Zifeng Wang

A self-healable and highly stretchable supercapacitor based on a dual crosslinked polyelectrolyte

Superior self-healability and stretchability are critical elements for the practical wide-scale adoption of personalized electronics such as portable and wearable energy storage devices. However, the low healing efficiency of self-healable supercapacitors and the small strain of stretchable supercapacitors are fundamentally limited by conventional polyvinyl alcohol-based acidic electrolytes, which are intrinsically neither self-healable nor highly stretchable. Here we report an electrolyte comprising polyacrylic acid dual crosslinked by hydrogen bonding and vinyl hybrid silica nanoparticles, which displays all superior functions and provides a solution to the intrinsic self-healability and high stretchability problems of a supercapacitor. Supercapacitors with this electrolyte are non-autonomic self-healable, retaining the capacitance completely even after 20 cycles of breaking/healing. These supercapacitors are stretched up to 600% strain with enhanced performance using a designed facile electrode fabrication procedure.

Multifunctional Energy Storage and Conversion Devices

Multifunctional energy storage and conversion devices that incorporate novel features and functions in intelligent and interactive modes, represent a radical advance in consumer products, such as wearable electronics, healthcare devices, artificial intelligence, electric vehicles, smart household, and space satellites, etc. Here, smart energy devices are defined to be energy devices that are responsive to changes in configurational integrity, voltage, mechanical deformation, light, and temperature, called self-healability, electrochromism, shape memory, photodetection, and thermal responsivity. Advisable materials, device designs, and performances are crucial for the development of energy electronics endowed with these smart functions. Integrating these smart functions in energy storage and conversion devices gives rise to great challenges from the viewpoint of both understanding the fundamental mechanisms and practical implementation. Current state-of-art examples of these smart multifunctional energy devices, pertinent to materials, fabrication strategies, and performances, are highlighted. In addition, current challenges and potential solutions from materials synthesis to device performances are discussed. Finally, some important directions in this fast developing field are considered to further expand their application.

Texturing in situ: N,S-enriched hierarchically porous carbon as a highly active reversible oxygen electrocatalyst

Facile yet rational design of an efficient reversible oxygen electrocatalyst is critical for many renewable energy conversion and storage technologies. Here we report a simple and general synthetic protocol for fabricating a hierarchically porous and heteroatom doped carbon catalyst, which exhibited outstanding oxygen reduction/evolution activities (with a metric potential difference of 0.72 V in 1 M KOH, the best value for metal-free catalysts reported to date) with good stability in different electrolytes. The excellent performances of the catalyst were primarily endowed by our synthetic protocol, which integrates good conductivity, abundant accessible dopant species and suitable porous architectures within an in situ pyrolysis reaction. As a result, the performances of rechargeable Zn–air batteries based on the optimized catalyst substantially outperform those afforded by a benchmark Pt/C catalyzer. Our work is expected to open up new avenues for developing other efficient catalysts in a facile and viable way.

Polymer composites of boron nitride nanotubes and nanosheets

Hexagonal boron nitride (h-BN) is a layered material with planar networks of BN hexagons, which is flexible to form various nanostructures. This feature article begins with an overall introduction of BN nanostructures and their novel properties, such as electrical insulating properties, high thermal conductivity, great mechanical strength, optical properties, and so on. Then a comprehensive review of polymer composites of BN nanostructures with distinguished properties for different applications is presented. Finally, the problems of using BN nanostructures for the fabrication of polymer composites are discussed.

A Highly Durable, Transferable, and Substrate-Versatile High-Performance All-Polymer Micro-Supercapacitor with Plug-and-Play Function

A highly durable high-performance all-polymer micro-supercapacitor with plug-and-play function is developed. Through the newly developed technology, these micro-supercapacitors can be transferred to any substrate with all functions well retained.

Photoluminescent Ti3C2 MXene Quantum Dots for Multicolor Cellular Imaging

The fabrication of photoluminescent Ti3 C2 MXene quantum dots (MQDs) by a facile hydrothermal method is reported, which may greatly extend the applications of MXene-based materials. Interestingly, the as-prepared MQDs show excitation-dependent photoluminescence spectra with quantum yields of up to ≈10% due to strong quantum confinement. The applications of MQDs as biocompatible multicolor cellular imaging probes and zinc ion sensors are demonstrated.

Polyurethane/Cotton/Carbon Nanotubes Core-Spun Yarn as High Reliability Stretchable Strain Sensor for Human Motion Detection

Smart yarns and textiles are an active field of researches nowadays due to their potential applications in flexible and stretchable electronics, wearable devices, and electronic sensors. Integration of ordinary yarns with conductive fillers renders the composite yarns with new intriguing functions, such as sensation and monitoring of strain and stress. Here we report a low cost scalable fabrication for highly reliable, stretchable, and conductive composite yarn as effective strain sensing material for human motion monitoring. By incorporating highly conductive single-wall carbon nanotubes (SWCNTs) into the elastic cotton/polyurethane (PU) core-spun yarn through a self-designed coating approach, we demonstrated that the yarn is able to detect and monitor the movement of human limbs, such as finger and elbow, and even the wink of eyes. By virtue of the covered structure of the cotton/PU yarn and the reinforcement effect of SWCNTs, the composite yarn can bear up to 300% strain and could be cycled nearly 300,000 times under 40% strain without noticeable breakage. It is promising that this kind of conductive yarn can be integrated into various fabrics and used in future wearable devices and electronic skins.

Highly Integrated Supercapacitor‐Sensor Systems via Material and Geometry Design

An ultimate integration strategy making use of material and geometry is applied in a proof-of-concept study. Integrated supercapacitor-sensor systems with the capability of photodetecting and strain sensing are fabricated based on multifunctional conducting polypyrrole and piezoresistive textile geometry, respectively. This integration strategy enables promising applications for self-powered smart sensory, wearable and healthcare electronics.

An extremely safe and wearable solid-state zinc ion battery based on a hierarchical structured polymer electrolyte

Flexible and safe batteries, coupled with high performance and low cost, constitute a radical advance in portable and wearable electronics, especially considering the fact that these flexible devices are likely to experience more mechanical impacts and potential damage than well-protected rigid batteries. However, flexible lithium ion batteries (LIBs) are vastly limited by their intrinsic safety and cost issues. Here we introduce an extremely safe and wearable solid-state zinc ion battery (ZIB) comprising a novel gelatin and PAM based hierarchical polymer electrolyte (HPE) and an α-MnO2 nanorod/carbon nanotube (CNT) cathode. Benefiting from the well-designed electrolyte and electrodes, the flexible solid-state ZIB delivers a high areal energy density and power density (6.18 mW h cm−2 and 148.2 mW cm−2, respectively), high specific capacity (306 mA h g−1) and excellent cycling stability (97% capacity retention after 1000 cycles at 2772 mA g−1). More importantly, the solid-state ZIB offers a high wearability and an extreme safety performance over conventional flexible LIBs, and performs very well under various severe conditions, such as being greatly cut, bent, hammered, punctured, sewed, washed in water or even put on fire. In addition, flexible ZIBs were integrated in series to power a commercial smart watch, a wearable pulse sensor, and a smart insole, which has been achieved to the best of our knowledge for the first time. These results demonstrate the promising potential of ZIBs in many practical wearable applications and offer a new platform for flexible and wearable energy storage technologies.

Toward enhanced activity of a graphitic carbon nitride-based electrocatalyst in oxygen reduction and hydrogen evolution reactions via atomic sulfur doping

Atomic doping has always been demonstrated as a feasible way to effectively alter the catalytic properties of metal-free electrocatalysts. Herein, we report the first experimental and theoretical investigation regarding the influence of sulfur doping on the activity of a carbon nitride (C3N4)-based electrocatalyst in the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). It is found that the sulfur dopant within the mesoporous carbon-supported C3N4 motif can remarkably boost its ORR activity, which rivals that of commercial Pt/C yet with better cross-over tolerance and durability, while the HER performance of the composite catalyst is superior than most other reported metal-free electrocatalysts and is even comparable to the most active non-noble metal-based HER materials. Theoretical calculations further reveal that the excellent activity of the doped composite stems from the high charge and spin densities in the C3N4 motif as well as altered competent adsorption energies of reaction intermediates via the atomic sulfur doping. The results in this work feature a facile and effective approach for engineering a high performance C3N4-based electrocatalyst, which may also enlighten the designing and fabrication of other metal-free materials as next-generation electrocatalysts.