Hierarchical Structured Materials Research Articles

Fabrication of hierarchical ZnCo2O4 nanosheets/oxidized Mo3C2 MXene for a high-performance supercapacitor

In this work, hierarchical structured materials composed of ZnCo2O4 nanosheets and MXene (Mo3C2) are successfully synthesized on a substrate using a simple solvothermal process. The Mo3C2/MoO3 heterostructure is generated through the rapid oxidation of Mo3C2 at moderate temperatures. The ZnCo2O4/Mo3C2/MoO3 electrode demonstrates remarkable specific capacitance and cycling stability, which can be ascribed to the rational design of the structure that promotes ion transport. In addition, the asymmetric supercapacitor (ASC) device exhibits excellent energy density of 44.6 Wh kg−1 at a power density of 375 W kg−1. The exceptional performance indicates that ZnCo2O4/Mo3C2/MoO3 structure is a promising candidate for electrode material in energy storage devices.

Self-supported FeCo2O4/CoO@CNTs film as cathode material to construct high energy density supercapacitor

A simple hydrothermal method was used to synthesize FeCo2O4/CoO@CNTs composite material as the cathode material of asymmetric supercapacitor. Based on the advantages of single/bimetal oxide and the synergistic effect after compounding, the hierarchical structure material can improve the energy density. The electrode material has a capacitance of 965 F g−1 at 1 A/g. The specific capacitance of an asymmetric supercapacitor assembled with FeCo2O4/CoO@CNTs as the positive electrode, carbon nanotubes (CNTs) as the negative electrode and KOH as the electrolyte is 142.5 F g−1 at 1 A/g. The capacity retention rate is 93.7 % after 10,000 cycles, and the device delivered efficient energy of 44.5 Wh kg−1 at 750 W kg−1. It demonstrates the application prospects of the prepared composite materials in energy storage.

Hierarchical polypyrrole@MXene (Ti3C2TX) fiber strain sensors for wearable healthcare electronics

Flexible sensors are an important component of wearable medical electronics and hold considerable promise for research. Presently, stretchable strain sensors face two primary challenges: balancing the sensing range with sensitivity, and ensuring compatibility between conductivity and mechanical properties. Here, flexible sensing fibers with high gauge factor (GF) and wide monitoring range are reported based on a hierarchical structure composed of electrostatic adsorption principle and hydrogen bonding interactions. The hierarchical structure material consists of thermoplastic polyurethane (TPU), MXene, polypyrrole (PPy) and waterborne polyurethane (WPU). Among them, MXene (2D) and PPy (3D) are uniformly distributed on the surface of the MXene/TPU fiber (1D) to form a conductive and sensing pathway. This multi-dimensional combination approach enables the fiber sensor to have a high sensing range (0 ∼ 106 %) and high sensitivity (60 ∼ 3.23 × 106). In addition, the WPU acts as a protective layer, which not only reduces the damage to the sensing layer, but also improves the stretchability (>750 %) and modulus (∼12 MPa) of the sensor. Therefore, it can function as fiber sensor for monitoring not only human movement but also swelling in the legs of patients with varicose veins. The sensor also has a joule heating effect, as well as the potential to be integrated into fabrics, providing an important case for the construction of multifunctional flexible wearable medical electronics with practical applications.

Preparation of hierarchical directional porous alumina microspheres with high porosity, low density, and low thermal conductivity via spray freeze drying with heat treatment

Hierarchical structure materials have been widely applied in various fields due to their unique structure. However, pores collapse at high temperatures may cause the properties loss of materials. Fortunately, the thermal stability of alumina could maintain the structure stable at high temperatures. In this research, Al(NO3)3·9H2O was selected as the alumina source, using spray freeze drying combined with heat treatment to fabricate hierarchical directional porous alumina microspheres (HDPAMs). The alumina microspheres fabricated by this method have the advantage of high porosity, low density, low thermal conductivity, and high-temperature structure stability. Furthermore, the relationship between the condition of fabrication and the parameters of HDPAMs was explored and the thermal conductivity of HDPAMs was investigated. Moreover, simulations using COMSOL Multiphysics have been conducted to explore the superiority of hierarchical directional porous structures in terms of thermal insulation.

Non-linear tendon fatigue life under uncertainties

Tendons play a pivotal role in facilitating joint movement by transmitting muscular forces to bones. The intricate hierarchical structure and diverse material composition of tendons contribute to their non-linear mechanical response. However, comprehensively grasping their mechanical properties poses a challenge due to inherent variability in biological tissues. This necessitates a thorough examination of uncertainties associated with properties measurements, particularly under diverse loading conditions. Given the cyclic loading experienced by tendons throughout an individual's lifespan, understanding their mechanical behaviour under such circumstances becomes crucial.This study addresses this need by introducing a generalised Paris Erdogan Law tailored for non-linear materials. To examine uncertainties within this proposed framework, Monte Carlo Analysis is employed. This approach allows for a thorough exploration of the uncertainties associated with tendon mechanics, contributing to a more robust comprehension of their behaviour under cyclic loading conditions.Finally, self-healing has been integrated into the fatigue law of tendons through the proposal of a healing function, formulated as a polynomial function of the maximum stress. This approach allows to account for an increase in the number of cycles for each stress value due to self-repair after the damage event generated by long-term cycling load over the individual's life span.

Implicitly Represented Architected Materials for Multi‐Scale Design and High‐Resolution Additive Manufacturing

AbstractBio‐inspired structured materials have achieved unprecedented progress in realizing exceptional, effective properties. However, a rational design paradigm that enables both tailoring complex 3D architectures and manufacturing the engineered hierarchical structured materials is still missing. To bridge this gap, this study presents a holistic design‐through‐printing framework with implicitly represents cellular materials for high‐resolution structured materials design and manufacturing. Attributed to the parameterized implicit function‐based representation (FRep), the material's microstructures can be effectively controlled to tune the material properties (e.g., isotropic, orthotropic, and anisotropic) while enabling functional gradation in the multi‐scale hierarchical design. Given prescribed material properties in different applications, the proposed framework finds the optimal layout of microstructures with an adaptive cluster‐based topology optimization algorithm. The geometry frustration problem brought by the mixture of distinct microstructures is simultaneously addressed with a spatial gradation scheme in the optimization loop. Lastly, the FRep‐based architected material enables efficient geometry processing (e.g., slicing) for modern AM processes, thus facilitating the manufacturing of high‐resolution delicate designed materials. The proposed framework is scalable and adaptable to accomplish a broad spectrum of design demands in various applications.

Ultrafine Co-Mo oxide nanocrystals embedded in hierarchical N-doped carbon microflowers for high-performance lithium-ion batteries

Constructing hierarchical architecture consisting of low-dimensional building blocks is attracting attention as an efficient strategy for achieving high electrochemical performance for lithium-ion batteries (LIBs). Herein, convenient synthesis of Co-Mo oxide composites embedded in a hierarchical N-doped carbon microflower (Co-Mo oxide/NC) is demonstrated. The Co-Mo/polydopamine (PDA) precursor prepared by the spontaneous coordination between the metal ion and dopamine can be easily transformed into Co-Mo oxide/NC by a two-step thermal annealing process. The as-obtained hierarchical microflowers have the advantages of hierarchical structured electrode materials, such as increased contact area with the electrolyte, abundant ion storage sites, and high electrical conductivity. Concurrently, the synergistic effect between molybdenum and cobalt ions can improve the electrochemical performance. Consequently, the hierarchical microflowers as LIB anode materials exhibit a high reversible specific capacity of 1115 mA h g−1 at 1.0 A g−1 after 200 cycles and superior rate performance with a capacity of 577 mA h g−1 at 30.0 A g−1. Moreover, in the long-term cycling stability at a high current density (10.0 A g−1), the electrode shows excellent cycling stability with a capacity of 508 mA h g−1 for 500 cycles. The present study reveals the importance of designing hierarchical structured materials to enhance electrochemical energy storage applications.

Electromagnetic Response of Multistage-Helical Nano-Micro Conducting Polymer Structures and their Enhanced Attenuation Mechanism of Multiscale-Chiral Synergistic Effect.

Nowadays, the rapidly development of advanced antidetection technology raises stringent requirements for microwave absorption materials (MAMs) to focus more attention on wider bandwidth, thinner thickness, and lower density. Adding magnetic medium to realize broadband absorption may usually result in the decline of service performance and accelerating corrosion of MAMs. Chiral MAMs can produce extra magnetic loss without adding magnetic medium due to the unique electromagnetic cross polarization effect. However, more efforts should be taken to furtherly promote efficient bandwidth of chiral MAMs and reveal attenuation mode and modulation method of chiral structure. Herein, a novel superhelical nano-microstructure based on chiral polyaniline and helical polypyrrole is successfully achieved via in situ polymerization strategy. The enhanced multiscale-chiral synergistic effect contributes to broaden effective absorption bandwidth, covering 8.6GHz at the thickness of 3.6mm, and the minimum reflection loss can reach -51.3dB simultaneously. Besides, to further explain response modes and loss mechanism of superhelical nano-microstructures, the electromagnetic simulation and test analysis are applied together to reveal their synergistic enhancement attenuation mechanism. Taken together, this strategy gives a new thought of how to design, prepare, and optimize the hierarchical structure materials to achieving broadband and high-performance microwave absorption.

One-step hydrothermal synthesis of ZnCo2O4 nanowire/Mxene-Ti3C2 nanolamella composites for high-performance supercapacitors

It is necessary to develop hierarchical structured materials with excellent electrochemical characteristics and stability for energy storage. In this work, we synthesize a novel structure of ZnCo2O4/Ti3C2 on Ni foam by a simple hydrothermal method. The frameworks accelerates the kinetic of the electrochemical reaction and promotes the transfer of electrons. The cycling stability of the device maintains 108.2% after 4000 cycles. The result indicates that the prepared sample is an excellent candidate material for energy storage.

Hierarchically organized gold nanoparticles by lecithin-directed mineralization approach

BackgroundBiomolecules have been universally used to direct the synthesis of nanomaterials, but the controllable synthesis of hierarchical structured materials remains a challenge. MethodsHerein, we show that lecithin can mediate the mineralization process of gold to form nanoparticles featuring a well-defined hierarchical structure. FindingThis structure is composed of primary gold branches, secondary bunches of gold branches, and tertiary gold nanoparticles hierarchically organized by the previous two basic structures. A molecular dynamics (MD) simulation reveals that the preferential adsorption of lecithin on the Au(111) plane directs the oriented growth and promotes the formation of the gold branch structure, and the hydrophobic force of amphiphilic lecithin leads to the spontaneous assembly of the primary gold branches into hierarchical gold nanoparticles. Specifically, hierarchical gold nanoparticles with tunable particle size from 52.6 to 549.8 nm and branch thickness from 7.4 to 16.4 nm are achieved by regulating the reaction conditions. Furthermore, two-generation HOGNPs with a new layer of gold branches growing on the one-generation HOGNPs are synthesized based on the method. This work represents an effective strategy and open an avenue for the controlled synthesis of hierarchical structured materials.

CuO nanomesh hierarchical structure for directional water droplet transport and efficient fog collection

Collecting water from fog is a promising approach to solve the shortage of water resources by micro-nano scale hierarchical structure material surface. Inspired by the structures of cactus and pine needles, CuO micro-nano scale structures attached to the surface of Cu foam are designed to increase the efficiency of fog collection and droplet transport. The structural evolution from CuO nanowires to CuO nanomesh and CuO nanosheets is achieved by regulating the synthesis conditions. The results show that the synthesized CuO nanomesh hierarchical structure is more favorable for fog collection, and the collection efficiency can achieve a rate of up to 34.6 mg/cm2 s. The tip structure can rapidly capture and coalesce small droplets in a foggy environment, which significantly improves the fog collection efficiency. In addition, the synthesized mesh structure and inter-neighborhood gaps have a strong ability to confine air, making the surface has small adhesion and enabling water droplets to fall quickly, which realizes the transport of the collected water efficiently and sustainably. The research work opens a new path for constructing surface structures to improve fog collection performance and has reference value and promotion for the design and development of fog collectors.

Cage-like Silicene/CNT Microspheres Synthesized by a Topochemical Reaction as Anodes for Enhanced Stable Lithium-Ion Batteries

Silicene has recently received increasing attention as an anode material in lithium-ion batteries (LIBs) due to its unique architectural properties. However, the synthesis of silicene still remains challenging, which limits its practical applications. In this work, silicene nanosheets with multilayer stacks are synthesized by the topochemical method and successfully combined with carbon nanotubes (CNTs) to form a cage-like structure composite. Benefiting from the hierarchical structure and two-dimensional active material, the cage-like silicene/CNTs increases the ionic and electric conductivity while reducing the volume expansion and relieving swelling stress. In addition, calculation also indicates a lower diffusion energy barrier of lithium ions in silicene than that in bulk silicon, which ultimately enhances the rate and cycling performance of the battery. The as-obtained electrodes exhibit a capacity of 690 mA h g–1 at 1 A g–1 after 500 cycles. This work not only introduces a facile topochemical method to prepare materials with two-dimensional multilayer silicene but also provides a new strategy for the application of silicene in LIBs.

Hierarchical and fractal structured materials: Design, additive manufacturing and mechanical properties

Novel rationally designed structured materials (SMs) exhibit unconventional mechanical properties that cannot be found in common materials. Although most microarchitectures of the developed SMs are based on regular unit cell tessellation design, few studies have explored the potential of fractal geometry as a design tool for creating new SMs. A novel strategy for creating fractal-like aperiodic SMs based on Hilbert self-filling fractal curves synthetization is presented here. Families of continuous Hilbert structured cubes derived from two separate Hilbert curve iterations at three different matching relative densities were obtained, additionally, a method to decompose the Hilbert curve to obtain non-continuous Hilbert structured cubes is proposed. To obtain a broad overview of their mechanical response, samples were manufactured out of thermoplastic polyurethane via fused filament fabrication and tested under compression. An apparent model of elasticity has been proposed to classify their mechanical performance under low and high strain. Results showed that relative stiffness, energy absorption and deformation could be tuned by adjusting parameters of the Hilbert structured cubes. By iterating the Hilbert curve from n = 4 to n = 5, a 51% increase in stiffness was obtained. A significant increment of 82% and 148% on stiffness was observed on non-continuous Hilbert structured cubes for the first and second orders, respectively; besides, energy absorption capabilities and great shape recovery were observed.

Enhancing the thermoelectric properties through hierarchical structured materials fabricated through successive arrangement of different microstructure

The importance of ZT in thermoelectric (TE) materials is critical for green power generation and cooling applications. Therefore, tremendous efforts were underway to improve ZT, in which we proposed a layer structured approach by successively arranging of coarse Bi0.5Sb1.5Te3 (BST) and fine BST/0.07Cu microstructure materials and investigated their transportation mechanism. The dual bulk microstructure was well-bonded and confirmed by analyzing the microstructure through scanning electron microscope (SEM), electron backscatter diffraction analysis (EBSD) and simulated the electrical potential and temperature distribution during spark plasma sintering with COMSOL software. The results indicate that the highest power factor of 3.8 mW/m-K2 was attained in the layer structured sample, which is significantly higher than other samples due to its synergistically optimized electrical conductivity and Seebeck coefficient. Through the varied microstructure, the κ was decreased at 400 K and consequently the ZT was improved to 1.25 at 400 K for the layer structure samples. Therefore, it is suggested that layered arrangement of different microstructure material could improve the thermoelectric properties of materials.

Lightweight and thermal insulation mullite fibers/whiskers hierarchical framework materials: Low-temperature in-situ growth method and mechanism

Mullite fibers/whiskers hierarchical structure materials (MFWs) were prepared via the three-stage method, i.e. seeds breeding, precursors introducing and whiskers growth. The mechanism of low-temperature in-situ synthesis of mullite whiskers during gas-phase reaction process has been discussed in detail. The seeds bred on mullite fibers (MFs) are the growth points and can effectively reduce the subsequent growth temperature of mullite whiskers (MWs). The precursors composed of aluminum source, silicon source and catalyst provided raw materials for whiskers growth. Under the heat treatment temperature of 800 °C, mullite seed grains were guided to in-situ transform into MWs. Moreover, MFWs fabricated via low-temperature in-situ growth mechanism on the MFs present low density (0.103–0.147 g/cm3) and ultralow thermal conductivity (0.0426–0.0514 W·m−1·K−1). Due to the lower whiskers growth temperature in this work than the ones in the most recent literatures, the three-stage method can be regarded as a viable strategy for low-temperature in-situ growth whiskers.

Dynamic mechanical response and deformation behavior of a novel hierarchical cellular structure material – The thousands of eyes Bodhi

Natural cellular structures encourage researchers to seek new design inspirations for impact protection engineering materials. The thousands of eyes Bodhi (TEB) is a novel hierarchical cellular structure material, which includes the first order filled-cells, the second order novel-closed-cells, and the third order open-cells. In this study, dynamic compressive tests at different high strain rates in the longitudinal and transverse directions were conducted by a split Hopkinson pressure bar (SHPB), respectively. A high-speed camera was employed to capture the macroscopic deformation mechanisms and a scanning electron microscope (SEM) was employed to study the microscopic failure mechanisms. The dynamic mechanical response and strain rate effects of TEB samples in the transverse and longitudinal directions were investigated. The anisotropic behavior of TEB samples is observed under dynamic compression tests. The tests results show that the dynamic mechanical properties of TEB samples and dynamic deformation behavior of each order cellular structure exist a significant strain rate dependence. The TEB material dissipates the impact energy through the dynamic compression mechanisms of each order cellular structure which improves the energy absorption and impact resistance. Thus, it provides a bio-inspired template for the design of energy absorption and crashworthiness engineering materials.

Hierarchical, Highly Open Microtubes and Columnar Liquid Crystals Self‐Assembled from Symmetrical and Asymmetrical Colloidal Rings

AbstractThe use of simple building blocks to produce hierarchical and porous structured materials is highly desired. Rings are simple colloidal particles but unique for their internal cavities. Here we report the self‐assembly (SA) of colloidal rings with tunable asymmetry mediated by a depletion force and demonstrate that a variety of porous colloidal superstructures from microtubes, flexible chains, (plastic) crystals to highly open liquid crystals (LCs) can be formed along the predesigned SA paths. In particular, the SA is staged in binary or ternary systems. Large rings first form complex ring‐in‐ring and ring‐in‐ring‐in‐ring assemblies by capturing smaller rings, which, as new building blocks, can further form multi‐walled microtubes and open columnar LCs. Moreover, a plastic columnar LC with alternating intracolumnar stacking is found from asymmetrical rings. The SA with colloidal rings opens a new avenue to construct hierarchical and porous ordered metamaterials.

Hierarchical, Highly Open Microtubes and Columnar Liquid Crystals Self-Assembled from Symmetrical and Asymmetrical Colloidal Rings.

The use of simple building blocks to produce hierarchical and porous structured materials is highly desired. Rings are simple colloidal particles but unique for their internal cavities. Here we report the self-assembly (SA) of colloidal rings with tunable asymmetry mediated by a depletion force and demonstrate that a variety of porous colloidal superstructures from microtubes, flexible chains, (plastic) crystals to highly open liquid crystals (LCs) can be formed along the predesigned SA paths. In particular, the SA is staged in binary or ternary systems. Large rings first form complex ring-in-ring and ring-in-ring-in-ring assemblies by capturing smaller rings, which, as new building blocks, can further form multi-walled microtubes and open columnar LCs. Moreover, a plastic columnar LC with alternating intracolumnar stacking is found from asymmetrical rings. The SA with colloidal rings opens a new avenue to construct hierarchical and porous ordered metamaterials.

Ni-Co-LDH and Zn-Co Prussian blue analogue derived hierarchical NiCo2O4@ZnO/ZnCo2O4 microspheres with enhanced electrochemical sensing performance towards pentachloronitrobenzene

In this work, we developed a hierarchical structure and multi-component synergistic metal oxide hybrid material, and explored its practical application in monitoring pentachloronitrobenzene (PCNB). We used the ZnO/ZnCo2O4, obtained by calcining Zn-Co Prussian blue analogue (PBA), as the substrate and integrated Ni-Co layered double hydroxide (LDH) on its surface and calcined to obtain hierarchical NiCo2O4@ZnO/ZnCo2O4 microspheres (MSs). Due to the p-n heterojunction characteristics of p-type semiconductor NiCo2O4 and ZnCo2O4 and n-type semiconductor ZnO and the high specific surface area of the microspheres supported by the hierarchical structure conductive network, when this material was used to modify the glassy carbon electrode (GCE), it significantly enhanced the electrochemical sensing performance towards PCNB. Therefore, a new type of electrochemical sensor was constructed based on NiCo2O4@ZnO/ZnCo2O4 MSs and molecularly imprinted polymer (MIP) for the sensitive and highly selective detection of PCNB. Among them, the MIP membrane was fabricated by cyclic voltammetry (CV), and differential pulse voltammetry (DPV) was used to detect PCNB. Under the optimum conditions, the reduction peak current density of PCNB was linearly related to the concentration from 0.05 to 5.5 μM with a detection limit of 8.33 nM and a good sensitivity of 6.118 μA⋅μM−¹⋅cm−². Furthermore, the proposed MIP sensor exhibited high selectivity, reproducibility, repeatability, and stability, and had been used for the detection of PCNB residues in licorice, river water, and soil samples with satisfactory results.

A hierarchical architecture of Fe/Co/Ni-doped carbon nanotubes/nanospheres grafted on graphene as advanced bifunctional electrocatalyst for Zn-Air batteries

Rational design and synthesis of non-precious-metal bifunctional catalysts for oxygen reduction and evolution reactions (ORR and OER) is highly pursued to improve reaction efficiency of Zn-air batteries. Herein, an innovative 0D-1D-2D hierarchical structure material (denoted as FeCoNi-N-rGO) is developed by a facile two-step synthesis strategy to construct N-doped carbon nanotubes (CNTs) and carbon nanospheres (CNSs) for encapsulating ternary Fe/Co/Ni alloy nanoparticles on the surface of reduced graphene oxide (rGO). Specifically, abundant Fe/Co/Ni alloy nanoparticles and M-N-C active sites generated by transition metals (Co, Ni, Fe) coupling with N-doped carbon (CNTs, CNSs, and rGO) can provide the FeCoNi-N-rGO with superior OER and ORR properties; meanwhile, the hierarchical structure endows large specific surface area to expose more active sites and to facilitate mass transfer. Typically, the FeCoNi-N-rGO exhibits a high ORR half-wave potential of 0.836 V and a low OER overpotential of 440 mV at 10 mA cm−2 in 0.1 M KOH. Moreover, the FeCoNi-N-rGO-based rechargeable Zn-air battery can deliver a high peak power density (152.5 mW cm−2), specific capacity (766 mAh g−1) and excellent stability (more than 200 h), surpassing commercial Pt/C-RuO2 catalysts. Therefore, this work will offer an easy fabrication strategy to design bifunctional catalysts with desirable performances for Zn-air batteries.