Hierarchical Porosity Research Articles

Coupling of Fe-Nx sites and Fe nanoparticles on nitrogen-doped porous carbon for boosting oxygen electroreduction in Zn-air batteries

Fe and nitrogen co-doped carbon (Fe-N-C) catalysts have emerged as attractive materials to substitute Pt-based catalysts for the oxygen reduction reaction (ORR) in Zn-air batteries (ZABs). However, the Fe-N-C catalysts with monotypic active component usually endow suboptimal catalytic performance and stability under both acid and alkaline medium. Herein, a nano ZnO template and two-step pyrolysis co-assisted strategy is proposed to achieve the coupling of Fe-Nx sites and metallic Fe nanoparticles in hierarchically porous N-doped carbon for ORR. The nano ZnO template contributes to the formation of meso/macropores structure, while the secondary pyrolysis is beneficial to the creation of more micropores. Besides the advanced hierarchical porosity, the combination of dispersed Fe-Nx sites and dominated metallic Fe nanoparticles is also conducive to boost ORR activity in both acid and alkaline solution. Impressively, the prepared Fe@FeHPNC-P2 electrocatalyst exhibits an excellent half-wave potentials (E1/2) of 0.88 V and 0.79 V in alkaline and acidic electrolyte, respectively. Meanwhile, the assembled liquid Zn-air battery using Fe@FeHPNC-P2 delivers a peak power density of 149.3 mW cm−2 and a maximum energy density of 957.1 Wh kgZn−1 along with long-term stability for 1000 cycles.

Protocrystallinity of Monodispersed Ultra-Small Templated Mesoporous Silica Nanoparticles.

Monodisperse and semi-faceted ultra-small templated mesoporous silica nanoparticles (US-MSNs) of 20-25 nm were synthesized using short-time hydrolysis of tetraethoxysilane (TEOS) at room temperature, followed by a dilution for nucleation quenching. According to dynamic light scattering (DLS), a two-step pH adjustment was necessary for growth termination and colloidal stabilization. The pore size was controlled by cetyltrimethylammonium bromide (CTAB), and a tiny amount of neutral surfactant F127 was added to minimize the coalescence between US-MSNs and to favor the transition towards internal ordering. Flocculation eventually occurred, allowing us to harvest a powder by centrifugation (~60% silica yield after one month). Scanning transmission electron microscopy (STEM) and 3D high-resolution transmission electron microscopy (3D HR-TEM) images revealed that the US-MSNs are partially ordered. The 2D FT transform images provide evidence for the coexistence of four-, five-, and sixfold patterns characterizing an "on-the-edge" crystallization step between amorphous raspberry and hexagonal pore array morphologies, typical of a protocrystalline state. Calcination preserved this state and yielded a powder characterized by packing, developing a hierarchical porosity centered at 3.9 ± 0.2 (internal pores) and 68 ± 7 nm (packing voids) of high potential for support for separation and catalysis.

Vanadium nitride /poly(0-methoxy aniline)- poly(3,4-ethylene dioxythiophene) interpenetrated into nanocomposite for efficient photocatalytic degradation of methylene blue and enhanced electrochemical sensing of mebendazole

Vanadium nitride-poly (0-methoxy aniline)- poly(3,4-ethylene dioxythiophene) (VN-POMA-PEDOT) hybrid was synthesized via ammonolysis and chemical oxidative polymerization technique using VN-POMA-PEDOT/GCE with electrocatalytic activity has two dimensional VN hierarchical porosity with POMA-PEDOT structure created VN-POMA-PEDOT modified GCE working electrode. Donor-acceptor behavior and double-layer growth enable enhanced electrochemical performance and catalytic activity of mebendazole (MBZ). This work investigated the electrochemical sensing conduct of a VN-POMA-PEDOT hybrid composite towards MBZ. The detection limit (DL) and quantification limit (QL) were determined to be 2.192 × 10−9 μM μA−1 and 5.245 × 10−9 M μA−1. Estimation of anti-interference ability, long-term stability, and reproducibility revealed that the prepared VN-POMA-PEDOT electrode is appropriate for the electrochemical sensing finding of MBZ in real analysis, such by way of anti-helminthic drug milk. The VN-POMA-PEDOT achieved 98.9% efficiency in the photocatalytic degradation of methylene blue (MB) within 50 min with degradation rate 8.3 × 10−3 min−1. The suppleness of this method was confirmed by the hybrid morphology VN-POMA-PEDOT, which shows an enormously superior and enhanced photocatalytic presentation of MB.

ZSM-5 monolithic microreactors with hierarchical porosity: Maximizing selective production of para-xylene

ZSM-5 monoliths with Si/Al ∼40 were achieved by steam assisted conversion of micro-/macroporous silica-alumina monoliths synthesized by an optimized combination of spinodal decomposition and sol-gel process. ZSM-5 monoliths exhibit a homogeneous and interconnected network of macropores of ∼30 μm diameter, with a macropore volume of ∼1 mL g−1 and a micropore volume of 0.16 mL g−1, as waited for pure ZSM-5. The skeleton of ZSM-5 monoliths featured a 3D aggregation of spherical particles of 6 μm in diameter. The latter were composed by a stacking of thin plate-like shaped crystallites. The catalytic properties of the ZSM-5 monoliths were assessed through their use as catalytic microreactor in the continuous flow alkylation of toluene with methanol. An outstanding for para-xylene selectivity of 81 % was achieved possibly ascribable due to the maximization of pore openings of sinusoidal channels as a result of the plate-like morphology of the ZSM-5 crystallites.

Activated carbon-reinforced polyurethane composite foams with hierarchical porosity for broadband sound absorption

The generation of various noise has caused severe noise pollution issues across a wide frequency spectrum, urgently requiring the development of sound-absorbing materials. Herein, we introduce composite polyurethane (PU) foams incorporating extremely nanoporous activated carbon (AC) including both meso- and macro-sized pores as an eco-friendly sound-absorbing material with superior and broadband sound absorption capabilities. The composite foam absorbs 95.8 % of the incident acoustic waves in the 2,000–5,000 Hz frequency range, i.e., the most sensitive range for the human auditory system, far outperforming pristine PU foam, which absorbs only 70.6 %. We demonstrate that sound absorption properties can be fine-tuned by adjusting the pore type and content of the AC. Significantly, the optimized composite foam structure absorbs 100 % of the incident waves at a specific frequency of 2,550 Hz. Collectively, we propose a master curve for the sound absorption properties derived from various composite foams, demonstrating that the properties can be precisely predictable and subsequently used for designing the pore characteristics and content of AC. Incorporating AC can also improve the mechanical properties of foams through interfacial adhesion phenomena. Our methodology provides valuable insights into the fabrication of composite foams with tunable sound absorption properties as a promising solution to noise pollution.

Hierarchical Porosity and Surface Oxygenation of Carbon-Based Cathodes Enhances Discharge Capacity and Decreases Discharge Overpotential of Potassium–Oxygen Batteries

Hierarchical Porosity and Surface Oxygenation of Carbon-Based Cathodes Enhances Discharge Capacity and Decreases Discharge Overpotential of Potassium–Oxygen Batteries

Double Unit-Cell Silicogermanate Nanosheets Developed by Salting-Out Mechanism for Biomass Conversion.

Zeolite nanosheets with an extremely thin thickness featuring both unique pore systems and low diffusion resistance have the potential to achieve enhanced catalytic performance in the conversion of bulky molecular biomass. The preparation of unit-cell level nanosheets generally requires complex and costly multifunctional surfactants or an organic structure-directing agent (OSDA). Commercially available and environmentally friendly ionic liquids can also direct the structure of zeolite nanosheets by π-π stacking when these kinds of OSDA are used in large amount. Herein, we first report unit-cell-sized silicogermanate nanosheets of NS-IM-20 (UWY topology), 5 nm in thickness, which were synthesized at a relatively low ionic liquid concentration with the assistance of halide ion (Cl-). The Pd-loaded NS-IM-20 nanosheets with a hierarchical porosity and moderate acidity act as promising bifunctional catalysts for selective biomass conversion.

High Pore Volume Hyper-Cross-Linked Polymers via Mixed-Solvent Knitting: A Route to Superior Hierarchical Porosity for Methane Storage and Delivery

High Pore Volume Hyper-Cross-Linked Polymers via Mixed-Solvent Knitting: A Route to Superior Hierarchical Porosity for Methane Storage and Delivery

Nanoengineered Cobalt Electrocatalyst for Alkaline Oxygen Evolution Reaction.

The alkaline oxygen evolution reaction (OER) remains a bottleneck in green hydrogen production owing to its slow reaction kinetics and low catalytic efficiencies of earth abundant electrocatalysts in the alkaline OER reaction. This study investigates the OER performance of hierarchically porous cobalt electrocatalysts synthesized using the dynamic hydrogen bubble templating (DHBT) method. Characterization studies revealed that electrocatalysts synthesized under optimized conditions using the DHBT method consisted of cobalt nanosheets, and hierarchical porosity with macropores distributed in a honeycomb network and mesopores distributed between cobalt nanosheets. Moreover, X-ray photoelectron spectroscopy studies revealed the presence of Co(OH)2 as the predominant surface cobalt species while Raman studies revealed the presence of the cubic Co3O4 phase in the synthesized electrocatalysts. The best performing electrocatalyst required only 360 mV of overpotential to initiate a current density of 10 mA cm-2, exhibited a Tafel slope of 37 mV dec-1, and stable OER activity over 24 h. The DHBT method offers a facile, low cost and rapid synthesis approach for preparation for highly efficient cobalt electrocatalysts.

Laser‐Induced Graphene Toward Flexible Energy Harvesting and Storage Electronics

AbstractEnergy harvesting and storage devices play an increasingly important role in the field of flexible electronics. Laser‐induced graphene (LIG) with hierarchical porosity, large specific surface area, high electrical conductivity, and mechanical flexibility is an ideal candidate for fabricating flexible energy devices which supply power for other electronic components. Through a simple laser irradiation process with designable routes, abundant precursors (or substrates) rapidly transform into patterned LIG without any other treatments. The structure and physicochemical properties of LIG can be regulated by controlling the processing strategies and parameters, enabling the optimization of device performance. The laser scribing method, as a non‐contact and in situ technique, proves to be efficient in integrating different LIG‐based devices, resulting in all‐in‐one flexible power platforms. Here, a systematic summary of recent advancements in LIG‐based flexible energy electronics is presented. The controllable synthesis of LIG, functional LIG, and 3D architectures are described by elucidating corresponding mechanisms and processing strategies. An overall review of flexible energy conversion and storage devices based on LIG is presented. Eventually, the challenges and opportunities of LIG‐based materials in flexible energy conversion and storage are briefly discussed.

LiF‐Rich Solid Electrolyte Interfaces Guarantee the Cycle Stability of Metal‐Organic Frameworks for Lithium Storage

Metal‐organic framework materials (MOFs) with hierarchical porosity, structural tunability, and rich redox‐active centers have attracted intensive attention as potential substitutes for carbonaceous anode materials. However, the practical commercialization of MOFs still remains a challenge, due to uncontrollable performance degradation. Inspired by the prolonged lifespans of traditional anode materials with LiF‐rich solid electrolyte interface (SEI), the roles of LiF are examined in enhancing the cycle stability of MOFs, with copper benzenedicarboxylate (Cu‐BDC) as an example. By adjusting the electrolyte composition, the cycle performance of Cu‐BDC material is optimized, due to the generation of LiF‐rich SEI. In the optimal 3 M LiPF6 electrolyte, the formed SEI membrane is the thinnest, and the LiF content is the highest, so the Cu‐BDC shows a specific charge/discharge capacity of 378/387.2 mAh g−1 after 100 cycles at 100 mA g−1, comparing to less than 200 mAh g−1 in the electrolyte with 1% vinyl carbonate.

Amidoximated‐Wood Derived Carbons as Advanced Self‐Standing Electrodes for Supercapacitor and Water Splitting

AbstractWood‐derived carbons demonstrate great potential as self‐standing electrodes in energy storage/conversion applications, including supercapacitors and water‐splitting devices. However, the key challenge remains the rational customization of surface functionalities for optimized performance. This study introduces an innovative approach to self‐standing wood‐derived carbons with tailored nitrogen and metal functionalities. In contrast to traditional impregnation techniques, which offer limited precision in surface modification, this approach entails the intentional attachment of amidoxime groups to the wood substrates. These groups serve as nitrogen sources, and create abundant surface anchoring sites for metal ions due to the chelation between the amidoxime groups and metals. The resulting carbons feature uniform and high dispersion of nitrogen and metal functionalities, along with a distinctive hierarchical porosity combining interconnected open channels with abundant mesopores. As a proof‐of‐concept, different metals are incorporated (i.e., Mn, Co, Ni) into the amidoximated‐wood precursors, and the resulting self‐standing carbons showcase excellent performance in both supercapacitors and water‐splitting applications. Leveraging the specific chelating ability of amidoxime groups toward metal ions, this strategy holds great potential as a generic approach to systematically tailoring the surface functionalities of carbon‐based materials for various electrochemical energy storage/conversion processes.

Tailoring porosity and acoustic properties in bi-layered diatomite-based foams through multiscale structural approach

A tailored multifunctional diatomite-based foam with porosity and density gradients has been developed through a new technology that enables an unprecedented integration of acoustic, mechanical and thermal properties. The production process consists of a custom-made pilot plant for foaming capable of mixing solid phases, such as diatomite, catalyst and silicon chemical blowing agent, with a liquid solution, made of sodium silicate cross-linking agent and vegetable foaming agent. The resulting foam exhibits a coin-like performance, with a side A showing an open cell morphology, high interconnectivity and low density, and a side B characterized by a partially open cells morphology, low interconnectivity and high density. This approach enables morphology and density to be layered along thickness. A transition zone with intermediate density and morphology separates the two sides, thus rendering the structure a gradient meta-material with hierarchical porosity. Macro- and micro-porosity are generated by physical and chemical foaming agents, while diatomite is responsible for the presence of nanoporosity. The gradient structure has a huge influence on functional properties, such as acoustic (α equal to 0.95 at 800 Hz for side A), thermal (thermal conductivity less than 0.061 W/(m·K) for side A and less than 0.12 W/(m·K) for side B) and mechanical properties.

Tungsten Strongly Inhibits Sintering of Porous Iron During High-Temperature Redox Cycling.

Freeze-cast Fe-25W (at%) lamellar foams show excellent resistance to degradation at 800°C during steam-hydrogen redox cycling between the metallic and oxide states, with fast reaction kinetics maintained up to at least 100 redox cycles with full Fe utilization. This very high stability stems from the sintering inhibition of W combined with the freeze-cast architecture and the chemical vapor transport (CVT) mechanism of reduction. These three factors create a hierarchical porosity in the foam, consisting of i) macroscopic elongated channels, ii) micro-scale sintering inhibition pores, and iii) submicron CVT pores. Microstructural characterization via SEM and EDS is combined with in situ XRD to fully explore the phase evolution and microstructural impact of W on Fe during redox cycling. Comparison with tapped Fe-25W (at%) powder beds reveals that the freeze-cast channels and lamellae are not critical to the performance of the material.

High-efficiency electromagnetic shielding based on multipolar effect in RGO/MXene aerogels decorated with ordered Fe3O4 cluster

With the widespread use of digital systems and electronic communication devices, there is an urgent need to develop lightweight and efficient electromagnetic interference (EMI) shielding materials to address the growing problem of radiation pollution. RGO/MXene/Fe3O4 aerogels were successfully designed and synthesised using a one-step hydrothermal process induced by an external magnetic field in this study. Reduced graphene RGO, MXene nanosheets and Fe3O4 nanoparticles were suitably assembled together to achieve the combined advantages. The aerogels exhibited large specific surface area and hierarchical porosity. The material not only achieves an effective synergy between magnetic loss and dielectric loss, but also exhibits satisfactory EMI shielding performance. Magnetic field induced RGO/MXene/Fe3O4 aerogels (MIRMFE-2) exhibits the best EMI shielding performance with an average SET value of 76.9 dB. The excellent shielding performance of MIRMFE is attributed to both its 3D porous structure and the high dielectric loss due to multiple polarization relaxation, magnetic loss due to eddy current loss and natural resonance. The synthesis of MIRMFE provides an effective method for, designing high-performance and lightweight EMI shielding materials.

Activated Carbon Derived from Cucumber Peel for Use as a Supercapacitor Electrode Material.

Biowaste conversion into activated carbon is a sustainable and inexpensive approach that relieves the pressure on its disposal. Here, we prepared micro-mesoporous activated carbons (ACs) from cucumber peels through carbonization at 600 °C followed by thermal activation at different temperatures. The ACs were tested as supercapacitors for the first time. The carbon activated at 800 °C (ACP-800) showed a high specific capacitance value of 300 F/g at a scan rate of 5 mV/s in the cyclic voltammetry and 331 F/g at the current density of 0.1 A/g in the galvanostatic charge-discharge analysis. At the current density of 1 A/g, the specific discharge capacitance was 286 F/g and retained 100% capacity after 2000 cycles. Their properties were analyzed by scanning electron microscopy, energy-dispersive X-ray analysis, porosity, thermal analysis, and Fourier-transform infrared spectroscopy. The specific surface area of this sample was calculated to be 2333 m2 g-1 using the Brunauer-Emmett-Teller method. The excellent performance of ACP-800 is mainly attributed to its hierarchical porosity, as the mesopores provide connectivity between the micropores and improve the capacitive performance. These electrochemical properties enable this carbon material prepared from cucumber peels to be a potential source for supercapacitor materials.

Hierarchically porous electrospun carbon nanofiber for high-rate capacitive deionization electrodes

Capacitive deionization (CDI) is a promising technology that has gained interest for the desalination of brackish water. Hierarchically porous carbons are commonly used as electrodes for CDI due to their high surface areas and controlled pore size distributions that maximize ion adsorption capacity and rate. Electrospinning is an effective way of generating carbon nanofibers with high inter-fiber macroporosity that can be further modified to improve surface area, total pore volume, and pore size distribution. This work describes the use of sacrificial mesopore formers in tandem with a micropore etching technique to induce hierarchical porosity in electrospun fibers. Mesopores are formed via the dissolution of silica nanoparticles that are introduced into the fibers during the electrospinning step. After mesopore formation, micropores are etched into the resulting surface through KOH impregnation and thermal activation. This sequential technique creates a hierarchical network of pores from the inherent macroporosity of the fiber network, to the mesopores, and finally micropores to simultaneously maximize surface area and accessibility. Micropore formation is optimized to maximize specific surface area while maintaining physical integrity of the fibers. The combination of mesopores and micropores enables fast ion adsorption rates and capacity. Carbon fiber electrodes fabricated in this method achieve specific surface areas exceeding 1400 m2 g−1, with pore volumes exceeding 1.0 cc g−1. The pore size distributions are highly controlled, with 80 % of total pore volume coming from pores <20 nm in radius. In 500 ppm constant voltage CDI tests, these fiber electrodes obtain a salt adsorption capacity of over 14 mg g−1 at a salt adsorption rate of ∼4 mg g−1 min−1, showcasing the high capacity matched with high rate of these easily fabricated, inexpensive materials.

Self‐Sacrificial Template Synthesis of Fe‐N‐C Catalysts with Dense Active Sites Deposited on A Porous Carbon Network for High Performance in PEMFC

AbstractIron‐nitrogen‐carbon (Fe‐N‐C) single‐atom catalysts are promising sustainable alternatives to the costly and scarce platinum (Pt) to catalyze the oxygen reduction reactions (ORR) at the cathode of proton exchange membrane fuel cells (PEMFCs). However, Fe‐N‐C cathodes for PEMFC are made thicker than Pt/C ones, in order to compensate for the lower intrinsic ORR activity and site density of Fe‐N‐C materials. The thick electrodes are bound with mass transport issues that limit their performance at high current densities, especially in H2/air PEMFCs. Practical Fe‐N‐C electrodes must combine high intrinsic ORR activity, high site density, and fast mass transport. Herein, it has achieved an improved combination of these properties with a Fe‐N‐C catalyst prepared via a two‐step synthesis approach, constructing first a porous zinc‐nitrogen‐carbon (Zn‐N‐C) substrate, followed by transmetallating Zn by Fe via chemical vapor deposition. A cathode comprising this Fe‐N‐C catalyst has exhibited a maximum power density of 0.53 W cm−2 in H2/air PEMFC at 80 °C. The improved power density is associated with the hierarchical porosity of the Zn‐N‐C substrate of this work, which is achieved by epitaxial growth of ZIF‐8 onto g‐C3N4, leading to a micro‐mesoporous substrate.

In-situ growth of metal-organic frameworks on cellulose nanofiber aerogels for rapid adsorption of heterocyclic aromatic amines

Heterocyclic aromatic amines (HAAs) are the main carcinogens produced during thermal processing of protein-rich foods. In this paper, a composite aerogel (TOCNFCa) with a stabilized dual-network structure was prepared via a template for the in-situ synthesis of UiO-66 on cellulose for the adsorption of HAAs in food. The dual-network structure of TOCNFCa provides the composite aerogel with excellent wet strength, maintaining excellent compressive properties. With the in-situ grown UiO-66 content up to 71.89 wt%, the hierarchical porosity endowed TOCNFCa@UiO-66 with the ability to rapidly adsorb HAAs molecules with high capacity (1.44–5.82 μmol/g). Based on excellent thermal stability, adsorption capacity and anti-interference, TOCNFCa@UiO-66 achieved satisfactory recoveries of HAAs in the boiled marinade, which is faster and more economical than the conventional SPE method. Moreover, TOCNFCa@UiO-66 could maintain 84.55 % of the initial adsorption capacity after 5 times of reuse.

Armoring hydrophilic wood-structured ultrathick electrode with bimetallic nitride enables high energy-density supercapacitor

Thick electrodes can reduce the ratio of inactive constituents in a holistic energy storage system while improving energy and power densities. Unfortunately, traditional slurry-casting electrodes induce high-tortuous ionic diffusion routes that directly depress the capacitance with a thickening design. To overcome this, a novel 3D low-tortuosity, self-supporting, wood-structured ultrathick electrode (NiMoN@WC, a thickness of ∼1400 μm) with hierarchical porosity and artificial array-distributed small holes was constructed via anchoring bimetallic nitrides into the monolithic wood carbons. Accompanying the embedded NiMoN nanoclusters with well-designed geometric and electronic structure, the vertically low-tortuous channels, enlarged specific surface area and pore volume, superhydrophilic interface, and excellent charge conductivities, a superior capacitance of NiMoN@WC thick electrodes (∼5350 mF cm−2 and 184.5 F g−1) is achieved without the structural deformation. In especial, monolithic wood carbons with gradient porous network not only function as the high-flux matrices to ameliorate the NiMoN loading via cell wall engineering but also allow fully-exposed electroactive substance and efficient current collection, thereby deliver an acceptable rate capability over 75% retention even at a high sweep rate of 20 mA cm−2. Additionally, an asymmetric NiMoN@WC//WC supercapacitor with an available working voltage of 1.0–1.8 V is assembled to demonstrate a maximum energy density of ∼2.04 mWh cm−2 (17.4 Wh kg−1) at a power density of 1620 mW cm−2, along with a decent long-term lifespan over 10,000 charging-discharging cycles. As a guideline, the rational design of wood ultrathick electrode with nanostructured transition metal nitrides sketch a promising blueprint for alleviating global energy scarcity while expanding carbon-neutral technologies.