Sun-Hwa Yeon

Effect of pore size on carbon dioxide sorption by carbide derived carbon

CO2 sorption at atmospheric and sub-atmospheric pressures is a key step towards carbon capture and sequestration (CCS) and materials capable of fast and efficient CO2 uptake are currently being studied extensively. Carbide-derived carbons (CDCs) show a very high sorption capacity for CO2 of up to 7.1 mol/kg at 0 °C and ambient pressure. This value is significantly higher than other carbon materials. Systematic experimental investigation of a large number of different CDCs derived from nano- and micrometer sized precursors with and without activation show a linear correlation between the CO2 uptake at a certain pressure and the pore volume. However, CO2 sorption is not limited by the total pore volume but only by pores smaller than a certain diameter. At 1 bar, pores smaller than 0.8 nm contribute the most to the CO2 uptake and at 0.1 bar pores smaller or equal to 0.5 nm are preferred. With lower total pressure, smaller pores contribute more to the measured amount of adsorbed CO2. The prediction of the CO2 uptake based on the pore volume for pores of a certain diameter is much more accurate than predictions based on the mean pore size or the specific surface area. This study provides guidelines for the design of materials with an improved ability to remove carbon dioxide from the environment at atmospheric and lower pressures.

Mesoporous carbide-derived carbon for cytokine removal from blood plasma

Porous carbons can be used for purification of bio-fluids due to their excellent biocompatibility with blood. Since the ability to adsorb a range of inflammatory cytokines within the shortest possible time is crucial to stop the progression of sepsis, the improvement of the adsorption rate is a key factor to achieving efficient removal of cytokines. Here, we demonstrate the effect of synthesis temperatures (from 600 degrees C to 1200 degrees C), carbon particle sizes (from below 35 microm to 300 microm), and annealing conditions (Ar, NH(3), H(2), Cl(2), and vacuum annealing) that determine the surface chemistry, on the ability of carbide-derived carbons (CDCs) to remove cytokines TNF-alpha, IL-6, and IL-1 beta from blood plasma. Optimization of CDC processing and structure leads to up to two orders of magnitude increase in the adsorption rate. Mesoporous CDCs that were produced at 800 degrees C from Ti(2)AlC with the precursor particle size of <35 microm and annealed in NH(3), displayed complete removal of large molecules of TNF-alpha in less than an hour, with >85% and >95% TNF-alpha removal in 5 and 30 min, respectively. This is a very significant improvement compared to the previously published results for CDC (90% TNF-alpha removal after 1h) and activated carbons. Smaller interleukin IL-6 and IL-1 beta molecules can be completely removed within 5 min. These differences in adsorption rates show that carbons with controlled porosity can also be used for separation of protein molecules.

Hierarchical porous carbide-derived carbons for the removal of cytokines from blood plasma.

Series of silicon carbonitride ceramics are utilized to obtain hierarchically porous carbide-derived carbons (CDCs) for cytokine removal. The removal rate of TNF-α and IL-6, as two examples of pro- and anti-inflammatory cytokines, is proportional to the surface area of pores larger than the size of the protein molecule

Preparation of a Reduced Graphene Oxide Wrapped Lithium-Rich Cathode Material by Self-Assembly

A lithium-rich cathode material wrapped in sheets of reduced graphene oxide (RGO) and functionalized with polydiallyldimethylammonium chloride (PDDA) was prepared by self-assembly induced from the electrostatic interaction between PDDA-RGO and the Li-rich cathode material. At current densities of 1000 and 2000u2005mAu2009g(-1), the PDDA-RGO sheet wrapped samples demonstrated increased discharge capacities, increasing from 125 to 155u2005mAu2009hu2009g(-1) and from 82 to 124u2005mAu2009hu2009g(-1), respectively. The decreased resistance implied by this result was confirmed from electrochemical impedance spectroscopy results, wherein the charge-transfer resistance of the pristine sample decreased after wrapping with the PDDA-RGO sheets. The PDDA-RGO sheets served as a protective layer sand as a conductive material, which resulted in an improvement in the retention capacity from 56 to 81% after 90u2005cycles.

Beyond Slurry-Cast Supercapacitor Electrodes: PAN/MWNT Heteromat-Mediated Ultrahigh Capacitance Electrode Sheets

Supercapacitors (SCs) have garnered considerable attention as an appealing power source for forthcoming smart energy era. An ultimate challenge facing the SCs is the acquisition of higher energy density without impairing their other electrochemical properties. Herein, we demonstrate a new class of polyacrylonitrile (PAN)/multi-walled carbon tube (MWNT) heteromat-mediated ultrahigh capacitance electrode sheets as an unusual electrode architecture strategy to address the aforementioned issue. Vanadium pentoxide (V2O5) is chosen as a model electrode material to explore the feasibility of the suggested concept. The heteromat V2O5 electrode sheets are produced through one-pot fabrication based on concurrent electrospraying (for V2O5 precursor/MWNT) and electrospinning (for PAN nanofiber) followed by calcination, leading to compact packing of V2O5 materials in intimate contact with MWNTs and PAN nanofibers. As a consequence, the heteromat V2O5 electrode sheets offer three-dimensionally bicontinuous electron (arising from MWNT networks)/ion (from spatially reticulated interstitial voids to be filled with liquid electrolytes) conduction pathways, thereby facilitating redox reaction kinetics of V2O5 materials. In addition, elimination of heavy metallic foil current collectors, in combination with the dense packing of V2O5 materials, significantly increases (electrode sheet-based) specific capacitances far beyond those accessible with conventional slurry-cast electrodes.

Molecularly designed, dual-doped mesoporous carbon/SWCNT nanoshields for lithium battery electrode materials

Formidable challenges facing lithium-ion rechargeable batteries, which involve performance degradations and safety failures during charge/discharge cycling, mostly arise from electrode–electrolyte interface instability. Here, as a polymeric ionic liquid (PIL)-mediated interfacial control strategy to address this long-standing issue, we demonstrate a new class of molecularly designed, ion/electron-conductive nanoshields based on single-walled carbon nanotube (SWCNT)-embedded, dual-doped mesoporous carbon (referred to as “SMC”) shells for electrode materials. The SMC shell is formed on cathode materials through solution deposition of the SWCNT/PIL mixture and subsequent carbonization. The PIL (denoted as “PVIm[DS]”) synthesized in this study consists of poly(1-vinyl-3-ethylimidazolium) cations and dodecyl sulfate counter anions, whose molecular structures are rationally designed to achieve the following multiple functions: (i) precursor for the conformal/continuous nanothickness carbon shell, (ii) dual (N and S)-doping source, (iii) porogen for the mesoporous structure, and (iv) SWCNT dispersant. Driven by such chemical/structural uniqueness, the SMC shell prevents direct exposure of cathode materials to bulk liquid electrolytes while facilitating redox reaction kinetics. As a consequence, the SMC-coated cathode materials enable significant improvements in cell performance and also thermal stability. We envision that the SMC shell can be suggested as a new concept of effective and versatile surface modification strategy for next-generation high-performance electrode materials.

One-pot surface engineering of battery electrode materials with metallic SWCNT-enriched, ivy-like conductive nanonets

A longstanding challenge facing energy conversion/storage materials is their low electrical conductivity, which often results in unwanted sluggish electrochemical reactions. Here, we demonstrate a new class of one-pot surface engineering strategy based on metallic single-walled carbon nanotube (mSWCNT)-enriched, ivy-like conductive nanonets (mSC nanonets). The mSC nanonets are formed on the surface of electrode materials through a poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO)-assisted sonication/filtration process. PFO is known as a dispersant for SWCNTs that shows a higher affinity for semiconducting SWCNTs (sSWCNTs) than for mSWCNTs. Driven by this preferential affinity of PFO, sSWCNTs are separated from mSWCNTs in the form of sSWCNT/PFO hybrids, and the resulting enriched mSWCNTs are uniformly deposited on electrode materials in the form of ivy-like nanonets. Various electrode materials, including lithium-ion battery cathodes/anodes and perovskite catalysts, are chosen to explore the feasibility of the proposed concept. Due to their ivy-like conductive network, the mSC nanonets increase the electronic conductivity of the electrode materials without hindering their ionic transport, eventually enabling significant improvements in their redox reaction rates, charge/discharge cyclability, and bifunctional electrocatalytic activities. These exceptional physicochemical advantages of the mSC nanonets, in conjunction with the simplicity/versatility of the one-pot surface engineering process, offer a new and facile route to develop advanced electrode materials with faster electrochemical reaction kinetics.