Hollow Polyhedron Research Articles

High performance humidity sensor based on 3D mesoporous Co3O4 hollow polyhedron for multifunctional applications

In this work, the three-dimensional (3D) hollow mesoporous Co3O4 was successfully prepared by calcining the Co-based zeolitic imidazolate framework-67 (ZIF-67). As-obtained Co3O4 inherited the rhombohedral framework structure of ZIF-67 and possessed mesoporous and hollow structure. Further, the humidity sensor based on Co3O4 was fabricated, and its humidity sensing properties were investigated at room temperature (25 °C). The results indicated that the Co3O4 humidity sensor exhibited high humidity sensing performance with a wide linear detection range (10%−95% relative humidity (RH)), small humidity hysteresis (2.6% RH), and fast response/recovery times (1.0/13.5 s). In particular, the Co3O4 humidity sensor was of high detection resolution (1% RH). The excellent performance was attributed to the strong hydrophilicity and the unique 3D porous structure of Co3O4. In addition, the potential applications of the fabricated Co3O4 humidity sensor in skin humidity, simulated diaper, human breathing, and non-contact switch were demonstrated. This work provides a promising humidity sensing material for fabricating high-performance humidity sensors.

Co/N-codoped carbon nanotube hollow polyhedron hybrid derived from salt-encapsulated core-shell ZIF-8@ZIF-67 for efficient oxygen reduction reaction

The rational design and construction of non-precious metal-based electrocatalysts with high activity and stability toward oxygen reduction reactions (ORR) are essential but challenging. In this work, a novel hybrid nanoporous structure of Co nanoparticles uniformly embedded in hollow porous carbon doped with nitrogen (CoNHPC) was constructed by a melt-evaporation-pyrolysis method, in which NaCl is utilized as an auxiliary template. The introduction to NaCl in this process served as the confining template to prevent nitrogen loss and promote graphitization, and the intercalating agent to form a mesoporous product. Due to the composite hierarchical porous structure, higher graphitization degree, and desirable nitrogen bonding type, the as-prepared CoNHPC-920 presents outstanding ORR electrocatalytic activity in terms of a half-wave potential of 0.87 V (vs. RHE) and onset potential of 0.97 V (vs. RHE). The composite material also shows higher selectivity and outstanding durability with most transition metal porous carbon materials reported. The strategy proposed in this study may provide ideas about metal nitrogen-carbon type catalysts enriched with carbon nanotubes and bare leaky hollow structures of the construction of advanced ORR electrocatalysts, opening up a new pathway.

In-situ formed Cu-doped RuS2 hollow polyhedrons integrated with simultaneously heterostructure engineering with metallic Ru for boosting hydrogen evolution in alkaline media

Promoting hydrogen evolution reaction (HER) in alkaline media is currently vital to practicing the sustainable development of hydrogen economy. As an emerging candidate, pyrite-structured ruthenium disulfide (RuS2) is a promising electrocatalyst for alkaline HER. Nevertheless, much less efforts have been devoted to RuS2, thus whose intrinsic properties still remain to be improved via promoting the water dissociation and hydrogen adsorption processes. Herein, we report the facile synthesis of Cu-doped RuS2 hollow polyhedrons coupled with metallic Ru from bimetallic MOF of RuCu-BTC to boost alkaline hydrogen evolution. In which, in-situ Cu doping integrated with simultaneous heterostructure engineering with metallic Ru are achieved for RuS2. Benefitting from modified electronic structure, heterogeneous interfaces and 3D hollow polyhedral morphology, the Cu-doped RuS2/Ru heterostructure exhibits admirable electrocatalytic activity with small overpotential of 169 mV at a high current density of 200 mA cm−2 in 1 M KOH, superior to that of commercial Pt/C. Density functional theory calculations indicate that the incorporation of Cu heteroatoms can not only decrease the energy barrier for water dissociation of RuS2 but also optimize its hydrogen adsorption. Simultaneously, the construction of heterointerfaces between RuS2 and metallic Ru demonstrates further improved conductivity, increased active sites and enhanced specific activity. This work discloses an innovative strategy for the simultaneous implementation of heteroatom doping and heterostructure engineering on RuS2 to collaboratively promote the HER electrocatalytic performance.

Constructing direct Z-scheme Mn0.5Cd0.5S/CdWO4 nanocomposite modified by hollow CoSx polyhedrons for highly efficient photocatalytic H2 evolution

Constructing heterojunction photocatalytic systems with highly spatial charge separation, strong photoredox ability and rapid surface reaction still remains an enormous challenge. Herein, hollow CoSx polyhedrons decorated hierarchically direct Z-scheme Mn0.5Cd0.5S/CdWO4 heterojunction photocatalyst is designed and constructed by a simple sonochemical approach and subsequent in situ deposition route. Such a constructed Mn0.5Cd0.5S/CdWO4/CoSx ternary composite exhibits a significantly boosted photoactivity toward H2 generation compared to bare Mn0.5Cd0.5S, binary Mn0.5Cd0.5S/CdWO4, Mn0.5Cd0.5S/CoSx and Mn0.5Cd0.5S/Pt samples with optimized composition ratio. Apart from the efficient charge transfer channels and preserved strong photoredox ability within the direct Z-scheme Mn0.5Cd0.5S/CdWO4 heterojunction, the hollow structure of CoSx polyhedrons could endow abundant surface-active sites, strengthen the light-harvesting capacity through the internal multilight scattering/reflection and decrease the overpotential for H2 evolution, which further contributes to the boosted photoactivity toward hydrogen production. This study demonstrates an alternate methodology for constructing high-performance multi-hierarchical Z-scheme/cocatalyst heterojunction photocatalysts for solar energy conversion.

Core-Shell ZIF-67@ZIF-8-derived multi-dimensional cobalt-nitrogen doped hierarchical carbon nanomaterial for efficient oxygen reduction reaction

Fuel cells have emerged as a charming candidate for next-generation energy conversion devices. However, it is highly desired but challenging to engineer advanced non-precious oxygen reduction catalysts with highly actives and stability due to the sluggish kinetics of oxygen reduction reaction (ORR) on fuel cell cathode. Herein, a novel hybrid architecture with Co nanoparticles embedded in N-doped carbon nanotubes and hollow nanocarbon polyhedron (Co@N-CNT-HC) was constructed from core-shell ZIF-67@ZIF-8 via a facile epitaxial growth-pyrolysis process. With the Co@N-CNT-HC as the catalyst, a remarkable ORR performance is achieved in terms of a high half-wave potential of 0.84 V, a large limiting current density of 4.70 mA/cm2, and excellent long-term durability ( 97.8% current retention after 8 h) in alkaline medium, which outperform commercial Pt/C catalyst. Further dynamic calculations indicated that ORR follows a four-electron reaction mechanism. The enhancement activity of Co@N-CNT-HC is mainly due to the effective integration of 0D Co nanoparticles, 1D carbon nanotubes and 3D hollow nanocarbon, which synergistically strengthen the interfacial reaction kinetics of oxygen and accelerate mass/charge transfer. The strategy reported in this work provides a new insight to synthesis of low-cost and well-designed carbon hybrid electrocatalyst for ORR.

Mofs as Template-Derived Nicomn-Ldh with a Hollow Polyhedron Structure for High-Performance Supercapacitors

Mofs as Template-Derived Nicomn-Ldh with a Hollow Polyhedron Structure for High-Performance Supercapacitors

Co3O4 modified Mn0.2Cd0.8S with different shells forms p-n heterojunction to optimize energy/mass transfer for efficient photocatalytic hydrogen evolution

The construction of an unique structure to optimize the energy/mass transfer for photocatalysts is an effective way to improve their solar-chemical energy conversion efficiency. Here, p-type Co3O4 polyhedrons and n-type Mn0.2Cd0.8S microrods were successfully coupled to construct Mn0.2Cd0.8S/Co3O4 p-n heterojunction. In order to optimize the energy/mass transfer in the Mn0.2Cd0.8S/Co3O4 p-n heterojunction photocatalyst, ZIF-67 was used as precursor to create hollow Co3O4 derivatives [Co3O4 porous polyhedrons (PPs), Co3O4 hollow double-shell polyhedrons (HDSPs), and Co3O4 hollow single-shell polyhedrons (HSSPs)]. And Co3O4 hollow single-shell polyhedrons (HSSPs) possesses these prominent advantages that strong light trapping ability, short carrier transport distance, and larger catalyst/solvent contact area in comparison with other two derivatives. More importantly, the band structures of the differently structural Co3O4 are distributed stepwise. The valence band potential of Co3O4 HSSPs is more positive meaning stronger oxidation ability, which effectively improves the separation efficiency of electron-hole pairs in Mn0.2Cd0.8S/Co3O4 p-n heterojunction system. Therefore, Mn0.2Cd0.8S/Co3O4 HSSPs showed more excellent hydrogen evolution activity (11222 μmol g−1 h−1) which was about 26 times and 2.34 times that of Mn0.2Cd0.8S and Mn0.2Cd0.8S/Co3O4 PPs, respectively. This work will provide broad prospects for the rational design of efficient photocatalysts.

Hollow CoFe-layered double hydroxide polyhedrons for highly efficient CO2 electrolysis

Hollow CoFe-layered double hydroxide polyhedrons for highly efficient CO2 electrolysis

Ag and MOFs-derived hollow Co3O4 decorated in the 3D g-C3N4 for creating dual transferring channels of electrons and holes to boost CO2 photoreduction performance

The rapid recombination of photoinduced charge carriers and low selectivity are still challenges for the CO2 photoreduction. Herein, we proposed that ZIF-67-derived Co3O4 hollow polyhedrons (CoHP) were embedded into NaCl-template-assisted synthesized 3D graphitic carbon nitride (NCN), subsequently, loading Ag by photo-deposition as efficient composites (CoHP@NCN@Ag) for CO2 photoreduction. This integration simultaneously constructs two heterojunctions: p-n junction between Co3O4 and g-C3N4 and metal–semiconductor junction between Ag and g-C3N4, in which Co3O4 and Ag serve as hole (h+) trapping sites and electron (e-) sinks, respectively, achieving spatial separation of charge carriers. The donor–acceptor structure design of NCN realize a good photogenerated e--h+ separation efficiency. The mesoporous structure of hollow Co3O4 facilitate gas-diffusion efficiency, light scattering and harvesting. And the introduction of plasmonic Ag further strengthens the light-harvesting and charge migration. Benefiting from the rational design, the optimized ternary heterostructures exhibit a high CO2-CO yield (562 μmol g−1), which is about 4-fold as high as that of the NCN (151 μmol g−1). Moreover, the conjectural mechanism was systematically summarized. We hope this study provides a promising strategy for designing efficient g-C3N4 systems for the CO2 photoreduction.

NiSe2–FeSe Double-Shelled Hollow Polyhedrons as Superior Electrocatalysts for the Oxygen Evolution Reaction

Rational design and construction of hollow structured hybrid electrocatalysts are impressive for efficient and sustainable water splitting process. This study emphasizes a MOF-based self-templating...

Step-by-step etching strategy to construct multiple-shell amorphous Co/Ni-(PO4)x(OH)y hollow polyhedron for supercapacitor application

Co/Ni-based hydroxide phosphate (CNHP) hollow polyhedrons with multiple-shell are synthesized by a cobalt-nickle layered double hydroxide (Co/Ni-LDH) coating and step-by-step phosphate etching strategy with ZIF-67 dodecahedron as templates. Through rational controlling the LDH coating and Na3PO4 etching time, double shells Co/Ni-(PO4)x(OH)y hollow polyhedron (DS-CNHP) and triple shells Co/Ni-(PO4)x(OH)y hollow polyhedron (TS-CNHP) are successfully constructed. The as-obtained TS-CNHP presents a high specific capacitance of 1506 ​F ​g−1 at the current density of 1 ​A ​g−1, and excellent ratio performance of maintaining 68% initial capacitance from 1 to 10 ​A ​g−1. Furthermore, a hybrid TS-CNHP//AC supercapacitor device is fabricated, and a high energy density of 34.4 ​Wh·kg−1 is achieved at the power density of 0.375 ​kW ​kg−1. Therefore, the step-by-step strategy in this work can provide valuable guidance to construct MOFs derived multiple-shell hollow structures with wide applications.

Fabrication of ZnSe/C Hollow Polyhedrons for Lithium Storage.

ZnSe has got extensive attention for high-performance LIBs anode due to its remarkable theoretical capacity and environmental friendliness. Nevertheless, the large volume variation for the ZnSe in the discharge/charge processes brings about rapid capacity fading and poor rate performance. Herein, ZnSe/C hollow polyhedrons are successfully synthesized by selenization of zeolitic imidazolate framework-8 (ZIF-8) with resorcinol-formaldehyde (RF) coating. The protection of C layer derived from RF coating layer and Ostwald ripening during the process of selenization play important roles in promoting formation of ZnSe/C hollow polyhedrons. The ZnSe/C hollow polyhedrons exhibit good rate performance and long-term cycle stability (345 mAh g-1 up to 1000 cycles at 1 A g-1 ) for lithium ion batteries (LIBs) anode. The improved electrochemical performance is benefit from the unique ZnSe/C hollow structure, in which the hollow structure can effectively avoid terrible volume expansion, and the thin ZnSe/C shell can not only provide adequate diffusion paths of lithium ions and but also enhance the electronic conductivity.

Metal organic framework-derived Co3O4/NiCo2O4 hollow double-shell polyhedrons for effective photocatalytic hydrogen generation

Hollow polyhedron materials have the characteristics of low density, high area ratio, strong light absorption and the short distance of mass transport, etc., which have come to the foreground in recent years. In this work, ZIF-67/Co-Ni double hydroxide (DH) was prepared using ZIF-67 as a precursor and then calcined to form Co3O4/NiCo2O4 hollow double-shell polyhedrons (HDSPs). This unique self-supporting hollow double-shell catalyst effectively avoids the aggregation of the catalyst and provides a unique reaction platform for the photocatalytic hydrogen production reaction. On the one hand, the thin shell reduces the penetration loss of incident light, and there are multiple refractions and scattering occur inside the shell, thereby effectively improving the light-trapping ability. On the other hand, the Co3O4/NiCo2O4 HDSPs not only shortens the transport distance of photo-generated carriers but also provides abundant active sites, which effectively inhibiting the recombination of electrons and holes. Density functional theory (DFT) calculations show that the formation of a NiCo2O4 shell outside of Co3O4 is more conducive to the separation and transfer of electrons. Therefore, the Co3O4/NiCo2O4 HDSPs can facilitate the separation and migration of carriers and effectively increase the hydrogen evolution rate of the catalyst. This work shows the important role of hollow double-shell materials and provides new ideas for the preparation of hollow double-shell catalysts.

Construction of CoNi2S4 hollow cube structures for excellent performance asymmetric supercapacitors

Although the synthesis of transition metal oxide hollow structures has been relatively perfect, it is extremely challenging to prepare mixed transition metal sulfides with excellent structures and high specific capacitance as electrode materials for supercapacitors. Here, we report a simple ion-exchange method and hydrothermal treatment to synthesize a novel hollow structure of ternary metal sulfide, which is nickel-cobalt sulfide hollow cubes. First, a uniform ZIF-67 (Zeolitic Imidazolate Framework-67) cube is synthesized as a precursor, and then a CoNi2S4 hollow polyhedron is successfully realized through the chemical transformation without annealing. As the electrode materials of supercapacitors, the specific capacitance of the hollow cube CoNi2S4 is 2448 F g−1 at the current density of 1.0 A g−1. In addition, an asymmetric supercapacitor (ASC) device based on CoNi2S4 hollow cubes was also assembled. The asymmetric supercapacitor shows long-term cycling performance with a high energy density of 62.19 Wh kg−1 at the power density of 775 W kg−1. The simple synthesis process, low production cost and excellent electrochemical performance indicate that it has broad application prospects in high-performance electrochemical capacitors.

Cobalt Selenide Hollow Polyhedron Encapsulated in Graphene for High-Performance Lithium/Sodium Storage.

Owing to the high specific capacities, high electrochemical activity, and various electronic properties, transition metal selenides are considered as promising anodes for lithium- and sodium-ion storage. However, poor electronic conductivity and huge volume expansion during cycling are still responsible for their restricted electrochemical performance. Herein, CoSe hollow polyhedron anchoring onto graphene (CoSe/G) is synthesized by self-assembly and subsequent selenization. In CoSe/G composites, the CoSe nanoparticles, obtained by in situ selenization of metal-organic frameworks (MOFs) in high temperature, are distributed among graphene sheets, realizing N element doping, developing robust heterostructures with a chemical bond. The unique architecture ensures the cohesion of the structure and endorses the reaction kinetics for metal ions, identified by in situ and ex situ testing techniques, and kinetics analysis. Thus, the CoSe/G anodes achieve excellent cycling performance (1259 mAh g-1 at 0.1 A g-1 after 300 cycles for lithium storage; 214 mAh g-1 at 2 A g-1 after 600 cycles for sodium storage) and rate capability (732 mAh g-1 at 5 A g-1 for lithium storage; 290 mAh g-1 at 5 A g-1 for sodium storage). The improved electrochemical performance for alkali-ion storage provides new insights for the construction of MOFs derivatives toward high-performance storage devices.

Promoting polysulfides redox conversion by sulfur-deficient ZnS1−x hollow polyhedrons for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are deemed as the attractive systems for high-energy storage. However, the polysulfides shuttling with slow redox kinetics has seriously hindered their practical applications. Herein, sulfur-deficient zinc sulfide (ZnS1−x) hollow polyhedrons are synthesized as the multifunctional sulfur host material via the sulfurization and high-temperature annealing method. The unique hollow structure could supply adequate void spaces for sulfur loading and alleviate volumetric expansion of sulfur upon the cycling process. Besides, ZnS1−x hollow polyhedrons with abundant sulfur vacancies can provide effective adsorption sites to chemically immobilize polysulfides and enhance polysulfides redox conversion as confirmed by theoretical calculation results and electrocatalytical experiments. Thus, the S/ZnS1−x cathode delivers the remarkable initial capacity (1206 mAh g−1 at 0.2 C) and excellent cycling stability (592 mAh g−1 after 500 cycles at 1 C). The study points out the idea of functional cathode material for Li-S batteries based on a simple yet efficient vacancy engineering method.

Self-Template Synthesis of Prussian Blue Analogue Hollow Polyhedrons as Superior Sodium Storage Cathodes

Prussian blue and its analogues with three-dimensional frame structures have been shown to be of great importance in the research and development of sodium-ion batteries (SIBs). Herein, we develop a simple and convenient self-template method to prepare a hollow-structured Prussian blue analogue (CoFe-PBA). This structure is conducive to buffer the volume changes during ion extraction and insertion processes and shorten the ion diffusion path. When further building a thin polydopamine (PDA) coating, the synthesized CoFe-PBA@PDA exhibits a high discharge capacity of 123.1 mAh g-1 at 0.1 A g-1 with a capacity retention of 71.5% after 500 cycles. Moreover, the capacity retention of CoFe-PBA@PDA after 100 cycles is 14.3% higher than that of the two comparison samples. In addition, the reversible structure of CoFe-PBA@PDA without forming a new phase was verified by in situ X-ray diffraction. This work may provide another design idea or strategy for improving the stability of the PBA cathodes used in SIBs.

Porous carbon/Co3S4 hollow polyhedron as sulfur carrier to enhance cyclic stability for lithium-sulfur batteries

The lithium-ion battery is subject to the limited theoretical specific capacity of electrode materials, which is difficult to achieve capacity breakthrough. However, the theoretical specific capacity of the sulfur cathode for lithium-sulfur battery is 1675 mAh g−1 and the energy density is 2600 Wh kg−1. However, lithium-sulfur batteries suffer from three problems: “shuttle effect,” sulfur electron/ion insulation, and volume expansion. Moreover, the carbon materials or metal sulfides alone cannot achieve the dual effects of excellent conductivity and chemisorption as sulfur carriers. Therefore, 350 nm and 1 μm of polyhedron with mesoporous carbon and Co3S4 were prepared (denoted as C/Co3S4@S (S) for the small one and C/Co3S4@S (L) for the large one, respectively) using PVP modified self-assembled Co-MOFs as a sacrificial template. The C/Co3S4 (S) carrier provided a sulfur-filled channel, and shortened the electron transport path with excellent conductivity. Simultaneously, the polar Co3S4 chemisorption of polysulfide and hollow structure provided a sufficient storage for sulfur. As the cathode of lithium-sulfur battery, C/Co3S4@S (S) exhibited an initial capacity of 1153 mAh g−1 at 0.5 C, and the capacity decay rate per cycle is only 0.057% during 500 cycles at 1 C, compared to 1 μm C/Co3S4@S (L) efficiently improved the cycle stability.

Hybrid cathode composed of pyrite-structure CoS2 hollow polyhedron and Ketjen black@sulfur materials propelling polysulfide conversion in lithium sulfur batteries

Lithium-sulfur (Li–S) batteries are considered to have great prospects in advanced energy storage devices in the future and have been considered in recent years. However, the shuttling of Li-polysulfides in electrolytes and sluggish electrochemical kinetics of polysulfides hinder the development of Li–S batteries. To address these stumbling blocks, we introduced pyrite-structure CoS2 hollow polyhedron modification of Ketjen black@sulfur (CoS2/KB@S) composite that adsorbs and provides sufficient sites with Li-polysulfides interaction. The CoS2 hollow polyhedron has a pivotal effect on the adsorption and catalysis performance of the polysulfides, which further accelerates the redox kinetics. Consequently, the CoS2/KB@S cathode with 3.1 mg cm−2 sulfur loading attained a high discharge capacity of 0.5 C current density and reversible capacity was 437 mA h g−1 after 500 cycles, which displayed great stability and the capacity attenuation rate of per cycle was only 0.1%. Meanwhile, it also shows excellent rate capabilities and still maintains a high capacity of 527 mA h g−1 at 2 C current density. Even at high sulfur loading of 5.1 mg cm−2, the CoS2/KB@S electrode still delivers a high initial area capacity of 4.36 mA h cm−2 at 0.3 C with capacity retention capacity of 3.63 mA h cm−2 after 100 cycles. The cyclic and rate properties of CoS2/KB@S were greatly improved over that of KB@S. The results suggest the multifunction pyrite-structure CoS2 hollow polyhedron that anchors effectively and catalysis is beneficial to realize the goal of large-scale application for Li–S batteries.

Construction of hollow carbon polyhedron supported Pt catalyst for methanol electrocatalytic oxidation

In this work, the hollow Pt/CP (carbon polyhedron) catalyst derived from ZIF-8 was obtained via a simple hydrothermal method for electrocatalytic methanol oxidation reaction (MOR). Compared with Pt/CB (carbon black) catalyst, the hollow Pt/CP had the higher ESCA, which was 60 m2 g−1, while the Pt/CB was only 41 m2 g−1. Similarly, the If/Ib of the hollow Pt/CP was 7.5, which was also obviously about 3 times higher than the Pt/CB (2.5). All the results verified that the electrocatalytic oxidation activity of hollow Pt/CP was greatly better than Pt/CB. According to a series of characterizations, it can be discovered that the hollow Pt/CP catalyst derived from ZIF-8 had more rich oxygen-containing functional groups, smaller Pt nanoparticles size, more Pt content, larger specific surface area, and so on, which were good for the improvement of MOR activity.