Hierarchical Nanostructured Materials Research Articles

Hydrovoltaic electricity generator using a hierarchical NiFe LDH-coated CuO nanowire mesh device

Innovative advancements in sustainable water-energy nexus solutions are paramount in the current global context. This study introduces a hydrovoltaic electricity generator with advanced capillary wicking under ambient conditions. A hierarchical nanostructure of nickel–iron layered double hydroxides (NiFe LDHs) was deposited on copper oxide nanowires (CuO NWs) on Cu meshes to enhance the diffusion of ion-rich water. The LDH coating improves the overall power, voltage, and robustness of the device. A 200 µL droplet of hygroscopic solutions on a device produces electricity at 0.2 V scale, one of which could be sustained for over 140 h. We explored the working mechanisms, parametric studies, and potential scalability through serial allocation for further applications. This study allows water-driven electricity generation using hierarchical nanostructured materials, effectively harnessing renewable energy from readily available hygroscopic salts or abundant seawater resources.

Electrocatalytic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid via metal-organic framework-structured hierarchical Co3O4 nanoplate arrays

Electrocatalytic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) was examined as an alternative to thermocatalytic methods in which two-dimensional (2D) cobalt-metal–organic framework (Co-MOF, ZIF-L-Co) nanoplate arrays were prepared on nickel foam (NF) and then transformed into hierarchical porous Co3O4 nanostructures by chemical etching and low temperature annealing to form electrode materials. Hierarchical porous nanoarrays formed during synthesis enlarged the surface area of the as-prepared catalysts introduced a large number of defects and exposed active sites leading to reduced charge diffusion, improved mass transfer and efficient HMF oxidation. Co3O4/NF electrode materials were able to achieve a current density of 10 mA·cm−2 at an overpotential of 105 mV in 1 M KOH with 10 mM HMF, which was reduced by 175 mV compared with water oxidation. Electrocatalytic oxidation experiments afforded 100 % HMF conversion and 96.7 % FDCA yields with a minimum 96.5 % faradaic efficiency at 1.43 V vs RHE. The proposed MOF-structured synthesis method fundamentally reduces charge diffusion, improves mass transfer of electrodes and is generally applicable to fabrication of hierarchical porous nanostructured materials.

Redox-active anomalous electrochemical performance of mesoporous nickel manganese sulfide nanomaterial as an anode material for supercapattery devices

In this work, we are reporting nickel manganese sulfide hierarchical redox-active nanostructured material synthesized using a facile one-step hydrothermal technique to investigate its potential for supercapattery devices. The surface morphology, crystallinity, elemental analysis/composition surface area, porosity, and homogeneity were investigated through X-ray diffraction (XRD), Energy dispersive X-ray (EDX) spectra, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Brunauer–Emmett–Teller (BET). The electrochemical characterizations were performed in a three-electrode standard cell whereas the electrolyte used was 1 M potassium hydroxide. These characterizations predict that sample S-0.4 is exhibiting superior performance over all other electrodes and therefore it was paired with activated carbon for the assembling of supercapattery (Ni–Mn–S//AC). This supercapattery was probed electrochemically with CV, GCD, EIS, and stability tests which reveals superb performance by delivering a high value of capacity (420.10 C/g) with a maximum energy density of 75.96 Wh/kg. The device was able to deliver the power density of 2865 W/kg, along with an outstanding cyclic life by sustaining 85% of capacity even after 5000 GCD cycles. Our analysis for this electrode material suggests that our synthesized material can be applied for future high-performance supercapattery devices.

Facile construction of hierarchical Co3S4/CeO2 heterogeneous nanorod array on cobalt foam for electrocatalytic overall water splitting

Herein, a hierarchical Co3S4/CeO2 nanorod array on cobalt foam (Co3S4/CeO2-CF) was successfully constructed via a facile one-step hydrothermal method. The fabrication of Co3S4/CeO2-CF was confirmed by X-ray diffraction, scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM). It is observed that CeO2 nanorod was fully covered with Co3S4 nanosheets, forming a hierarchical core–shell nanostructure. Furthermore, CeO2 and Co3S4 were doped with each other during the one-step hydrothermal process, forming a heterogeneous Co3S4/CeO2 nanostructure. Density functional theory (DFT) calculations suggest that the introduction of CeO2 in Co3S4 is effective in reducing the free energy barrier of OER process. To achieve current density of 10 mA cm−2, only small overpotentials of 74.9 mV and 213 mV are required for HER and OER in 1.0 M KOH solution, respectively. In particular, the Co3S4/CeO2-CF based electrolysis cell for overall water splitting only needs an output voltage of 1.64 V in the alkaline medium, lower than that of Pt/C–RuO2-based electrolysis cells (1.70 V). Such hierarchical heterogeneous catalyst also shows ultra-stable catalytic activity. Therefore, with the favorable heterointerfaces and hierarchical structures, Co3S4/CeO2-CF could be a promising bifunctional electrocatalyst for overall water splitting and this study may also provide a facile method for the preparation of hierarchical heterogeneous nanostructured materials.

Hierarchical CuO nanostructured materials for acetaldehyde sensor application

A nanocrystalline CuO with mixed morphologies (nanorods, nanoplates and nanoparticles) were prepared using simple room temperature wet chemical synthesis route. The nanostructured CuO material was characterized using FESEM, TEM, EDS, elemental mapping, UV–visible spectroscopy, and BET surface area techniques for various physicochemical characteristics. The gas sensor device was fabricated using CuO nano-powder and its acetaldehyde gas sensing properties was investigated. The CuO sensor showed excellent sensing response towards 20–100 ppm acetaldehyde. The acetaldehyde response of the CuO sensor was recorded at various operating temperatures as well as concentrations. The responses of 418% and 115% were noted for 100 ppm and 20 ppm acetaldehyde concentration at 180 °C respectively. The higher selectivity of the CuO sensor was observed towards acetaldehyde among various gases. The transient response of the sensor was observed to be consistent with concentrations. The dynamic repetitive response of the sensor was tested at 100 ppm acetaldehyde that revealed to be same. The sensor's stability was tested and observed to be quite stable. A brief acetaldehyde sensing mechanism for CuO sensor was elucidated. The easy and large-scale formation of CuO nanostructures without growth controlling surfactants, and the good selectivity of the high response acetaldehyde sensor at relatively low operating temperatures may pave pathway for future gas sensor technology.

Zirconium Phosphate Supported on g-C3N4 Nanocomposite for Sensitive Detection of Nitrite

Food protection and preservation aims to prevent spoilage and contamination, which can improve consumer health, but prolonged and excessive consumption of food preservatives can cause serious health risks. Nitrite (NO2 −) anion, a widely used food preservative, is associated with possible carcinogenic effects in prolonged exposures that require the implementation and identification of methods for immediate quantification. In this sense, hierarchical nanostructured materials have enormous material advancement potential that can be applied to real-time analysis of undesirable ions. The ordered geometric arrangement and multiple components of these structures offer synergistic effects, increased active surface area, and multiple functionalities, outperforming their bulk counterparts and enhancing various properties. The present work deals with the synthesis of α-zirconium phosphate (α-ZrP) that is composited with graphitic carbon nitride (CN) via ultrasonication for the electrochemical determination of NO2 −. The facile ion-exchange capability of the former inorganic layered compound can effectively manage the disposition of NO2 −, which is further accelerated by the interspersing of a carbonaceous material such as CN. The sensing capacity of the nanocomposite shows comprehensive response ranges, high selectivity and sensitivity towards NO2 − detection that allows the fabrication of real-time analysers based on ion-exchange materials for the remediation of environmental contaminants.

Boosting the energy density of highly efficient flexible hybrid supercapacitors via selective integration of hierarchical nanostructured energy materials

A preeminent technique to boost the energy density of flexible hybrid supercapacitor (FHSCs) is to develop unique, extremely efficient, and smart positive and negative current collectors with hierarchical nanoarchitectures integration of various electroactive materials. Herein, we present a facile and flexible approach towards the synthesis of selective integration of hierarchical leaflet-like Ni(OH)2 nanoflake arrays with ZnO–ZnCo2O4 nanowire arrays (Ni(OH)2 NFAs@ZnO–ZnCo2O4 NWAs) on Ni foam mesh for ultrahigh-capability electrodes. The innovative strategy results in hierarchical architecture with highly altered electronic nanostructure, which not only enhances the specific surface area but also provides ultrafast transportations between ions and electrons. Under electrochemical conditions, the battery-type materials of the hierarchical leaflet-like Ni(OH)2 NFAs@ZnO–ZnCo2O4 NWAs electrodes show ultrahigh specific capacity of 237.7 mA h g−1 at 2 A g−1; this value is 2.16, 1.53 and 1.30 times than those of ZnO–ZnCo2O4 NWAs, CoO NFAs@ZnO–ZnCo2O4 NWAs and ZnO NFAs@ZnO–ZnCo2O4 NWAs electrodes, respectively. Most importantly, in flexible assembly, the Ni(OH)2 NFAs@ZnO–ZnCo2O4 NWAs//Fe2O3@NF NFAs FHSCs device delivers an ultrahigh energy density of 80.10 W h kg−1 a superior life-spam performance, and retention around 98.2% of initial capacity after 5000 cycles. The new innovative strategy could be very promising for future flexible electronics devices.

Multi-scale interface design of strong and damage resistant hierarchical nanostructured materials

Synthesis of damage resistant nanostructured materials with high strength and fracture toughness is a challenging task. In this work, multi-scale interfaces were implemented into a hierarchical TiN/SiOx microstructure to mimic stepwise crack growth behaviour of the hard and damage resistant bivalve mollusc Saxidomus purpuratus shell. In situ micromechanical testing in scanning and transmission electron microscopes revealed multi-scale crack deflection events at grain boundaries of individual alternately-tilted TiN crystallites, at kinks of their repeatedly tilted columnar grains as well as crack interaction with perpendicular interfaces of elastic amorphous SiOx layers. These events induced an increase in the crack surface area, reduction of the crack driving force and dissipation of local stress and energy at the crack tip with subsequent crack slow-down or arrest, resulting in fracture toughness exceeding by ~200% the toughness of monolithic TiN nanoceramics. By this perspective biomimetic microstructural design, catastrophic failure of brittle ceramics may be turned into a predictable and controllable process increasing reliability of strong materials in various challenging safety-critical engineering applications. It also shows potential paths for the development of strong and simultaneously tough materials with high mechanical and thermal stability.

Controllable syngas production on gold nanowires/nickel foam electrode in non-aqueous system

A hierarchical electrode is prepared with Au nanowires grown on nickel foam. With large specific active surface area, it is used for producing syngas (H2/CO) with controllable ratio, through electrochemical process in DMF. The synthetic innovation lies in the use of 3-cyanopropyltriethoxysilane, to achieve the adsorption of appropriate amount of Au seeds for the one-dimensional growth of ultrathin Au nanowires (d ≈ 5 nm). With the nanowires forest on the three-dimensional porous nickel foam substrate, syngas is produced by electro-catalysis with high overall Faradic efficiency and tunable H2/CO ratios. This synthetic strategy opens a facile way to synthesize the hierarchical nanostructured materials, and broaden the choice of the catalysts for electrochemical applications.

Metal-organic framework derived directional growth of ultrathin amorphous NiCo hydroxide nanosheets on NiCo2O4 nanowire arrays for enhanced electrochemical properties

The rational design of hierarchical nanostructured electrode materials is critical for achieving high electrochemical property for supercapacitor (SC) applications. Herein, we report a facile method for fabricating hierarchical NiCoO@NiCo–OH core-shell nanowire array (NiCoO@NiCo–OH NWA) on flexible carbon fiber clothes by using a cobalt-based metal organic framework (Co-MOF) as an intermediate. The growth mechanism study shows the formation process is completed by a localized dissolution of Co-MOF followed by a directional growth of NiCo–OH nanosheets on NiCo2O4 nanowires. The unique hierarchical nanostructure endows the material a high surface area, rich active sites, fast electron transport, and efficient electrolyte ion diffusion. Consequently, the as-prepared material exhibited an over 3 times’ higher specific capacity than the pristine NiCo2O4 nanowire arrays and an excellent rate capability at 40 A g−1 for SCs. Moreover, the NiCoO@NiCo–OH NWA based hybrid supercapacitor (HSC) exhibited a considerably high energy density of 57.2 Wh kg−1, a high power density of 17.6 kW kg−1, and ultralong cycling stability of over 10 000 cycles (retention rate of 91.8%), outperforming most of the current state-of-the-art SCs. The directional growth strategy using MOFs as intermediates reported here provides a simple but effective way to fabricate hierarchical nanostructured electrode materials for advanced energy storage applications.

Designing hierarchical NiCo2S4 nanospheres with enhanced electrochemical performance for supercapacitors

Hierarchical nanostructure materials have attracted significant attention due to their fascinating structural features for the application of high-performance supercapacitors. In this report, nanosheets interconnected hierarchical NiCo2S4 (NCS) nanospheres were synthesized by a facile hydrothermal method. The growth process was explored by performing different reaction temperature conditions (140, 150, 160, and 170 °C), and their electrochemical properties were studied. The electrochemical properties of NCS products (coated on conductive Ni foam substrate) at different reaction temperatures were measured in a traditional three-electrode electrochemical system. The optimized hierarchical NCS nanospheres (prepared at 150 °C) delivered better electrochemical results due to their synergetic morphological features and higher specific surface area. The NCS-150 nanospheres–based electrode exhibited its maximum specific capacity of 155 mA h g−1 at 2 A g−1 and further showed a good capacity retention value of 115 mA h g−1 at a higher current density of 5 A g−1. Besides, cycling analysis was proceeded up to 4000 cycles to test the practical ability of the designed electrode, and it retained 76% of capacity after performing the cycles. These results demonstrate that the nanosheets interconnected hierarchical NCS nanospheres (prepared at 150 °C) could be a promising electrode material for high-performance supercapacitors.

Ultrafast Response and High Selectivity toward Acetone Vapor Using Hierarchical Structured TiO2 Nanosheets.

For the development of high-performance gas sensors, ultrafast response and high selectivity are critical requirements for many practical applications. An alternative strategy is to employ hierarchical nanostructured materials in gas sensors. In this work, we report newly synthesized TiO2 hexagonal nanosheets with a hierarchical porous structure, which demonstrate an ultrafast gas response and high selectivity toward acetone vapor for the first time. A simple one-step annealing process to prepare hierarchical TiO2 nanosheets derived from layered TiSe2 nanosheet templates is reported. The hierarchical structure interlaced with anatase TiO2 nanosheets showed an open porous characteristic. The average pore size was about 20 nm examined using a high-resolution TEM. The gas sensing properties toward acetone vapor of the novel hierarchical structured TiO2 nanosheets were characterized in detail including optimal operation temperature, sensitivity, selectivity, response/recovery time, and long-term stability. The gas sensing response and recovery times were 0.75 s and 0.5 s, respectively. We attribute these superior response properties to its unique hierarchical pore structure with a high specific surface area. The results show great potential for acetone vapor detection, particularly in dynamic ultrafast monitoring by using the synthesized hierarchical structured TiO2 nanosheets.

Hierarchical Nanostructured Electrocatalysts for Oxygen Reduction Reaction.

Hierarchical nanostructured materials, which possess the porous structure of multiscale porosities on different pore diameters from micro-, meso- to macropores based on International Union of Pure and Applied Chemistry, are much desired to present the synergistic attractive advantages of each scale of hierarchical pores in the development of catalysis, adsorption, separation, energy, and biochemistry. The use of hierarchical nanostructured materials as oxygen reduction reaction (ORR) electrocatalysts is advanced to increase specific surface area for active sites dispersion and exposure as well as enhance reactants/products transfer. However, complex and costly templateincorporated methods and relatively uncontrollable template-free methods motive us to develop novel and efficient preparation methods. Herein, recent developments and synthesis strategies that have been made in the field of hierarchical nanostructured materials as well as their application for ORR electrocatalysts are reviewed.

A Special Section on Hierarchical Nanostructured Materials for Sustainable Catalysis.

A Special Section on Hierarchical Nanostructured Materials for Sustainable Catalysis.

Construction of T-Nb2O5 nanoparticles on/in N-doped carbon hollow tubes for Li-ion hybrid supercapacitors

In recent years, hybrid supercapacitors (HSCs) with good characteristics of both lithium batteries (LIBs) and supercapacitors (SCs) have become a hot research topic to meet the growing market demand for electric and hybrid electric vehicles. The key for high-performance HSCs is the reaction kinetics imbalance between the slow faradaic intercalation anode and fast non-faradaic physical adsorption/desorption cathode. Herein, we simultaneously grow ultrafine Nb2O5 nanoparticles on the inner walls and outer surface of hollow heteroatomic (N) carbon tube, giving a unique hierarchical hybrid nanostructure materials named T-Nb2O5@NC. The LIB test show its excellent high-rate capability and long-term cyclic stability. At current density of 0.25C (1.0–3.0 V, vs Li/Li+), the reversible specific capacity of this material is up to 194 mAh g−1. Importantly, the HSC device, assembled by T-Nb2O5@NC as anode and commercial activated carbon as cathode with an organic electrolyte, exhibits good electrochemical performance, including high energy density (49.7 Wh kg−1) and power density (8750 W kg−1), obviously superior to traditional HSC electrode materials. The results prove that T-Nb2O5@NC can be used as a promising HSC anode material.

Hierarchical three-dimensional graphene-based carbon material for high-performance lithium ion batteries

Hierarchical three-dimensional graphene-based carbon materials have been successfully prepared via a template-assisted approach. It is found that the structure, morphology, graphitization degree, surface area and pore volume for the obtained carbon materials could be easily controlled by adjusting the amount of reactant and template. The results show that the obtained hierarchical nanostructured carbon material possesses a very stable reversible capacity of 395 mAh g−1 at 1C and exhibits extremely high reversible capacity of 163 mAh g−1 at the high rate of 20C. The large macroporous network and small mesopores in the materials can facilitate electrolyte and lithium ion transportation. The hollow carbon nanoparticles composed of stacked graphene can favor the electron diffusion within the materials. The micropores in the carbon materials can also increase the reversible capacity.

Fe‐doped CoNi0.5P Hierarchical Arrays as Efficient Bifunctional Electrocatalysts for Overall Water Splitting: Evolution of Morphology and Coordination of Catalytic Performance

AbstractDesign and synthesis of bifunctional electrocatalysts with high efficient and durability for electrolytic water splitting still remain an important matter for the research of renewable energy systems. Herein, a series of CoNi0.5FexP/CC (x=0, 0.08, 0.125, 0.25, 0.5) catalysts have been successfully prepared by a simple hydrothermal and phosphorization process, and directly used as bifunctional electrocatalysts for OER and HER. Benefiting from the suitable Fe element doping content and novel nanowire‐nanosheet co‐existent hierarchical nanostructure, the optimal CoNi0.5Fe0.125P/CC catalyst shows an outstanding bifunctional catalytic performance, with 344 mV low overpotential to reach at 100 mA cm−2 during OER process and 74 mV overpotential to reach at 10 mA cm−2 during HER process. The water electrolysis device employing CoNi0.5Fe0.125P/CC as cathode and anode at the same time, it only requires as low as 1.61 V of voltage to achieve the current density of 10 mA cm−2 in alkaline solution, implying a great practical application value of this novel hierarchical nanostructured material for overall water splitting.

Direct growth of WO3 nanostructures on multi-walled carbon nanotubes for high-performance flexible all-solid-state asymmetric supercapacitor

The rational design and development of highly conductive hierarchical nanostructured materials are of great importance to improve the electrochemical performance of supercapacitors. Great efforts have been committed to the development of positive electrodes for asymmetric supercapacitors (ASC). However, it is still necessary to develop better negative electrodes for practical applications. In present investigation, a multi-walled carbon nanotubes-tungsten trioxide (MWCNT-WO3) hybrid nanostructure is prepared as a negative electrode for ASC. The MWCNT-WO3 hybrid electrode is prepared using a simple two-step approach, which involves coating of MWCNTs on carbon cloth substrates followed by hydrothermal treatment to deposit WO3 nanorods on the MWCNT-coated carbon cloth. The MWCNT-WO3 hybrid electrode exhibits a maximum specific capacitance (areal capacitance) of 429.6 F g−1 (1.55 F cm−2) and capacity retention of 94.3% after 5000 cycles, which are higher than the 155.6 F g−1 (0.43 F cm−2) and 84.9% shown by pristine WO3 in 1 M LiClO4 electrolyte. A flexible all-solid-state ASC is self-assembled with MWCNT-WO3 as a negative electrode, MnO2 as a positive electrode, and PVA-LiClO4 as a gel electrolyte. The MnO2//MWCNT-WO3 ASC achieve specific capacitance of 145.6 F g−1 at a current of 2 mA and specific energy of 39.63 Wh kg−1 at a specific power of 546 W kg−1. Specifically, the ASC exhibits superior long-term cycling stability (77% over 10000 cycles) and excellent mechanical flexibility with less capacitance loss. These remarkable results demonstrate the potential of using MWCNT-WO3 hybrid nanostructures for the fabrication of high-performance energy storage devices.

Selective integration of hierarchical nanostructured energy materials: an effective approach to boost the energy storage performance of flexible hybrid supercapacitors

A selective integration of Ni(OH)2 NNAs@NiO–NiCo2O4 NSAs was rationally designed and directly utilized as a binder-free flexible electrode for hybrid SCs with excellent energy density.

Hydrogen‐Bonded Siloxane Liquid Crystals for Hybrid Nanomaterials

The self‐assembly of molecular inorganic/organic hybrid building blocks into ordered hierarchical nanomaterials with a tunable morphology is an enormous challenge. Here, we describe the synthesis and characterization of a novel liquid crystalline hydrogen‐bonding hepta(dimethylsiloxane) azobenzene carboxylic acid dimer. This inorganic/organic hybrid dimer forms sub‐5 nm lamellar features in the bulk and at the liquid solid interface. When mixed with a complementary hydrogen‐bonding disk‐shaped small molecule, a columnar hexagonal phase is formed. When adding a block copolymer containing hydrogen bond‐accepting moieties, a hierarchical nanostructured material is obtained with a hexagonal columnar arrangement perpendicular to lamellae super structure. Our supramolecular approach shows that hierarchical hybrid nanomaterials can be fabricated with controlled properties which is appealing for applications such as nanoporous materials, organic electronics, and nanolithography.