Flexible and Adaptable Fuel Cell Pack with High Energy Density Realized by a Bifunctional Catalyst

Mangrove Root-Inspired Carbon Nanotube Film for Micro-Direct Methanol Fuel Cells

The functional microporous layer, acting as a mass-transfer control medium with a rational structure and surface morphology as well as high electrical conductivity, significantly affects the performance of micro-direct methanol fuel cells (μDMFCs). Bioinspired by the architecture and multi-functional properties of mangrove roots, this study develops a simple and versatile strategy based on magnetron sputtering and chemical vapor deposition to fabricate a mangrove root-inspired carbon nanotube film (MR-CNTF) as the functional interface in μDMFCs. It has features such as ultralightweight, high porosity, and good electrical conductivity. During the synthesis process, an apex-growth model of CNTF is identified. The results indicate that the MR-CNTF used as a cathodic microporous layer can remarkably facilitate the oxygen transport and water management. Because of its multi-functional structure and excellent material characteristics, the passive μDMFC displays a peak power density of 14.9 mW cm^-2 at 68 mA cm^-2. This value is 88.6% higher than the highest power density of the one based on a carbon nanotube array (7.9 mW cm^-2) and 45% higher than that of the conventional carbon black (10.7 mW cm^-2). We believe that this novel material with its multi-functional structure illuminates a promising application for fuel cells and other energy storage and conversion devices.

Low-Temperature Methanol-Water Reforming Over Alcohol Dehydrogenase and Immobilized Ruthenium Complex

Hydrogen is one of the most promising sustainable energy carriers for its high gravimetric energy density and abundance. Nowadays, hydrogen production and storage are the main constraints for its commercialization. As a current research focus, hydrogen production from methanol-water reforming, especially at low temperature, is particularly important. In this study, a novel reaction path for low-temperature methanol reforming through synergistic catalysis was developed. Alcohol dehydrogenase (ADH) and coenzyme I (nicotinamide adenine dinucleotide, NAD⁺ ) were employed for methanol catalytic dehydrogenation at low temperature, which could generate formaldehyde and reductive coenzyme I (NADH). Covalent triazine framework-immobilized ruthenium complex (Ru-CTF) was prepared afterwards. On one hand, the catalyst exhibited high activity for the formaldehyde-water shift reaction to generate hydrogen and carbon dioxide. On the other hand, the NADH dehydrogenation was also catalyzed by the Ru-CTF, producing NAD⁺ and hydrogen. Additionally, the catalyst also showed high biocompatibility with ADH. Through the synergistic effect of the above two main processes, methanol could be converted into hydrogen and carbon dioxide stably at low temperature for more than 96 h. The hydrogen production rate was dependent on the pH of the reaction solution as well as the ADH dosage. A hydrogen production rate of 157 mmol h^-1  mol^-1 _Ru was achieved at the optimum pH (8.1). Additionally, the hydrogen production rate increased linearly with the ADH dosage, reaching 578 mmol h^-1  mol^-1 _Ru when the ADH dosage was 180 U at 35 °C. This research could not only help overcome the difficulties for methanol reforming near room temperature but also give new inspiration for designing new reaction pathways for methanol reforming.

Hydrogel Ionic Diodes toward Harvesting Ultralow-Frequency Mechanical Energy

Energy harvesting from human motion is regarded as a promising protocol for powering portable electronics, biomedical devices, and smart objects of the Internet of things. However, state-of-the-art mechanical-energy-harvesting devices generally operate at frequencies (>10 Hz) well beyond human activity frequencies. Here, a hydrogel ionic diode formed by the layered structures of anionic and cationic ionomers in hydrogels is presented. As confirmed by finite element analysis, the underlying mechanism of the hydrogel ionic diode involves the formation of the depletion region by mobile cations and anions and the subsequent increase of the built-in potential across the depletion region in response to mechanical pressure. Owing to the enhanced ionic rectification ratio by the embedded carbon nanotube and silver nanowire electrodes, the hydrogel ionic diode exhibits a power density of ≈5 mW cm^-2 and a charge density of ≈4 mC cm^-2 at 0.01 Hz, outperforming the current energy-harvesting devices by several orders of magnitude. The applications of the self-powered hydrogel ionic diode to tactile sensing, pressure imaging, and touchpads are demonstrated, with sensing limitation is as low as 0.01 kPa. This work is expected to open up new opportunities for ionic-current-based ionotronics in electronics and energy devices.

Anisotropic cellulose nanofiber/chitosan aerogel with thermal management and oil absorption properties

Attributed to low cost, renewable, and high availability, cellulose-based aerogels are desirable materials for various applications. However, mechanical robustness and functionalization remain huge challenges. Herein, we synthesized a recoverable, anisotropic cellulose nanofiber (CNF) / chitosan (CS) aerogel via directional freeze casting and chemical cross-link process. The chitosan was performed as strength polymers to prohibits the shrinkage and retains the structural stability of 3D cellulose nanofiber skeleton, endowing the composite aerogel with satisfactory deformation recovery ability (without loss under 60 % stress cycled 100 times). The CNF/CS composite aerogel has ultralow density (∼8.4 mg/cm³), high temperature-invariant (above 300 °C) and high porosity (98 %). The CNF/CS aerogel demonstrates anisotropic thermal insulation properties with low thermal conductivity (28 mWm^-1 K^-1 in rational direction and 36 mW m^-1 K^-1 in the axial direction). Moreover, the composite aerogel (water contact angle ∼148°) exhibited outstanding oil/water selectivity and high absorption capacity (82-253 g/g) for various oils and organic solvents. Therefore, the multifunctional CNF/CS composite aerogels are potential materials for thermal management and oil absorption applications.

Soft Materials for Wearable/Flexible Electrochemical Energy Conversion, Storage, and Biosensor Devices

Next-generation wearable technology needs portable flexible energy storage, conversion, and biosensor devices that can be worn on soft and curved surfaces. The conformal integration of these devices requires the use of soft, flexible, light materials, and substrates with similar mechanical properties as well as high performances. In this review, we have collected and discussed the remarkable research contributions of recent years, focusing the attention on the development and arrangement of soft and flexible materials (electrodes, electrolytes, substrates) that allowed traditional power sources and sensors to become viable and compatible with wearable electronics, preserving or improving their conventional performances.