3D Hierarchical Structure Research Articles

Supercapacitor electrode fabrication through chemical and physical routes

In recent years, efficient energy storage devices that exhibit superior power and energy densities have attracted major attention to meet the demands of emerging applications such as wearable systems. In this regard, supercapacitors (SCs) in various forms offer attractive solutions. The performance of SCs is highly dependent on the synthesis route used for electrode materials preparation. This review outlines various techniques for electrode materials fabrication, such as i) solution-based chemical techniques, ii) physical methods, and iii) deposition techniques. Accordingly, different solution-based procedures such as hydrothermal/solvothermal, sol-gel, microwave, and in-situ polymerization techniques offer facile and cost-effective routes to synthesise electrode materials. Physical deposition techniques such as vacuum filtration and mechanochemical methods are also explained. The scalability to develop flexible structures is an attractive feature of physical approaches. Chemical vapour deposition, electro-polymerization/electrochemical deposition and direct growth techniques are also discussed in detail. It is suggested that incorporating electrode materials with 3D conductive substrate and hierarchical structures minimizes the excessive mass loading in commercial scale-up of SCs. Supercapacitor electrodes with shape memory properties for developing smart textiles are also presented. It is concluded that incorporating more than one synthetic approach makes it possible to obtain the electrode material for excellent electrochemical properties.

Atomically dispersed Co in a cross-channel hierarchical carbon-based electrocatalyst for high-performance oxygen reduction in Zn–air batteries

Rational design of the 3D cross-channel hierarchical structure and defect-modified atomic Co–N4sites for CoSA@NPC can effectively achieve the construction of high-density triple-phase interfaces and high intrinsic active sites for the ORR.

In situ generated iron silicate on porous carbon derived from rice husks for high-performance supercapacitor and full utilization of resource

The high-performance Fe2SiO4 electrode material is prepared for supercapacitor through KHCO3 activating the carbon and simultaneously etching SiO2 derived from rice husks and hydrothermal treatment process. The prepared electrode material has a 3D hierarchical interconnected pore structure, which provides abundant channels and shorter diffusion pathways for electrons and ions. The SiO2 of rice husks is converted into Fe2SiO4 by loading Fe element, which provides the larger specific capacitance. The SiOC bond in the cell wall of rice husks can reduce the electron transfer barrier at the heterogeneous interface. The single electrode shows the specific capacitance of 534.345F·g−1 at the current density of 0.5 A·g−1, surpassing the silicate materials previously studied. The assembled solid-state asymmetric supercapacitor device of FeSi//activated carbon has a large energy density and power density, reaching 0.69 Wh·m−2 at 13.50 W·m−2. Additionally, the device presents good cycle performance for 8000 cycles with 85% retention. This work provides a new strategy for the green application of rice husks and promotes the development of low-cost electrode materials for supercapacitors.

The synergetic effect of the mixed phase of NiMoO4 with a 1D–2D–3D hierarchical structure for a highly efficient and stable urea oxidation reaction

Benefitting from the unique 1D–2D–3D hierarchical structure and the synergetic effects of α and β phases of NiMoO4, α/β-NiMoO4@NF exhibits better UOR performance that can save hydrogen production energy and purify urea-containing wastewater.

An amorphous NiCuFeP@Cu3P nanoarray for an efficient hydrogen evolution reaction

The exposure of abundant active sites attributed to a 3D hierarchical structure and electronic interactions between amorphous NiCuFeP and Cu3P enhances the HER performance of NiCuFeP@Cu3P/CF.

Hierarchical porous structure construction for highly stable self-supporting lithium metal anode

Lithium (Li) metal, with extremely high specific capacity and low reduction potential, is considered one of the most promising anode candidates for next-generation batteries. However, uncontrolled growth of dendritic Li and extreme volume fluctuation during cycles hinder the broad application of Li metal anodes. Herein, Li dendrite growth can be effectively suppressed by constructing a unique hierarchical porous structure. ~300 nm rigid carbon nano-box contains abundant ~20 nm Cu3P/CoP heterostructural nanobubbles. Densely growth villiform carbon tubes tangled with ~50 µm carbon nanotubes cover the surface of the carbon nano-box. This flexible interlaced matrix (Cu3P/CoP@C/CNT) possessing 3D hierarchical porous interspace and structure can effectively confine metallic Li. More than physical confinement, strong chemical bonding between Cu3P/CoP heterostructures and Li atoms is also proved by DFT calculation to regulate Li plating behavior. The LiǀCu3P/CoP@C/CNT composite anode exhibits a high average efficiency of 94.6% over 220 cycles and a long-running lifespan for 400 h with an exceptionally low voltage hysteresis of 24 mV. LiFePO4|Li@Cu3P/CoP@C/CNT full cells can be cycled 300 times at a negligible capacity decay of 0.01% per cycle at 1 C. This work inspires a self-supporting and hollow heterostructured Li container design, promoting the development of Li metal host anodes.

A Mesoporous Lead-Doped Titanium Oxide Compound with High Performance and Recyclability in I2 Uptake and Photocatalysis.

A three-dimensional (3D) mesoporous material with an atomically precise structure, Ti16Pb5O16(C6H5CO2)2(OCH3)40 (Ti16Pb5), comprised of a novel high-nuclearity Pb-doped titanium oxide cluster (TOC), was synthesized. Ti16Pb5 exhibited a surface area of 45 m2 g-1 and a pore diameter of 3.5 nm. It exhibited an uptake capacity of I2 of ≤2.2 g g-1 in vapor, and the performance was maintained after seven uptake-release cycles. Ti16Pb5 also showed a high adsorption ratio and capacity (93% and 3.1 g g-1) in hexane. The characterization data, including Fourier transform infrared, Raman, and powder X-ray diffraction, suggested the lattice structure of Ti16Pb5 was rigid and I2 was accommodated in the pores of Ti16Pb5. To the best of our knowledge, this is the first example of using a TOC in I2 adsorption. In addition, Ti16Pb5 showed excellent activity and recyclability in visible-light degradation of dye pollutants and photocurrent generation. Our structural analysis suggested the alkoxide ligands within the channels of Ti16Pb5 build up a confined polar environment and thereby facilitate I2 accommodation, and meanwhile, the improved performances and stabilities of Ti16Pb5 are correlated with its cluster-based, 3D hierarchical structure.

Tunable microwave absorption features in bi-layer absorber based on mesoporous CuS micro-particle with 3D hierarchical structure and nanosphere like NiCo2O4

There has been a growing demand for materials with superior absorption capabilities, such as strong absorbing capacity, thin thickness, and light weight, to solve challenges related to EM radiation pollution. While the majority of the research is focused on optimizing material compositions, component microstructure and absorber structure are also critical factors for improving microwave absorption performance. In this research, we show how the microstructure of components and absorber design may increase dissipation features. Solvothermal and hydrothermal methods were utilized for synthesizing mesoporous CuS micro-particles with a 3D hierarchical structure as a dielectric component and nanospheres like NiCo2O4 as magnetic components respectively. The formation of pure phases with the mentioned microstructures was confirmed via XRD, FTIR, UV–Vis, XPS, VSM, FESEM and BET analysis. According to VNA results, the minimum reflection loss can be achieved to −33 dB at 11 GHz with a total thickness of 2 mm in which each layer thickness was considered 1 mm (CuS placed at top layer and NiCo2O4 placed at bottom layer). The RL values of bilayer absorber were strongly affected by both the microstructure of the components and tuning the thickness and arrangement of each layer. We offer a potential technique for enhancing microwave dissipation performance by combining the synergistic effects between the microstructure, thickness and arrangement of layers in a bilayer absorber.

Trisiloxane functionalized melamine sponges for oil water separation

The trisiloxane modified melamine sponges (3Si-MS) have been successfully fabricated via the formation of polydopamine (PDA) layer with nanoaggregates and the covalent grafting of 3-mercaptopropyltrisiloxane. The 3Si-MS were confirmed and verified by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR), contact angle, the separation/adsorption tests and recyclability tests. As investigated by SEM, 3Si-MS exhibited 3D hierarchical structure with high density of nanoaggregates on the interconnected skeleton of melamine sponges. By combining the shorter and wider hydrophobic group of trisiloxane and hierarchically rough structure, 3Si-MS illustrated highly hydrophobic (water contact angle of 139.3°), outstanding absorption capacity, and easy reusability. Meanwhile, 3Si-MS could be used for continuous oil-water separation. The results of this work demonstrate a facile and cost-effective method to prepare highly hydrophobic melamine sponges for oil-water separation.

2D-2D MXene/ReS2 hybrid from Ti3C2Tx MXene conductive layers supporting ultrathin ReS2 nanosheets for superior sodium storage

Rhenium disulfide (ReS2) is a promising 2D-layered anode material for rechargeable batteries. However, this material suffers from severe agglomeration and volume expansion during ions insertion/extraction, leading to inferior battery performance. Building 3D hierarchical structure is an effective strategy to overcome these problems and simultaneously manifest synergistic effects. Herein, a one-pot hydrothermal method is introduced to construct N-doped carbon confined ReS2 ultrathin nanosheets anchored on few-layered Ti3C2Tx MXene substrate (MXene@ReS2@C). The MXene flakes can effectively reduce agglomeration of ReS2 nanosheets during charge/discharge process and generate chemical interaction with ReS2 nanosheets, thereby promoting charge transfer kinetic of hierarchical composite. Carbon incorporation not only stabilizes MXene from successive oxidation during hydrothermal procedure but also alleviates volume expansion of ReS2, ensuring cycling durability of electrode. When used as anode material of SIBs, this hierarchical MXene@ReS2@C hybrid with strong interfacial interactions demonstrates improved electrochemical performances with satisfying rate capability (138 mAh g−1 at 5.0 A g−1) and cycling stability (202 mAh g−1 at 2.0 A g−1 after 200 cycles). This work provides a new scope of synthesizing MXene-based transition metal sulfide composite for practical application in sodium ion batteries.

Molten-Salt-Assisted Synthesis of Nitrogen-Doped Carbon Nanosheets Derived from Biomass Waste of Gingko Shells as Efficient Catalyst for Oxygen Reduction Reaction

Developing superior efficient and durable oxygen reduction reaction (ORR) catalysts is critical for high-performance fuel cells and metal–air batteries. Herein, we successfully prepared a 3D, high-level nitrogen-doped, metal-free (N–pC) electrocatalyst employing urea as a single nitrogen source, NaCl as a fully sealed nanoreactor and gingko shells, a biomass waste, as carbon precursor. Due to the high content of active nitrogen groups, large surface area (1133.8 m2 g−1), and 3D hierarchical porous network structure, the as-prepared N–pC has better ORR electrocatalytic performance than the commercial Pt/C and most metal-free carbon materials in alkaline media. Additionally, when N–pC was used as a catalyst for an air electrode, the Zn–air battery (ZAB) had higher peak power density (223 mW cm−2), larger specific-capacity (755 mAh g−1) and better rate-capability than the commercial Pt/C-based one, displaying a good application prospect in metal-air batteries.

Highly Sensitive Flexible Tactile Sensors in Wide Sensing Range Enabled by Hierarchical Topography of Biaxially Strained and Capillary-Densified Carbon Nanotube Bundles.

Flexible tactile sensors with high sensitivity have received considerable attention for their use in wearable electronics, human-machine interfaces, and health-monitoring devices. Although various micro/nanostructured materials are introduced for high-performance tactile sensors, simultaneously obtaining high sensitivity and a wide sensing range remains challenging. Here, a resistive tactile sensor is presented based on the hierarchical topography of carbon nanotubes (CNTs) prepared by a low-cost and straightforward manufacturing process. The 3D hierarchical structure of the CNTs over large areas is formed by transferring vertically aligned CNT bundles to a prestrained elastomer substrate and subsequently densifying them through capillary forming, providing a monotonic increase in the contact area as applied pressure. The deformable and hierarchical structure of CNTs allows the sensor to exhibit a wide sensing range (0-100kPa), high sensitivity (141.72kPa-1 ), and low detection limit (10Pa). Additionally, the capillary-formed CNT structure results in increased durability of the sensor over repeated pressures. Based on these advantages, meaningful applications of tactile sensors, such as object recognition gloves and multidirectional force perceptions, are successfully realized. Given the scalable fabrication method, 3D hierarchically structured CNTs provide an essential step toward next-generation wearable devices.

NiO-functionalized In2O3 flower-like structures with enhanced trimethylamine gas sensing performance

NiO-functionalized In2O3 flower-like structures were successfully synthesized via a simple one-step hydrothermal route and applied in gas sensors for trimethylamine (TMA) detection. By virtue of the unique 3D hierarchical flower-like structures, p-n heterojunctions and the catalytic activity of NiO, NiO-functionalized In2O3 shows enhanced TMA gas sensing performance. Specifically, the sensor fabricated from 0.05-NiO-In2O3 composites with well-defined flower-like structures shows the highest response of about 20.5 to 10 ppm TMA at 200 °C, which is 4.7 times higher than that of the pure In2O3 flower-like structures (4.4 to 10 ppm TMA). Besides, this sensor shows good reproducibility and stability, high selectivity and a ppb-level detection limit of 1.5 to 0.5 ppm (500 ppb) TMA, providing a widely applicable strategy to improve the gas sensing properties of metal oxides semiconductors.

Controllable synthesis various morphologies of 3D hierarchical MnOx-TiO2 nanocatalysts for photothermocatalysis toluene and NO with free-ammonia

Via various hydrothermal synthetic conditions, controllable synthesis various morphologies of MnOx-TiO2 catalysts for simultaneous removal toluene and NO with free-ammonia under the photothermocatalysis system based on UV light irradiation. The morphologies obtained included 3D hierarchical sheet structure (C sample), 3D hierarchical sheet stacked MnOx-TiO2 microspheres (P sample), and 3D hierarchical sticks stacked MnOx-TiO2 microspheres (N sample). Compared with other samples, N sample exhibited the excellent catalytic activity for the toluene and NO, with the conversion rates of toluene and NO achieved 72% and 91% at 240 °C, respectively. Using a variety of characterization and analysis methods, it was confirmed that the morphology of the catalysts would affect its catalytic performance by affecting the specific surface area, surface-adsorbed oxygen species, oxygen vacancies, the high-valence atomic species and reducibility. This was the reason why the N sample could show remarkable performance. Moreover, this work demonstrated a new strategy for simultaneously removing toluene and NO with free-ammonia under the photothermocatalysis system based on UV light irradiation.

Synthesis of hierarchical porous nitrogen-doped reduced graphene oxide/zinc ferrite composite foams as ultrathin and broadband microwave absorbers

Magnetic graphene foams with three-dimensional (3D) porous structure, low bulk density and multiple electromagnetic loss mechanisms have been widely recognized as the potential candidates for lightweight and high-efficiency microwave attenuation. Herein, zinc ferrite hollow microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/ZnFe2O4) composite foams were prepared via a solvothermal and hydrothermal two-step method. Results demonstrated that the attained magnetic composite foams possessed the ultralow bulk density (12.9–13.5 mg·cm−3) and 3D hierarchical porous netlike structure constructed through stacking of lamellar NRGO. Moreover, the microwave dissipation performance of binary composite foams could be notably improved through annealing treatment and further elaborately regulating the annealing temperature. Remarkably, the attained composite foam with the annealing temperature of 300.0 °C presented the integrated excellent microwave attenuation capacity, i.e. the strongest reflection loss reached −40.2 dB (larger than 99.99% absorption) and broadest bandwidth achieved 5.4 GHz (from 12.4 GHz to 17.8 GHz, covering 90.0% of Ku-band) under an ultrathin thickness of only 1.48 mm. Furthermore, the probable microwave dissipation mechanisms were illuminated, which derived from the optimized impedance matching, strengthened dipole polarization, interfacial polarization and multiple reflection, notable conduction loss, natural resonance and eddy current loss. Results of this work would pave the way for developing graphene-based 3D lightweight and high-efficiency microwave absorption composites.

High-activity daisy-like zeolitic imidazolate framework-67/reduced grapheme oxide-based colorimetric biosensor for sensitive detection of hydrogen peroxide

Colorimetric biosensors, based on enzyme-like nanomaterials, have come into the spotlight in virtue of their visual detection. Herein, a daisy-like zeolitic imidazolate framework-67/reduced grapheme oxide (ZIF-67/rGO) nanozyme with unique 3D hierarchical structures has been designed to realize visual detection of hydrogen peroxide (H2O2) that is recognized as a strong oxidizing agent or reactive oxygen species associated with oxidative stress in biological systems. The daisy-like ZIF-67/rGO is prepared by a facile one-step liquid-phase method conducted under room temperature. The successful introduction of rGO endows the daisy-like ZIF-67/rGO nanozyme with abundant porous structure, high specific surface area, and good charge transfer capability, which significantly accelerates the adsorbability and recognition towards the substrates and the oxidation rate of TMB-H2O2 reaction, and thus improving the nanozyme activity observably. It is conductive to nanozyme-modulated H2O2 determination. The established colorimetric biosensor platform based on ZIF-67/rGO nanozyme exhibits remarkable sensitivity and high specificity for the application in visual detection of H2O2. The detection limit of ZIF-67/rGO-based biosensor platform is as low as 3.81 μM, which is nearly 8 times lower than that of ZIF-67-based biosensor platform. Moreover, its potential applicability as an ideal platform for colorimetric biosensors is demonstrated by testing the concentration of H2O2 in milk samples, which sheds light on the promising application of the proposed biosensing system in point-of-care detection.

SnS2 with Flower-like Structure for Efficient CO2 Photoreduction under Visible-Light Irradiation.

Photocatalytic CO2 reduction using solar energy is a promising way to obtain renewable-energy sources for replacing fossil fuels. Through a hydrothermal process, we successfully designed and synthesized three-dimensional (3D) flower-like structured SnS2 with a sheet-like structured quasi-hexagon as the building block. The 3D hierarchical structure is conducive to light capture and absorption, the sheet structure can shorten the transmission path and promote separation of the carriers, and the self-supporting effect can effectively prevent catalyst agglomeration during the catalytic reaction. Therefore, when used in photocatalytic CO2 reduction, SnS2 with a flower-like structure showed excellent photocatalytic performance compared with SnS2 nanoparticles (NPs) under visible-light irradiation with a gas-solid reaction system.

A flexible photoelectrochemical aptasensor using heterojunction architecture of α-Fe2O3/d-C3N4 for ultrasensitive detection of penbritin

The performance of photoelectrochemical (PEC) analysis system relies closely on the properties of the photoelectric electrodes. It is of great significance to integrate photoactive materials with flexible substrates to construct ultra-sensitive PEC sensors for practical application. This work reports a novel photoelectrode developed by immobilizing α-Fe2O3 nanoparticles (NPs)/defect-rich carbon nitride (d-C3N4), an excellent Z-scheme heterojunction photoelectric material, onto three-dimensional (3D) flexible carbon fiber textile. Specifically, 3D hierarchical structure of flexible carbon fiber textile provides larger specific surface area and higher mechanical strength than traditional electrodes, resulting in more reaction sites and faster reaction kinetics to achieve signal amplification. Simultaneously, α-Fe2O3/d-C3N4 Z-scheme heterojunction exhibits enhanced light absorption capability and high redox ability, thus dramatically improving the PEC performance. This photoelectrode was used to construct a flexible PEC aptasensor for ultrasensitive detection of penbritin, demonstrating excellent performance in terms of wide linear range (0.5 pM–50 nM), low detection limit (0.0125 pM) and high stability. The design principle is applicable to the manufacture of other photoelectric sensing systems, which provides an avenue for the development of portable environmental analysis and field diagnostics equipment.

Interwoven nickel(II)-dimethylglyoxime nanowires in 3D nickel foam for dendrite-free lithium deposition

Metal skeletons, such as Nickel Foam (NF) has attracted worldwide interests as stable host for lithium metal anode because of its high stability, large specific surface area and high conductivity. However, most metal skeletons have lithophobic surface and uneven current distribution that result in sporadic lithium nucleation and uncontrolled dendrites growth. Herein, we describe a sequential immersing strategy to generate interwoven Nickel(II)-dimethylglyoxime (Ni-DMG) nanowires at NF to obtain composite skeleton (NDNF), which can be used as an stable host for Li metal storage. The Ni-DMG has proved effective to realize uniform lithium nucleation and dendrite-free lithium deposition. Combing with the three dimensional (3D) hierarchical porous structure, the composite host shows a significantly improved coulombic efficiency (CE) than pristine commercial nickel foam. Moreover, the corresponding Li||Li symmetrical cells can run more than 700 h with low voltage hysteresis 22 mV at 1.0 mA/cm2, and Li@NDNF||LiFePO4 full-cell exhibits a high capacity retention of 82.03% at 1.0 C during 630 cycles. These results proved the effectiveness of metal-organic complexes in governing Li metal growth and can be employed as a new strategy for dendrite-free Li metal anode and safe Li metal batteries (LMBs).

Oxide-derived Tin Nanospheres for Efficient CO2 Electroreduction to Formate

Rational design and engineering of electrocatalysts for electrochemical CO2 reduction (CO2RR) is crucial to effectively, selectively converting CO2 into carbon-neutral chemicals and fuels. In this work, we have developed hierarchical tin oxide nanosphere electrocatalysts to boost the production of formate. Three-dimensional (3D) SnO2 spheres constructed from small crystalline nanoparticles exhibited 71-81% Faradaic efficiencies (FE) and energy efficiency (40-50%) toward formate production at partial current densities of 22-72.4 mA/cmgeo 2 from -0.9 V to -1.3 V vs. the reversible hydrogen electrode (RHE). Such hierarchical sphere-like catalysts outperformed non-hierarchical SnO2 nanoparticles and commercially benchmarking catalysts, achieving a peak 81% FE at superior formate current density of ~50 mA/cmgeo 2 at -1.2 V vs. RHE. The spherical oxide-derived Sn catalysts were highly stable up to 36 hours, preserving long-term partial current density of ~ 45 mA/cmgeo 2 and 68% FE for formate. Such an outstanding performance can be credited to the 3D hierarchical structure, which offers enlarged surface area, larger number of electrochemically active sites, and strongly suppressed H2 evolution. Our results may provide more guidelines for the introduction of hierarchical porosity into CO2RR electrocatalysts for large-scale applications.