An Iron-Decorated Carbon Aerogel for Rechargeable Flow and Flexible Zn-Air Batteries.

Mechanically stable and foldable air cathodes with exceptional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities are key components of wearable metal-air batteries. Herein, a directional freeze-casting and annealing approach is reported for the construction of a 3D honeycomb nanostructured, N,P-doped carbon aerogel incorporating in situ grown FeP/Fe2 O3 nanoparticles as the cathode in a flexible Zn-air battery (ZAB). The aqueous rechargeable Zn-air batteries assembled with this carbon aerogel exhibit a remarkable specific capacity of 648 mAh g-1 at a current density of 20 mA cm-2 with a good long-term durability, outperforming those assembled with commercial Pt/C+RuO2 catalyst. Furthermore, such a foldable carbon aerogel with directional channels can serve as a freestanding air cathode for flexible solid-state Zn-air batteries without the use of carbon paper/cloth and additives, giving a specific capacity of 676 mAh g-1 and an energy density of 517 Wh kg-1 at 5 mA cm-2 together with good cycling stability. This work offers a new strategy to design and synthesize highly effective bifunctional air cathodes to be applied in electrochemical energy devices.

Direct Preparation of Cellulose Nanofibers from Bamboo by Nitric Acid and Hydrogen Peroxide Enables Fibrillation via a Cooperative Mechanism.

Separating the fibers, deconstructing both the interlamellar structures and the intermicrofibrils structures in the cell wall, and cleaving the amorphous regions of cellulose (all reached in one bath chemical-assisted treatment), then extracting cellulose nanofibers (CNFs) from biomass, is both challenging and imperative. A simple, cost-effective and green strategy for extracting CNFs from bamboo using nitric acid and hydrogen peroxide (NCHP), to enable fibrillation via a cooperative mechanism, is demonstrated herein. NCHP-CNFs 13.1 ± 2.0 nm wide, with a high aspect ratio, 74% crystallinity, excellent UV resistance and high thermal stability, were successfully extracted by treatment in HNO3 aqueous solution, at a concentration of 3.2 mol/L, and treatment with 60.00 mmol/g H2O2 at 50 °C for 48 h. The yields of NCHP-CNFs reached 73% and 99% based on biomass and cellulose, respectively, due to the high delignification selectivity of OH+ and the mild aqueous conditions during the NCHP treatment. These NCHP-CNFs with excellent UV resistance can potentially be applied in the field of UV-resistant coatings, to replace organic and inorganic materials.

Superelastic Carbon Aerogel with Ultrahigh and Wide-Range Linear Sensitivity.

Compressible and elastic carbon materials offer many advantages and have promising applications in various electronic devices. However, fabricating carbon materials with super elasticity, fatigue resistance, and high and wide-range linear sensitivity for pressure or strain remains a great challenge. Herein, a facile and sustainable route is developed to fabricate a carbon aerogel with not only superior mechanical performances but also exceptionally high and wide-range linear sensitivity by using chitosan as a renewable carbon source and cellulose nanocrystal as a nanoreinforcement or support. The as-prepared carbon aerogel with wave-shaped layers shows high compressibility, super elasticity, stable strain-current response, and excellent fatigue resistance (94% height retention after 50 000 cycles). More importantly, it demonstrates both an ultrahigh sensitivity of 103.5 kPa-1 and a very wide linear range of 0-18 kPa. In addition, the carbon aerogel has a very low detection limit (1.0 Pa for pressure and 0.05% for strain). The carbon aerogel also can be bended to detect a small angle change. These superiorities render its applications in various wearable devices.