Biomimetic Superoxide Disproportionation Catalyst for Anti-Aging Lithium-Oxygen Batteries.

Reactive oxygen species or superoxide (O2-), which damages or ages biological cells, is generated during metabolic pathways using oxygen as an electron acceptor in biological systems. Superoxide dismutase (SOD) protects cells from superoxide-triggered apoptosis by converting superoxide to oxygen and peroxide. Lithium-oxygen battery (LOB) cells have the same aging problems caused by superoxide-triggered side reactions. We transplanted the function of SOD of biological systems into LOB cells. Malonic acid-decorated fullerene (MA-C60) was used as a superoxide disproportionation chemocatalyst mimicking the function of SOD. As expected, MA-C60 as the superoxide scavenger improved capacity retention along charge/discharge cycles successfully. A LOB cell that failed to provide a meaningful capacity just after several cycles at high current (0.5 mA cm-2) with 0.5 mAh cm-2 cutoff survived up to 50 cycles after MA-C60 was introduced to the electrolyte. Moreover, the SOD-mimetic catalyst increased capacity, e.g., more than a 6-fold increase at 0.2 mA cm-2. The experimentally observed toroidal morphology of the final discharge product of oxygen reduction (Li2O2) and density functional theory calculation confirmed that the solution mechanism of Li2O2 formation, more beneficial than the surface mechanism from the capacity-gain standpoint, was preferred in the presence of MA-C60.

Antioxidative Lithium Reservoir Based on Interstitial Channels of Carbon Nanotube Bundles.

Lithium (Li) metal has garnered considerable attention in next-generation battery anodes. However, its environmental vulnerability, along with the electrochemical instability and safety failures, poses a formidable challenge to commercial use. Here, we describe a new class of antioxidative Li reservoir based on interstitial channels of single-walled carbon nanotube (SWCNT) bundles. The Li preferentially confined in the interstitial channels exhibits unusual thermodynamic stability and exceptional capacity even after exposure to harsh environmental conditions, thereby enabling us to propose a new lithiation/delithiation mechanism in carbon nanotubes. To explore practical application of this approach, the Li confined in the SWCNT bundles is electrochemically extracted and subsequently plated on a copper foil. The resulting Li-plated copper foil shows reliable charge/discharge behavior comparable to those of pristine Li foils. Benefiting from the confinement effect of the interstitial channels, the SWCNT bundles hold great promise as an environmentally tolerant, high-capacity Li reservoir.

Coffee-Driven Green Activation of Cellulose and Its Use for All-Paper Flexible Supercapacitors.

Cellulose, which is one of the most-abundant and -renewable natural resources, has been extensively explored as an alternative substance for electrode materials such as activated carbons. Here, we demonstrate a new class of coffee-mediated green activation of cellulose as a new environmentally benign chemical-activation strategy and its potential use for all-paper flexible supercapacitors. A piece of paper towel is soaked in espresso coffee (acting as a natural activating agent) and then pyrolyzed to yield paper-derived activated carbons (denoted as "EK-ACs"). Potassium ions (K+), a core ingredient of espresso, play a viable role in facilitating pyrolysis kinetics and also in achieving a well-developed microporous structure in the EK-ACs. As a result, the EK-ACs show significant improvement in specific capacitance (131 F g-1 at a scan rate of 1.0 mV s-1) over control ACs (64 F g-1) obtained from the carbonization of a pristine paper towel. All-paper flexible supercapacitors are fabricated by assembling EK-ACs/carbon nanotube mixture-embedded paper towels (as electrodes), poly(vinyl alcohol)/KOH mixture-impregnated paper towels (as electrolytes), and polydimethylsiloxane-infiltrated paper towels (as packaging substances). The introduction of the EK-ACs (as an electrode material) and the paper towel (as a deformable and compliant substrate) enables the resulting all-paper supercapacitor to provide reliable and sustainable cell performance as well as exceptional mechanical flexibility. Notably, no appreciable loss in the cell capacitance is observed after repeated bending (over 5000 cycles) or multiple folding. The coffee-mediated green activation of cellulose and the resultant all-paper flexible supercapacitors open new material and system opportunities for eco-friendly high-performance flexible power sources.

COF-Net on CNT-Net as a Molecularly Designed, Hierarchical Porous Chemical Trap for Polysulfides in Lithium-Sulfur Batteries.

The hierarchical porous structure has garnered considerable attention as a multiscale engineering strategy to bring unforeseen synergistic effects in a vast variety of functional materials. Here, we demonstrate a "microporous covalent organic framework (COF) net on mesoporous carbon nanotube (CNT) net" hybrid architecture as a new class of molecularly designed, hierarchical porous chemical trap for lithium polysulfides (Li2Sx) in Li-S batteries. As a proof of concept for the hybrid architecture, self-standing COF-net on CNT-net interlayers (called "NN interlayers") are fabricated through CNT-templated in situ COF synthesis and then inserted between sulfur cathodes and separators. Two COFs with different micropore sizes (COF-1 (0.7 nm) and COF-5 (2.7 nm)) are chosen as model systems. The effects of the pore size and (boron-mediated) chemical affinity of microporous COF nets on Li2Sx adsorption phenomena are theoretically investigated through density functional theory calculations. Benefiting from the chemical/structural uniqueness, the NN interlayers effectively capture Li2Sx without impairing their ion/electron conduction. Notably, the COF-1 NN interlayer, driven by the well-designed microporous structure, allows for the selective deposition/dissolution (i.e., facile solid-liquid conversion) of electrically inert Li2S. As a consequence, the COF-1 NN interlayer provides a significant improvement in the electrochemical performance of Li-S cells (capacity retention after 300 cycles (at charge/discharge rate = 2.0 C/2.0 C) = 84% versus 15% for a control cell with no interlayer) that lies far beyond those accessible with conventional Li-S technologies.

Graphene oxide and laponite composite films with high oxygen-barrier properties.

The design and fabrication of oxygen barrier films is important for both fundamental and industrial applications. We prepared three different thin films composed of graphene oxide (GO) and laponite (LN), a typical low cost inorganic clay, with the GO/LN volume ratios of 1.9/0.1, 1.7/0.3 and 1.5/0.5 together with a double layer film of the GO and LN. We found that the films with GO/LN = 1.9/0.1 and the double layers exhibited high oxygen barrier and oxygen transmission rate values that reached 0.55 and 0.37 cm(3) per m(2) per atm per day, respectively, which were much lower than those of the films prepared from the pure GO, only LN and GO/LN = 1.7/0.3 and 1.5/0.5. This study is important for the design and fabrication of a film from GO-based all inorganic nanomaterials for applications in gas-barrier membranes.

Molecular recognition at the nanoscale interface within carbon nanotube bundles.

Molecular adsorption onto carbon nanotube surfaces is one of the important topics in the science and technology of carbon nanotubes due to their specific 1D structures with very high aspect ratios. In order to reveal the effect of bundles of single-walled carbon nanotubes (SWNTs) on molecular adsorption at the molecular level, we introduce an HPLC system; namely, we fabricated HPLC columns coated with bundled-SWNTs, isolated-SWNTs or graphene as the stationary HPLC phase, and discovered that polycyclic aromatic hydrocarbons having a one-dimensional shape, such as p-terphenyl and anthracene, exhibit an unusually high affinity to the bundled SWNTs compared to that of the isolated SWNTs. In contrast, no such notable specificity was obtained on a graphene-coated HPLC column. These results indicated that grooves with one-dimensional structures formed by the SWNT-bundles provide a favorable spatial geometry for the specific molecular recognition of aromatic hydrocarbons.

Evaluation of affinity of molecules for carbon nanotubes.

Recent developments of non-covalent functionalization of carbon nanotubes (CNTs) require a systematic understanding of the interaction between molecule and CNTs (CNT-molecular interaction); however, it has been difficult to evaluate the "net" interaction between the CNTs and molecules. We now use silica gel particles coated with the pristine single-walled carbon nanotubes (SWNTs) in a monolayer fashion as the stationary phase of a HPLC column. The newly developed column (SWNT-column) worked as a powerful tool for ranking the interactions between the SWNTs and molecules with a high precision. We describe the binding affinity analysis of polyaromatic hydrocarbons onto the surfaces of SWNTs. The obtained ranking is determined in the order of benzene < naphthalene < biphenyl < fluorene < phenanthrene < anthracene ∼ pyrene < triphenylene < p-terphenyl < tetraphene < tetracene.