Mesopore Content Research Articles

Stabilization of compound lead and arsenic contaminated soils by using two iron-based materials: Long-term efficacy

Long time scale tests are a key step in verifying the effectiveness and practicability of remediation materials in treating soil contaminated by heavy metal(oids)s (HMs). In this study, two materials, compound calcium oxide and ferrous sulfate (inorganic-inorganic combined material, denoted as IIM), and goethite nanoparticles modified biochar (organic-inorganic combined material, denoted as OIM), were tested for stabilization of arsenic (As) and lead (Pb) co-contaminated soil. Monitoring occurred at several fixed intervals up to 180 days, which includes leaching toxicity assessment, microstructure, and mechanical strength testing. The results indicate that IIM exhibited superior remediation effect within the initial 7 days but was less effective than OIM from 30 to 180 days. After 180 days, stabilization rates of IIM and OIM were 65.53% and 93.58% for As, and 99.27% and 99.71% for Pb, respectively. The cohesion of IIM-treated soils increased by 24.80% to improve the shear strength, while OIM-treated soil mainly rose the internal friction angle by 14.94%. This can be attributed to fact that IIM has a mean weight diameter (MWD) of 0.69mm with better stability and a richer macropore structure, while OIM aggregates are slightly less stable at 0.64mm of MWD, with mesoporous content at 49.79%. These findings provide valuable data and guidance on the long-term efficacy of remediation materials in HMs contaminated soils.

Preparation and characterization of high performance super activated carbon based on coupled coal/sargassum precursors

High electrochemical performance supercapacitors require activated carbon with high specific surface area, suitable pore size distribution and surface properties, and high electrical conductivity as electrode materials, whereas there exists a trade-off relationship between specific surface area and electrical conductivity, which is not well met by a single type of carbon source. To solve this problem, the coal and sargassum are adopted to obtain the coupling product via co-thermal dissolution, followed by carbonization and KOH activation. The effects of mixing mass ratio and activation temperature on the prepared activated carbon (AC) are investigated using single factor experimental method. The experimental results show that AC1/3-800 has abundant micropore and mesopore content, good pore structure connectivity, high electrical conductivity and good wettability, and superior electrochemical properties compared with other activated carbons prepared in this experiment. Its total specific surface area is up to 2098.5 m2·g–1, the pore volume is up to 1.33 cm3·g–1, the content of mespores with diameter of 6–8 nm is significantly increased, and the pore size distribution is wide and uniform. When the current density increases from 0.1 A·g–1 to 10 A·g–1, the gravimetric capacitance decreases from 219 F·g–1 to 186 F·g–1 with a capacitance retention of 84.9%, the equivalent series resistance is very small, and the rate performance and reversibility of charging and discharging have also been excellent.

Structure and Magnetic Properties of Fe<sub>3</sub>O<sub>4</sub>/C Composites Synthesized from Wheat Straw

The porous structure and magnetic properties of nanostructured Fe3O4/C composites based on wheat straw were investigated in this work. The synthesis was carried out by a one- and two-step method using FeCl3 and ZnCl2 as activating agents. X-ray diffraction methods have shown the presence of an additional phase of magnetite Fe3O4 in both synthesized composites, along with the amorphous carbon phase. Magnetic measurements have shown that the composite synthesized in one step has better magnetic properties, in particular, a higher specific saturation magnetisation. However, the samples of the composite synthesized in two steps are characterised by a higher content of micropores and mesopores, which causes an increase in the specific surface area to 884 m2/g compared to 405 m2/g for the samples synthesized in one step. Based on the dependence of the coercive force on the particle diameter in Fe3O4 dispersions, it was found that the average size of the magnetite particles is ~25 nm for both synthesized magnetoresponsive composites.

Activation and Zr precursor influence on UiO-66-NH2 composites for efficient cationic and anionic dye removal

This study investigates the synthesis of UiO-66-NH2@HTC composites, focusing on the control of surface charge, textural properties, and crystallinity. Surface charge modification was achieved through activation processes to enhance affinity for specific pollutants. By utilizing ZrCl4 and ZrOCl2⋅8H2O precursors, the textural properties were optimized, leading to higher mesopore content and improved crystallinity with the ZrOCl2⋅8H2O precursor. The UiO-66-NH2(ZrCl4)@HTC composite exhibited a crystallinity of 51.7 %, with 40 % mesopores and 57 % micropores, while the UiO-66-NH2(ZrOCl2)@HTC composite showed a crystallinity of 60 %, consisting of 60 % mesopores and 37 % micropores. Adsorption followed the Langmuir isotherm model, with maximum adsorption capacities of 263.1 mg/g for methylene blue (MB) and 277.77 mg/g for Congo red (CR), driven by hydrogen bonding and electrostatic interactions. The activated UiO-66-NH2@HTC composites demonstrated remarkable reusability. These findings emphasize the significant role of surface charge modification, pore structure optimization, and crystallinity enhancement in developing high-performance adsorbents.

Highly porous activated carbon derived from plant raw material as high-performance anode for aqueous sodium-ion supercapacitors

High power sodium energy generation devices, such as symmetric and hybrid supercapacitors, have great potential for cheap and green post-lithium applications. However, it is imperative to obtain porous structures with large surfaces and optimized pore size to enhance the electrode sorption property and to ensure fast electrochemical reactions. In this work, we investigated the influence of KOH carbon activation conditions on the morphology, porosity, and electrochemical parameters in aqueous sodium electrolytes. Our activated carbon had a maximum surface area of 1556 m2/g and a notably high mesopore content, this varying from 5 to 19 % of the total pore area. Electrochemical parameters are not only influenced by the total number of pores, but also by the optimal ratio of meso and micro pores. It is shown that in the case of sodium-based electrolytes, mesopores provide good electrode-electrolyte contact, and the capacity is mainly provided by micropores. High operating values of activated carbon in sodium aqueous electrolytes (specific capacity about 78 F/g, energy density 11 W*h/kg and power density 470 W/kg) indicates that the optimal electrode materials for a high-power device are activated carbon with a high content of mesopores obtained by the ratio of C and KOH as 1:4.

High-quality mesoporous adsorbent derived from pomegranate pomace for efficient removal of azo dye from textile wastewater: Influencing factors, reusability, and mechanism studies

The solid waste from the processing of pomegranate (Punica granatum L.) juice, known as pomegranate pomace, was utilized as an economical and readily available precursor to produce high-quality activated carbon (AC). The AC was synthesized using a low-cost method at a carbonization temperature of 600 °C, employing a 1:1 impregnation ratio (precursor/H3PO4), and activating for 1 h. Various characterization techniques, including SEM imaging, XRD analysis, FT-IR analysis, BET surface area analysis with pore size determination, and other physicochemical assessments, were conducted on the produced AC. To assess its efficacy in treating textile wastewater, Basic Yellow 28 (BY 28) dye was selected as a representative pollutant. The results displayed a mesoporous structure in the produced AC with a mesopore content of 78.82 %. Notably, it exhibited a high BET surface area of 1089.08 m2/g and a total pore volume of 1 cm3/g. The Langmuir non-linear isotherm model emerged as the most fitting for explaining the adsorption equilibrium data, revealing a substantial monolayer adsorption capacity of 659.13 mg/g at 20 °C. The experimental data fit into a pseudo-second-order kinetic model, where the rate-determining step was found to be intra-particle diffusion. Thermodynamic analysis revealed that the adsorption of BY 28 dye onto the produced AC was an exothermic process. The produced AC exhibited high stability, as demonstrated in desorption studies, maintaining effectiveness through multiple uses. These results signify the potential of using pomegranate pomace, an environmentally problematic waste, as a novel precursor for producing sustainable and cost-effective AC.

Mesopore Catalytic Activated‐Carbon to Reduce Harmful Gases Indoors: Adsorption, Catalytic Oxidation, and Prediction Mechanism

ABSTRACTModification of local bamboo‐based catalytic activated carbon with metallic Ag can produce mesopore and micropore types, with a mesopore content of 86%. One of the best ways to reduce formaldehyde concentrations is through catalytic adsorption. In combination with Ag nanoparticle catalyst, formaldehyde adsorption capacity is improved. Adsorption and oxidation reaction experiments are performed in a fixed bed column (di = 10 mm, length = 90 mm). The increase in formaldehyde adsorption associated with the reaction rate of formaldehyde oxidation by metallic Ag is 51 g/mmol. The oxidation reaction of Ag nanoparticles is a bimolecular reaction based on the Langmuir–Hinshelwood mechanism. Formaldehyde can be reduced by 59% and 41% through the role of adsorption and support of catalytic oxidation, respectively. Additionally, harmless gases such as CO2 and H2O are produced within the column.

Mesoporous carbon with extremely low micropore content synthesized from graphene oxide modified with alkali metal nitrates

High-temperature thermal exfoliation is a simple, rapid, and cost-efficient method for transforming graphene oxide (GO) materials into reduced graphene oxide (rGO) materials. In this study, GO materials were dispersed with alkali metal nitrates (MNO3), leading to the preparation of porous rGO materials characterized by high specific surface area (SSA) and pore volume via high-temperature thermal exfoliation. Experimental data indicate that the metal cations of MNO3 tend to react directly with the oxygen functional groups (OFG) of GO, modulating the OFG content. Simultaneously, nitrate anions have preferential interaction with alkali metal ions and adhere to the surface of the GO. The presence of MNO3 on the surface of GO facilitates the thermal exfoliation process and leads to the formation of structures with an extremely high proportion of mesoporous content. The isothermal gas adsorption results show that the exfoliation efficiency of the samples activated with different nitrate salts decreases in the order rGO-KNO3 > rGO-NaNO3 > rGO-LiNO3. Among these samples, rGO modified with KNO3 exhibited the greatest exfoliation efficiency, with a mesopore-to-micropore volume ratio of 22.4, more than 1.7 times that of rGO. Its SSA and pore volume were 359 m2 g−1 and 1.26 cm3 g−1, respectively. These values significantly surpass those of rGO. Our research findings demonstrate that activation with MNO3 significantly increases the SSA and pore volume of the GO material after high-temperature annealing.

Pore Structure Characterization and Fractal Characteristics of Tight Limestone Based on Low-Temperature Nitrogen Adsorption and Nuclear Magnetic Resonance

Pore structure characterization and fractal analysis have great significance for understanding and evaluating tight limestone reservoirs. In this work, the pore structure of tight limestone, low-temperature nitrogen adsorption (LTNA), and low-field nuclear magnetic resonance (NMR) are characterized, and the fractal dimension of the pore structure of tight limestone is discussed based on LTNA and NMR data. The results indicate that the pores of tight limestone have H3 and H4 types, the pore size distribution (PSD) of the H3 type is a wave distribution ranging from 2 to 10 nm, and the PSD of the H4 type is a unimodal distribution ranging from 2 to 10 nm. The transverse relaxation time (T2) spectrum of tight limestone shows a single peak (DF), double peak (SF), and triple peak (TF), and the ranges for the T2 spectra for micropores, mesopores, and macropores are 0.1 to 10 ms, 10 to 100 ms, and greater than 100 ms, respectively. The LTNA fractal dimension of tight limestone (DL) ranges between 2.4446 and 2.7688, with an average of 2.5729, and the NMR fractal dimensions of micropores (DNMR1), mesopores (DNMR2), and macropores (DNMR3) are distributed between 0.3744 and 1.1293, 2.4263 and 2.9395, and 2.6582 and 2.9989, respectively. Moreover, there is a negative correlation between DL and average pore radius, a positive correlation between DL and specific surface area, and a positive correlation between DNMR2 and DNMR3 and micropore content, while DNMR2 and DNMR3 are negatively correlated with the content of mesopores and macropores.

Effect of Thermal Activation on the Structure and Electrochemical Properties of Carbon Material Obtained from Walnut Shells.

A simple activation method has been used to obtain porous carbon material from walnut shells. The effect of the activation duration at 400 °C in an atmosphere with limited air access on the structural, morphological, and electrochemical properties of the porous carbon material obtained from walnut shells has been studied. Moreover, the structure and morphology of the original and activated carbon samples have been characterized by SAXS, low-temperature adsorption porosimetry, SEM, and Raman spectroscopy. Therefore, the results indicate that increasing the duration of activation at a constant temperature results in a reduction in the thickness values of interplanar spacing (d002) in a range of 0.38-0.36 nm and lateral dimensions of the graphite crystallite from 3.79 to 2.52 nm. It has been demonstrated that thermal activation allows for an approximate doubling of the specific SBET surface area of the original carbon material and contributes to the development of its mesoporous structure, with a relative mesopore content of approximately 75-78% and an average pore diameter of about 5 nm. The fractal dimension of the obtained carbon materials was calculated using the Frenkel-Halsey-Hill method; it shows that its values for thermally activated samples (2.52, 2.69) are significantly higher than for the original sample (2.17). Thus, the porous carbon materials obtained were used to fabricate electrodes for electrochemical capacitors. Electrochemical investigations of these cells in a 6 M KOH aqueous electrolyte were conducted by cyclic voltammetry, galvanostatic charge/discharge, and impedance spectroscopy. Consequently, it was established that the carbon material activated at 400 °C for 2 h exhibits a specific capacity of approximately 110-130 F/g at a discharge current density ranging from 4 to 100 mA/g.

Study on enhancing the union dyeing of cotton/modal blended fabrics with cationic modifier

AbstractCotton/modal blended fabrics are favoured by the market because not only do they have the advantages of the dimensional stability of cotton and drape wear resistance of modal, they also overcome their shortcomings, displaying a sense of stiffness and smooth feel. However, because of the differences in the physical and chemical properties between each component, the dyeing of blended fabrics with reactive dyes is prone to problems such as low fixation percentage, different dyeing percentages and colour depth. Here, two cationic modifiers, 2,3‐epoxypropyltrimethyl ammonium chloride (GTA) and methaacryloyloxyethyltrimethyl ammonium chloride (DMC), were applied for cationic modification of cotton/modal blended fabrics, and their role in the dyeability and union dyeing of cotton/modal blended fabrics was studied. The results showed that the K/S and fixation percentage of the blended fabric treated with GTA and DMC cationic agents could be significantly improved compared with the control group, and that the colour fastness of the blended fabric can reach grade 4‐5. Compared with GTA, DMC‐modified cotton/modal blended fabric showed better union dyeing properties because of its better diffusion performance in the fibre. The mesoporous volume of the cotton fibre is higher than that of the modal fibre, while the micropore volume is the opposite. Consequently, DMC macromolecules, through free radical graft polymerisation, were more likely to diffuse into cotton fibres with more mesoporous content, increased the interaction force between anionic reactive dye and cotton fibre, and improved the dyeability of the cotton component and the union dyeing performance of the blended fabric.

Green synthesis of CaxLa1-xMnO3 with modulation of mesoporous and vacancies for efficient low concentration phosphate adsorption

Phosphate concentrations in eutrophic surface waters are usually low, and efficient removal of low concentration phosphate remains a challenge. In this study, Ca-doped LaMnO3 synthesized at doping ratios, designated as CaxLa1-xMnO3 (x = 0, 0.2, 0.4, 0.7), were compared. It was found that, the adsorption capacity of Ca0.4La0.6MnO3 material reached 63.01 mg/g at pH = 5, increased by 63.6% over the undoped LaMnO3 perovskite. For long-term adsorption, Ca0.4La0.6MnO3 could constantly adsorb phosphate to avoid phosphate accumulation (<0.05 mg/L). This proves that Ca0.4La0.6MnO3 has the ability to control dynamic water eutrophication. Characterization and density functional theory results confirmed that CaxLa1-xMnO3 can increase the content of mesopores and oxygen vacancies, providing additional active sites. This reduces the adsorption energy of the La site, promotes electron transfer, and increases its affinity. It provides a new method for removing low-concentration phosphates.

The main controlling factors of tensile strength in sight of shale reservoir under horizontal bedding: Example of the Lower Paleozoic Niutitang Formation shale from Micangshan, China

Understanding the mechanical characteristics of marine shale during fracturing is essential for shale gas development, and its core scientific problem is what factors in shale control its mechanical properties. The 12 shale samples from the Lower Paleozoic Niutitang Formation in Micangshan are tested for tensile strength and examined using X-ray diffraction, low-field nuclear magnetic resonance (NMR), EA2000 elemental analyzer, and scanning electron microscopy to explore the main controlling factors of shale tensile strength under horizontal bedding conditions. The findings are as follows. (1) The tensile strength of the shale is relatively high, ranging from 10.05 MPa to 20.34 MPa. Quartz is the largest proportion of the shale minerals, accounting for 53.2 wt%–59.0 wt%, followed by anorthose and clay minerals. Total organic carbon (TOC) concentration ranges from 1.7 wt% to 4.1 wt%. (2) NMR results indicate that the pore structure of shale is mainly mesoporous, accounting for 75.76%–88.03%, followed by macropores (12.57%–21.24%) and micropores (0.68%–4.91%). Low-pressure nitrogen adsorption and desorption results indicate that the average pore diameter of shale is 12.58–16.02 nm, which is basically consistent with NMR results. The negative correlation between fractal dimension D2 and tensile strength indicates that the higher the tensile strength of the shale, the lower the complexity of its seepage pores. (3) Micropores occur mainly in clay minerals, whereas quartz indicates positively correlation with mesoporous content. The higher the proportion of mesopores, the lower the tensile strength. This indicates that the mesopores are the main factor controlling the tensile strength, and the quartz content in minerals is a secondary factor restricting the tensile strength. TOC has little controlling action on the tensile strength. This contribution provides a theoretical basis for shale fracturing.

Development of hierarchical MOF-based composite phase change materials with enhanced latent heat storage for low-temperature battery thermal optimization

Most of the composite phase change materials (PCMs) based on metal-organic frameworks (MOFs) have much lower latent heat than pure PCMs due to nanoconfined effects, which limits their application in the field of battery insulation. In this work, a series of hierarchical porous carbon nanotubes (CNT)/MOF-199 were synthesized by adjusting the content of N-methyl pyrrolidone (NMP) in the solvent components, and scattered in stearic acid (SA) to obtain a novel composite PCM. The results show that there is a nearly linear relationship between the impregnation ratio, crystallization fraction and impregnation efficiency of PCMs and the mesoporous content of the supporting materials at the maximum loading rate of 70 wt%, which may provide an idea for selecting MOFs supporting materials for PCMs. The latent heat of SA/CNT/MOF-199-2 (SA/CM-2) composite PCM is 97.1/96.2 J·g−1, with a heat loss percentage of only 0.96%. Furthermore, when the lithium-ion battery is discharged 2C at −20 °C, SA/CM-2 used as insulation material can increase the discharge energy by 8.27%. Accordingly, this novel composite PCMs would be hopefully applied to thermal optimization of batteries at low temperatures.

Early-age shrinkage behavior of cement-fly ash paste under wind speeds: A study using BSE-IA and MIP techniques

While laboratory studies have shown that fly ash (FA) can reduce shrinkage in cement-based materials in the absence of wind, its impact on cement-based materials under wind speed conditions has not been extensively studied. This research investigates the influence of FA on the early-age shrinkage of cement paste under various wind speeds. The corresponding changes in pore structure were tested using mercury intrusion porosimetry (MIP) and backscattered electron image analysis (BSE-IA). The results show that under wind speed conditions, FA is not effective in reducing early-age shrinkage of cement paste. In fact, high levels of FA content can increase shrinkage values under wind speed conditions. Both wind speed and FA increase water evaporation, but they have different impact times. Although both wind speed and FA decrease mesopore content below 50 nm and increase water evaporation, they have opposite effects on early-age shrinkage. This suggests that mesopore content and water evaporation alone cannot fully characterize the change trend of early drying shrinkage. The two-factor parameter rs, which combines water evaporation and MIP-based pore size distribution, can effectively characterize drying shrinkage trends under the combined effects of wind speed and FA. BSE-IA can intuitively characterize pore size distribution above 200 nm, while the results of MIP underestimate the distribution of large capillary pores. Therefore, the current rs obtained based on MIP may be smaller than the actual value. With the advancement of testing technology in the future, rs can be further optimized.

Regulation of the pore structure of carbon nanosheets based electrocatalyst for efficient polysulfides phase conversions

The practical applications of lithium-sulfur (Li-S) batteries are hampered by the sluggish redox kinetics and polysulfides shuttle in the cyclic process, which leads to a series of problems including the loss of active materials and poor cycling efficiency. In this paper, the pore structures of carbon nanosheets based electrocatalysts were precisely controlled by regulating the content of water-soluble KCl template. The relationship between pore structures and Li-S electrochemical behavior was studied, which demonstrates a key influence of pore structure in polysulfides phase conversions. In the liquid-sloid redox reaction of polysulfides, the micropores and small mesopores (d < 20 nm) exhibited little impact, while the mesopores (d > 20 nm) and macropores played a decisive role. As a typical exhibition, the nickel-embedded carbon nanosheets (Ni-CNS) with a high content of large mesopores and macropores can aid Li-S batteries in exhibiting stable cycling performance (760.1 mAh g−1 at 1 C after 300 cycles) and superior rate capacity (847.8 mAh g−1 at 2 C). Furthermore, even with high sulfur loading (8 mg cm−2) and low electrolyte (E/S is around 6 µL mg−1), the high area capacity of 7.7 mAh cm−2 at 0.05 C could be achieved. This work can provide a guideline for the design of the pore structure of carbon-based electrocatalysts toward high-efficiency sulfur species redox reactions, and afford a general, controllable, and simple approach to constructing high performance Li-S batteries.

Boosting the Capacitive Performance of Supercapacitors by Hybridizing N, P-Codoped Carbon Polycrystalline with Mn3O4-Based Flexible Electrodes.

Chitosan, a biomass raw material, was utilized as a carbon skeleton source and served as a nitrogen (N) atom dopant in this study. By co-doping phosphorus (P) atoms from H3PO4 and nitrogen (N) atoms with a carbon (C) skeleton and hybridizing them with Mn3O4 on a carbon fiber cloth (CC), an Mn3O4@NPC/CC electrode was fabricated, which exhibited an excellent capacitive performance. The N, P-codoped carbon polycrystalline material was hybridized with Mn3O4 during the chitosan carbonization process. This carbon polycrystalline structure exhibited an enhanced conductivity and increased mesopore content, thereby optimizing the micropore/mesopore ratio in the electrode material. This optimization contributed to the improved storage, transmission, and diffusion of electrolyte ions within the Mn3O4@NPC electrode. The electrochemical behavior was evaluated via cyclic voltammetry and galvanostatic charge-discharge tests using a 1 M Na2SO4 electrolyte. The capacitance significantly increased to 256.8 F g-1 at 1 A g-1, and the capacitance retention rate reached 97.3% after 5000 charge/discharge cycles, owing to the higher concentration of the P-dopant in the Mn3O4@NPC/CC electrode. These findings highlight the tremendous potential of flexible supercapacitor electrodes in various applications.

Highly efficient reduction of nitrophenols by Fe-N-C single-atom catalyst: Performance and mechanism insights

In this study, the properties and mechanism of Fe-N-C single-atom catalyst for reducing nitrophenols were investigated. A variety of Fe-N-C catalysts were prepared using the space-limited way with heating rate of 2 ℃ min−1, 5 ℃ min−1, and 10 ℃ min−1 during calcinating, respectively. FeNC-2 showed the best catalytic efficiency for 4-nitrophenol (4-NP) reduction due to the highest mesoporous content, defect degree and atomically dispersed Fe-Nx site. Under optimal conditions, 0.2 mM 4-NP could be rapidly reduced to 4-AP within 80 s at a low catalyst dose (5 mg FeNC-2). Experiments and density functional theory (DFT) calculations confirmed that Fe-Nx site could effectively catalyze the cleavage of the B-H bond. The electron transfer process of the reaction was confirmed by EPR spectra and chronoamperometry test. In addition, FeNC-2 also showed satisfactory cycle stability and practicality. This research supplies a new perspective for treating nitrophenols-containing wastewater with non-noble metal-based catalysts.

Effects of water-to-binder ratios (w/b) and superplasticizer on physicochemical, microstructural, and mechanical evolution of limestone calcined clay cement (LC3)

This study investigated the effects of water-to-binder ratios (w/b) and a commercial polycarboxylate ether (PCE)-based superplasticizer on various characteristics of limestone calcined clay cement (LC3). Zeta potentials, rheology, hydration kinetics, and chemical, microstructural, and mechanical properties were assessed. A low w/b of 0.25 significantly reduced the hydration of the LC3. LC3 attained a more negative zeta potential in water due to negatively charged clay. The admixture dosage requirement was higher for LC3 than Portland cement, attributed to a high surface area and water uptake for saturation of the calcined clay. The admixture slowed the early-age hydration, yet the resulting enhanced particle dispersion compensated the heat evolution at the w/b of 0.25. LC3 reaction products were mainly characterized as C-(A-)S-H, portlandite, ettringite, monosulfate, and carboaluminates. Their morphologies at the low w/b were less apparent due to space confinement and associated constriction on crystal growth. Despite a higher mesopore content, an LC3-based high-performance concrete could be designed to achieve a strength of more than 100 MPa.

Spherical mesoporous Fe–N–C catalyst for the air cathode of membrane-less direct formate fuel cells

Fe–N–C catalysts with excellent performance regarding the oxygen reduction reaction (ORR) have aroused enormous interest in direct-formate fuel cells (DFFCs). However, their limited mass transfer ability, insufficient ORR active sites, and complex fabrication processes remain significant obstacles to the widespread application of Fe–N–C catalysts. Herein, we propose a simple hydrothermal-annealing method with agarose powders to synthesize a uniform spherical Fe–N–C catalyst (∼3 μm) with well-developed mesopores (Fe/rG@C/H-Agar-900). The resultant Fe/rG@C/H-Agar-900 catalyst possesses rich oxygen-containing functional groups and enhanced interconnected pores, which can significantly boost the content of catalytic sites and facilitate mass transport, resulting in a high content of active sites. In the meantime, the mesopore content of Fe/rG@C/H-Agar-900, which can facilitate the formation of the three-phase gas/electrolyte/catalyst interfaces, was optimized by varying the annealing temperature. As a result, the Fe/rG@C/H-Agar-900 demonstrates a half-wave potential of 0.91 V vs. RHE, nearly four-electron pathway selectivity, excellent durability, and excellent formate tolerance for ORR. Furthermore, when used as the air cathode in membrane-less DFFCs, the Fe/rG@C/H-Agar-900-based device exhibits a remarkable peak power density of 24.5 mW cm−2, significantly outperforming the 20 wt% commercial Pt/C. This research facilitates the synthesis of an advanced Fe–N–C catalyst and promotes the practical development of membrane-less DFFCs.