Sodium borohydride (NaBH4) has been proposed as a potential hydrogen storage material for fuel cells, and the development of highly active and robust catalysts for hydrolyzing NaBH4 is the key for the practical usage of NaBH4 for fuel cells. Herein we report Co-nanocrystal assembled hollow nanoparticles (Co-HNP) as an active and robust catalyst for the hydrolysis of NaBH4. A hydrogen generation rate of 10.8 L·min–1·g–1 at 25 °C was achieved by using the Co-HNP catalyst with a low activation energy of 23.7 kJ·mol–1, which is among the best performance of reported noble and non-noble catalysts for hydrolyzing NaBH4. Co-HNP also showed good stability in the long term cycling tests. The mechanism of the catalytic hydrolysis of NaBH4 on Co-HNP was studied by using 1H and 11B solid-state NMR, which provided unambiguous experimental evidence of the Co–H formation. The systematically designed NMR experiments unveiled the key role of Co-HNP in the activation of borohydride and the subsequent transfer of H– to water for generating H2 gas and helped to distinguish various hypotheses proposed for catalytic H2 generation reactions. The porous hollow nanostructure of the Co-HNP catalyst provides large surface area and facilitates mass transfer. The facile preparation and outstanding performance of Co-HNP enables it as a very competitive catalyst for hydrogen production.

We report that a postsynthesis physical process (freeze–thaw cycles) can reform the microstructure of conductive polymer hydrogels from clustered nanoparticles to interconnected nanosheets, leading to enhanced mechanical and electrochemical properties. The polyaniline–poly(vinyl alcohol) hydrogel after five freeze–thaw cycles (PPH-5) showed remarkable tensile strength (16.3 MPa), large elongation at break (407%), and high electrochemical capacitance (1053 F·g–1). The flexible supercapacitor based on PPH-5 provided a large capacitance (420 mF·cm–2 and 210 F·g–1) and high energy density (18.7 W·h·kg–1), whose robustness was demonstrated by its 100% capacitance retention after 1000 galvanostatic charge–discharge cycles or after 1000 mechanical folding cycles. The outstanding performance enables PPH-5 based supercapacitor as a promising power device for flexible electronics, which also demonstrates the merit of freeze–thaw cycles for enhancing the performance of functional hydrogels.Keywords: conducting polymers hydrogels; flexible supercapacitors; freeze−thaw cycles; polyaniline; supramolecular self-assembly;

Inspired by the dynamic network structure of animal dermis, we have designed and synthesized a series of polyol-polypyrrole (polyol-PPy) composites. Polyols and polypyrrole are cross-linked by hydrogen bonding and electrostatic interactions to form a dynamic network, which helps to dissipate destructive energy. We have found a clear correlation between the mechanical properties of polyol-PPy composites and the polyols structure. Particularly, the PEE-PPy film shows both high strength and flexibility, leading to a remarkable tensile toughness comparable to cocoon silk. The combination of outstanding strength, ductility, and conductivity enables polyol-PPy composites (especially PEE-PPy) as potential electronic materials for making flexible electronics.Keywords: bioinspired materials; conducting polymers; flexible electronics; polypyrrole; tough polymers;

Herein we report a simple electrochemical approach to synthesize cobalt-based nanosheet arrays as efficient and robust electrocatalysts for overall water splitting in alkaline electrolytes. The Co nanosheet array and CoFeBO nanosheet array are electrochemically deposited on Ni foam electrodes, which are able to drive a large current density at low overpotentials, and offer stable operation under heavy-loading conditions over an extended period, exceeding the performance of Pt/C and IrO2. To the best of our knowledge, the CoFeBO NS‖Co NS couple is currently the most active and stable non-noble electrocatalyst pair for overall water splitting in alkaline electrolytes. In addition, the facile synthesis method is suitable for designing and screening highly active and stable electrocatalysts with micro- and nano-structures.

Herein we report the fabrication of a moisture-driven actuator by incorporating superparamagnetic nanoparticles into a water-responsive polypyrrole film. Under the direction of a magnetic field, the actuator can harvest energy from moisture and quickly transport cargo that is 5-times heavier than itself to the destination, serving as a powerful mini-tractor.

An efficient method to deliver active proteins into cytosol is highly desirable to advance protein-based therapeutics. Arginine-rich cell-penetrating peptides (RPPs) have been intensively studied for intracellular protein delivery, and their applications require further improvement on delivery efficiency, serum stability, and cytotoxicity. Designing synthetic analogs of RPPs provides an alternative way to achieve efficient cytosolic protein delivery. Herein we report the design and synthesis of a dendritic small molecule TG6, which is composed of one rigid planar core and four flexible arms with one guanidinium on each arm. Protein structure and function are well preserved in the TG6–protein conjugates, which are readily internalized into cytosol. Our study demonstrates that TG6 is a serum-stable and low-toxic molecular transporter delivering both small cargoes and large active proteins efficiently into cytosol.Keywords: cell penetrating peptides; cytosolic delivery; guanidinium; protein delivery; structure design

•A self-sustaining water vapor-driven pyroelectric nanogenerator (PNG) is achieved.•The large-area flexible PNG is readily made of commercial available components.•Fast temperature oscillation is achieved by water condensation and evaporation.•The powerful PNG can drive a low-power electronic device to work continuously.Energy harvesting via pyroelectric nanogenerators (PNGs) is emerging as an attractive way to utilize waste heat. However, most of current PNGs need mechanical or electrical alternating devices to achieve the fast temperature oscillation, which is the key for PNGs to work. Herein we report a self-sustaining polymeric PNG driven by water vapor, without any energy-consuming alternating devices. Due to the high latent heat of water vapor, a fast temperature oscillation up to 23 °C/s was achieved by automatic water condensation and evaporation on the surface of the PNG. Thus, the PNG based on commercial polyvinylidene difluoride polymer was able to output an open-circuit voltage of 145 V and a short-circuit current of 0.12 μA/cm2. The peak power density was 1.47 mW/cm3 by volume and 4.12 μW/cm2 by area, which is comparable to previously reported PNGs relying on alternating devices. Our PNG could provide uninterrupted electricity to drive a low-power electronic device (such as a digital watch) to work continuously. The electricity could also be stored in a capacitor for high-power tasks, such as flashing multiple blue LED lights once per minute. The self-sustaining PNG driven by water vapor provides a new strategy for efficiently recovering energy from hot water vapor that are wasted in industry and in our daily life.

Herein we report the fabrication of a moisture-driven actuator by incorporating superparamagnetic nanoparticles into a water-responsive polypyrrole film. Under the direction of a magnetic field, the actuator can harvest energy from moisture and quickly transport cargo that is 5-times heavier than itself to the destination, serving as a powerful mini-tractor.