High “C” rate Li-S cathodes: sulfur imbibed bimodal porous carbons

It takes two: Ordered dual-mesoporous silica with two sets of well-configured pores can be synthesized by evaporation-induced step-by-step aggregating assembly in which the non-ionic block copolymer PEO-b-PMMA (red spheres) and the cationic surfactant alkyltrimethyl ammonium bromide (yellow rods) serve as co-templates in an acidic THF/H2O solution containing tetraethyl orthosilicate as the silica source (SiO2 oligomers shown as green balls in the picture). Detailed facts of importance to specialist readers are published as "Supporting Information". Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Carbon-sulfur composites as the cathode of rechargeable Li-S batteries have shown outstanding electrochemical performance for high power devices. Here, we report the promising electrochemical charge-discharge properties of a carbon-sulfur composite, in which sulfur is impregnated in porous hollow carbon spheres (PHCSs) via a melt-diffusion method. Instrumental analysis shows that the PHCSs, which were prepared by a facile template strategy, are characterized by high specific surface area (1520 m2·g−1), large pore volume (2.61 cm3·g−1), broad pore size distribution from micropores to mesopores, and high electronic conductivity (2.22 S·cm−1). The carbon-sulfur composite with a sulfur content of 50.2 wt.% displays an initial discharge capacity of 1450 mA·h·g−1 (which is 86.6% of the theoretical specific capacity) and a reversible discharge capacity of 1357 mA·h·g−1 after 50 cycles at 0.05 C charge-discharge rate. At a higher rate of 0.5C, the capacity stabilized at around 800 mA·h·g−1 after 30 cycles. The results illustrate that the porous carbon-sulfur composites with hierarchically porous structure have potential application as the cathode of Li-S batteries because of their effective improvement of the electronic conductivity, the repression of the volume expansion, and the reduction of the shuttling loss.

Core Ideas Soil water retention curves of the paddy soil were bested fitted with bimodal models. Computed‐tomography imaging and retention curves generated similar bimodal pore structure. Combined use of organic and inorganic fertilizers increased structural porosity. Textural porosity was not affected by fertilization treatments. Well‐structured soils are considered to have bimodal pore structure, including textural pores between particles and structural pores between aggregates. Pore structure can be inferred from the soil water retention curve (SWRC) but our understanding of the 3‐D pore geometry that regulates this curve is limited. This study investigated the pore structure of a paddy soil under different fertilization regimes by both SWRC and X‐ray micro‐computed tomography (micro‐CT) imaging with the aim of comparing the two methods. Undisturbed soil aggregates and cores were collected from the surface layer of long‐term unfertilized (CK), inorganically fertilized (NPK), and organically and inorganically fertilized (NPKOM) paddy soils. Aggregates and cores were scanned with micro‐CT and pore structures were analyzed. The SWRCs were measured on the same CT‐scanned cores. Three unimodal models, three bimodal models, and one trimodal model were evaluated for fitting the SWRC and to derive soil pore size distribution (PSD). Results showed the SWRC of the paddy soil were best fitted with the bimodal lognormal (BLN) and double‐exponential (DE) models, with the derived PSD showing distinct bimodality. The micro‐CT images revealed the hierarchy structure of the paddy soil and a bimodal pattern in the PSDs. The structural porosities from BLN, DE models and CT imaging were consistent and correlated with the natural logarithm of saturated hydraulic conductivity. Long‐term application of NPKOM increased structural porosity though no significant differences were recorded in the textural porosity compared with the NPK and CK treatment, while the latter two showed a near identical pore structure. These results demonstrated the benefits of both approaches especially for soil structures with a bimodal pore structure such as the well‐structured paddy soil.

Synergy of macro-meso bimodal pore and Ni-Co alloy for enhanced stability in dry reforming of methane

Constructing tunable bimodal porous structure in ultrahigh molecular weight polyethylene membranes with enhanced water permeance and retained rejection performance

Uniform poly(l‐lactic acid) (PLLA) microbeads with unimodal or bimodal porous structures are fabricated using a simple fluidic device based on a single oil‐in‐water emulsion method, where an alkane (octane, undecane, tridecane, and pentadecane) serves as the porogen. During the solvent evaporation, the alkanes spontaneously undergo a microphase separation, resulting in a highly porous structure. The size and size distribution of the pores in the PLLA microbeads can be easily controlled by changing the alkane type and concentration. When the undecane, tridecane, and pentadecane are used as the porogen at 6 wt%, the PLLA microbeads have the bimodal porous structure with a large hollow pore in the center and many small pores. In vitro and in vivo studies reveal that those PLLA microbeads with the bimodal porous structure readily facilitate the penetration and proliferation of cells and host tissues compared with the other PLLA microbeads. These results indicate that the superior properties of PLLA porous microbeads with a bimodal porous structure are suitable for diverse biomedical applications such as tissue engineering, cell delivery, and plastic surgery.

The success of the rechargeable Li-S cell is limited in part by the dissolution of lithium-polysulfide in the electrolyte. Remarkably, it is found that removal of the conventional membrane separator in a Li-S cell improves sulfur utilization and cycling performance, whether the sulfur is initially contained in the cathode or electrolyte. An optimized cell design yields discharge capacities as high as 980 mA h g-1 after 100 cycles.

Effect of various structure directing agents on the physicochemical properties of the silica aerogels prepared at an ambient pressure

Guard-bed catalyst: Impact of textural properties on catalyst stability and deactivation rate

Macroporous polyacrylamide gels (MPAAG) with iminodiacetic acid (IDA) functionality were prepared by (i) chemical modification of polyacrylamide gel, (ii) co-polymerization of acrylamide with allyl glycidyl ether (AGE) and N,N'metylene-bis(acrylamide) (MBAAm) followed by coupling IDA ligand or (iii) by copolymerization of acrylamide and MBAAm with functional monomer carrying IDA-functionality (1-(N,N-bis(carboxymethyl)amino-3-allylglycerol). Screening for optimized conditions for the production of the MPAAG with required porous properties was performed in a 96-well chromatographic format that allowed parallel production and analysis of the MPAAG prepared from reaction mixtures with different compositions. Scanning electron microscopy of the fabricated MPAAG revealed two different types of the porous structures: monomodal macroporous structure with large interconnected pores separated by dense non-porous pore walls in case of plain gels or gels produced via copolymerization with AGE. The other type of the MPAAG (gel produced via co-polymerization with functional monomer carrying IDA-functionality) had bimodal pore structure with large interconnected pores separated by the pore walls pierced through with micropores. The effect of different modifications of MPAAG monoliths and of porous structure of the MPAAG (monomodal and bimodal porous structure) on protein binding has been evaluated.

Nerve conduits have been paid attention to as a useful technique for bridging the gap between damaged peripheral nerve stumps. In particular, the development of nerve conduits with a higher porosity and surface area is necessary for providing the conditions needed for nerve tissue regeneration. Here we fabricated poly(lactic-co-glycolic acid)/poly(γ-glutamic acid)/Pluronic 17R4 nerve conduits containing three-dimensional bimodal pore structures using the thermally induced phase separation technique. The dope composition of polymers and separation temperature were found to significantly affect the fabrication of the nerve conduits; the optimum dope composition was found to be 58:19:23 at a concentration of 26 w/v%, and the optimum separation temperature was 40 °C. The results of bioactivity tests demonstrated that PP40 fabricated under the optimum conditions promoted more rapid Schwann cell proliferation than other nerve conduits because of their three-dimensionally interconnected bimodal pore structures, large surface area, and hydrophilicity. Our results suggest that neve conduits with bimodal open pore structures could be used as nerve graft substitutes for nerve regeneration.

The scale transition from discrete pore network model (PNM) simulations to one-equation continuum model (CM) of drying has been investigated in previous studies for uniformly structured porous media. This investigation is extended in the present work to porous media with widely different pore size distributions, as well as to those with spatially correlated networks of small and large pores. The key questions examined here are how and to what extent pore-structural features can be reflected in the local macroscopic parameters of the one-equation CM derived by traditional homogenization. For this purpose, three-dimensional model capillary structures with monomodal and bimodal pore size distributions are generated and drying simulations are conducted at the limit of viscous-capillary dominated regime. By leveraging volume-averaged data obtained from PNM simulations the one-equation CM is parameterized and thus its local parameters are expressed in dependence on the pore structure. The simulation results show that for the monomodal and bimodal pore structures the profiles of the moisture transport coefficients are complex and non-unique over the entire drying process. Moreover, the deviation of the water vapor partial pressure from the saturation vapor pressure in the presence of liquid water – which is referred to as non-local equilibrium effect – is less pronounced for the bimodal pore structure compared to the monomodal pore structures. Finally, comparisons are performed between the volume-averaged data obtained at different stages of drying by the discrete simulations with monomodal and bimodal pore structures and results of the continuum model of drying.

Efficient synthetic approach for nanoporous adsorbents capable of pre- and post-combustion CO2 capture and selective gas separation

The bead type MgO-MgAl2O4 catalyst supports with bimodal pore structures were fabricated via an extrusion molding of gels derived from the precursor mixture of mesoporous MgO particles and aluminum magnesium hydroxide, followed by heat treatment. To investigate the effect of macro pore structures on the catalytic activity of the Ni/MgO-MgAl2O4 catalysts in the steam and carbon dioxide reforming of methane (SCR), two kinds of the catalysts with largely different macro pore volumes and sizes but nearly the same meso pore volume and size were compared. The bimodal catalyst with a large macro pore size and volume exhibited a highly enhanced CO2 conversion from 22.3 to 37.1% but a slightly reduced CH4 conversion from 95.3 to 92.1% at the same feed ratio. The SCR results show that the large macro pores can lead to a highly enhanced mass transfer rate of CO2 absorption into the pore channels of the magnesium alumina spinel.

Graphite/SnSe hybrid-embedded monolithic foams with hierarchical and bimodal pores for high performance solar desalination membranes with spontaneous salt rejection