Dominant Pore Diameter Research Articles

Facile fabrication and supercapacitive properties of mesoporous zinc cobaltite microspheres

Mesoporous zinc cobaltite (ZnCo2O4) microspheres have been successfully prepared by a facile solvothermal method followed by an annealing process. The as-prepared ZnCo2O4 displays uniform sphere-like morphology composed of interconnected ZnCo2O4 nanoparticles. The Brunauer–Emmett–Teller (BET) surface area of mesoporous ZnCo2O4 microspheres is about 51.4 m2 g−1 with dominant pore diameter of 7.5 nm. The novel ZnCo2O4 material exhibits high specific capacitance of 953.2 F g−1 and 768.5 F g−1 at discharge current densities of 4 A g−1 and 30 A g−1, respectively. The energy density can be estimated to be 26.68 Wh kg−1 at a power density of 8 kW kg−1. The specific capacitance retention is 97.8% after 3000 cycles, suggesting its excellent cycling stability. The superior electrochemical performance is mainly attributed to the uniformity of the surface structure and the porosity of the microspheres, which benefit electrons and ions transportation, provide large electrode-electrolyte contact area, and meanwhile reduce volume change during the charge–discharge process. This method of constructing porous microspheres is very effective, yet simple, and it could be applied in other high-performance metal oxide electrode materials for electrochemical capacitors, as well as in Li-ion batteries.

Multivariable linear models of structural parameters to predict methane uptake in metal–organic frameworks

A key challenge preventing CH4-driven energy future is the lack of effective, economic and safe on-board CH4 storage systems. In this study, computational tools were utilized to examine CH4 storage capacity of metal–organic frameworks (MOFs) under practical operating conditions. Grand Canonical Monte Carlo (GCMC) simulations were performed to calculate CH4 uptake capacity of 45 MOFs. Results were confirmed with experimental data available in the literature. Motivated from the good agreement between experiments and simulations, a quantitative structure–property relationship (QSPR) analysis was performed. Making use of this analysis, multivariable linear models with one-, two-, three-, and four-variables that can accurately predict CH4 uptake of MOFs at room temperature and pressures ranging from 1 to 65bar were developed. Model parameters were based on easily measurable/computable structural properties, such as pore volume, surface area, and density. Models that predict CH4 uptake at 5 and 35bar were studied in detail to investigate the viability of reaching CH4 storage target for vehicular systems set by DOE. At both pressures the models with four-variables outperformed other models at the same pressures, and void fraction (Vf) and isosteric heat of adsorption (Qst) were found to be the most significant parameters. In order for a material to exceed the DOE target of 0.5g/g CH4 uptake at a storage pressure of 35bar, the material should have high gravimetric surface area (Sg), reaching 6000m2/g, void fraction (Vf), as high as 0.9, dominant pore diameter (DPD) approximately 30Å, and Qst value around 30kJ/mol. Results of this work reveal the structural properties controlling the CH4 storage capacity of MOFs. Such information can guide experimental studies to tune the MOFs in the way of designing new materials with desirable structural properties that will reach the storage targets.

Template-free and large-scale synthesis of hierarchical dandelion-like NiCo2O4 microspheres for high-performance supercapacitors

In this work, dandelion-like NiCo2O4 mesoporous microspheres were uniformly assembled from slim nanowires via a large-scale and template-free method. The Brunauer–Emmett–Teller (BET) surface area of NiCo2O4 microspheres was determined to be about 35.2m2g−1 with dominant pore diameter of 10.9nm and narrow size distribution of 8–20nm. Furthermore, the electrochemical properties of NiCo2O4 microspheres were evaluated by cycle voltammetric (CV) and galvanostatic charge–discharge (GCD) measurements. The results demonstrated that the NiCo2O4 microspheres exhibited high specific capacitance (372Fg−1 at 1Ag−1), good rate capability, and excellent cycling stability (88.3% retention after 2000 cycles). In principle, this synthetic approach could be extended for the fabrication of other microstructure materials for promising electrode candidates in energy storage devices.

High Electrochemical Performance of Monodisperse NiCo2O4Mesoporous Microspheres as an Anode Material for Li-Ion Batteries

Binary metal oxides have been regarded as ideal and potential anode materials, which can ameliorate and offset the electrochemical performance of the single metal oxides, such as reversible capacity, structural stability and electronic conductivity. In this work, monodisperse NiCo(2)O(4) mesoporous microspheres are fabricated by a facile solvothermal method followed by pyrolysis of the Ni(0.33)Co(0.67)CO(3) precursor. The Brunauer-Emmett-Teller (BET) surface area of NiCo(2)O(4) mesoporous microspheres is determined to be about 40.58 m(2) g(-1) with dominant pore diameter of 14.5 nm and narrow size distribution of 10-20 nm. Our as-prepared NiCo(2)O(4) products were evaluated as the anode material for the lithium-ion-battery (LIB) application. It is demonstrated that the special structural features of the NiCo(2)O(4) microspheres including uniformity of the surface texture, the integrity and porosity exert significant effect on the electrochemical performances. The discharge capacity of NiCo(2)O(4) microspheres could reach 1198 mA h g(-1) after 30 discharge-charge cycles at a current density of 200 mA g(-1). More importantly, when the current density increased to 800 mA·g(-1), it can render reversible capacity of 705 mA h g(-1) even after 500 cycles, indicating its potential applications for next-generation high power lithium ion batteries (LIBs). The superior battery performance is mainly attributed to the unique micro/nanostructure composed of interconnected NiCo(2)O(4) nanocrystals, which provides good electrolyte diffusion and large electrode-electrolyte contact area, and meanwhile reduces volume change during charge/discharge process. The strategy is simple but very effective, and because of its versatility, it could be extended to other high-capacity metal oxide anode materials for LIBs.

Nanocrystal-Constructed Mesoporous Single-Crystalline Co3O4 Nanobelts with Superior Rate Capability for Advanced Lithium-Ion Batteries

In this paper, one-dimensional (1D) mesoporous single-crystalline Co₃O₄ nanobelts are synthesized by a facile hydrothermal method followed by calcination treatment. The as-prepared nanobelts have unique mesoporous structures, which are constructed by many interconnected nanocrystals with sizes of about 20-30 nm. And typical size of the nanobelts is in the range of 100-300 nm in width and up to several micrometers in length. The BET surface area of Co₃O₄ nanobelts is determined to be about 36.5 m² g⁻¹ with dominant pore diameter of 29.2 nm. Because of the 1D structure, mesoporous morphologies and scrupulous nanoarchitectures, the Co₃O₄ nanobelts show excellent electrochemical performances such as high storage capacity and superior rate capability. The specific capacity of Co₃O₄ nanobelts could remains over 614 mA h g⁻¹ at a current density of 1 A g⁻¹ after 60 cycles. Even at a high current density of 3 A g⁻¹, these Co₃O₄ nanobelts still could deliver a remarkable discharge capacity of 605 mA h g⁻¹ with good cycling stability.

Electrochemical synthesis of mesoporous FePO 4 nanoparticles for fabricating high performance LiFePO 4/C cathode materials

Unique amorphous FePO 4 with particle size ranging from 20 to 80 nm has been successfully synthesized by a new cost-effective electrochemical method. This FePO 4 possesses a mesoporous structure with specific surface area of 65.2 m 2 g −1 and dominant pore diameter of 23.6 nm. The basic formation mechanism has been discussed. These amorphous mesoporous FePO 4 nanoparticles can be used as precursors to prepare LiFePO 4/C nanocrystals with porous structure. The obtained LiFePO 4/C cathode materials exhibit excellent cycling performances. At a 0.5 C rate, the discharge capability is above 140.0 mA h g −1 and the capacity retention rate is higher than 98% after 50 cycles. The microstructural and electrochemical analyses reveal that these amorphous mesoporous FePO 4 nanoparticles are the perfect precursors to prepare LiFePO 4/C composite. Furthermore, this facile, cost-effective and green electrochemical strategy can be easily scaled up for commercialization, and also could open avenues towards synthesizing other mesoporous phosphate materials.

Preparation of cresol–formaldehyde carbon aerogels via drying aquagel at ambient pressure

Carbon aerogels were prepared from mixed cresol (Cm) and formaldehyde (F) via the sol–gel process followed by drying at ambient pressure and carbonization. The inexpensive feedstock of mixed cresol and the simple drying process could be as an alternative economical route to the classical resorcinol–formaldehyde synthesis process. In our process, organic precursor gels were synthesized via polycondensation of cresol with formaldehyde in an aqueous alkaline (NaOH) solution. After gelation the solvent was removed via drying at ambient pressure to obtain organic aerogels that exhibit a drying shrinkage below 5% (linear). Upon carbonization of the organic aerogels at 1173K, monolithic carbon aerogels (denoted as CmF carbon aerogels) can be produced. Nitrogen adsorption results showed that the CmF carbon aerogels have abundant mesopores and micropores with a dominant pore diameter of 25–40nm. An increase of the BET surface area and a modification of the pore size distribution of CmF can be realized by a CO2 activation. The images of scanning electron microscopy (SEM) indicated that the microstructure of carbon aerogels can be effectively controlled and tailored by varying the synthetic conditions during the initial sol–gel process.

Comparison of the characteristics of electric double-layer capacitors with an activated carbon powder and an activated carbon fiber

The characteristics of electric double-layer capacitors (EDLCs) with activated carbon powder (ACP), pulverized activated carbon fiber (ACF), and ACF-cloth have been compared. The BET surface areas of the ACP and ACF were estimated to be 1740 and 1970 m2 g−1, respectively. In the pore-size distribution curve of the ACP and ACF, the most dominant pore diameter was 1.8 and 1.1 nm for the ACP and ACF, respectively. Disc- and cloth-type of electrodes were fabricated using ACP and ACF. The electrical resistance of the ACF-disc and ACF-cloth electrodes was four orders of magnitudes lower than that of the ACP-disc electrodes. In accordance with the lower electrical resistance of the ACF-disc and ACF-cloth, the d.c. resistance of the EDLC with the ACF-disc and with ACF-cloth was lower than that of the EDLC with the ACP-disc. The highest specific volume capacitance of 28.3 F cm−3 (capacitance / volume of total ACF in the EDLC) was achieved with the ACF-disc. In the cyclic voltammograms of the ACF-disc, the stable electric double-layer charging and discharging behavior was observed.

Influence of superplasticizer and curing on porosity and pore structure of cement paste

Most concrete produced today contains admixtures. Superplasticizers (SP) are used for the purpose of improving workability and reducing the water to cement ratio; therefore producing more durable concrete. SP cause better dispersion even at high water to cement ratio. Although SP improves the dispersion of particles, it is not quite clear how the addition of SP affect the porosity and pore size distribution of cement paste. The purpose of this study was to examine the influence of one type of SP on porosity and pore size distribution under different curing regimes. Paste specimens with and without SP were prepared at constant water to cement ratio of 0.45. Specimens were cured for 28 days and some for six months. Specimens were exposed to high temperature (45°C) and normal temperature curing (20°C) and also subjected to different relative humidities (∼100%, 55% and 25%). Curing at high temperature was carried out to simulate temperature in hot climates. Tests on porosity and pore size distribution were conducted using mercury intrusion porosimetry. The results show that the inclusion of SP decreases the total intruded pore volume of paste. The dominant pore diameter, however, does not seem to be affected and the percentage of pores smaller than 100 nm increases in the presence of SP.

Characterization of aluminium surface treatments by means of gas adsorption measurements

Adsorption measurements were used to determine the specific surface area of a.c. electrolytically grained aluminium and the porosity distribution diagram of porous anodized aluminium. Alternating current electrolytic graining of aluminium is used to increase the specific surface area for the preparation of litho sheets or capacitor foil. The specific surface area S (calculated by the BET procedure from the nitrogen adsorption isotherm) was studied as a function of the graining frequency between 0.1 and 1000 Hz. The results were related to the graining morphology by comparing them with scanning electron microscopy micrographs. It is concluded that in contrast to the more common surface investigation techniques the method can be used to measure quantitatively the gain in surface area after such a treatment as a.c. electrolytic graining. In the second part of the paper the pore size distribution diagrams are calculated from the adsorption isotherm for porous sulphuric acid films. It is shown that the dominant pore diameter corresponds rather well to the pore diameter observed in transmission electron microscopy sectional views. This means that the adsorption method can be applied to study the porosity of the aluminum oxide films. The method was then used to study the influence of the pretreatment on the porous oxide film morphology.