Abundant Mesopores Research Articles

Front Cover: Fine‐Tuning Texture of Highly Acidic HZSM‐5 Zeolite for Efficient Ethanol Dehydration (ChemCatChem 9/2023)

The Front Cover illustrates how different morphologies of highly acidic ZSM-5 zeolite control the product distribution of ethanol dehydration. In their Research Article, E. J. M. Hensen, C. Wattanakit and co-workers demonstrate that very thin nanolayers of this zeolite with a large external surface area and abundant mesopores enhance the ethylene yield up to 95% with a high longevity. In contrast, nanoplate and bulk structures of ZSM-5 result in low ethanol conversion, high selectivity to diethyl ether, and rapid deactivation. Reducing the crystal size of highly acidic zeolites to ultra-thin nanosheets can shorten the residence time of ethanol and its intermediates in the shape-selective environments, significantly suppressing the formation of coke precursors and achieving high and stable yield of the important chemical building block ethylene. More information can be found in the Research Article by E. J. M. Hensen, C. Wattanakit and co-workers.

Rational design of Ni nanoparticles loaded porous N-doped carbon nanostructures for efficient hydrogenation reduction of Cr(VI): Performance, critical role of hydrogen species and mechanism insight

Catalytic hydrogenation via formic acid (FA) activation is an important way for the control of Cr(VI)-contaminated water. In the present study, three-dimensional porous N-doped carbon nanostructures loaded with quasi-spherical Ni nanoparticles (Ni@NC) are rationally prepared by a facile carbonization strategy and developed as a robust catalyst to effectively activate FA for hydrogenation reduction conversion of Cr(VI) to Cr(III). Such carbon nanostructures with large specific surface areas and abundant mesopores not only protect the anchored Ni nanoparticles from poisoning, but also coordinate with Ni nanoparticles to diversify active sites, significantly promoting Cr(VI) reduction efficiency. The optimal Ni@NC catalyst presents the excellent activity for catalytic FA activation and achieves high-efficiency Cr(VI) reduction, delivering the enhanced rate constant of 0.059 min−1 and favorable k-value of 3.15 μmol s−1 g−1, attributing to collaborative cooperation of high-electron-density Ni sites and self-polarized NC. More importantly, the Ni@NC catalyst exhibits robust tolerance of coexisting ions and good reusability for Cr(VI) reduction in acidic environment. Spectroscopic analysis and electrochemical evaluation unveil the critical role of the surface-bonded Ni–Hads* species and hydrogen radicals (·H) in-situ generated in Ni@NC/FA system for hydrogenation reduction of Cr(VI).

Tremella-like Boron-doped hierarchical CN and dispersion Co phthalocyanine assembling heterojunction for photocatalytic hydrogen evolution

Semiconducting photocatalysts' electronic configuration significantly impacts their band gaps, charge carrier transport properties, and photocatalytic activities. Boron-doped tremella-like hierarchical CN and ultrathin Co phthalocyanine (CoPe) heterojunction (B1.5HCN-Co0.5%) formation via strengthened H-bonding interfacial connection possess excellent photocatalytic activities in water where the small amounts of catalysts exhibit a high photocatalytic H2 evolution activity with H2 evolution rate of 17818.82 μmol h−1 g−1 under simulated sunlight and 5558.81 μmol h−1 g−1 under visible light (≥420 nm). According to detailed characterization, the unique tremella-like hierarchical structure with abundant mesopores shortens the charge diffusion length. At the same time, incorporating CoPe improves the charge transport properties of B1.5HCN achieving effective spatial separation, which is primarily responsible for the improved performance. Both a significant amount of experimental data and theoretical calculations demonstrated the critical role of boron-doped and CoPe in photocatalytic H2 evolution. Heteroatom doping and heterojunction construction are essential in rationally regulating band structure to construct more efficient CN-based photocatalysts.

Preparation of Biochar with Developed Mesoporous Structure from Poplar Leaf Activated by KHCO3 and Its Efficient Adsorption of Oxytetracycline Hydrochloride

The effective removal of oxytetracycline hydrochloride (OTC) from the water environment is of great importance. Adsorption as a simple, stable, and cost-effective technology is regarded as an important method for removing OTC. Herein, a low-cost biochar with a developed mesoporous structure was synthesized via pyrolysis of poplar leaf with potassium bicarbonate (KHCO3) as the activator. KHCO3 can endow biochar with abundant mesopores, but excessive KHCO3 cannot continuously promote the formation of mesoporous structures. In comparison with all of the prepared biochars, PKC-4 (biochar with a poplar leaf to KHCO3 mass ratio of 5:4) shows the highest adsorption performance for OTC as it has the largest surface area and richest mesoporous structure. The pseudo-second-order kinetic model and the Freundlich equilibrium model are more consistent with the experimental data, which implies that the adsorption process is multi-mechanism and multi-layered. In addition, the maximum adsorption capacities of biochar are slightly affected by pH changes, different metal ions, and different water matrices. Moreover, the biochar can be regenerated by pyrolysis, and its adsorption capacity only decreases by approximately 6% after four cycles. The adsorption of biochar for OTC is mainly controlled by pore filling, though electrostatic interactions, hydrogen bonding, and π-π interaction are also involved. This study realizes biomass waste recycling and highlights the potential of poplar leaf-based biochar for the adsorption of antibiotics.

Chiral Skeletons of Mesoporous Silica Nanospheres to Mitigate Alzheimer's β-Amyloid Aggregation.

Chiral mesoporous silica (mSiO2) nanomaterials have gained significant attention during the past two decades. Most of them show a topologically characteristic helix; however, little attention has been paid to the molecular-scale chirality of mSiO2 frameworks. Herein, we report a chiral amide-gel-directed synthesis strategy for the fabrication of chiral mSiO2 nanospheres with molecular-scale-like chirality in the silicate skeletons. The functionalization of micelles with the chiral amide gels via electrostatic interactions realizes the growth of molecular configuration chiral silica sols. Subsequent modular self-assembly results in the formation of dendritic large mesoporous silica nanospheres with molecular chirality of the silica frameworks. As a result, the resultant chiral mSiO2 nanospheres show abundant large mesopores (∼10.1 nm), high pore volumes (∼1.8 cm3·g-1), high surface areas (∼525 m2·g-1), and evident CD activity. The successful transfer of the chirality from the chiral amide gels to composited micelles and further to asymmetric silica polymeric frameworks based on modular self-assembly leads to the presence of molecular chirality in the final products. The chiral mSiO2 frameworks display a good chiral stability after a high-temperature calcination (even up to 1000 °C). The chiral mSiO2 can impart a notable decline in β-amyloid protein (Aβ42) aggregation formation up to 79%, leading to significant mitigation of Aβ42-induced cytotoxicity on the human neuroblastoma line SH-ST5Y cells in vitro. This finding opens a new avenue to construct the molecular chirality configuration in nanomaterials for optical and biomedical applications.

Core-shell Fe/Fe3C heterostructure@carbon layers anchored on N-doped porous carbon for boosting oxygen reduction reaction

It is still challenging but crucial to plumb non-noble metal-based oxygen reduction reaction (ORR) catalysts with comparable or better performance than benchmark Pt/C catalysts. Herein, we proffer an unconventional core-shell-structured iron-based heterostructure electrocatalyst constructed by a Fe/Fe3C heterostructure nanoparticle core wrapped by a graphitic shell embedded on a conductive N-doped mesoporous graphite skeleton (Fe/Fe3C@NC) via facile pyrolysis of MIL-53(Fe) (MIL = Matérial Institute Lavoisier) and melamine. The Fe/Fe3C@NC catalyst delivers more positive half-wave potential (E1/2) of 0.86 V and a low Tafel slope of 56 mV dec−1 for ORR, outpacing the benchmark Pt/C catalyst, and it also shows remarkable long-term durability and excellent methanol tolerance. The marvelous ORR behaviors can be attributed to its distinctive morphologic structure: the heterostructure can enhance intrinsic ORR activity; the core-shell nanostructure can enhance ORR activities through unique electron transfer between iron species and their conductive carbon shells, which can also act as protective barriers to ensure long-term stability; the high-content pyridinic-N doping can be used as additional active centers; and the abundant mesopores facilitate the diffusion of electrolyte, which can further upgrade ORR activities. This study proffers a strategy to design and fabricate non-noble catalysts with well-designed nanoarchitecture and high catalytic activity.

Study on isothermal pyrolysis and product characteristics of basic components of waste wind turbine blades

Pyrolysis is an effective method for recycling waste wind turbine blades. However, there have been few studies on the pyrolysis mechanism of the basic components of blade composites. In this study, isothermal pyrolysis experiments on four basic components (epoxy resin, thermoplastic polyurethane, carbon fiber and glass fiber) of blades were carried out in a tube furnace at 600 ℃. The product distribution and properties of each basic component were then analyzed after pyrolysis. The results showed that the pyrolysis reactions of the matrix materials were intense, and the mass loss rates reached 90%. A certain amount of gas products, mainly CO2 and CO, were released during the pyrolysis process; CO2 was eliminated from the ester and carboxyl groups of the aromatic compounds and CO was formed from the decomposition of the carbonyl groups. A large number of liquid products were also produced, including phenol and p-isopropenylphenol, and these could be reused as industrial raw materials. The resins were decomposed from blocks into fragments after pyrolysis. The pore structures of resins became more abundant and developed mesopores and micropores, and the microcrystalline structures were disordered. The fiber materials barely reacted, and the mass loss of each was only approximately 1%. The surface morphologies and microcrystalline structures of the fiber materials did not change significantly, but the pore diameter distributions showed diametrically opposite trends relative to those of the resins. These results indicated that the resin matrix could be removed from the composites via pyrolysis and that the structures of the fiber materials could be retained. This research on the pyrolytic characteristics of the basic components of blade composites shows the thermochemical characteristics of each component and provides basic data and reference information for pyrolytic recycling of scrap blades.

Controllable preparation of N-doped porous carbons with enhanced porosity and energy storage capacity using high internal phase emulsion template

In this work, a series of N-doped porous carbons (NPCs) are prepared via high internal phase emulsion (HIPE) template, followed by growing polyaniline (PANI) arrays and subsequent carbonization/activation. As evidenced by SEM and N2 absorption/desorption results, the NPCs have interconnected hierarchical porous structures with abundant micropores and mesopores inside. The morphology and porous structures of NPCs can be tuned by changing aniline concentration and polymerization time, respectively. With the increase of aniline concentration or polymerization time, the porous structure of NPC becomes more and more serried, however too high aniline concentration (>0.75 M) makes the porous structure become sparse, which is because excess PANI will nucleate itself and make it detach from the surface of NPC. As a result, the specific surface area (SSA) of NPCs first increases to 1769 m2/g and then decreases. Electrochemical performances of the obtained NPCs are evaluated in detail. The test results indicate that both aniline concentration and polymerization time have notable influence on the specific capacitance of NPCs. The specific capacitance of NPC obtained under optimized conditions reaches up to 241 F/g at 1 A/g with a retention ratio of 97.8% after 10, 000 cycles at a high current density, proving its excellent energy storage capability and cycling stability. In two-electrode system, the NPC provides an energy density of 27 Wh/kg at a power density of 400 W/kg and remains a high energy density of 19 Wh/kg at a high power density of 10002 W/kg.

Controls on the formation and evolution of multimodal pore network in lower cretaceous limestone reservoir, Abu Dhabi, United Arab Emirates

Petrographic and petrophysical analyses of a Lower Cretaceous limestone reservoir, Abu Dhabi, United Arab Emirates provide new insights into the formation and diagenetic evolution of bimodal pore network. The most important diagenetic controls include: (i) widespread development of microporosity by micritization of allochems and partial cementation by grain-rimming calcite during eogenesis at or below the seafloor, (ii) partial to complete dissolution of peloids and concomitant precipitation of equant calcite cement during early mesogenesis, and (iii) stylolitization and development of tension gashes and concomitant massive cementation of the macropores by coarse-crystalline calcite and partial cementation of the micropores by calcite micro-overgrowths around micrite during late mesogenesis. Lateral compression owing to ophiolite obduction in late Cretaceous allowed flow of hot basinal brines along stylolites and tension gashes, which resulted in the precipitation of saddle dolomite and pyrite. Abundant depositional interparticle macropores were preserved in the grainstones by sparse grain rimming, dogtooth-like calcite cement that reduced the effect of mechanical compaction. Micro- and macropores are well interconnected yet the moldic, fracture pores, and intraparticle micropores within peloids are less well connected with the pore system. Hydrocarbon emplacement in the naturally oil/mixed-wet carbonate reservoir both increases the fluid pore pressure within the pore spaces of the rock thus reducing overburden stress and effective compaction; and reduces nucleation sites for cement growth thus retarding chemical diagenesis. However, the hydrocarbon emplacement occurred gradually and selectively filled the crestal limestones from the top to bottom in a way that its effect on rate of diagenesis differ vertically and spatially across the study area. Constraining the formation, evolution, and distribution of multimodal porosity network, including abundant micropores and mesopores allows better detection and evaluation of low-resistivity pay zones in carbonate successions.

Integrated Geological and Petrophysical Approaches for Characterizing the Pre-Cenomanian Nubian Sandstone Reservoirs in Ramadan Oil Field, Central Gulf of Suez, Egypt

The present study integrates multidisciplinary geological and petrophysical approaches to characterize and evaluate the potential of the pre-Cenomanian Nubian sandstone reservoirs in the Ramadan oil field, the central offshore part of the Gulf of Suez, Egypt. The different petrophysical parameters of the Nubian sandstone reservoirs (shale volume, porosity, water saturation as well as gross and net-pay thicknesses) were mapped, and 3D slicing models for the hydrocarbon phases saturation were constructed to understand the reservoir heterogeneity and the distribution of the best reservoir facies. The petrophysical results of the pre-Cenomanian Nubian succession highlight very good reservoir intervals in the Nubian C sandstones containing thick pay zones (> 120 m). On the other side, the Nubian A and B reservoir rocks are less prospective with pay zone horizons (< 10 m). Integrated reservoir models and wireline log analysis elucidate that clay volume is the most detrimental factor to the reservoir quality as the pay zone thickness and hydrocarbon saturation often increase where the clay volume decreases. Therefore, the presence of scattered pay zone intervals in Nubian A and B is mainly related to their elevated clay content which acts as barriers for fluids flowing within the reservoir facies. The Nubian C succession contains three different reservoir rock types (RRT) with variable compositional and petrophysical properties. RRTI and RRTII sandstones comprise quartzose sandstones with very low clay content (< 10%) and are characterized by an open pore system dominated by macropores. These sandstones are less impacted by overburden pressure and therefore can preserve their depositional porosity and permeability. On the other hand, RRTIII reservoir rocks are clay rich (> 10%) with abundant mesopores that are more prone to compressibility and hence reduction of the pore volume and pore throat. The present study highlights the significance of comprehensive integration between wireline logs, cores, and 3D reservoir models in directing exploration endeavors toward prospective reservoirs in mature basins.

Controllable synthesis of micro-mesoporous Pd@N-doped carbon derived from ZIF@NiCoLDH for enhanced phenol hydrogenation to cyclohexanone

A hollow nitrogen-doped carbon (CN) material, featuring abundant mesopores and high content of graphitic nitrogen, has been synthesized by annealing of the core-shell precursor composed of zeolitic imidazolate framework-67 as core and layered double hydroxides as shell. The proportion of mesopores and nitrogen species in the CN materials significantly vary with the shell thickness of layered double hydroxides in the core-shell precursor by adjusting the etching amount and etching time of nickel nitrate. The as-prepared Pd@CN-1.4–30 catalyst exhibits superior catalytic performance in the hydrogenation of phenol to cyclohexanone, and its turnover frequency (TOF) value is about ten times higher than Pd@CN obtained without the nickel etching, resulting from the abundant mesopores, high graphitic N content, and easy reduction of palladium species. Moreover, Pd@CN-1.4–30 has good reusability during at least six reaction cycles.

Hierarchically porous MIL-100(Fe) with large mesopores for cationic dye adsorption

Iron-based metal organic framework (MIL-100(Fe) (MIL: Materials of the Institut Lavoisier)) is attractive candidate for adsorption, separation, and catalysis owing to their high surface area and permanent porosity. However, most of MIL-100(Fe)s only possess micropores and small mesopores, which prevent the transportation of large guest molecules and hinder their applications in macromolecules. In addition, corrosive hydrofluoric acid (HF)-free synthesis of MIL-100(Fe) can contribute to large scale production. Thus, constructing hierarchically porous HF-free MIL-100(Fe)s with large mesopores is highly desirable. In this study, six HF-free MIL-100(Fe)s were prepared in pure H2O and DMF using FeCl3, Fe(NO3)3 and Fe2(SO4)3 under hydrothermal/solvothermal conditions. The results indicated that applying FeCl3 as iron source and DMF as solvent can form pure MIL-100(Fe) (i.e., Cl-DMF) with abundant (79 ​vol%) mesopores (22 ​nm) and some macropores. The obtained samples were employed in removal of methylene blue (MB), rhodamine B (RhB) and methyl orange (MO) as dyes and chromium(VI) as metal ion. The Cl-DMF exhibited more excellent adsorption performance toward the macromolecular dye RhB compared to other five products. Adsorption of RhB onto Cl-DMF was obeyed the pseudo-second order and Freundlich isothermal models. Maximum adsorption capacity of RhB was 207 ​mg/g for Cl-DMF, which is considerably higher than other MIL-100(Fe)s reported. The adsorption mechanism investigation indicated that it can be related to a combination of physical adsorption and electrostatic reaction.

One-step synthesis of hierarchical ZSM-5 zeolites with low defect density as long-lived MTH catalysts

The combination of introducing mesopores and minimizing framework defects in zeolite catalysts has been proved to be highly effective in improving their catalytic lifetime in the MTH reaction. However, there is currently a lack of simple method to realize these two purposes at the same time. In this work, we report a simple one-step approach which not only completed the introduction of abundant mesopores into zeolite catalyst but also simultaneously realized the reduction of framework defects. Secondary template, fluoride media and post-treatment technology were not used during the synthetic process. As an example, a hierarchical ZSM-5 zeolite catalyst with low defect density was successfully synthesized. In the MTH reaction, the synergy effect of the hierarchical pore structure and the less framework defects endowed the prepared zeolite catalyst with a very long lifetime, which is 7.1 times that of the reference catalyst.

Carbon Confined Mesoporous Catkin-like SnPS3 Nanostructure for Lithium Storage with Great Superiority

Metal phosphosulfides (MPSs) are members of a category of emerging energy storage and conversion materials, particularly having significant potentials in lithium storage due to their phosphorus and sulfur dual anion centers and unique two-dimensional channels. Nevertheless, it is still very challenging for the controllable design and synthesis of MPSs nanomaterials with complex-element components. Herein, a distinctive carbon confined mesoporous catkin-like SnPS3 nanostructure (SnPS3@C) is controllably synthesized and fabricated based on the partial volatilization of the reduced tin and the following bottom-up phosphosulfuration by a chemical vapor deposition method. As the anode material of lithium ion batteries, the catkin-like SnPS3@C offers multiple active centers for lithium insertion, complete carbon shell to protect inner active materials, interlaced fibrous networks for efficient electron transfer as well as abundant inner mesopores for Li+ diffusion and volume buffer, thus showing prominent structure advantages in lithium storage. The catkin-like SnPS3@C electrode demonstrated superior electrochemical capability with a very high reversible capacity (1302 mAh g–1 at 300 mA g–1), excellent rate property (630 mAh g–1 at 8000 mA g–1) and distinguished cycling stability (1030 mAh g–1 after 1000 cycles at 1000 mA g–1). This work offers a new avenue to develop high-performance MPSs materials for advanced lithium ion batteries.

Efficient esterification over hierarchical Zr-Beta zeolite synthesized via liquid-state ion-exchange strategy

The eco-friendly zeolite-based solid acid catalysts constitute an important alternative to the liquid acid catalyst for the production of plasticizer tributyl citrate (TBC), due to their non-corrosive, high hydrothermal stability and easiness to recycle. Herein, a simple acid treatment to the H-Beta zeolite and subsequent incorporation of ZrIV ions into the vacated Al sites were conducted by liquid-state ion-exchange of ZrO(NO3)2 aqueous solution. The ZrIV ions were incorporated into the framework by the expand of the unit cell size, verified by XRD patterns, the emerging new band at ∼198 nm on UV–vis spectra, the enhanced binding energies of the Zr 3d5/2 and Zr 3d3/2 on XPS spectra, as well as the variations of isolated terminal silanol groups (Si-OH) by FTIR and the change of integrated intensity ratio of Q3/Q4 by 29Si MAS NMR. It was illustrated that the Lewis acid sites was the main active sites for esterification reaction and the produced abundant mesopores in the Zr-Beta-x catalysts would facilitate the transportation of TBC. The maximum conversion of citric acid as high as 80 % was obtained on Zr-Beta-128 (SiO2/ZrO2 molar ratio = 128) catalyst with the highest Lewis acid amount. Furthermore, the Zr-Beta-128 zeolite exhibited high stability without any detectable deactivation after 6 cycles with the 100 % selectivity to TBC. The efficient Zr-Beta catalyst could supply a novel possibility for the development of an environmentally-friendly solid acid catalyst with good performance for the TBC production.

Study on gas desorption-diffusion behavior from coal particles using triple-pore structure models: Experimental, mathematical models, and numerical solutions

To accurately describe gas emissions from coal particles, a conceptual model comprising macropores, mesopores, and micropores has been proposed. On the basis of the conceptual model, two mathematical models were developed for gas diffusion from coal particles: Model Ⅰ includes the effect of desorption, while Model Ⅱ does not. The models were then validated by comparing them to experimental data obtained from gas desorption diffusion kinetic tests. Meanwhile, the effective diffusion coefficients for pores of varying scales were gained and analyzed. The results indicated that both models were capable of providing a reasonable fit to the experimental data; however, Model Ⅱ was unable to provide a good fit to the experimental data from the initial stage, which Model Ⅰ captured well. This indicates that gas desorption could accelerate gas emission from coal particles in their initial state; the increase of the porosity of micropore or macropore has a significant effect on total gas emission and a moderate effect on the initial gas emission volume, whereas the variation of the porosity of mesosphere could have a remarkable influence. This demonstrated that the intensity of gas desorption in coal with abundant mesopores is greater than that of coal with fewer mesopores in the initial desorption phase. In Model Ⅰ, the effective coefficients for pores of different scales varied significantly with increasing pressure, whereas in Model Ⅱ, this was not the case, with the exception of the effective diffusivity of macropores. The results of the current study have significant implications for the determination of gas contents for gas resources calculations, gas flow in the coal matrix, and the prediction of coal seams outburst.

Hierarchical porous carbon synthesis by carbonized polymer dots-based sacrificial template for high-performance supercapacitors

The performance of carbon-based supercapacitors is primarily determined by their porous carbons with customizable structures. Targeted regulation of the porous' size and amount is a crucial but challenging research topic to pursue higher power density and energy density. Additional loading of carbonized polymer dots (CPDs) on existing materials to optimize pore structures and modify pseudocapacitive groups is a feasible alternative. CPDs are treated as the desirable hard template, due to their high stability and controlled small-size to tailor reasonable pore distribution. Here, the hierarchical porous carbon was fabricated by activating the composite of CPDs and hyper-crosslinking polymer (HCP), which originated from the Friedel-Crafts reaction of small molecules. After the CPDs self-sacrificing template method based on the “excavation” of CPDs with small size (＜10 nm) by KOH, the optimal material owned abundant small mesopores (2 ∼ 10 nm) and large specific surface area (4241 m2·g−1). Thanks to the excellent structures, the optimized product yielded ultrahigh energy density at high power density (35.8 Wh·kg−1at 37497 W·kg−1) in 1 M TEATFB/PC. Thus, the CPDs-based pore-formation and regulation strategy is a potentially helpful alternative for fabricating high performance carbon-based supercapacitors.

Highly Cross-Linked 3D ε-Fe2O3 Networks Organized by Ultrathin Nanosheets as High-Performance Anode Materials for Lithium-Ion Storage

The rational design and engineering of three-dimensional (3D) micro-/nano-architectures still remains a technological challenge for electrochemical energy storage materials. In the current work, a facile and scalable structural engineering strategy is described for the synthesis of highly cross-linked 3D ε-Fe2O3 networks via an in situ manipulation of the molecular framework-engaged reactions. The as-obtained ε-Fe2O3 with a large specific surface area and abundant mesopores possesses a 3D interlocked architecture organized by ultrathin nanosheets. The formation mechanism of this unique structure is explored, which is shown to be Fe(CN)64–-mediated molecular-level template action leading to the self-assembly of a 3D framework. As a conversion-type anode for LIBs, the optimized ε-Fe2O3 networks exhibit a high reversible specific capacity, good rate capability, as well as long-term stability, with a reversible capacity of 953.8 mAh g–1 that is retained beyond 600 cycles at 1.0 A g–1. In addition, the excellent Li storage performance can be ascribed to the microarchitectured ε-Fe2O3 networks, which provide multiscale dimensions, mesoporous structure, some oxygen deficiencies, as well as good structural integrity upon prolonged cycling. Furthermore, the experimental results and DFT calculations showed that ε-Fe2O3 was able to form a key Li5Fe5O8–x phase during the lithiation/delithiation process, in which the structural properties of ε-Fe2O3 inherently favor the intercalation of Li+ ions within ε-Fe2O3, thus leading to the experimentally observed high performance rates.

Cobalt Nanoparticles Encapsulated with N-Doped Bamboo-Like Carbon Nanofibers as Bifunctional Catalysts for Oxygen Reduction/Evolution Reactions in a Wide pH Range

Nonprecious bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) catalysts in wide pH electrolytes are crucial for the versatile use of electrochemical energy storage and conversion devices. Non-noble metal/nitrogen-doped carbon (M–N/C) has been reported as a promising candidate for efficient and cost-effective bifunctional catalysts. Nevertheless, the stability and catalytic activity of M–N/C bifunctional catalysts in a wide pH range are still limited, especially in neutral and acidic electrolytes. Here, we synthesized directly grown N-doped bamboo-like carbon nanofiber-encapsulated cobalt nanoparticles on carbon flakes (Co–N/C fiber) via pyrolysis of 2D cobalt–zeolitic imidazolate framework and tubular g-C3N4. The in situ growth of N-doped carbon nanofiber incorporated with Co nanoparticles exposes large active sites and enhances charge transfer. Moreover, abundant mesopores with high loading of pyridinic-N, graphitic-N, Co@N/C, and Co–Nx facilitate high catalytic activity in a wide pH condition. Co–N/C fiber shows superior ORR performance in alkaline, neutral, and acidic electrolytes with high onset potentials of 1.003, 0.820, and 0.800 V vs RHE, respectively. A comparable OER performance of Co–N/C fiber to the Ir/C benchmark in alkaline and neutral conditions can be obtained with 397 and 570 mV overpotentials at 10 mA cm–2. Utilizing Co–N/C fiber in alkaline and neutral Zn–air batteries exhibits power densities of 155 and 67 mW cm–2, with excellent stability for over 180 h. This study offers a strategy for developing a bifunctional M–N/C catalyst that is applicable across a wide pH range via hybrid nanostructuring.

Synergistic Bimetallic CoCu-Codecorated Carbon Nanosheet Arrays as Integrated Bifunctional Cathodes for High-Performance Rechargeable/Flexible Zinc-Air Batteries.

The unremitting exploration of well-architectured and high-efficiency oxygen electrocatalysts is promising to speed up the surface-mediated oxygen reduction/evolution reaction (ORR/OER) kinetics of rechargeable zinc-air batteries (ZABs). Herein, bimetallic CoCu-codecorated carbon nanosheet arrays (CoCu/N-CNS) are proposed as self-supported bifunctional oxygen catalysts. The integrated catalysts are in situ constructed via a simple sacrificial-templated strategy, imparting CoCu/N-CNS with 3D interconnected conductive pathways, abundant mesopores for electrolyte penetration and ion diffusion, as well as Cu-synergized Co-Nx /O reactive sites for improved catalytic activities. By incorporating a moderate amount of Cu into CoCu/N-CNS, the bifunctional activities can be further increased due to synergistic oxygen electrocatalysis. Consequently, the optimized CoCu/N-CNS realizes a low overall overpotential of 0.64V for OER and ORR and leads to high-performance liquid ZABs with high gravimetric energy (879.7Wh kg-1 ), high peak power density (104.3mW cm-2 ), and remarkable cyclic stability upon 400h/1000 cycles at 10mA cm-2 . More impressively, all-solid-state flexible ZABs assembled with the CoCu/N-CNS cathode exhibit superior rate performance and exceptional mechanical flexibility under arbitrary bending conditions. This CoCu/N-CNS monolith holds significant potential in advancing cation-modulated multimetallic electrocatalysts and multifunctional nanocatalysts.