Casey Yan

Wearable energy-dense and power-dense supercapacitor yarns enabled by scalable graphene-metallic textile composite electrodes

One-dimensional flexible supercapacitor yarns are of considerable interest for future wearable electronics. The bottleneck in this field is how to develop devices of high energy and power density, by using economically viable materials and scalable fabrication technologies. Here we report a hierarchical graphene–metallic textile composite electrode concept to address this challenge. The hierarchical composite electrodes consist of low-cost graphene sheets immobilized on the surface of Ni-coated cotton yarns, which are fabricated by highly scalable electroless deposition of Ni and electrochemical deposition of graphene on commercial cotton yarns. Remarkably, the volumetric energy density and power density of the all solid-state supercapacitor yarn made of one pair of these composite electrodes are 6.1 mWh cm−3 and 1,400 mW cm−3, respectively. In addition, this SC yarn is lightweight, highly flexible, strong, durable in life cycle and bending fatigue tests, and integratable into various wearable electronic devices.

Polymer‐Assisted Metal Deposition (PAMD): A Full‐Solution Strategy for Flexible, Stretchable, Compressible, and Wearable Metal Conductors

Metal interconnects, contacts, and electrodes are indispensable elements for most applications of flexible, stretchable, and wearable electronics. Current fabrication methods for these metal conductors are mainly based on conventional microfabrication procedures that have been migrated from Si semiconductor industries, which face significant challenges for organic-based compliant substrates. This Research News highlights a recently developed full-solution processing strategy, polymer-assisted metal deposition (PAMD), which is particularly suitable for the roll-to-roll, low-cost fabrication of high-performance compliant metal conductors (Cu, Ni, Ag, and Au) on a wide variety of organic substrates including plastics, elastomers, papers, and textiles. This paper presents i) the principles of PAMD, and how to use it for making ii) flexible, stretchable, and wearable conductive metal electrodes, iii) patterned metal interconnects, and d) 3D stretchable and compressible metal sponges. A critical perspective on this emerging strategy is also provided.

Waterproof, Ultrahigh Areal-Capacitance, Wearable Supercapacitor Fabrics

High-performance supercapacitors (SCs) are promising energy storage devices to meet the pressing demand for future wearable applications. Because the surface area of a human body is limited to 2 m2 , the key challenge in this field is how to realize a high areal capacitance for SCs, while achieving rapid charging, good capacitive retention, flexibility, and waterproofing. To address this challenge, low-cost materials are used including multiwall carbon nanotube (MWCNT), reduced graphene oxide (RGO), and metallic textiles to fabricate composite fabric electrodes, in which MWCNT and RGO are alternatively vacuum-filtrated directly onto Ni-coated cotton fabrics. The composite fabric electrodes display typical electrical double layer capacitor behavior, and reach an ultrahigh areal capacitance up to 6.2 F cm-2 at a high areal current density of 20 mA cm-2 . All-solid-state fabric-type SC devices made with the composite fabric electrodes and water-repellent treatment can reach record-breaking performance of 2.7 F cm-2 at 20 mA cm-2 at the first charge-discharge cycle, 3.2 F cm-2 after 10 000 charge-discharge cycles, zero capacitive decay after 10 000 bending tests, and 10 h continuous underwater operation. The SC devices are easy to assemble into tandem structures and integrate into garments by simple sewing.

Machine-Washable Textile Triboelectric Nanogenerators for Effective Human Respiratory Monitoring through Loom Weaving of Metallic Yarns

Textile triboelectric nanogenerators for human respiratory monitoring with machine washability are developed through loom weaving of Cu-PET and PI-Cu-PET yarns. Triboelectric charges are generated at the yarn crisscross intersections to achieve a maximum short circuit current density of 15.50 mA m-2 . By integrating into a chest strap, human respiratory rate and depth can be monitored.

Bio-inspired chemical fabrication of stretchable transparent electrodes

Stretchable and transparent electrodes are fabricated by chemical deposition of metal thin films on natural veins of leaves at ambient conditions. These vein-based transparent electrodes show excellent electro-optical property (0.9 Ω sq(-1) at 83% T) even at 50% tensile strains, ideal for flexible and stretchable optoelectronic devices.

Photoreactive and Metal‐Platable Copolymer Inks for High‐Throughput, Room‐Temperature Printing of Flexible Metal Electrodes for Thin‐Film Electronics

Photoreactive and metal-platable copolymer inks are reported for the first time to allow high-throughput printing of high-performance flexible electrodes at room temperature. This new copolymer ink accommodates various types of printing technologies, such as soft lithography molding, screen printing, and inkjet printing. Electronic devices including resistors, sensors, solar cells, and thin-film transistors fabricated with these printed electrodes show excellent electrical performance and mechanical flexibility.

A Transparent, Highly Stretchable, Autonomous Self-Healing Poly(dimethyl siloxane) Elastomer

An innovative self-healing polydimethylsiloxane (PDMS) elastomer, namely, PDMS-TFB, is reported by incorporating the reversibly dynamic imine bond as the self-healing points into the PDMS networks. The PDMS-TFB elastomer features good optical transmittance (80%) in full visible light region, high stretchability (≈700%), and excellent autonomous self-healing ability at room temperature. Surprisingly, the self-healing behavior can take place in water and even at a temperature as low as -20 °C in air, showing a promising outlook for broader applications. As a proof-of-concept, this study demonstrates the use of the PDMS-TFB elastomer for preparing anticorrosion coating and adhesive layer, and also the use of such an elastomer to be the platform for fabricating the flexible interconnector and chemical sensor. Remarkably, no significant difference is observed between the pristine and healed samples. Taking full advantage of these unique properties, it is anticipated that such a PDMS-TFB elastomer shows wide applications in the fields of materials science, electronics, biology, optics, etc.

Monolithic hierarchical gold sponges for efficient and stable catalysis in a continuous-flow microreactor

Monolithic hierarchical gold sponges are prepared by the polymer-assisted metal deposition method under air- and moisture-compatible conditions. These sponges feature excellent catalytic properties, robustness and chemical recyclability for the reduction reaction of 4-nitrophenol, and are also available for the scale-up catalysis of the same reaction in a continuous-flow microreactor.

Visible-Light Photolabile, Charge-Convertible Poly(ionic liquid) for Light-degradable Films and Carbon-Based Electronics

We report for the first time an innovative visible-light photolabile poly(ionic liquid) (VP-PIL). The as-prepared VP-PIL features low Tg (47 °C), good thermal stability (Td ≈ 284 °C) and solubility in ranges of polar solvents. Upon blue light irradiation (∼452 nm), C-O bonds of picolinuim units are photocleaved, and the charges of PILs are simultaneously converted from positive to negative. Taking full advantages of these excellent properties of VP-PIL, a visible light degradable film for the first time is fabricated. Moreover, to demonstrate its applications in electronics, we prepared high-quality VP-PIL-containing conductive ink for flexible interconnects and graphene electrodes for supercapacitors.