Ammonia Borane Promoted Synthesis of Graphene Aerogels as High Efficient Dye Adsorbent.

Graphene aerogels (GA) hold great promise as a practical adsorbent to remove contaminants from water thanks to their high specific surface area and stable chemical properties. In this work, we demonstrated a strategy by introducing ferrous ions-ammonia borane as a synergistic reducing agent for hydrothermal reduction of graphene oxide to synthesize high-performance graphene aerogel adsorbents. Reducing agent system features four aspects: (1) Ferrous ions themselves as reducing agent, (2) Ferrous ions as catalyst for ammonia borane decomposition to release hydrogen, (3) Released hydrogen as a secondary reducing agent, (4) Involved hydrogen gas bubbles facilitating the formation of pores in GA. As-synthesized GAs exhibited larger specific surface area and smaller pore diameter than only using ferrous ions as reducing agent, which benefit a lot to the adsorption and water cleaning. Adsorption experiments showed that as-synthesized GAs was high efficient in the adsorption of both cationic dye (Rhodamine B) and anionic dye (Orange G) with adsorption capacity as high as 103.6 mg·g-1 and 87.4 mg ·g-1, respectively, which is comparable to the most of state-of-the-art sorbents. The adsorption rate was greatly improved. Besides, the great adsorption performance was not limited to a certain kind of dye which is different from that of most dye adsorbents. Furthermore, kinetic investigations showed the adsorption followed a pseudo-second-order kinetics model, indicating a chemical adsorption. The adsorption isothermal studies revealed that the adsorption process was more likely took place in a monolayer manner. Thanks to the facile synthesis and excellent adsorption performance, the as-prepared GAs can be potentially applied to the practical water treatment.

Gas-Permeable, Ultrathin, Stretchable Epidermal Electronics with Porous Electrodes.

We present gas-permeable, ultrathin, and stretchable electrodes enabled by self-assembled porous substrates and conductive nanostructures. An efficient and scalable breath figure method is employed to introduce the porous skeleton, and then silver nanowires (AgNWs) are dip-coated and heat-pressed to offer electric conductivity. The resulting film has a transmittance of 61%, sheet resistance of 7.3 Ω/sq, and water vapor permeability of 23 mg cm-2 h-1. With AgNWs embedded below the surface of the polymer, the electrode exhibits excellent stability in the presence of sweat and after long-term wear. We demonstrate the promising potential of the electrode for wearable electronics in two representative applications: skin-mountable biopotential sensing for healthcare and textile-integrated touch sensing for human-machine interfaces. The electrode can form conformal contact with human skin, leading to low skin-electrode impedance and high-quality biopotential signals. In addition, the textile electrode can be used in a self-capacitance wireless touch sensing system.

Sulfur in Mesoporous Tungsten Nitride Foam Blocks: A Rational Lithium Polysulfide Confinement Experimental Design Strategy Augmented by Theoretical Predictions.

To enhance the utilization of sulfur in lithium-sulfur batteries, three-dimensional tungsten nitride (WN) mesoporous foam blocks are designed to spatially localize the soluble Li2S6 and Li2S4 within the pore spaces. Meanwhile, the chemisorption behaviors of polysulfides and the capability of WN as an effective confiner are systematically investigated through density functional theory calculations and experimental studies. The theoretical calculations reveal a decrease in chemisorption strength between WN and the soluble polysulfides (Li2S8 > Li2S6 > Li2S4), while the interactions between WN and the insoluble Li2S2/Li2S show a high chemisorption strength of ca. 3 eV. Validating theoretical insights through electrochemical measurements further manifest that the assembled battery configurations with sulfur cathode confined in the thickest WN blocks exhibit the best rate capabilities (1090 and 510 mAh g-1 at 0.5C and 5C, respectively) with the highest initial Coulombic efficiency of 90.5%. Moreover, a reversible capacity of 358 mAh g-1 is maintained with a high Coulombic efficiency approaching to 100%, even after 500 cycles at 2C. As guided by in silico design, this work not only provides an effective strategy to improve the retentivity of polysulfides but also underpins that properly architectured WN can be effective retainers of polysulfides.

Bendable Network Built with Ultralong Silica Nanowires as a Stable Separator for High-Safety and High-Power Lithium-Metal Batteries.

Separators are key safety components for electrochemical energy storage systems. However, the intrinsic poor wettability with electrolyte and low thermal stability of commercial polyolefin separators cannot meet the requirements of the ever-expanding market for high-power, high-energy, and high-safety power systems, such as lithium-metal, lithium-sulfur, and lithium-ion batteries. In this study, scalable bendable networks built with ultralong silica nanowires (SNs) are developed as stable separators for both high-safety and high-power lithium-metal batteries. The three-dimensional porous nature (porosity of 73%) and the polar surface of the obtained SNs separators endue a much better electrolyte wettability, larger electrolyte uptake ratio (325%), higher electrolyte retention ratio (63%), and ∼7 times higher ionic conductivity than that of commercial polypropylene (PP) separators. Moreover, the pore-rich structure of the SNs separator can aid in evenly distributing lithium and, in turn, suppress the uncontrollable growth of lithium dendrites to a certain degree. Furthermore, the pure inorganic structure endows the SNs separators with excellent chemical and electrochemical stabilities even at elevated temperatures, as well as excellent thermal stability up to 700 °C. This work underpins the utilization of SNs separators as a rational choice for developing high-performance batteries with a metallic lithium anode.

Facile reduction of graphene oxide at room temperature by ammonia borane via salting out effect.

Nascent hydrogen as a strong reducing and environmentally benign agent can be used as the efficient reductant of graphene oxide. The common method is to dissolve metal in acid graphene oxide (GO) solution to generate nascent hydrogen and reduce graphene oxide. However, hydrophobic metal particles cannot contact well with hydrophilic GO. Lots of nascent hydrogen atoms generated surrounding metal particles would quickly form hydrogen instead of reducing GO, which results in low reduction efficiency. In this work, based on the salting effect of GO, we report a facile approach to synthesize graphene by mild reducing of GO using NH3BH3 as the reducing agent and Co3O4 as the catalyst at room temperature. This method exhibited higher nascent hydrogen reduction efficiency and higher C/O atomic ratio of reduced graphene oxide than using Fe, Zn, and Al among others. Also the reaction is conducted under mild conditions (room temperature), resulting in fewer defects.