Hierarchical Porous Microstructure Research Articles

Direct pyrolysis fabrication of N/O/S self-doping hierarchical porous carbon from Platycladus Orientali leaves for supercapacitor

Direct pyrolysis fabrication of N/O/S self-doping hierarchical porous carbon from Platycladus Orientali leaves for supercapacitor

Analysis on Component of Cultured Diatoms and Their Application as Li‐Ion Battery Anodes

AbstractDiatom is a kind of unicellular organism, whose cell wall is composed of hydrated amorphous silica. Herein, we conducted content and component analysis for three typical genera of self‐cultured diatoms, and explored their fascinating properties to construct anodes of lithium ion batteries (LIBs). Three types of diatoms (Chaetoceros, Navicula, and Stephanodiscus) were extracted and purified for detailed characterization, which verified their main components (e. g., water, protein, carbohydrate, fat, frustule) and delicate hierarchical porous microstructures. Besides, a facile treatment was applied to prepare the diatom‐based anode composites for LIBs. A series of electrochemical tests were conducted to verify their excellent performance of high Initial Coulombic Efficiency(ICE), superior rate capacity and reusability. These fascinating properties could be ascribed to integration of the protoplasmic carbon and unique microstructure. This work offers a feasible strategy to construct renewable natural materials with remarkable anode performance for advanced LIBs.

Hierarchical Cellulose Aerogel Reinforced with In Situ-Assembled Cellulose Nanofibers for Building Cooling.

The development of new structural materials for passive daytime radiative cooling (PDRC) of buildings will significantly reduce global building energy consumption. Cellulose aerogels are potential PDRC materials for building cooling, but the cooling performance and mechanical strength of cellulose aerogels are considered as challenges for their practical applications. Herein, a bio-inspired hierarchically structured cellulose aerogel (HSCA) was fabricated through an assembly strategy assisted by a high-voltage electrostatic field. The HSCA possesses outstanding PDRC performance and moderate mechanical strength owing to aligned hierarchical porous network microstructures reinforced with in situ-assembled crystalline cellulose nanofibers. Promisingly, the HSCA achieves a max cooling temperature of 7.2 °C and exhibits 1.9 MPa axial compressive strength. There was no significant cooling performance degradation after the hydrophobically modified HSCA was placed outdoors for 3 months. A simulation of potential cooling energy savings shows that by using HSCA as the building envelopes (side wall and roof), it can save 52.7% of cooling energy compared to the building baseline consumption. This new strategy opens up the possibility of developing advanced functionally regenerated cellulose aerogel, which is expected to provide a revolutionary improvement in aerogel materials for building cooling.

Enhanced Photothermal Steam Generation and Gold Using the Efficiency of Ultralight Gold Foam with Hierarchical Porosity

Controlling the optical properties of metal plasma nanomaterials through structure manipulation has attracted great attention for solar steam generation. However, realizing broadband solar absorption for high-efficiency vapor generation is still challenging. In this work, a free-standing ultralight gold film/foam with a hierarchical porous microstructure and high porosity is obtained through controllably etching a designed cold-rolled (NiCoFeCr)99Au1 high-entropy precursor alloy with a unique grain texture. During chemical dealloying, the high-entropy precursor went through anisotropic contraction, resulting in a larger surface area compared with that from the Cu99Au1 precursor although the volume shrinkage is similar (over 85%), which is beneficial for the photothermal conversion. The low Au content also results in a special hierarchical lamellar microstructure with both micropores and nanopores within each lamella, which significantly broadens the optical absorption range and makes the optical absorption of the porous film reach 71.1-94.6% between 250 and 2500 nm. In addition, the free-standing nanoporous gold film has excellent hydrophilicity, with the contact angle reaching zero within 2.2 s. Thus, the 28 h dealloyed nanoporous gold film (NPG-28) exhibits a rapid evaporation rate of seawater under 1 kW m-2 light intensity, reaching 1.53 kg m-2 h-1, and the photothermal conversion efficiency reaches 96.28%. This work demonstrates the enhanced noble metal gold using efficiency and solar thermal conversion efficiency by controlled anisotropic shrinkage and forming a hierarchical porous foam.

Complex Impedance and Modulus Analysis on Porous and Non-Porous Scaffold Composites Due to Effect of Hydroxyapatite/Starch Proportion.

This study aims to investigate the electric responses (complex modulus and complex impedance analysis) of hydroxyapatite/starch bone scaffold as a function of hydroxyapatite/starch proportion and the microstructural features. Hence, the non-porous and porous hydroxyapatite/starch composites were fabricated with various hydroxyapatite/starch proportions (70/30, 60/40, 50/50, 40/60, 30/70, 20/80, and 10/90 wt/wt%). Microstructural analysis of the porous hydroxyapatite/starch composites was carried out by using scanning electron microscopy. It shows that the formation of hierarchical porous microstructures with high porosity is more significant at a high starch proportion. The complex modulus and complex impedance analysis were conducted to investigate the electrical conduction mechanism of the hydroxyapatite/starch composites via dielectric spectroscopy within a frequency range from 5 MHz to 12 GHz. The electrical responses of the hydroxyapatite/starch composites are highly dependent on the frequency, material proportion, and microstructures. High starch proportion and highly porous hierarchical microstructures enhance the electrical responses of the hydroxyapatite/starch composite. The material proportion and microstructure features of the hydroxyapatite/starch composites can be indirectly reflected by the simulated electrical parameters of the equivalent electrical circuit models.

A flexible hierarchical MoS2 nanosheet coated glass fabric via direct hydrothermal deposition for efficient solar-driven steam generation

A flexible and tailorable solar evaporator has a hierarchical porous microstructure assisting light harvesting and water transportation.

Enhanced interfacial charge migration through fabrication of p-n junction in ZnIn2S4/NiFe2O4/biochar composite for photocatalytic doxycycline hydrochloride degradation

• ZnIn 2 S 4 /NiFe 2 O 4 /biochar composite was prepared. • The photocatalytic performance was studied by doxycycline degradation. • The effects of various experimental and practical factors were studied. • The involved radicals, by-products and mechanism were proposed. • The magnetic composite exhibited excellent reusability. Photo-induced electron-hole pair recombination, light response ability and surface property of photocatalyst greatly affect its activity. In this paper, a p-n junction ZnIn 2 S 4 /NiFe 2 O 4 with biochar (ZIS/NFO/BC) was prepared, presenting improved charge carrier mobility, excellent light absorption and hierarchical porous micro-structure. ZIS/NFO/BC exhibited good photodegradation efficiency and TOC removal rate towards doxycycline hydrochloride under simulated sunlight, as well as good stability and reusability after six cycles. Biochar inhibited the agglomeration of nanoparticles, improved charge carrier mobility and light absorption ability. The synergy between adsorption of biochar and photocatalytic degradation of p-n junction greatly promoted photodegradation efficiency. Photo-induced holes (h + ) played a major role during photodegradation. The effects of pH, coexisting ions (Cl - , NO 3 - , CO 3 2- ) and humic acid on photodegradation were investigated. Furthermore, the photodegradation mechanism was proposed and possible pathway was illustrated. This work provides new route for the development of magnetic recyclable photocatalyst with high potential for wastewater treatment.

3D printed electrospun nanofiber-based pyramid-shaped solar vapor generator with hierarchical porous structure for efficient desalination

Solar vapor generation is regarded as a promising approach to alleviate the water shortage crisis via desalination, while the efficiency is limited by the insufficient vapor escape and adverse effect of salt deposition. Herein, a pyramid structural solar vapor generator is developed combing electrospun polyacrylonitrile/carbon nanotubes (PAN/CNTs) nanofibers and 3D printing technology. Benefiting from the excellent light absorption (98.3%) and photothermal property as well as the good water transportation ability, the optimum sample with concave-convex macroscopic morphology and hierarchical porous microstructure exhibits the evaporation rate up to 2.62 kg m-2h−1 under one sun illumination. Moreover, with the merit of crisscross stacking characteristic of the sample, the evaporation rate can improve further to 8.31 kg m-2h−1 under the convective flow of 4 m s−1. More importantly, the evaporator can still achieve a high-level evaporation rate and has good self-cleaning property in high-concentration brine. The unique preparation strategy enables the resultant 3D printed electrospun nanofiber-based pyramid-shaped evaporator to act as a reliable and efficient platform for efficient desalination.

A high-performance planar anode-supported solid oxide fuel cell with hierarchical porous structure through slurry-based three-dimensional printing

Three-dimensional (3D) printing is considered to its the ability to make complex structures with modified properties in functional materials. In this work, a planar multi-layer anode-supported solid oxide fuel cell (SOFC) is fabricated through slurry-based 3D printing. The composition of 65 wt% NiO-YSZ (60:40 wt%)–35 wt% graphite is selected for fabrication of anode support by pressing. The low viscosity slurry with good homogeneity is prepared for fabricating of anode functional layer (AFL) consisting of NiO-YSZ (50–50), electrolyte (YSZ), and cathode (LSM) layers. After sintering of layers, uniform hierarchical porous microstructures are obtained with interconnected large pores up several microns and smaller pores of 100 nm in the AFL and cathode layer. In meanwhile, the electrolyte layer is achieved a relatively dense microstructure. The maximum power density at the output voltage of 0.5 V is achieved at 0.84 W/cm2 at an open-circuit voltage (OCV) of 1.06 V at 800 °C with H2 gas as fuel. The results are shown that the hierarchically macro-mesopores can create higher power density. Also, modification of geometry such as thickness and structure of layers can be improved electrochemical performance. Furthermore, the OCV exhibited a few fuel leakage due to the relatively dense structure and crack-free electrolyte layer.

Elimination of zinc ions from aqueous solution by a hydroxylapatite-biochar composite material with the hierarchical porous microstructures of sugarcane waste

A hydroxylapatite-biochar composite material with the hierarchical porous microstructures of sugarcane top internodes (HAP/C-SC) was produced by carbonizing sugarcane top stalks, an agricultural waste residue, and then soaking them in limewater and (NH 4 ) 2 HPO 4 solution in turns. The HAP/C-SC with the surface area of 8.52–28.44 m 2 /g inherited various macropores from parallel vessels, thick-walled cells of sclerenchyma, thin-walled cells of storage parenchyma, and pits in cell and vessel walls of sugarcane top stalks. When the initial Zn 2+ concentration is 5–400 mg/L, the Zn 2+ absorption capacity of HAP/C-SC is 19.91, 22.54, and 25.37 mg/g at 25 °C, 35 °C, and 45 °C, respectively, which is equivalent to the Zn 2+ absorption capacity of synthetic nano-hydroxyapatite. The HAP/C-SC showed a good removal performance for Zn cations, and the adsorption followed Langmuir model and pseudo-second-order kinetic model well. The Zn-containing hydroxylapatite solid solutions [(Zn x Ca 1‒x ) 5 (PO 4 ) 3 (OH)] were considered to be the key mechanism for Zn 2+ elimination, which formed through the co-action processes including adsorption, ion exchange (x = 0.06–0.12) and dissolution-precipitation (x = ∼0.27). The M(2) vacancy sites are believed to be energetically more favorable for the Zn ion occupation. The substitution and occupation of M(2) sites by Zn ions may be affected by spatial constraints. • One kind of porous biomorph-genetic composite of HAP/C was prepared. • The material retained the hierarchical porous microstructure of sugarcane top. • The material has different pores from vascular, parenchyma, sclerenchyma and pits. • The elimination capacity for Zn(II) is comparable to nano-hydroxyapatite. • The adsorption followed the pseudo-second-order equation and Langmuir isotherm.

High-performance LiFePO4 and SiO@C/graphite interdigitated full lithium-ion battery fabricated via low temperature direct write 3D printing

Lithium-ion batteries (LIBs) composed of thin tape–casted electrodes face some intrinsic challenges especially the trade-off between energy density and power density. Three-dimensional (3D) structural batteries fabricated by 3D printing have the potential to overcome this challenge. Silicon oxide–based materials are promising candidates for the next-generation high-performance LIBs. In this study, interdigitated full batteries composed of comb-like LiFePO 4 3D cathodes and comb-like SiO@C/graphite 3D anodes are fabricated via low temperature direct writing 3D printing process. The 3D printing at a low temperature of below −20 °C enables the 3D-printed SiO@C/graphite electrodes obtain a high porosity of ∼60% and tri-modally hierarchical porous microstructure . Comb-like 3D SiO@C/graphite anodes with the thickness of ∼418 μm, ∼692 μm, and ∼806 μm and corresponding mass loading of ∼39.2 mg cm -2 , ∼60.9 mg cm -2 , ∼84.3 mg cm -2 , respectively, are fabricated to evaluate their electrochemical performance. These thick 3D electrodes display impressive areal capacities of ∼17.9, ∼26.7, and ∼33.2 mA h cm -2 @ 0.3 C depending on their electrode thickness. Coupled with comb-like LiFePO 4 3D cathodes, interdigitated full batteries with two N/P ratios of 0.91 and 0.82 are fabricated. These full batteries exhibit high energy density, high power density, and stable cycling performance. • Comb-like 3D SiO@C/graphite anodes are fabricated via low temperature direct writing 3D printing. • 3D LiFePO 4 cathode and 3D SiO@C/graphite anode are assembled into interdigitated full batteries. • The interdigitated full battery shows excellent electrochemical properties with stable cycling performance.

Synergistically Enhanced Single-Atom Nickel Catalysis for Alkaline Hydrogen Evolution Reaction.

The feature endowing atomic Ni-N-C electrocatalysts with exceptional intrinsic alkaline hydrogen evolution activity is hitherto not well-documented and remains elusive. To this end, we rationally exploited the hierarchical porous carbon microstructures as scaffolds to construct unique Ni-N2+2-S active sites to boost the sluggish Volmer reaction kinetics. Density functional theory reveals an obvious d-band center (ϵd) upshift of the edge-hosted Ni-N2+2-S sites compared with pristine Ni-N4, which translates to a more stabilized OH adsorption. Moreover, the synergetic dual-site (Ni and S atom) interplay gives rise to a decoupled regulation of the adsorption strength of intermediate species (OHad, Had) and thereby energetic water dissociation kinetics. Bearing these in mind, sodium thiosulfate was deliberately adopted as an additive in the molten salt system for controllable synthesis, considering the simultaneous catalyst morphology and active-site modulation. The target Ni-N2+2-S catalyst delivers a low working overpotential (83 mV@10 mA cm-2) and Tafel slope (100.5 mV dec-1) comparable to those of representative transition metal-based electrodes in alkaline media. The present study provides insights into the metal active-site geometry and promising synergistic effects over single-atom catalysis.

Dynamic Adsorption of As(V) onto the Porous α-Fe2O3/Fe3O4/C Composite Prepared with Bamboo Bio-Template

Arsenic (As(V)), a highly toxic metalloid, is known to contaminate wastewater and groundwater and is difficult to degrade in nature. However, the development of highly efficient adsorbents, at a low cost for use in practical applications, remains highly challenging. Thus, to investigate the As(V) adsorption mechanism, a novel porous α-Fe2O3/Fe3O4/C composite (PC-Fe/C-B) was prepared, using bamboo side shoots as a bio-template, and the breakthrough performance of the PC-Fe/C-B composite-packed fixed-bed column in As(V) removal was evaluated, using simulated wastewater. The PC-Fe/C-B material accurately retained the hierarchical porous microstructure of the bamboo bio-templates, and the results demonstrated the great potential of PC-Fe/C-B composite, as an effective adsorbent for removing As(V) from wastewater, under the optimal experimental conditions of: influent flow 5.136 mL/min, pH 3, As(V) concentration 20 mg/L, adsorbent particle size < 0.149 mm, adsorption temperature 35 °C, PC-Fe/C-B dose 0.5 g, and breakthrough time 50 min (184 BV), with qe,exp of 21.0 mg/g in the fixed-bed-column system. The CD-MUSIC model was effectively coupled with the transport model, using PHREEQC software, to simulate the reactive transportation of As(V) in the fixed-bed column and to predict the breakthrough curve for column adsorption.

3D printing of ultrathick natural graphite anodes for high-performance interdigitated three-dimensional lithium-ion batteries

• Comb-like 3D natural graphite anodes are fabricated via a low temperature direct write 3D printing technology. • 3D-printed graphite anodes have thickness of 347.3, 581.7 and 786.7 μm and areal mass loading reaches 16.3, 24.4 and 32.9 mg cm −2 . • The 3D-printed graphite anode display high areal capacities and stable cycling performance. Graphite has been the major anode material of choice for lithium-ion batteries (LIBs) for over 30 years. This study reports three-dimensional (3D) printing of comb-like 3D natural graphite (NG) electrodes for high-performance interdigitated 3D LIBs. Printable NG inks were developed and 3D NG electrodes with the thickness of 347.3 μm, 581.7 μm and 786.7 μm (corresponding areal mass loading: 16.3 mg cm −2 , 24.4 mg cm −2 and 32.9 mg cm −2 ) were fabricated via a low temperature direct write 3D printing technology. The 3D-printed electrodes had tri-modally hierarchical porous microstructures with a high porosity of 54.84%. In addition, these thick electrodes showed excellent electrochemical performance with an impressive areal capacity of 13.68 mAh cm −2 @ 0.1C for electrodes with the thickness of 786.7 μm. With this type of 3D electrodes, the capacity fade over the increase of discharge rates was greatly reduced in comparison with tape casted electrodes with the same electrode thickness. This study demonstrates the potential of 3D-printed NG electrodes for high-performance LIBs.

Phosphorus doped hierarchical porous carbon nanosheet array as an electrocatalyst to enhance polysulfides anchoring and conversion

• MgO is used as hard template to form hierarchical porous carbon nanosheet array. • Phosphorous doping is introduced by the copolymerization of resorcinol, formaldehyde and phytic acid. • Phosphorous doping exhibits a metal-like LiPSs anchoring effect by forming Li-P and S-P bonds. • Phosphorus doping reduces energy barrier for LiPSs reactions and facilitates Li 2 S precipitation. • The resultant LSB delivers an excellent capacity and long-term cycling stability. The sluggish redox kinetics and severe lithium polysulfides (LiPSs) shutting effect in lithium sulfur batteries (LSBs) greatly hinder their practical applications. In this work, phosphorus doped carbon nanosheet array (MPC) separator coating layer was synthesized by MgO template, and used as metal-free electrocatalyst to concurrently fulfill efficient polysulfide interception and conversion. By regulating the addition of phytic acid, copolymerization rate of formaldehyde, resorcinol and phytic acid can be conveniently adjusted to form a hierarchical porous MPC microstructure. Phosphorus doping introduces surface defects and enhances the polarity of MPC, which exhibits a metal-like LiPSs anchoring effect by forming Li-P and S-P bonds, avoiding the undesirable oxidation of LiPSs during adsorption. Symmetrical cell and Li 2 S precipitation experiments reveal that phosphorus doping reduces energy barrier for LiPSs reactions and facilitates Li 2 S precipitation behavior, exhibiting a strong electrocatalytic effect on Li-S chemistry. Stemming from the above advantages of MPC coated separator, cells exhibit a low interfacial reaction resistance and good anode stability. A capacity of 1161 mAh g −1 at 0.2C and a low attenuation of 0.056% per cycle at 1C over 800 cycles are achieved. For a high sulfur loading up to 4 mg cm −2 , the areal capacity can still be stabilized at 2.86 mAh cm −2 .

Solution combustion synthesis of hierarchical porous LiFePO4 powders as cathode materials for lithium-ion batteries

Hierarchical porous LiFePO4 powders were prepared by solution combustion method using a mixture of cetyltrimethylammonium bromide (CTAB) and glycine as fuel. The effects of fuel contents on structural, microstructural, and electrochemical properties were studied by various characterization methods such as X-ray diffraction, infrared spectroscopy, scanning electron microscopy, N2 adsorption–desorption isotherms, and galvanostatic charge/discharge. Single phase LiFePO4 powders were crystallized by calcination at 700 °C. Phase evolution was depended on the nature and amount of intermediate phases. The hierarchical porous microstructure was obtained at an appropriate amount of mixed fuels. LiFePO4 powders showed the high specific discharge capacity of 110 mAh g−1 and high capacity retention of 98% at 1C which were attributed to their high crystallinity and high specific surface areas. The porous microstructure and small particle size were benefitted for the electrode kinetics, as indicated by electrochemical impedance spectroscopy.

Gas Altered Hierarchical Porous Graphene Aerogel with High Energy Density

A hierarchical porous graphene aerogel (HP-GA) with hand tearing bread like macro-morphology is achieved through hydrothermal treatment a mix suspension of manganese dioxide (MnO2) and hydrogen chloride (HCl) containing graphite oxide (H-GO) before freeze drying. The chlorine gas (Cl2 as a result of the reaction of HCl and MnO2 is responsible for the formation of the hierarchical porous microstructure and hand tearing bread like macro-morphology. When used as the active electrode material in supercapacitors, the HP-GA exhibits a large specific capacitance of 284 F g-1 at 1 A g-1 and ultrahigh energy density of 10 Wh kg-1 at 250 W kg-1 in aqueous electrolyte. This work provides a versitile, simple and easy-to-controlled way to alter the microstructure and macromorphology of graphene-based areogels that have promissing applications in many areas including adsorption, energy storage, heat insulation, acoustical insulation and intelligent sensing.

Hierarchical porous ceramics with multiple open pores from boehmite gel emulsions

AbstractCeramic foam materials with highly porous microstructure are playing vital role in increasing areas, especially for those with requirements for open channels and superior specific surface area. In this work, a simple and versatile approach to prepare ceramic foams with open pores has been proposed, that is gelation of boehmite nanoparticle‐assembled emulsions. Notably, hierarchical porous microstructure with open channels and uniform pore structure has been built. High specific surface area up to389.4 m2/g is attainable, making it excellent adsorption material when combining the merit of hierarchical pore structure. Furthermore, lattice‐shaped ceramics are prepared via direct ink writing gelled emulsion, displaying the potential of forming lightweight material with complex shape and designable macrostructure. The three‐dimensional (3D) printed foams exhibit multiple open pores, which cover length scale from mm scale, to μm scale and nm scale, making them promising materials in several fields like adsorption and gas filtrations, etc.

Characterization of High-Temperature Hierarchical Porous Mullite Washcoat Synthesized Using Aluminum Dross and Coal Fly Ash

Mixture of aluminum dross (AD) and coal fly ash (CFA) was used to produce high-temperature porous mullite for washcoat application. CFA is the combustion by-product of pulverized coal in a coal-fired power plant, while AD is a waste product produced in secondary aluminum refining. In this study, 80 wt% of AD and 20 wt% of CFA was used to prepare a mullite precursor (MP) via acid leaching and dry-milling. The precursor was coated on a substrate and subsequently fired at 1500 °C. The results showed that the precursor transformed to a hierarchical porous microstructure assembled by large interlocked acicular mullite crystals. The pore structures consisted of large interconnected open pores and small pores. The specific surface area of the mullite washcoat was 4.85 m2g−1 after heating at 1500 °C for 4 h. The specific surface area was compatible with the specific surface area of other high-temperature washcoats.

Multiscale homogenization and localization of materials with hierarchical porous microstructures

Abstract Using an efficient, elasticity-based homogenization theory, we investigated the effect of porosity redistribution at different microstructural scales on the homogenized moduli and local stress fields of periodic materials with hierarchical porosities. A recursive algorithm was developed wherein homogenized moduli and local stress fields obtained from the homogenization and localization analysis at one scale are used in the calculation of homogenized moduli at the next scale. This recursive algorithm is employed until the largest scale is reached. We illustrate the developed computational capability for a two-scale periodic material by generating homogenized moduli and stress concentrations during the process of porosity redistribution between the scales. Results of extensive parametric studies, enabled by the elasticity-based hierarchical homogenization algorithm, show that largest homogenized moduli and lowest stress concentration may be obtained through proper choice of relevant parameters. The algorithm is also applicable to hierarchical materials with nanoscale porosities with surface-elasticity effects taken into account using the Gurtin-Murdoch model. Coupling the integrated homogenization/localization framework with the Particle Swarm Optimization facilitates direct identification of multiscale porous microstructures with the lowest stress concentration for a given targeted homogenized modulus, verified upon comparison with the parametric study results. The present work provides guidelines for the design of multiscale porous materials.