Biological tissues generally exhibit excellent anisotropic mechanical properties owing to their well-developed microstructures. Inspired by the aligned structure in muscles, a highly anisotropic, strong, and conductive wood hydrogel is developed by fully utilizing the high-tensile strength of natural wood, and the flexibility and high-water content of hydrogels. The wood hydrogel exhibits a high-tensile strength of 36 MPa along the longitudinal direction due to the strong bonding and cross-linking between the aligned cellulose nanofibers (CNFs) in wood and the polyacrylamide (PAM) polymer. The wood hydrogel is 5 times and 500 times stronger than the bacterial cellulose hydrogels (7.2 MPa) and the unmodified PAM hydrogel (0.072 MPa), respectively, representing one of the strongest hydrogels ever reported. Due to the negatively charged aligned CNF, the wood hydrogel is also an excellent nanofluidic conduit with an ionic conductivity of up to 5 × 10 S cm at low concentrations for highly selective ion transport, akin to biological muscle tissue. The work offers a promising strategy to fabricate a wide variety of strong, anisotropic, flexible, and ionically conductive wood-based hydrogels for potential biomaterials and nanofluidic applications.

Aerogels can be used in a broad range of applications such as bioscaffolds, energy storage devices, sensors, pollutant treatment, and thermal insulating materials due to their excellent properties including large surface area, low density, low thermal conductivity, and high porosity. Here we report a facile and effective top-down approach to fabricate an anisotropic wood aerogel directly from natural wood by a simple chemical treatment. The wood aerogel has a layered structure with anisotropic structural properties due to the destruction of cell walls by the removal of lignin and hemicellulose. The layered structure results in the anisotropic wood aerogel having good mechanical compressibility and fragility resistance, demonstrated by a high reversible compression of 60% and stress retention of ∼90% after 10 000 compression cycles. Moreover, the anisotropic structure of the wood aerogel with curved layers stacking layer-by-layer and aligned cellulose nanofibers inside each individual layer enables the wood aerogel to have an anisotropic thermal conductivity with an anisotropy factor of ∼4.3. An extremely low thermal conductivity of 0.028 W/m·K perpendicular to the cellulose alignment direction and a thermal conductivity of 0.12 W/m·K along the cellulose alignment direction can be achieved. The thermal conductivity is not only much lower than that of the natural wood material (by ∼3.6 times) but also lower than most of the commercial thermal insulation materials. The top-down approach is low-cost, scalable, simple, yet effective, representing a promising direction for the fabrication of high-quality aerogel materials.

The global fresh water shortage has driven enormous endeavors in seawater desalination and wastewater purification; among these, solar steam generation is effective in extracting fresh water by efficient utilization of naturally abundant solar energy. For solar steam generation, the primary focus is to design new materials that are biodegradable, sustainable, of low cost, and have high solar steam generation efficiency. Here, we designed a bilayer aerogel structure employing naturally abundant cellulose nanofibrils (CNFs) as basic building blocks to achieve sustainability and biodegradability as well as employing a carbon nanotube (CNT) layer for efficient solar utilization with over 97.5% of light absorbance from 300 to 1200 nm wavelength. The ultralow density (0.0096 g/cm) of the aerogel ensures that minimal material is required, reducing the production cost while at the same time satisfying the water transport and thermal-insulation requirements due to its highly porous structure (99.4% porosity). Owing to its rationally designed structure and thermal-regulation performance, the bilayer CNF-CNT aerogel exhibits a high solar-energy conversion efficiency of 76.3% and 1.11 kg m h at 1 kW m (1 Sun) solar irradiation, comparable or even higher than most of the reported solar steam generation devices. Therefore, the all-nanofiber aerogel presents a new route for designing biodegradable, sustainable, and scalable solar steam generation devices with superb performance.

A direct wood-to-carbon-sponge transformation is realized via a facile chemical treatment and subsequent carbonization process. Removing the lignin and hemicellulose from balsa wood cell walls is a significant step toward converting the lattice-like wood structure to a spring-like lamellar structure. Magic transformation from brittle wood carbon to compressible wood carbon sponge thus becomes achievable. The wood carbon sponge exhibits a sensitive electrical response as a strain sensor and attractive features for other potential applications.

cycling life, and the second results in a large charge-discharge overpotential, and the last impedes the transport of ions (electrolyte) and/or O 2 gas, both of which are essential for an effective electrochemical reaction. In addition, conventional Li-O 2 batteries generally demonstrate limited areal capacity (usually less than 10 mAh cm −2 ) with low active material loading, which limits their potential for practical applications that require high areal capacity and energy density.Tremendous efforts have been dedicated to overcome the electrolyte decomposition and Li 2 O 2 issues. For example, Zhang and Zhou [10] developed an ionic liquid (IL)-based gel electrolyte for Li-O 2 batteries to replace the liquid organic electrolyte widely used in conventional lithium ion batteries. The ILs demonstrate excellent nonvolatility, hydrophobicity, high thermal stability, and broad electrochemical windows, thus ensuring both electrochemical and environmental stability under repeated charging/discharging in ambient conditions. Under similar conditions, several solid-state or hybrid electrolytes have also been developed to prevent the attack of O 2 radicals. [11][12][13] Meanwhile, Huang and co-workers [4] recently proposed a novel strategy to resolve the insulating nature of the Li-O 2 discharge products using solution-based catalysts and redox mediators. However, very limited progress has been made in electrode structure engineering to construct decoupled or triple pathways for the multiphase and more effective transport of electrons, Li + ions, and O 2 gas, [10,14] especially for thick electrode design where these multiphase transports become more difficult.Multiphase transport occurs continuously in trees, with water transporting ions from the roots to the upper trunk and photosynthetic products from the leaves being distributed throughout the organism (Figure 1A). The interconnected passages comprising lumina and vessels (i.e., wood channels) are vital for multiphase transport in trees. Inspired by such an efficient and noncompetitive transport system, we developed a flexible wood (F-Wood)-based current-collector-free cathode directly from natural balsa wood ( Figure 1B). Mechanical flexibility was imparted using a facile chemical treatment to remove lignin and hemicellulose, and subsequent carbon nanotube (CNT) coating was used to generate high electrical conductivity.Trees have an abundant network of channels for the multiphase transport of water, ions, and nutrients. Recent studies have revealed that multiphase transport of ions, oxygen (O 2 ) gas, and electrons also plays a fundamental role in lithium-oxygen (Li-O 2 ) batteries. The similarity in transport behavior of both systems is the inspiration for the development of Li-O 2 batteries from natural wood featuring noncompetitive and continuous individual pathways for ions, O 2 , and electrons. Using a delignification treatment and a subsequent carbon nanotube/Ru nanoparticle coating process, one is able to convert a rigid and electrically insulating wood membrane ...