Hard Template Strategy Research Articles

Synergistic effects of nitrogen/oxygen co-doping in 3D mesoporous carbon nanospheres for enhanced microwave absorption

Mesoporous carbon nanospheres have attracted significant attention in the microwave absorption (MA) field due to the broad benefits provided by their mesoporous structure. This study presents a facile hard template strategy to construct distinctive 3D N/O co-doped mesoporous carbon nanospheres (NOCS). The high surface area, abundant mesopores, and high nitrogen (N) doping levels, with proper defects on the surface provide multiple sites to absorb electromagnetic waves (EMW). Mesoporous carbon nanospheres achieve significant reflection loss (RL) of −48.19 dB and extensive effective absorption bandwidth (EAB) up to 5.52 GHz. Moreover, computer simulation technology (CST) demonstrated that all simulated Radar cross-section (RCS) values were below 20 dB m2. Thus, this work holds significant promise for effective microwave absorbers using mesoporous carbon nanospheres.

Boron-doping tunes nitrogen species to abundant edge-N and B-N matrix for efficient phosphate removal in capacitive deionization: Additional accessible sites and defective centers

The elimination of eutrophication necessitates the implement of a clean and efficient phosphate removal strategy. Capacitive deionization (CDI) is recently regarded a promising approach for removing pollutants from aqueous environment with high-efficiency, facile operation, and low-energy consumption. Development of electrode materials with good properties is crucial for CDI. In this study, novel edge-N-modified boron-doped hierarchical carbon composites (MBCNs) were prepared via a hard template strategy for phosphate electrosorption. According to the pseudo-second-order kinetic, the MBCN2 electrode exhibited a dynamic capacity of 196.02 mg PO43− g−1 in 150 min with an initial concentration of 100 mg PO43− L−1 at 1.2 V. And it also demonstrated an exceptional saturation capacity of 399.70 mg PO43− g−1 under the Langmuir model. Based on theoretical analysis and experimental results, the incorporation of boron atoms in the carbon framework indicated a dual reinforcement. This included an enhanced proportion of edge-N modifications for defective centers and sufficient high-polarity B-N matrix for additional available active sites. The joint contribution of edge-N and B-N matrix revealed favorable electrical double layer capacitance, which resulted in good phosphate removal performance. This work disclosed the synergistic impact of dual nonmetallic atom doping, providing insights into the efficient phosphate removal anode for CDI.

Tri-functional Fe-based electrocatalyst with sturdy three-dimensional frame construction for the ORR, OER and HER

The catalyst Fe3C–Fe/NC-800 with a hollow interconnected honeycomb structure was prepared using a hard template strategy. It showed excellent ORR, OER and HER properties and favourable applications in ZABs and the overall water splitting device.

Design of Fe/Co–N doped porous carbon sheets using a hard template strategy as an oxygen reduction catalyst for Mg–air batteries

Schematic of the synthesis procedure of Fe–Co–C–N.

Structural Engineering of Hard-Soft Carbon Hybrid Anodes for Ultrafast and Ultradurable Potassium-Ion Storage.

Hard-soft carbon hybrid materials, harvesting the expanded interlayer spacing of hard carbon and the high conductivity of soft carbon, hold great promise as anode materials for potassium-ion batteries, but efficient and precise structural control remains a major challenge. Herein, hollow porous bowl-like hard-soft carbon hybrid materials (BHSCs) are facilely synthesized by an in situ hard-template strategy. It is found that the outer and inner walls of the hard carbon bowls are uniformly wrapped by graphene-like soft carbon, which accelerates electron transport and promotes the insertion of potassium ions. Finite element simulation further reveals that the soft-hard-soft carbon shell structure releases stress during the insertion of potassium ions. As a result, BHSC anode exhibits an extraordinary rate capability (209mAh g-1 at 10A g-1) and excellent cycle stability with a capacity of 208mAh g-1 after 5000 cycles at 2A g-1. Impressively, the as-assembled potassium-ion hybrid capacitor based on BHSC anode delivers a great energy/power density (116Wh kg-1/12980W kg-1) and outstanding capacity retention of 83% after 8000 cycles. This work provides guidance for rational structural design of hard-soft carbon hybrid materials to improve their potassium-ion storage performance.

Rational design of p-ZnS@CN with 3D interconnected hierarchical pore structure through pyrolysis of an organic hybrid zinc thiocyanide for electrochemical lithium storage

3D interconnected porous carbon-coupled metal-sulfide composites have been demonstrated as promising lithium storage materials owing to their large surface areas as well as the acceleration effect to electrochemical kinetics. However, constructing these materials with ordered hierarchical pore structure is still a challenge. To address this issue, we found that the crystals of an organic hybrid zinc thiocyanide [Zn(NCS)2(phen)2] (phen = 1,10-phenanthroline) could become a fluid at 400 °C, and during the melting process, the phen ligand was simulatneously carbonized to form nitrogen-doped carbon materials, while the Zn(NCS)2 species were converted into ZnS quantum dots. This property could allow us to employ a hard template strategy for preparation of a porous p-ZnS@CN composite featuring 3D interconnected hierarchical structure, namely employing SiO2 nanospheres as sacrificial template and [Zn(NCS)2(phen)2] as precursor and thermal treatment this mixture at 400 °C. The as-obtained p-ZnS@CN (p = porous structure, CN = nitrogen-doped carbon) composite possesses ordered macro- and mesoporous nitrogen-doped carbon structures, where the ZnS quantum dots are embedded in. Due to their structural features, p-ZnS@CN showed a superior lithium storage performance in comparison with ZnS nanoparticles. The well-defined 3D interconnected hierarchical pore structure not only enhances the efficiency of lithium-ion diffusion, but also offers ample void space to buffer the volume expansion during lithiation. Given the diversity of crystalline organic hybrid metal thiocyanates, this work opens a new avenue of preparing 3D interconnected porous carbons-coupled metal-sulfide composites.

Fullerene Fragment Restructuring: How Spatial Proximity Shapes Defect-Rich Carbon Electrocatalysts.

Fullerene transformation emerges as a powerful route to construct defect-rich carbon electrocatalysts, but the carbon bond breakage and reformation that determine the defect states remain poorly understood. Here, we explicitly reveal that the spatial proximity of disintegrated fullerene imposes a crucial impact on the bond reformation and electrocatalytic properties. A counterintuitive hard-template strategy is adopted to enable the space-tuned fullerene restructuring by calcining impregnated C60 not only before but also after the removal of rigid silica spheres (∼300 nm). When confined in the SiO2 nanovoids, the adjacent C60 fragments form sp3 bonding with adverse electron transfer and active site exposure. In contrast, the unrestricted fragments without SiO2 confinement reconnect at the edges to form sp2-hybridized nanosheets while retaining high-density intrinsic defects. The optimized catalyst exhibits robust alkaline oxygen reduction performance with a half-wave potential of 0.82 V via the 4e- pathway. Copper poisoning affirms the intrinsic defects as the authentic active sites. Density functional theory calculations further substantiate that pentagons in the basal plane lead to localized structural distortion and thus exhibit significantly reduced energy barriers for the first O2 dissociation step. Such space-regulated fullerene restructuring is also verified by heating C60 crystals confined in gallium liquid and a quartz tube.

Defect-Enriched Hollow Porous Carbon Nanocages Enable Highly Efficient Chlorine Evolution Reaction.

Metal-free carbon-based catalysts are crucial for the electrocatalytic chlorine evolution reaction (CER) to reduce the usage of noble metals and industrial cost. However, the corresponding catalytic activity of high overpotential and low durability hinders their wide application. Here, a hollow porous carbon (HPC) nanocage with a controlled oxygen electronic state around designed carbon defects for CER activity is reported. Alkali etching can bring defects in zeolite with a hollow structure. In a hard template strategy, the type of carbon defects is directly related to etching degree of the zeolite template. More importantly, the oxygen atoms can be "borrowed" from the zeolite framework by the defective carbon. The electron density around unsaturated O atoms can be decreased on the minor defects in carbon compared with that on large defects which is favorable for the adsorption of Cl- . Consequently, the as-synthesized HPC nanocages with minor defects show excellent electrocatalytic performance for CER with a low overpotential of 94mV at current density of 10mA cm-2 with good stability, which is superior to the commercial precious metal catalyst of dimensionally stable anode (DSA), and the best in the reported carbon materials. The designed carbon materials provide an option for metal-free industrial catalysts with significant CER activities.

Wastewater flocculation substrate derived three-dimensional ordered macroporous Co single-atom catalyst for singlet oxygen-dominated peroxymonosulfate activation

Herein, wastewater flocculation substrate is used as a carbon source to prepare a three-dimensional ordered macroporous (3DOM) structure carbon-based catalyst with the CoN4 coordination active sites (Co-NC-PS) through a hard-template strategy. Abundant single-atom CoN4 active sites endow the Co-NC-PS with splendid performance in degrading organic pollutants by activating peroxymonosulfate (PMS). Experiment results show that the singlet oxygen (1O2) is the main reactive oxygen species (ROSs) for bisphenol A (BPA) degradation. The strong coordination of Co atoms with N atoms not merely avoids the leaching of Co and improves the stability of the catalyst but also establishes stable adsorption configuration and facilitates the generation of 1O2 proven by density functional theory (DFT) calculations. This study provides the design of efficient Co carbon-based catalysts in mint conditions with high stability for water treatment, as well as a new idea for the preparation of high-value-added products from the recycling of flocculated waste.

Covalent Furan‐Benzimidazole‐Linked Polymer Hollow Fiber Membrane for Clean and Efficient Photosynthesis of Hydrogen Peroxide

AbstractPhotocatalytic H2O2 production by conversion of O2 in aqueous solution is often challenged by the use of sacrificial agents, the separation of powdery photocatalysts, solution, and contaminants, and low activity of photocatalyst. Herein, a membrane of covalent furan‐benzimidazole‐linked polymer (Furan‐BILP) with both O‐ and N‐containing heterocycles bonded via OCCN is reported for the first time as a photocatalyst to harvest clean H2O2 in pure water with high‐performance. A coordination‐polymer hard template strategy is developed to produce Furan‐BILP hollow microfibers that can be further assembled into membranes with desired sizes. The resultant Furan‐BILP membrane directly delivers clean H2O2 solution as the product with a high H2O2 production rate of 2200 µmol g−1 h−1 in pure water. Density functional theory calculations and experiment results indicate that the C atom from Furan ring on the linkage binds to the adsorbed OOH*, the H atom of OOH* forms a hydrogen bond with the N atom in the benzimidazole ring, thus the intermediate six‐membered ring structure stabilizes the OOH* and favors 2e‐ORR. The strategy using both molecular engineering to tune the electronic structure and macrostructural engineering to shape the morphology may be applied to design other coordination organic polymer photocatalysts with further improved performance.

Ultrathin Nitrogen‐Doped Carbon Encapsulated Ni Nanoparticles for Highly Efficient Electrochemical CO2 Reduction and Aqueous Zn‐CO2 Batteries

Electrochemical CO2 reduction reaction (CO2 RR), powered by renewable electricity, has attracted great attention for producing high value-added fuels and chemicals, as well as feasibly mitigating CO2 emission problem. Here, this work reports a facile hard template strategy to prepare the Ni@N-C catalyst with core-shell structure, where nickel nanoparticles (Ni NPs) are encapsulated by thin nitrogen-doped carbon shells (N-C shells). The Ni@N-C catalyst has demonstrated a promising industrial current density of 236.7mA cm-2 with the superb FECO of 97% at -1.1V versusRHE. Moreover, Ni@N-C can drive the reversible Zn-CO2 battery with the largest power density of 1.64mW cm-2 , and endure a tough cycling durability. These excellent performances are ascribed to the synergistic effect of Ni@N-C that Ni NPs can regulate the electronic microenvironment of N-doped carbon shells, which favor to enhance the CO2 adsorption capacity and the electron transfer capacity. Density functional theory calculations prove that the binding configuration of N-C located on the top of Ni slabs (Top-Ni@N-C) is the most thermodynamically stable and possess a lowest thermodynamic barrier for the formation of COOH* and the desorption of CO. This work may pioneer a new method on seeking high-efficiency and worthwhile electrocatalysts for CO2 RR and Zn-CO2 battery.

Rational design of 3DOM porous TiO2 matrix decorated with Co nanoparticles as novel sulfur hosts for high-performance lithium-sulfur batteries

In this work, we devise a hard-templating strategy to realize the controllable synthesis of three-dimensional ordered porous TiO2 matrix decorated with Co nanoparticles as sulfur hosts for Li/S batteries. Specifically, TiO2 matrix with unique 3D ordered porous structure not only can facilitate rapid lithium ion and electron transport, but also provide high affinity for lithium polysulfides. Besides, the Co nanoparticles embedded in TiO2 matrix possesses inherent metallic conductivity and enables boosted kinetics of polysulfide transformation to mitigate the shuttle effect. As expected, the S/3DOM Co-TiO2 perform exceptionally first discharge capacity of 929.6 mAh g−1 at 0.2 C, and improved rate discharge capacity of 517.5 mAh g−1 at 3 C, as well as an enhanced cycling performance.

A Search for New Mesoporous Carbon Solids with Cubic Ordered Porosity

A three-dimensional material comprised exclusively of carbon whose underlying structure lies on a triply periodic minimal surface (TPMS) is a member of the class of hypothetical carbon allotropes known as schwarzites. Such materials are highly sought-after due to their fundamental significance (the last remaining unknown crystalline allotrope of sp2-hybridized carbon) and likely interesting properties (e.g., ballistic conduction at room temperature). Other properties include a large pore volume and high surface area for gas and ion adsorption, making them a class of candidate materials for many applications such as supercapacitor electrodes and gas storage. A true schwarzite has never been synthesized, despite their predicted low energies of formation compared to fullerenes.This research focuses on the synthesis of an interpenetrating schwarzite-like material. A hard-templating strategy has been designed to achieve this through the synthesis of a free-standing graphene foam material whose structure lies on a cubic TPMS. The specific material of interest herein requires an ordered mesoporous silicate template that carries the Ia-3d space group with an optimal pore to wall ratio. Pore and wall structure as well as composition for these materials can be optimized by changing the hydrothermal synthesis temperature, the addition of different precursors, and by varying the cationic and neutral structure-directing agents. We present our recent progress in this effort and also propose future work to achieve optimal templates for schwarzite-like materials synthesis. Figure 1

Synthesis and electrochemical properties of ZnMn2O4 with hollow porous panpipe-like structure as anode material for Li-ion battery

In this work, ZnMn2O4 anode material with excellent lithium storage performance is prepared by combining the carbon gel–combustion method and the hard template strategy (a polypropylene membrane with high porosity). The as–obtained ZnMn2O4 sample has a hollow panpipe–like structure with rich pore characteristics. The phase composition, micro–nano structure, crystallinity, pore size distribution, specific surface area, element distribution and valence state of the samples are systematically tested and analyzed by XRD, ICP–AES, FESEM, TEM, HRTEM, N2 adsorption/desorption measurement and XPS. When assembled into a half–cell with metallic lithium as the counter electrode, the ZnMn2O4 electrode material exhibits higher reversible capacity (under low and high current densities), excellent cycle stability and rate capability with better dynamic properties compared with the ZnMn2O4 sample obtained without using the organic template agent. Porous structure characteristics, small particle size, high specific surface area, high crystallinity and special micro–nano structure help to effectively improve the kinetic properties and structural stability of the electrode material during charge/discharge processes for achieving high energy and power densities.

A biomass-based hierarchical carbon via MOFs-assisted synthesis for high-rate lithium-ion storage

A hierarchical nanostructured biomass-based carbon material derived from banana peels slurry and ZIF-8 hybrids (HNBZC) is introduced with excellent lithium-ion storage and rate capability. HNBZC was prepared through a hollow MOFs-assisted hard template strategy, in which we can easily control the pore size and doping element content to further improve the electrochemical performance of biomass-based carbon. HNBZC can reversibly deliver a capacity of 620 mAh g−1 at current densities of 20 mA g−1, and 61 mAh g−1 is still obtained at a high current density of 50 A g−1. Furthermore, a capacity retention ratio of 80% is achieved after 780 cycles at 5 A g−1. Our results indicate a promising method to obtain a carbon material with enhanced electrochemical performance based on natural biomass waste.

Fabrication of complex, 3D, branched hollow carbonaceous structures and their applications for supercapacitors

A unique “integrated hard-templating strategy” is described for facile synthesis of a carbonaceous material with a novel three-dimensional (3D) branched hollow architecture. A set of steps, including template formation, surface coating and template removal, all occur in a spontaneous and orderly manner in the one-pot hydrothermal process. Investigations on structural evolution during the process reveal that pre-synthesized zeolitic imidazolate framework-8 (ZIF-8) nanoparticles are first dissociated and then self-assembled into 3D branched superstructures of ZnO as templates. Initial self-assembly is followed by coating of the glucose-derived carbonaceous materials and etching of interior ZnO by organic acids released in situ by hydrolysis of glucose. The 3D-branched hollow architecture is shown to greatly enhance supercapacitor performance. The research described here provides guidance into the development of strategies for complex hollow carbonaceous architectures for a variety of potential applications.

Heterostructure of Ta3N5 nanorods and CaTaO2N nanosheets fabricated using a precursor template to boost water splitting under visible light

Fabrication of heterostructure composed of one-dimensional (1D) and 2D semiconductors has inspired extensive interest in promoting photogenerated charge separation as well as performances of solar fuel production, but it is still challenging for (oxy)nitride photocatalysts due to their uncontrollable ammonia thermal preparative process. In this work, we report a synthesis on heterostructure of Ta3N5 nanorods and CaTaO2N (CTON) nanosheets (denoted as Ta3N5/CTON) by directly nitriding a 2D Dion-Jacobson (DJ) type of perovskite KCa2Ta3O10 (KCTO) precursor under the assistance of K2CO3 flux. It is demonstrated that the 2D morphology of KCTO can be well inherited to get 2D CTON, and the Ta-rich (non-stoichiometric ratio of Ca:Ta compared to CTON) feature of the KCTO as well as the easy evaporation of K species results in the formation of 1D Ta3N5 nanorods. Meanwhile, the formation of intermediate species K2Ca2Ta3O9N owning similar crystal lattice as Ta3N5 was detected and deduced to be responsible for the generation of Ta3N5 nanorods and observation of intimate interface between CTON and Ta3N5. Benefitting from the formation of special 1D/2D type-II heterostructure, obviously promoted charge separation as well as photocatalytic water splitting performance can be obtained. Extended discussion demonstrates the generality of the hard-template preparative strategy developed here. To our knowledge, this should be the first fabrication of 1D/2D heterostructure for the (oxy)nitride semiconductors, and the developed hard-template strategy may provide an alternative way of fabricating heterostructures of other semiconductors prepared at high temperature.

Enhanced oxygen evolution activity on mesoporous cobalt-iron oxides.

To solve the energy crisis and environmental pollution problems, the use of clean and renewable energy to replace fossil energy has become a top priority. The oxygen evolution reaction (OER) is the core of many renewable energy technologies. Developing low-cost and high-performance OER electrocatalysts is the key to implementing efficient energy conversion processes. Here, we synthesize ordered mesoporous iron-cobalt oxides using a hard template strategy. As a mesoporous oxide catalyst, meso-CoFe0.05Ox exhibits low OER overpotentials of 280 and 373 mV at current densities of 10 and 100 mA cm-2, respectively, and does not show deactivation for at least 18 hours at 100 mA cm-2. The introduction of iron can change the electronic structure of Co, and the orbital electrons are easily transferred from cobalt to iron. The enhanced OER performance can be attributed to concerted catalysis between the iron and cobalt sites that lowers the OER energy barrier, and the large specific surface area of the porous oxide providing efficient active sites for the reaction.

Hard template strategy for the synthesis of porous MoS2/MoO2 hybrid electrocatalyst for hydrogen evolution reaction

Constructing the porous structure and inserting active defects are two effective ways to improve the performance of MoS2-based electro-catalyst for hydrogen evolution reaction (HER). In this work, the porous MoS2/MoO2 hybrid was successfully fabricated by a facile hard template strategy based on redox solid-phase reaction (SPR). Firstly, Fe2O3/MoS2 composite were prepared by an in-situ growth method. After the redox SPR between MoS2 and Fe2O3, part of Fe2O3 were transformed into Fe3O4 phase, whilst some MoO2 was instead of MoS2. After the etching of Fe2O3 and Fe3O4 NPs in precursor MoS2/MoO2/Fe3O4/Fe2O3, designed MoS2/MoO2 hybrid was obtained. Different techniques were adapted to reveal the well-defined phase interfaces between MoS2 and MoO2, which contained plenty of unsaturated Mo, S, and O active centers. The obtained porous MoS2/MoO2 hybrid was investigated for HER in alkaline. The low overpotential of 157 mV at 10 mA cm−2 and the excellent cycling stability demonstrate the remarkable catalytic activity of porous MoS2/MoO2 hybrid.

N-carbon supported hierarchical Ni/Ni0.2Mo0.8N nanosheets as high-efficiency oxygen evolution electrocatalysts

Abstract Rational development of high-performance and cost-effective electrocatalysts for the oxygen evolution reaction (OER) is of particular importance for renewable energy conversion and storage technologies. Herein, we developed a facile and easily scalable hard-template strategy to fabricate hierarchical Ni/Ni0.2Mo0.8N nanosheets (~4.37 nm in thickness) in situ coupled with N-doped carbon (Ni/Ni0.2Mo0.8N@N-C) as an efficient electrocatalyst for the OER. The elaborate construction of Ni/Ni0.2Mo0.8N can validly regulate the electronic structure, increase the number of active sites, and facilitate diffusion kinetics. Benefiting from the coupling effect between hierarchical Ni/Ni0.2Mo0.8N and the N-carbon matrix, the resultant Ni/Ni0.2Mo0.8N@N-C exhibits excellent OER performance in alkaline media, including a low overpotential of 260 mV at 10 mA cm−2, a small Tafel slope of 46 mV dec−1, as well as remarkable stability for long-term electrolysis operation, significantly exceeding the findings for most previously reported OER electrocatalysts. Theoretical studies demonstrate that incorporation of Ni into Ni0.2Mo0.8N can effectively optimize water adsorption energy and enhance electronic states density near the Fermi level, which is conducive to accelerating the OER process. This work underlines a rational and new perspective for designing inexpensive and robust Mott-Schottky electrocatalysts toward OER for energy storage and conversion devices.