemical characteristics and potential chemical reaction carriers. However, its catalytic efficiency is ultimately limited by the sluggish kinetics of surface/interfacial photoexcitation charges and visible photons absorption. Herein, we report the exquisite design and construction of hierarchically layered heterostructures BCN-ZnIn2S4 that involve solution-processed surface growth of ZnIn2S4 subunits on the ultrathin sheet-shaped BCN nanostructures. The intimate interface contact of BCN and ZnIn2S4 architectures accelerate the separation/mobility of light-induced charges, as well as provides more active sites. In addition, the highly visible light response of the ZnIn2S4 component resulting from a suitable bandgap structure is favourable to the effective visible photons adsorption and utilization. The optimized BCN-ZnIn2S4 composite remarkably enhanced the photo-redox efficiency in the reductive CO2 deoxygenation (CO-releasing rate of 38.6 μmol h−1) and oxidative aromatic alcohols dehydrogenation (conversion of 81.6%) under visible light, which is 386-fold and 2-fold enhance performance compared to the pristine ultrathin BCN nanosheets, respectively.

Synergistic effect of oxidation etching and phase transformation triggered by controllable ion-bath microenvironments toward constructing ultra-thin porous nanosheets for accelerated industrial water splitting at high current density

Precisely tailoring the structure of inorganic materials at the micron and nanometer scales, especially in collaboration with component customization to design efficient, stable and low-cost transition-metal-based catalysts for industrial electrocatalytic water splitting (EWS) is a key renewable energy technology, but still facing a daunting challenge. Here, the controllable escape of Ni atom is adopted to disturb the hydrothermal ion-bath environment, thereby resulting in the coexistence of high valence Ni and Fe ions. Combined with a one-step hydrothermal coordination strategy, the timeline-adjusted ion-bath microenvironment can effectively trigger the phase transformation of carbonate hydroxide hydrate nanosheets (NFCH) to nickel ferrite intercalated NFCH ultra-thin porous nanosheets (NF-CH-O). Thanks to the high-energy phase boundary synergistic effect and the rapid mass transfer advantages of ultra-thin porous nanostructures, the as-prepared NF-CH-O nanosheets exhibit remarkable oxygen and hydrogen evolution reaction (OER/HER) catalytic activity and stability, with low overpotentials of 207/191 mV at 50 mA cm−2, respectively, as well as the activity retention for 100 h. The alkaline water electrolyzer set up with NF-CH-O as both anodic and cathodic electrodes only requires a cell potential of 1.688 V to reach 50 mA cm−2 in a continuous operation of 100 h. More impressively, NF-CH-O only requires overpotentials of 266, 292 mV and 1.877 V to drive high current densities up to 500 mA cm−2 for OER, HER and EWS, respectively, and exhibits excellent stability with a reduction in the activity of less than 10% over cycles of more than 65 h. This work highlights the room-temperature controllable ion-bath oxidative etching strategy to design efficient bifunctional catalysts with ultra-thin porous structure and high-current–density activity. Meanwhile, combined with the advantages of direct growth on the substrate for mass production, such meticulous consideration of nanostructured design will be more competitive in the H2-production industry.

Pencil Scripted Ultrathin Graphene Nanostructure as Binder‐Free Battery‐Type Electrode for Li‐Ion Micro‐Capacitors with Excellent Performance

Herein, a binder‐free graphene nanostructure anode formulated by drawing on Cu current collector with a commercial 10B pencil is reported. The prepared pencil‐trace electrode (10B pencil graphite, 10B PG) shows an excellent cycling profile with ≈87% capacity retention characteristics after 1000 cycles. Further, a dual‐carbon lithium‐ion capacitor (LIC) is fabricated using the pencil‐trace electrode as battery‐type electrode and commercial activated carbon (AC) as capacitor electrode in aprotic organic solutions. The 10B PG is pre‐lithiated prior to LIC fabrication to ensure an ample supply of Li‐ions during cycling. The developed LIC, 10B PG/AC assembly, displays a remarkable energy density of 109.9 Wh kg−1 irrespective of the applied current density, that is, power.

Constructing La-doped ultrathin Co-based nanostructured electrocatalysts for high-performance water oxidation process

Constructing highly efficient and low cost electrocatalysts for oxygen evolution reaction (OER) is pivotal to various energy storage and conversion devices. In this work, five different rare earth (RE) metals doped (La, Ce, Pr, Nd, Er) Ag-nanoparticles-decorated α-Co(OH) 2 nanostructured electrocatalysts, which are grown on nickel foam (NF), are successfully prepared by a facile one-step hydrothermal approach. It is found that La-doped 2D ultrathin (∼2.0 nm) CoAg nanosheets arrays (denoted as La–CoAg/NF) can demonstrate the highest electrochemical activity towards OER in 1 M KOH solution among these RE-doped electrocatalysts. It delivers the lowest overpotential at 10 mA cm −2 (233 mV), the smallest Tafel slope (44.3 mV dec −1 ) and extraordinary stability for 35 h with no significant change during harsh OER process. The reasons for the enhanced performance may come from unique ultrathin 2D nanostructure and La-induced strong electronic interaction among Co, Ag, and La atoms. This work provides an essential insight to the development of RE-metal doped electrocatalysts for energy conversion. • Rare earth metal doped CoAg nanosheet is synthesized by a facile approach. • La–CoAg/NF exhibits excellent OER activity in 1 M KOH solution. • The enhancement mechanism by La-doping was revealed.