Zengxia Pei

From Industrially Weavable and Knittable Highly Conductive Yarns to Large Wearable Energy Storage Textiles

Wearable electronic textiles that store capacitive energy are a next frontier in personalized electronics. However, the lack of industrially weavable and knittable conductive yarns in conjunction with high capacitance, limits the wide-scale application of such textiles. Here pristine soft conductive yarns are continuously produced by a scalable method with the use of twist-bundle-drawing technique, and are mechanically robust enough to be knitted to a cloth by a commercial cloth knitting machine. Subsequently, the reduced-graphene-oxide-modified conductive yarns covered with a hierarchical structure of MnO2 nanosheets and a polypyrrole thin film were used to fabricate weavable, knittable and wearable yarn supercapacitors. The resultant modified yarns exhibit specific capacitances as high as 36.6 mF cm(-1) and 486 mF cm(-2) in aqueous electrolyte (three-electrode cell) or 31 mF cm(-1) and 411 mF cm(-2) in all solid-state two-electrode cell. The symmetric solid-state supercapacitor has high energy densities of 0.0092 mWh cm(-2) and 1.1 mWh cm(-3) (both normalized to the whole device) with a long cycle life. Large energy storage textiles are fabricated by weaving our flexible all-solid-state supercapacitor yarns to a 15 cm × 10 cm cloth on a loom and knitting in a woollen wrist band to form a pattern, enabling dual functionalities of energy storage capability and wearability.

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.

Magnetic-Assisted, Self-Healable, Yarn-Based Supercapacitor

Yarn-based supercapacitors have received considerable attention recently, offering unprecedented opportunities for future wearable electronic devices (e.g., smart clothes). However, the reliability and lifespan of yarn-based supercapacitors can be seriously limited by accidental mechanical damage during practical applications. Therefore, a supercapacitor endowed with mechanically and electrically self-healing properties is a brilliant solution to the challenge. Compared with the conventional planar-like or large wire-like structure, the reconnection of the broken yarn electrode composed of multiple tiny fibers (diameter <20 μm) is much more difficult and challenging, which directly affects the restoration of electrical conductivity after damage. Herein, a self-healable yarn-based supercapacitor that ensures the reconnection of broken electrodes has been successfully developed by wrapping magnetic electrodes around a self-healing polymer shell. The strong force from magnetic attraction between the broken yarn electrodes benefits reconnection of fibers in the yarn electrodes during self-healing and thus offers an effective strategy for the restoration of electric conductivity, whereas the polymer shell recovers the configuration integrity and mechanical strength. With the design, the specific capacitance of our prototype can be restored up to 71.8% even after four breaking/healing cycles with great maintenance of the whole devices mechanical properties. This work may inspire the design and fabrication of other distinctive self-healable and wearable electronic devices.

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.

Ultrathin MXene-Micropattern-Based Field-Effect Transistor for Probing Neural Activity.

A field-effect transistor (FET) based on ultrathin Ti3 C2 -MXene micropatterns is developed and utilized as a highly sensitive biosensor. The device is produced with the microcontact printing technique, making use of its unique advantages for easy fabrication. Using the MXene-FET device, label-free probing of small molecules in typical biological environments and fast detection of action potentials in primary neurons is demonstrated.

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.

A shape memory supercapacitor and its application in smart energy storage textiles

As a result of the popularization of wearable electronics, a variety of compact flexible energy storage devices have been successfully developed recently. During practical application, these delicate devices unavoidably experience all kinds of deformations. These deformations would become irreversible under the long-term concentration of local stresses, leading to structure and functional fatigue. To solve this problem, a shape memory supercapacitor (SMSC) is successfully fabricated for the first time. The SMSC is flexible and easily deformed below its activation temperature. Once it is heated over a trigger temperature, it would automatically recover its original shape, meanwhile restoring all deformations. By embedding with shape memory functions, all potential damage to the supercapacitor would be nipped in the bud, while simultaneously prolonging the life span of the device. Furthermore, an energy storage shape memory textile woven with these SMSCs and traditional fabrics can work as a smart sleeve. It can “remember” its pre-designed shape and realize automatic cooling when it is over-heated, demonstrating a diversity of potential applications other than energy storage.

Extremely Stable Polypyrrole Achieved via Molecular Ordering for Highly Flexible Supercapacitors

The cycling stability of flexible supercapacitors with conducting polymers as electrodes is limited by the structural breakdown arising from repetitive counterion flow during charging/discharging. Supercapacitors made of facilely electropolymerized polypyrrole (e-PPy) have ultrahigh capacitance retentions of more than 97, 91, and 86% after 15000, 50000, and 100000 charging/discharging cycles, respectively, and can sustain more than 230000 charging/discharging cycles with still approximately half of the initial capacitance retained. To the best of our knowledge, such excellent long-term cycling stability was never reported. The fully controllable electropolymerization shows superiority in molecular ordering, favoring uniform stress distribution and charge transfer. Being left at ambient conditions for even 8 months, e-PPy supercapacitors completely retain the good electrochemical performance. The extremely stable supercapacitors with excellent flexibility and scalability hold considerable promise for the commerical application of flexible and wearable electronics.