Hollow-structured Materials Research Articles

Architecting double-shelled hollow carbon nanocages embedded bimetallic sites as bifunctional oxygen electrocatalyst for zinc-air batteries

Rational design of complex hollow nanostructures offers a great opportunity to construct various functional nanostructures. A novel in situ disassembly-polymerization-pyrolysis approach was developed to synthesize atomically dispersed Fe single atoms (Fe SAs) and tiny Co nanoparticles (Co NPs) binary sites embedded in double-shelled hollow carbon nanocages (Co NPs/Fe SAs DSCNs) without removing excess templates. The Co NPs/Fe SAs DSCNs displayed excellent bifunctional activity, boosting the realistic rechargeable zinc-air batteries with high efficiency, long-term durability, and reversibility, which is comparable to noble metal catalysts (Pt/C and RuO2). The enhanced catalytic activity should be attributed to as well as the strong interactions between Fe SAs and Co NPs with the nitrogen-doped carbon matrix, the exposure of more active sites, and the high-flux mass transportation. In addition, the confinement effect between the double C-N shells prevented the aggregation and corrosion of metal atoms, thus improving the durability of the Co NPs/Fe SAs DSCNs, further highlighting the structural advantages of carbon nanoreactor. This work provides guidance for further rational design and preparation of complex hollow structure materials with advanced bifunctional air cathodes.

Reasonable design of PBA-derived interfacial modified ternary compounds and hollow structure materials in high-performance asymmetric supercapacitors

Prussian blue analogues (PBA), common metal-organic frameworks (MOFs), are typically binary metal compounds. In this study, chromium was incorporated during the preparation of nickel‑cobalt PBA, resulting in the adjustment of the micro-morphology of PBA and the synthesis of small-sized PBA (sPBA) electrode materials with diameters ranging from 20 to 30 nm. These materials underwent various interfacial modifications to yield ternary metal phosphide (sPBA-P) and hollow nanostructures (sPBA-C). Additionally, by integrating graphene oxide (GO) as the growth substrate, successful preparation of GO@sPBA-P and GO@sPBA-C electrode materials was achieved. Significantly, these materials showcase outstanding electrochemical properties and interesting interfacial reactions when employed as cathode and anode components. Through a comprehensive series of characterization analyses, the electrochemical properties and reaction mechanisms of these materials were thoroughly investigated. Ultimately, an asymmetric supercapacitor (ASC) was assembled using the synthesized GO@sPBA-P and GO@sPBA-C to explore the material's potential in energy materials applications.

A Review of Metal-Organic Frameworks Derived Hollow-Structured Photocatalysts: Synthesis and Applications.

Photocatalysis is a most important approach to addressing global energy shortages and environmental issues due to its environmentally friendly and sustainable properties. The key to realizing efficient photocatalysis relies on developing appropriate catalysts with high efficiency and chemical stability. Among various photocatalysts, Metal-organic frameworks (MOFs)-derived hollow-structured materials have drawn increased attention in photocatalysis based on advantages like more active sites, strong light absorption, efficient transfer of pho-induced charges, excellent stability, high electrical conductivity, and better biocompatibility. Specifically, MOFs-derived hollow-structured materials are widely utilized in photocatalytic CO2 reduction (CO2RR), hydrogen evolution (HER), nitrogen fixation (NRR), degradation, and other reactions. This review starts with the development story of MOFs, the commonly adopted synthesis strategies of MOFs-derived hollow materials, and the latest research progress in various photocatalytic applications are also introduced in detail. Ultimately, the challenges of MOFs-derived hollow-structured materials in practical photocatalytic applications are also prospected. This review holds great potential for developing more applicable and efficient MOFs-derived hollow-structured photocatalysts.

Stable Structure and Fast Ion Diffusion: A Flexible MoO2@Carbon Hollow Nanofiber Film as a Binder-Free Anode for Sodium-Ion Batteries with Superior Kinetics and Excellent Rate Capability.

Designing innovative anode materials that exhibit excellent ion diffusion kinetics, enhanced structural stability, and superior electrical conductivity is imperative for advancing the rapid charge-discharge performance and widespread application of sodium-ion batteries. Hollow-structured materials have received significant attention in electrode design due to their rapid ion diffusion kinetics. Building upon this, we present a high-performance, free-standing MoO2@hollow carbon nanofiber (MoO2@HCNF) electrode, fabricated through facile coaxial electrospinning and subsequent heat treatment. In comparison to MoO2@carbon nanofibers (MoO2@CNFs), the MoO2@HCNF electrode demonstrates superior rate capability, attributed to its larger specific surface area, its higher pseudocapacitance contribution, and the enhanced diffusion kinetics of sodium ions. The discharge capacities of the MoO2@HCNF (MoO2@CNF) electrode at current densities of 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 A g-1 are 195.55 (155.49), 180.98 (135.20), 163.81 (109.71), 144.05 (90.46), 121.16 (71.21) and 88.90 (44.68) mAh g-1, respectively. Additionally, the diffusion coefficients of sodium ions in the MoO2@HCNFs are 8.74 × 10-12 to 1.37 × 10-12 cm2 s-1, which surpass those of the MoO2@CNFs (6.49 × 10-12 to 9.30 × 10-13 cm2 s-1) during the discharging process. In addition, these prepared electrode materials exhibit outstanding flexibility, which is crucial to the power storage industry and smart wearable devices.

Controllable hollow cube Cu7S4 cathode for aqueous zinc-ion batteries application

Hollow structure materials are considered as a promising candidates for energy storage and conversion systems. In this paper, hollow cube shape Cu7S4 nanomaterial was creatively constructed by a simple template method, which was used as high performance cathode material of zinc ion batteries, firstly. The results indicate that the discharge specific up to 335 mAh g−1 at the current density of 0.1 A g−1, which is higher than other materials. Moreover, the prepared Cu7S4 material has super-stable cyclic stability, with a capacity of about 320 mAh g−1 after 100 reversible cycles. The unique hollow cube structure increases the active contact area, reduces the transmission path, and improves the electrochemical performance. The design and synthesis strategies of electrode materials can provide a valuable reference significance for other electrode materials in energy storage applications.

Preparation strategy of bimetallic MOF hollow photocatalysts for hydrogen evolution

Hollow structure materials have been proved to be excellent photocatalysts due to their advantages in the separation of electron-hole pairs. However, the synthesis of such materials is complex, time-consuming, and poor versatility. In this study, Cu-DHTP/ZIF-67 (DHTP = 2,5-dihydroxyterephthalic acid) hollow materials containing both Co and Cu were designed and synthesized by a simple one-step etching and ligand exchange strategy. It is worth noting that the bimetallic hollow catalyst can be synthesized in the presence of both Cu(Ⅱ) and DHTP within 5 min at room temperature. The synthesized hollow bimetallic catalyst has improved photoresponse performance and electron-hole pair separation ability, which results in the best catalytic performance compared with DHTP/ZIF-67, Cu/ZIF-67, and ZIF-67 when used in the photocatalytic water splitting reaction. The hydrogen evolution yield of Cu-DHTP/ZIF-67 can reach 39.7 mmol g−1, which is 6 times than that of pure ZIF-67. This study demonstrates the promising potential of Cu-DHTP/ZIF-67 photocatalyst in the field of photocatalytic water reduction and hydrogen evolution, and provides a new idea for designing and preparing more hollow structure bimetallic photocatalysts with excellent performance.

Tailoring the Hollow Structure within CoSn(OH)6 Nanocubes for Advanced Supercapacitors.

The enhanced application performance of hollow-structured materials is attributed to their large surface area with more active sites. In this work, the hollow CoSn(OH)6 nanocubes with increased surface area and mesopores were derived from dense CoSn(OH)6 nanocube precursors by alkaline etching. As a result, the hollow CoSn(OH)6 nanocubes-based cathode electrode exhibited a higher area-specific capacitance of 85.56 µF cm-2 at 0.5 mA cm-2 and a mass-specific capacitance of 5.35 mF g-1 at 0.5 mA cm-2, which was more extensive than that of the dense precursor. Meanwhile, the current density was increased 4-fold with good rate capability for hollow CoSn(OH)6 nanocubes.

Preparation of hierarchical hollow CoFe Prussian blue analogues and its heat-treatment derivatives for the electrocatalyst of oxygen evolution reaction

The microstructure of materials importantly affects their performance. As electrocatalyst materials, the performance of hollow-structure materials is usually better than that of solid materials because of the larger specific surface area, lower density, and more exposed active sites of hollow structure. Bimetallic catalysts usually exhibit better catalytic activity than monometallic catalysts because of the synergistic effects between different metal elements. Prussian blue and its analogues (PB/PBAs) are ideal precursors for preparing hollow-structure bimetallic catalysts due to their structure and composition characteristics. In this study, ZIF-67 hollow sphere (HS) was used as the template to prepare hierarchical hollow CoFePBA (H-SCP) through anion-exchange method. The oxygen evolution reaction (OER) catalytic performance of H-SCP was further improved by low-temperature heat treatment in N2 atmosphere. The H-SCP-350 sample, which was obtained at a heat-treatment temperature of 350 ℃, was a bimetallic nanocomposite. Part of H-SCP was converted into metallic cobalt and cobalt-iron alloy during heat treatment. The synergistic effect among the different components effectively improved the electrocatalytic activity of the material. Therefore, H-SCP-350 showed the best OER catalytic performance among all samples. The overpotential was only 291mV at a current density of 10 mA cm−2 when tested in 1 M KOH electrolyte.

Creation of hollow silica-fiberglass soft ceramics for thermal insulation

Hollow-structured materials show promise in thermal insulation because the shells encapsulating gaseous voids can interrupt heat transport pathways. Here, we present two low-cost routes to fabricate hollow silica nanoshells, via gas-phase and liquid-phase methods. The gas-phase synthesis method generates hollow shells by a droplet surface precipitation mechanism in a flame aerosol reactor. The liquid-phase synthesis route forms hollow shells by removal of a carbon template, which is produced by hydrothermal reaction of glucose. Both approaches (gas- and liquid-phase) provide hollow silica with amorphous structure, low thermal conductivity (0.023 and 0.026 W m−1 K−1), small particle size (442 and 383 nm), thin shell (35 and 36 nm), and low density (0.015 and 0.033 g cm−3). We employed high shear mechanical mixing to fabricate hollow silica-fiberglass composite ceramics. The resulting three-dimensional network provides the ceramics with robust mechanical elasticity and fire-retardancy while maintaining low thermal conductivity, dramatically outperforming an analogous material using commercial silica gel in place of the hollow nanoshells. Our findings provide two practical routes to synthesize hollow silica, either of which can be used to manufacture a class of hollow shell-fiber nanocomposite soft ceramics for energy-saving applications.

Fabrication of Co0.85Se@CN double-walled hollow cages to address the volume expansion of anode and enhance ion diffusion for sodium-ion storage

Constructing hollow-structured materials is an efficient route to address the volume expansion of anode and enhance ion diffusion for sodium-ion battery (SIB). Superior to the single-walled products, multi-walled hollow-structured anode materials possess more storage sites, enhanced robustness, and higher volumetric capacity; nevertheless, synthesis of the multi-walled hollow structure often requires harsh synthesis conditionand complicated etching process. Herein, we report fabrication of Co0.85Se double-walled hollow cages coated by a nitrogen-doped carbon layer (Co0.85Se@CN) as high-performance anode materials for SIB. Using ZIF-67 as precursor, a facile ion exchange strategy is employed with no aid of high temperature treatment and complex etching process. The resultant Co0.85Se@CN exhibit distinct double-walled hollow structure with abundant lacunas on the walls, which increases the accessible area, shortens the ion transport path and most importantly provides appropriate buffer space against volume expansion. Moreover, the C protective layer on both sides of the inner- and outer-walls further benefits high conductivity, chemical stability, and robustness during charge/discharge process. As a result, the Co0.85Se@CN anode deliver a high reversible capacity of 402 mAh g–1 at 50 mA g–1 and 316 mAh g–1 at 100 mA g–1 after 100 cycles for SIB.

The art of framework construction: hollow-structured materials toward high-efficiency electromagnetic wave absorption

The art of framework construction: hollow-structured materials toward high-efficiency electromagnetic wave absorption

Zeolitic Imidazolate Framework 67-Derived Ce-Doped CoP@N-Doped Carbon Hollow Polyhedron as High-Performance Anodes for Lithium-Ion Batteries

Zeolitic Imidazolate Framework 67 (ZIF-67) and its derivates have attracted extensive interest for lithium-ion batteries (LIBs). Here, Cerium-doped cobalt phosphide@nitrogen-doped carbon (Ce-doped CoP@NC) with hollow polyhedron structure materials were successfully synthesized via ionic-exchange with Co and Ce ions using the ZIF-67 as a template followed with a facile low-temperature phosphorization treatment. Benefitting from the well-designed hollow polyhedron, steady carbon network, and Ce-doping structural merits, the as-synthesized Ce-doped CoP@NC electrode demonstrated superior performance as the anode in LIBs: a superior cyclability (400 mA h g−1 after 500 cycles) and outstanding rate-capability (590 mA h g−1, reverted to 100 mA g−1). These features not only produced more lithium-active sites for LIBs anode and a shorter Li-ion diffusion pathway to expedite the charge transfer, but also the better tolerance against volume variation of CoP during the repeated lithiation/delithiation process and greater electronic conductivity properties. These results provide a methodology for the design of well-organized ZIFs and rare earth element-doped transition metal phosphate with a hollow polyhedron structure.

Entangled ZnO on Ultrathin Hollow Fibers for UV-Aided Pollutant Decomposition.

Zinc oxide (ZnO), a widely used ultraviolet (UV) degrading substance, offers high selectivity for wastewater treatment, but the leaching of ZnO into water could cause secondary contamination. Using porous substrates to fix and load ZnO is a promising technical method to improve the water purification efficiency and recycling durability of ZnO. However, limited by the slow kinetics and shielding effects, it is challenging to use traditional techniques to introduce ZnO into the interior of a hollow structure. Here, inspired by an ancient dyeing procedure, we formed a unique single-molecule bio-interfacial entanglement as an absorption layer to capture the catalyst for ZnO electroless deposition (ELD) on the surface of natural ultrathin hollow-structured Kapok fibers. With curcumin serving as a linking bridge, ELD allowed the spontaneous formation of intensive ZnO nanocrystals on both the outer and inner walls. ZnO-kapok as the catalyst for ultraviolet photodecomposition of organic pollutants (methylene blue (MB) and phenol as model pollutants) delivered a decomposition efficiency of 80% and outstanding durability. Further modification of the ZnO-kapok catalyst by doping with reduced graphene oxide (rGO) showed an improvement in photodegradation performance of 90% degradation under 2-h irradiation with 21.85 W/dm2 light power. Moreover, to the best of our knowledge, this is the first report featuring ZnO loading on both the outer and inner walls of a fiber-structured hollow kapok material, which provides inspiration for immobilization of metallic oxides on hollow-structured materials for further applications in renewable catalysis, chemical engineering, and energy storage fields.

Rapid Fabrication of Patterned Gels via Microchannel-Conformal Frontal Polymerization.

From the perspective of both fundamental and applied science, it is extremely advisable to develop a facile and feasible strategy for fabricating gels with defined structures. Herein, the authors report the rapid synthesis of patterned gels by conducting frontal polymerization (FP) at millimeter-scale (2mm), where a series of microchannels, including linear-, parallel-, divergent-, snakelike-, circular- and concentric circular channels, were used. They have investigated the effect of various factors (monomer mass ratio, channel size, initiator concentration, and solvent content) on FP at millimeter-scale, along with the propagating rule of the front during FP in these microchannels. In addition, we developed a new microfluidic-assisted FP (MFP) strategy by combining the FP and microfluidic technique. Interestingly, the MFP can realize the production of hollow-structured gel in a rapid and continuous fashion, which have never been reported. Our work not only offers an effective pathway towards patterned gels by the microchannel-conformal FP, but also gives new insight into the continuous production of hollow-structured materials. Such a method will be beneficial for fabricating vessel and scaffold materials in a flexible, easy-to-perform, time and energy saving way.

Hollow structures as drug carriers: Recognition, response, and release.

Hollow structures have demonstrated great potential in drug delivery owing to their privileged structure, such as high surface-to-volume ratio, low density, large cavities, and hierarchical pores. In this review, we provide a comprehensive overview of hollow structured materials applied in targeting recognition, smart response, and drug release, and we have addressed the possible chemical factors and reactions in these three processes. The advantages of hollow nanostructures are summarized as follows: hollow cavity contributes to large loading capacity; a tailored structure helps controllable drug release; variable compounds adapt to flexible application; surface modification facilitates smart responsive release. Especially, because the multiple physical barriers and chemical interactions can be induced by multishells, hollow multishelled structure is considered as a promising material with unique loading and releasing properties. Finally, we conclude this review with some perspectives on the future research and development of the hollow structures as drug carriers.

Fabrication of Cu2S hollow nanocages with enhanced high-temperature adsorption activity and recyclability for elemental mercury capture

Transition metal sulfides have attracted great interest in nonferrous smelting industries for elemental mercury (Hg0) capture owing to their high activity, low cost and resistance to SO2. However, the major obstacle was the deactivation of active sites in adsorbents after the use or at high temperature. Herein, we fabricated rhombic dodecahedral Cu2S hollow nanocages by using high-quality Cu2O crystals as sacrificial templates. Benefiting from the unique structure and composition, such Cu2S hollow nanocages exhibited not only the enhanced high-temperature adsorption activity for Hg0 (120 °C, removal efficiency > 95%), but also had outstanding recyclability (five cycle, removal efficiency > 85%) without additional reactivation treatment. And the saturation adsorption capacity was about 26.6 mg∙g−1. Further study of the structure-performance correlation indicated that the environmental features of interior architecture might offer inner active S1- sites with the shelter of nanocage shell at high temperature, combining with Hg0 to form HgS. Besides, the recovered adsorption activity was ascribe to the thermal migration of active Cu2+ ions. Thus, this work provides a promising adsorbent for Hg0 capture at high temperature, while opening a new field to design hollow-structured materials for environmental applications.

Multi-shelled NiO hollow microspheres as bifunctional materials for electrochromic smart window and non-enzymatic glucose sensor

A multi-shelled NiO hollow sphere was synthesized by a facile glucose-mediated hydrothermal route. The carbonaceous microsphere was utilized as a sacrificial template for the formation of multi-shells. All the shells were formed by a single pyrolysis step. The multi-shelled hollow sphere can provide enhanced active surface area and additional reactive sites, which facilitate faster ion intercalation and deintercalation, and play key roles in electrochromic devices and sensing application, including glucose sensing. Herein, we employed the as-synthesized material for electrochromic devices. As expected, NiO multi-shelled hollow microspheres exhibit a superior transmission modulation (ΔT = 47%) and yield a coloration efficiency of ~ 85.3 cm2 C−1, which is ~ 2.37 times higher than that of NiO microflakes which was synthesized in the absence of glucose. The geometry of the self-supported multi-shelled architecture ensures that the active faradaic sites can be in intimate contact with the electrolyte to enhance ionic diffusion. The observed colored and bleached switching time of multi-shelled hollow sphere is 6.7 s and 2.7 s respectively. A quasi-solid-state electrochromic device is also displayed with the aid of gel electrolyte with reversible color change from dark brown to transparent. Furthermore, the multi-shelled NiO displayed excellent catalytic activity towards non-enzymatic glucose sensing with a high sensitivity of 1646 ± 5 μA cm−2 mM−1 over a linear range of 2 μM–2.6 mM with a lowest detection limit of 1.5 ± 0.2 μM. Analysis on blood serum as a real biological sample reflects the practicability of the fabricated sensor. Developing hollow structured multi-shelled materials based on metal oxides will pave the way to design advanced electrode materials for electrochromic smart windows and non-enzymatic glucose sensors.

Template Synthesis of a Heterostructured MnO2@SnO2 Hollow Sphere Composite for High Asymmetric Supercapacitor Performance

We design a new type of heterostructured MnO2@SnO2 hollow spheres composite. The particular hollow heterostructured structure materials contain two parts, one is the MnO2 hollow spheres and the oth...

Construction of hierarchical nanoporous bimetallic copper‑cobalt selenide hollow spheres for hybrid supercapacitor

The search for novel materials with advanced electrochemical performance is attracted considerable attention, especially in portable energy storage devices. Metal selenides with high conductivity are attaining eminence as potential electrode materials in electrochemical energy-storage fields; nevertheless, their electrochemical performance is restricted by an insignificant active surface area. Thus, hollow structured materials with more active sites due to the improved surface area have attracted much attention for high-performance hybrid supercapacitors (HSC). Accordingly, for the first time, we successfully designed and synthesized hierarchical nanoporous hollow copper‑cobalt selenide microspheres (CCSe) through a simple self-template procedure. The electrodes fabricated based on hollow CCSe material revealed outstanding electrochemical efficiency and great specific capacity of 562C g−1 at 2 A g−1 whereas excellent cycling stability according to preserving >94.5% of the initial capacity even after 5000 cycles. The asymmetric cell fabricated based on CCSe microspheres electrode with activated carbon (AC) anode electrode revealed ultrahigh performance with an energy density of 32.4 Wh kg−1, the power density of 16 kW kg−1, which are superior to those of conventional supercapacitors. In addition, two asymmetric systems assembled in series can efficiently light two red light-emitting diodes (LEDs). This study has introduced hollow CCSe as an ideal candidate for electrode materials of HSC apparatuses.

Nanostructured Ni2SeS on Porous-Carbon Skeletons as Highly Efficient Electrocatalyst for Hydrogen Evolution in Acidic Medium.

Nickel dichalcogenides have received extensive attention as promising noble-metal-free nanocatalysts for a hydrogen evolution reaction. Nonetheless, their catalytic performance is restricted by the sluggish reaction kinetics, limited exposed active sites, and poor conductivity. In this work, we report on an effective strategy to solve those problems by using an as-designed new porous-C/Ni2SeS nanocatalyst with the Ni2SeS nanostubs anchored on with porous-carbon skeletons process. On the basis of three advantages, as the enhancement of the intrinsic activity using the ternary sulfoselenide, increased number of exposed active sites due to the 3D hollow substrate, and increased conductivity caused by porous-carbon skeletons, the resulting porous-C/Ni2SeS requires an overpotential of only 121 mV at a current density of 10 mA cm-2 with a Tafel slope of 78 mV dec-1 for hydrogen evolution in acidic media and a good long-term stability. Density functional theory calculations also show that the Gibbs free energy of hydrogen adsorption of the Ni2SeS was -0.23 eV, which not only is close to the ideal value (0 eV) and Pt reference (-0.09 eV) but also is lower than those of NiS2 and NiSe2; large electrical states exist in the vicinity of the Fermi level, which further improves its electrocatalytic performance. This work provides new insights into the rational design of ternary dichalcogenides and hollow structure materials for practical applications in HER catalysis and energy fields.