Smaller Average Pore Diameter Research Articles

Nanopore Structure and Multifractal Characteristics of Continental Shale Oil Reservoir: A Case Study from Ziliujing Shales in the Sichuan Basin

Thermal maturity of the shales from the Ziliujing Formation of the Jurassic age in the Sichuan Basin is in the hydrocarbon generation window, which makes it a candidate for shale oil and gas development. The meso- and macropore characteristics and heterogeneity of shales are important factors affecting the occurrence and development of oil and gas. However, the meso- and macropores of the Ziliujing shales have not been systematically studied. Thus, the mineral compositions and total organic carbon (TOC) of samples from this formation, as well as its pore structure, are analyzed by low-temperature N2 adsorption technique. Moreover, the heterogeneity of the pores was determined by multifractal analysis. The results show that the Ziliujing shales can be classified into three types according to the distributions of mineral compositions of carbonate and mixed and argillaceous shales. Results revealed that the smallest meso- and macropore volume (PV), the smallest specific surface area (SSA), and the largest average pore diameter (APD) occur in the carbonate shales. However, the largest PV and SSA and the smallest APD are observed in the argillaceous shales. The porosity of carbonate shales is mainly concentrated between 5 nm and 30 nm. Compared with carbonate shales, the porosity with pore sizes less than 30 nm of mixed and argillaceous shales shows a rapid increase. Furthermore, inorganic minerals are the main factors affecting the pore distributions, while TOC shows a weak effect. Herein, clay minerals significantly increase the mesopore volume and the pore number with a size of less than 30 nm. The Dq-q curves reveal that the meso- and macropore distributions of Ziliujing shales show multifractal behavior, but the multifractal characteristics of pores of various shales are distinctly different. The information dimension D1, the Hurst exponent H, and the width of the right side D0–D10 are key indicators to distinguish the local variations within the pore structure of different types of shales. The carbonate shales have the largest multifractal spectra width and the smallest D1 and H, while the opposite trend is found for the argillaceous shales. Clay minerals reduce the heterogeneity of the meso- and macropore distributions and increase the pore connectivity. Nevertheless, the carbonate minerals exhibit a reverse trend. Finally, it was found that TOC does not impact pore complexity as much. Collectively, this study supports our understanding of the occurrence of shale oil within various reservoir facies, thereby providing a guideline for future explorations in the Ziliujing Formation of the Jurassic age in the Sichuan Basin.

Pore structure characterization of solvent extracted shale containing kerogen type III during artificial maturation: Experiments and tree-based machine learning modeling

Shale samples with type III kerogen from the Damoguaihe formation were exposed to hydrous and anhydrous pyrolysis (HP and AHP) in the temperature range of 300–450 °C. Next, soluble organic matter (OM) and the liquid yield were removed from the pyrolyzates after each step of thermal maturation. N2 adsorption tests were performed to assess the pore structures of the samples. Furthermore, deconvolution and fractal dimension analyses were executed to unveil pore clusters and discern the complexity of the pore network within each sample. Finally, two tree-based machine learning algorithms, random forest (RF) and extra trees (ET) were applied to model the N2 adsorption/desorption data of pyrolyzates to predict pore structure variations. Based on the results, HP pyrolyzates had higher bitumen reflectance (BRo%) values than AHP ones at all temperature sequences, which confirms water controls thermal maturity. AHP pyrolyzates exhibited larger average pore diameters across all temperatures, while HP pyrolyzates displayed higher BET surface areas in contrast to AHP pyrolyzates. Also, the average pore diameter of HP pyrolyzates with soluble OM and liquid yield extracted did not change significantly during thermal maturation, while the average pore diameter of AHP ones increased, peaking at 400 °C in post-mature stage. The largest total pore volume of HP samples was observed at the end of the wet gas window, while this was observed for AHP samples in the dry gas window. Three mesopore and four macropore clusters were identified in the original sample. Moreover, pore clusters of the pyrolyzates underwent diverse changes during thermal maturation, without following a specific trend, influenced by both temperature and pyrolysis conditions. Abundance of micropores, finer mesopores (2–10 nm), and a smaller average pore diameter in HP pyrolyzates compared to the AHP is the main reason for the higher fractal dimensions showing a more complex pore structure and/or rougher pore surface. Intelligence modeling exhibited that RF outperformed ET in estimating N2 adsorbed/desorbed volumes for the samples. Ultimately, sensitivity analysis revealed that water exerted a more significant influence on pore development in shales during thermal progression, outweighing the impact of temperature.

Preparation of mesoporous strontium carbonate nanospheres with the enhanced photoactivity for TC degradation under visible light

Strontium carbonate (SrCO3), as a wide band gap material, has gradually been applied in the field of photocatalysis. In this paper, mesoporous SrCO3 nanospheres with large specific surface area (243 m2 g−1), narrow pore distribution and small average pore diameter (4.42 nm) were prepared at room temperature, where sodium citrate was used as a capping agent, water and ethylene glycol was used to dissolve Na2CO3 and Sr(NO3)2, separately. The as-prepared mesoporous SrCO3 exhibited excellent photocatalytic activity for the degradation of tetracycline (TC) under visible light, and the degradation efficiency reached 82.5% within 60 min of irradiation. In this photoreaction system, TC molecules adsorbed on the catalyst surface were responsible for visible light absorption and electron excitation, and a possible mechanism for TC degradation on mesoporous SrCO3 has been proposed.

Effect of oxygen-containing functional groups and pore structure characteristics of coal on the slurryability of coal wastewater slurry

The physical and chemical characteristic of coal have an important influence on the slurryability of coal wastewater slurry. In this paper, eight different coals are used to make coal wastewater slurry, and the effects of oxygen containing functional groups and pore structure characteristics of different coal samples on the slurryability are analyzed. Results show that (a) Coal with more oxygen-containing functional groups on surface have stronger hydrophilicity, higher surface activity and have stronger adsorption capacity for water molecules, this will lead to the reduction of free water and the increase of viscosity of the slurry. (b) Coal with larger BET specific surface area and pore volume and smaller average pore diameter have the stronger ability to adsorb and store water in coal wastewater slurry, thus the concentration of coal wastewater slurry prepared from these coal is low. The conclusion of this paper can provide reference for coal selection in the preparation of coal wastewater slurry.

Influence of slurry characteristics on the bubble stability in foamed concrete

Foamed concrete is a porous material widely used in construction, but its production remains challenging due to bubble stability issues. To address these problems, this study analyzed the influence of bubble characteristics and paste viscosity on bubble stability in foamed concrete, specifically examining pore diameter distribution, collapse depth, and density deviation. Results showed that increasing the strength of the bubble film led to a decrease in the collapse depth of foamed concrete, along with a more uniform distribution of pores and a smaller average pore diameter, indicating improved bubble stability. Adequate viscosity in the cement paste was crucial for limiting the collapse and decreasing density deviation of foamed concrete, as well as ensuring a uniform distribution of early strains. Furthermore, the bubble duration remained unruptured for longer than the setting time of foamed concrete, which was necessary for bubbles to stay stable. A theoretical model of paste viscosity and bubble film strength, based on force analysis of bubbles in foamed concrete, was developed and can predict the required paste viscosity for bubble stability. This study provides important insights into the production of stable foamed concrete and offers a theoretical basis for future research in this area.

Influence of coalification on pore structure evolution in middle-ranked coals

The influence of coalification on coal structure evolution in middle ranked coals is significant for physical assessment of coalbed methane (CBM) reservoirs, which provides insights on the intrinsic connection between coalification jump and pore heterogeneity. A total of 26 middle-ranked coals were samples covering Liupanshui Coalfield in Guizhou Province, Anhe Coalfield in Henan Province, Huaibei Coalfield in Anhui Province, Sanjiang Basin in Heilongjiang Province, Ordos Basin in Shaanxi Province and Qinshui Basin in Shanxi Province. Based on a series of experiments including vitrinite reflectance, coal maceral identification, nitrogen adsorption and the pore fractal method, the inner link between physical property parameters of coal reservoirs and coal rank was revealed. The results show that the coal maceral in middle rank coals is dominated by vitrinite and inertinite and two types of adsorption pores are divided according to the nitrogen adsorption/desorption curves along with pore size distribution. The specific surface area is positively correlated with total pore volume, micropore volume and negatively correlated with averaged pore size and transitional pore volume. The coal samples with low average pore sizes have relatively high total pore volume, specific surface area and micropore volume per unit nm. With the increase of coal rank, the fluctuating points of micropore and transitional pore volume correspond to 1.16%–1.19%, 1.41%–1.43% and 1.86%–1.91% of Ro, max, respectively. The boundary of Ro, maxcorresponding to the second coalification jump can be more specifically defined as 1.16%–1.19% from the established nominal range of 1.1%–1.3%. The pore fractal dimension DNA1and DNA2increase with increasing specific surface area. Furthermore, the DNA2has a negative correlation with micropore volume and averaged pore size, indicating that the coal with smaller average pore diameter and lower micropore content has a more complex pore structure.

Salt migration and capillary absorption characteristics of cement mortar partially immersed in NaCl solution

Salt crystallization represents a major reason for the damage observed for porous building materials in humid coastal areas. Despite the several theories developed to explain the process, no unanimous opinion has been proposed for the mechanism underlying the damage. A better understanding of the migration, crystallization, and distribution of salts in porous building materials in the presence of water is thus warranted to improve the durability for cultural heritages and new buildings. This paper reports an experimental study of crystal distribution, micromorphology, chloride ion migration, pore structures, and capillary absorption behaviors of cement-mortar specimens (side-coated and side-uncoated) at three different water-cement ratios (0.4, 0.6, and 0.8) after 120-day partial immersion in 5 wt% NaCl solution. Results showed that the different pore characteristics and side-coating treatment of the specimens governed not only capillary absorption, but also salt migration and distribution. The specimens with a large average pore diameter and greater porosity yielded more external salt crystals, while those with a small average pore diameter and dense surfaces demonstrated the reverse. For vertical migration, the Cl− concentration changed slightly with height of the specimens, except for the top segment. For horizontal migration, the Cl− concentrations in the central samples were higher than the edge samples. Of note, the side-coated specimens were associated with reduced external salt crystals and lower Cl− concentration in their edge samples. Compared with the salt-free specimens, both the capillary absorption coefficient (Acap) and capillary moisture content (Wcap) of the salt-contaminated specimens were lower (water-cement ratio = 0.6, −45.72%, −56.39%; water-cement ratio =0.8, −60.8%, −56.34%), illustrating the inhibitory effect of salt crystallization on the hygroscopic properties of the porous materials. Lastly, both the Acap and Wcap of the side-coated specimens were lower than uncoated ones.

Quantitative evaluation of pore structures within micron-scale laminae of lacustrine shales from the Second Member of the Kongdian Formation in Cangdong Sag, Bohai Bay Basin, China

Lamina is the basic and typical “building block” of organic-rich shales, which has significant impact on the generation, migrition, and accumulation of hydrocarbon. Integrated methods, including X-ray diffraction (XRD), scanning electron microscopes (SEM), and image processing technology, were applied to explore the pore type, pore size, and pore morphology of laminae in shales selected from the Second Member of the Kongdian Formation in Bohai Bay Basin. The application of image stitching and processing technology intuitively and accurately obtained the pore structure among different types of laminae including siliceous laminae, mixed laminae, dolomite laminae, and calcite laminae. The results showed that the average SEM-based surface porosity of laminae was in the following order: siliceous laminae > calcite laminae > dolomite laminae > mixed laminae. The siliceous lamina was dominated by interparticle pores between rigid grains, and was characterized by high volume of macropore. In addition to the pores between rigid grains, pores between clay platelets resulted in a large volume of nano-scale pores. Therefore, mixed lamina was characterized by the smallest average pore diameter and the lowest SEM-based surface porosity. The SEM-based surface porosity of calcite lamina and dolomite lamina was between that of siliceous lamina and mixed lamina, and abundant interparticle pores between grains and intraparticle pores within carbonate minerals were observed in calcite lamina and dolomite lamina. The porosity and pore type of calcite laminae are similar with that of dolomite laminae in certain aspects, while the pore size distribution range of dolomite lamina was wider than that of calcite lamina and the dissolution pores of the calcite lamina contributed more pore volume than that of dolomite lamina. Diverse pore structures among different laminae may be attribute to the synergistic effect of different mineral compositions and diagenetic processes.

Deep Adsorption Desulfurization of Fluid Catalytic Cracking Light Gasoline on NiO/ZnO-TiO2 Adsorbents with a High Breakthrough Sulfur Capacity.

Two kinds of NiO/ZnO-TiO2 adsorbents were prepared by equal volume impregnation (NiO/ZnO-TiO2-1) and kneading (NiO/ZnO-TiO2-2) methods. The adsorbents were characterized by X-ray diffraction, mercury intrusion porosimetry, scanning electron microscopy, energy dispersive X-ray spectroscopy, H2 temperature-programmed reduction, and H2 temperature-programmed desorption. It was found that NiO/ZnO-TiO2-2 had a smaller average pore diameter and a larger specific surface area as well as a more uniform distribution of the nickel element. Additionally, more Ni0 active sites together with a stronger interaction between the active component and the support were detected on the surface of NiO/ZnO-TiO2-2, which was beneficial to the inhibition of olefin saturation during desulfurization. The desulfurization performance of the adsorbents was investigated in a fixed bed reactor with fluid catalytic cracking light gasoline as a feed oil. The evaluation results confirmed NiO/ZnO-TiO2-2 with a better desulfurization performance with less olefin saturation. It could reduce the total sulfur content from 300 ppmw to less than 5 ppmw, and the breakthrough time and breakthrough sulfur capacity were 91 h and 6.71% (67.1 mg S/g adsorbent), respectively.

New cognition on pore structure characteristics of Permian marine shale in the Lower Yangtze region and its implications for shale gas exploration

Shale of the Middle–Upper Permian Dalong Formation and Gufeng Formation in the Lower Yangtze region is characterized by large thickness, high total organic carbon (TOC), wide distribution and moderate organic thermal evolution degree, so it may be the next important field of shale gas exploration. In order to point out the target and direction of shale gas exploration and development in this region, this paper selects the Dalong Formation and Gufeng Formation shale in the Xuanjing area of Lower Yangtze as the research object to quantitatively describe the development characteristics of shale pores of different scales by means of scanning electron microscopy (SEM), high pressure mercury injection, CO2 and N2adsorption. Then, the fractal dimension of sample pores is calculated by using the FHH (Frenkel–Halsey–Hill) model. Finally, combined with TOC and mineral compositions, the relationship between pore structure and fractal dimension is discussed. And the following research results are obtained. First, dominant lithofacies of Dalong Formation are argillaceous-rich siliceous shale and argillaceous-rich/siliceous mixed shale, which has smaller specific surface area and pore volume, larger average pore diameter. The pore development is mainly controlled by clay mineral content. Dominant lithofacies of Gufeng Formation is siliceous shale, which has a larger specific surface area and pore volume, and smaller average pore diameter. The pore development is controlled by organic matter and brittle mineral content. Second, the influencing factors of fractal dimension can be attributed to the controlling factors of micropore development. The fractal dimension D1of Dalong Formation ranges from 2.4515 to 2.5513 (average 2.5227), and D2ranges from 2.5817 to 2.6578 (averagely 2.6246). The fractal dimension D1of Gufeng Formation ranges from 2.5817 to 2.6578 (averagely 2.6246), and D2ranges from 2.7227 to 2.871 (averagely 2.813). Gufeng Formation shale presents the characteristics of more complex pore structure. Third, the fractal dimension D1is more sensitive to specific surface area, pore development and mineral composition, while D2is more effective in characterizing the average pore diameter. In conclusion, Dalong Formation shale with high D1and D2and Gufeng Formation shale with low D1and high D2can be taken as the favorable exploration targets of Permian marine shale gas in the Lower Yangtze region, and the regional overpressure zones (belts) with weaker structural deformation in hydrocarbon rich sags will be the favorable shale gas exploration targets in this area.

Waste coffee grounds derived nanoporous carbon incorporated with carbon nanotubes composites for electrochemical double-layer capacitors in organic electrolyte

Carbon nanotube (CNT)-incorporated nanoporous carbon (NPC) derived from the waste coffee ground composite was proposed as a potential electrode material for electrochemical double layer supercapacitors with an organic electrolyte. CNT-incorporated NPC pastes with different CNT contents were fabricated via a simple ball-milling method and then coated on a carbon nanofiber paper using a doctor blade technique. According to structural characterization data, the 3%CNT/NPC material offered a high specific surface area of 1157.8 m2 g−1 with a small average pore diameter of 1.42 nm owing to the intercalation of CNT structures between the NPC flakes. From electrochemical measurements, a coin cell using 3%CNT/NPC in 1 M TEABF4/ACN exhibited a high specific capacitance of 132 Fg−1 and a high specific energy of 37.7 Wh kg−1 at 0.5 Ag−1, which are considerably higher than those using NPC (74 Fg−1 and 20.1 Wh kg−1) and CNT (48 Fg−1 and 14.7 Wh kg−1). In addition, the composite possessed higher rate capability, better cycling stability, and lower self-discharge rate compared with NPC and CNT electrodes. Hence, the 3%CNT/NPC composite was promising as an active material for producing advanced supercapacitors.

Microstructure analysis and image-based modelling of face masks for COVID-19 virus protection

SARS-CoV-2 may spread through respiratory droplets released by infected individuals. The viruses are transmitted in moist droplets which cause coronavirus disease. Many countries have mandated the wearing of face masks, to various extents. However, the efficacy of masks is yet to be well rationalised given the limited microstructure information. Here, three common face masks and associated air permeations were revealed by coupling X-ray tomographic imaging and infrared thermal imaging techniques. Quantitative parameters have been extracted from the 3D images. Also, image-based modelling was performed to simulate the permeability to show how droplets pass through the porous structure. Our results show that the N95 mask has the smallest average pore diameter (~30 µm) and the densest nanoscale fibres which provides superior droplet filtration among all cases. Modifications to the N95 masks are proposed to develop the next generation mask with higher efficacy and better breathability.

Study on Preparation and Interfacial Transition Zone Microstructure of Red Mud-Yellow Phosphorus Slag-Cement Concrete.

Open stockpiling and the continual production of industrial solid wastes such as red mud (RM) and yellow phosphorus slag (YPS) have caused serious environmental pollution issues. Additionally, concrete prepared easily and with high strength is a widely applied building material. Therefore, replacing part or all of the cement for preparing concrete with RM and YPS will greatly reduce this kind of solid waste and, thus, decrease environmental pressures. This study investigated the best ratio for the replacement of concrete with RM and YPS, testing the mechanical properties as well as the morphology, material composition, and microporous structure of the interface transition zone (ITZ). The results showed for the concrete prepared with ordinary Portland cement replaced by 10.00 wt.% RM and 18 wt.% YPS, compared to ordinary Portland cement concrete, the compressive strength of concrete with basalt aggregate and dolomite aggregate increased by 25.04% and 27.27%, respectively, when the concrete was cured with steam for 28 days. Furthermore, it had a smaller average pore diameter and crystal size in the ITZ. The aggregate and matrix were more closely intertwined. This was because RM had a low cementitious activity and mainly had a filling effect when added to concrete, while the highly active silica in YPS could react with the Ca(OH)2 crystal (CH) produced from cement hydration to form calcium silicate hydrate (CSH) gel, improving the mechanical properties and microstructure of the concrete.

Optimisation of Mass Transport Parameters in a Polymer Electrolyte Membrane Electrolyser Using Factorial Design-of-Experiment

Optimised mass transport is crucial for high current density operations in Polymer Electrolyte Membrane Water Electrolysers (PEMWEs). This study investigates the effect and interactions of mass transport parameters on the performance of a PEMWE using a 23 full-factorial Design-of-Experiments (DoE) approach with replication. The effects of anode flow-field design, anode porous transport layer (PTL) and water flow rate on the cell performance were studied. At 95% confidence level, the result shows that all three factors and their two-way interactions significantly affect the cell performance. Among them, the water flow rate showed the most significant contribution, followed by the interaction between the flow-field and the PTL. A regression model was developed to relate the cell performance and the mass transfer parameters. Results of analysis of variance (ANOVA), regression analysis and R2 test indicated good accuracy of the model. The best PEMWE cell performance was obtained with a parallel flow-field configuration, a small average pore diameter of PTL and high anode water flow rate. The DoE is shown to be a suitable method for investigating interactions and optimising the operating conditions to maximise PEMWE performance.

Controlling the foam morphology of supercritical CO2‐processed poly(methyl methacrylate) with CO2‐philic hybrid nanoparticles

AbstractHighly CO2‐philic nanoparticles, octatrimethylsiloxy polyhedral oligomeric silsesquioxanes (POSS) are used to increase the affinity of poly(methyl methacrylate) (PMMA) to CO2 in supercritical carbon dioxide (scCO2) foaming, thus to improve its foaming performance and the foam morphology. PMMA and PMMA‐POSS composite foams were produced based on the two‐factorial design, at the upper and lower experimental conditions of pressure, temperature, processing time, and venting rate. The foams of PMMA‐5% POSS composites exhibited smaller average pore sizes and higher pore densities than neat PMMA and PMMA‐0.5% POSS composites. The smallest average pore diameter (0.3 μm) and the highest pore density (6.33 × 1012 cm−3) were obtained with this composite processed at 35°C, 32 MPa, for 24 h and depressurized with fast‐venting rate (0.4 MPa/s). ScCO2 processing decreased the density of the polymer by more than 50%.

Derivation of Luminescent Mesoporous Silicon Nanocrystals from Biomass Rice Husks by Facile Magnesiothermic Reduction.

High-quality silicon (Si) nanocrystals that simultaneously had superior mesoporous and luminescent characteristics were derived from sticky, red, and brown rice husks via the facile and cost-effective magnesiothermic reduction method. The Si nanocrystals were confirmed to comprise an aggregated morphology with spherical nanocrystals (e.g., average sizes of 15–50 nm). Due to the surface functional groups formed at the nanocrystalline Si surfaces, the Si nanocrystals clearly exhibited multiple luminescence peaks in visible-wavelength regions (i.e., blue, green, and yellow light). Among the synthesized Si nanocrystals, additionally, the brown rice husk (BRH)-derived Si nanocrystals showed to have a strong UV absorption and a high porosity (i.e., large specific surface area: 265.6 m2/g, small average pore diameter: 1.91 nm, and large total pore volume: 0.5389 cm3/g). These are indicative of the excellent optical and textural characteristics of the BRH-derived Si nanocrystals, compared to previously reported biomass-derived Si nanocrystals. The results suggest that the biomass BRH-derived Si nanocrystals hold great potential as an active source material for optoelectronic devices as well as a highly efficient catalyst or photocatalyst for energy conversion devices.

Pore characterization of Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation shale gas reservoirs, Sichuan Basin, China

In order to investigate pore structure characteristics of Wufeng and Longmaxi Formations shales in the Sichuan Basin, the organic geochemical parameter and petrologic experiments, N2 and CO2 adsorptions, field emission scanning electron microscopy analysis and helium porosity measurement are carried out. Results showed that the thermal maturity of shales belong to over-maturity stage with TOC content and porosity of 1.84%–6.82% and 2.6%–5.1%, respectively. The TOC content has a good correlation with quartz, weak correlation with clay and no correlation with carbonate, indicating that the organic matter is mainly controlled by quartz content. The N2 and CO2 specific surface areas of organic-rich shale is generally 16.86–29.71 m2/g and 13.76–26.47 m2/g, respectively and the average N2 and CO2 specific surface area of organic-poor shale are 8.91 m2/g and 9.11 m2/g respectively, which indicating that the organic-rich shale has higher specific surface area, pore volume and smaller average pore diameter than that of organic-poor shale. The specific surface area in organic-rich shale is mainly contributed by micropores, while the pore volume is mainly contributed by mesopores, followed by micropores. There is a very strong correlation between TOC and CO2 and N2 specific surface area, indicating that pores were controlled by organic matter. Both porosity and specific surface have a positive relation when clay content is less than 28% for organic-rich shale, and its correlation is not obvious when clay content is more than 28% for organic-poor shale, indicating that the clay has a certain effect on reservoir.

Pore Structure Characteristics of Coal and Their Geological Controlling Factors in Eastern Yunnan and Western Guizhou, China.

Coalbed is the carrier for coalbed methane (CBM) enrichment and migration. The pore structure characteristics of coal and their main geological controlling factors are critical to the exploration and development of CBM. In this paper, 20 coal samples were collected from eastern Yunnan and western Guizhou, China. Based on vitrinite reflectance, proximate analysis, maceral analysis, and low-temperature N2 adsorption/desorption (LT-N2GA) experiments, the hysteresis coefficient of low-temperature N2 desorption was proposed, the types of pore structure were identified, and the effects of coal facies and rank on the pore structure were revealed. The results show that the Ro,max values of the 20 coal samples are between 0.74 and 3.38%, which belong to medium- and high-rank coal. In the coal macerals, the vitrinite is mainly collodetrinite. The inertinite is dominated by semifusinite, and some coal samples contain exinite. The coal samples investigated can be divided into two types. Type A samples mainly contain open pores, while type B samples are rich in bottle-shaped pores. Compared with type A coal samples, type B samples have the characteristics of smaller total pore volume (TPV), smaller average pore diameter (APD), larger specific surface area (SSA), and larger hysteresis coefficient. The coal samples are located in three regions of different coal facies, including low-level swamp (reed) facies, wetland herbaceous swamp facies, and wet forest swamp facies. The tissue preservation index (TPI) values of most coal samples are less than unity, which indicates that herbaceous plants have absolute dominance in the coal-forming plants in eastern Yunnan and western Guizhou. The maximum vitrinite reflectance (Ro,max), gelification index (GI), TPI, vitrinite content (V), inertinite content (I), Barrett-Joyner-Halenda pore volume (VBJH), Brunauer–Emmett–Teller SSA (SBET), and low-temperature N2 desorption total hysteresis coefficient (Ht) were clustered using the R-type cluster analysis method. It is found that TPI is the main controlling factor of the pore structure of type A coal samples, while the pore structure of type B coal samples are jointly controlled by TPI and coal rank. Type B coal samples are mainly located in Zhuzang and Laochang high-rank coal research areas, while the distribution of type A coal samples is mainly in other medium–high-rank coal research areas. These results will contribute to the exploration and development of CBM and also guide the study of pore structures of other unconventional gas reservoirs.

Character of Selective Anodic Dissolution. Influence of the Alloy Composition

The corrosion electrochemical behavior of copper-based alloys (L63, cupronickel, Monel, Cu–Al) in high-temperature salt electrolytes of various compositions in the galvanostatic mode is studied. Brass L63 is the most promising copper-based alloy for the production of nanoporous and mesoporous materials in salt melts. L63 brass samples have the smallest average pore diameter in experiments with a chloride melt. The pore size was 1.1 μm in the galvanostatic mode under the specified conditions (200 A/m2, 500°C). The results of cyclic voltammetry can be applied to predict the character of electrochemical destruction and to analyze the stages of conjugated anodic processes. The influence of the nature of the second alloy component on the character of electrochemical destruction and the formation of the developed surface layer of the alloys is found.

Cobalt ion intercalated MnO2/C as air cathode catalyst for rechargeable aluminum–air battery

Overcoming the self-corrosion and surface passivation of aluminum anode, and the slow kinetics of cathodic electrochemical reactions are of great significance for the practical application of aluminum–air battery. In this study, we replaced the traditional aqueous electrolyte with AlCl3-urea ionic liquid electrolyte, and prepared Co–MnO2/C catalysts as cathode catalyst. Structures and electrocatalytic activity of the x % Co–MnO2/C (x is the mole percent of Co to Mn, x = 0, 10, 20, 30, 40 and 50) catalysts have been investigated systematically. After Co ions intercalation, the specific surface area of the catalyst increased and average pore diameter decreased. The unique interaction between Co ions and MnO2 led to an increase in the catalytic activity of the catalyst in the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) compared with MnO2/C. In particular, 40% Co–MnO2/C showed the largest specific surface area (154.25 m2 g−1) and the smallest average pore diameter (6.47 nm). It showed the most positive half-wave potential (0.727 V vs. RHE) and the biggest limiting current density (4.744 mA cm−2) in ORR process, and also exhibited the lowest onset potential (1.593 V) and the biggest limit current density (15.177 mA cm−2) in OER process. Furthermore, aluminum–air battery assembled with 40% Co–MnO2/C demonstrated excellent reversible charge and discharge performance, which had an average discharge voltage of 1.5 V and an average charge voltage of 2 V during 30 cycles at a limited battery capacity of 375 mAh g−1. Our results reveal the possibility of designing a rechargeable aluminum-air battery working at ambient conditions based on the Co–MnO2/C air cathode catalyst for the first time. Our work opens up a new way to achieve the rechargeability of aluminum-air batteries, and our highly active electrocatalytic materials can be used in a wider range of electrochemical energy applications.