Flexible and Free-Standing Reduced Graphene Oxide and Polypyrrole Coated Air-Laid Paper-Based Supercapacitor Electrodes

Flexible Paper-Based Room-Temperature Acetone Sensors with Ultrafast Regeneration

Paper-based lightweight, degradable, low-cost, and eco-friendly substrates are extensively used in wearable biosensor applications, albeit to a lesser extent in sensing acetone and other gas-phase analytes. Generally, rigid substrates with heaters have been employed to develop acetone sensors due to the high operating/recovery temperature (typically above 200 °C), limiting the use of papers as substrates in such sensing applications. In this work, we proposed fabricating the paper-based, room-temperature-operatable acetone sensor using ZnO-polyaniline-based acetone-sensing inks by a facile fabrication method. The fabricated paper-based electrodes showed good electrical conductivity (80 S/m) and mechanical stability (∼1000 bending cycles). The acetone sensors showed a sensitivity of 0.02/100 ppm and 0.6/10 μL with an ultrafast response (4 s) and recovery time (15 s) at room temperature. The sensors delivered a broad sensitivity over a physiological range of 260 to >1000 ppm with R² > 0.98 under atmospheric conditions. Further, the role of the surface, interfacial, microstructure, electrical, and electromechanical properties of the paper-based sensor devices has been correlated with the sensitivity and room-temperature recovery observed in our system. These versatile, green, flexible electronic devices would be ideal for low-cost, highly regenerative, room-/low-temperature-operable wearable sensor applications.

Collaboration of two-star nanomaterials: The applications of nanocellulose-based metal organic frameworks composites

Nanocellulose, as the star nanomaterial in carbohydrate polymers, has excellent mechanical properties, biodegradability, and easy chemical modification. However, further practical applications of nanocellulose are limited by their inadequate functionalization. Metal-organic frameworks (MOFs), as the star nanomaterial in functional polymers, have a large surface area, high porosity, and adjustable structure. The collaboration of nanocellulose and MOFs is a desirable strategy to make composites especially interesting for multifunctional and multi-field applications. What sparks will be produced by the collaboration of two-star nanomaterials? In this review article, we highlight an up-to-date overview of nanocellulose-based MOFs composites. The sewage treatment, gas separation, energy storage, and biomedical applications are mainly summarized. Finally, the challenges and research trends of nanocellulose-based MOFs composites are prospected. We hope this review may provide a valuable reference for the development and applications of carbohydrate polymer composites soon.

Multiresponsive MXene (Ti3C2Tx)-Decorated Textiles for Wearable Thermal Management and Human Motion Monitoring

Over the past few years, wearable electronics and smart textiles have seen tremendous growth in both academia and industries. However, it is still a challenge to prepare robust, flexible, wearable, and multiresponsive textile electronics. A newly blooming two-dimensional (2D) transition-metal carbide/nitride (MXene) is regarded as an ideal active material to build multifunctional electronics due to its intriguing properties. Herein, a hydrophobic and multifunctional textile composite (Si-MAP) was prepared by decoration of conductive MXene nanosheets onto air-laid paper, followed by wrapping with poly(dimethylsiloxane) (PDMS). These obtained smart textiles exhibited excellent electronic/photonic/mechanical triresponsive properties: Si-MAPs could reach high equilibrium temperatures (104.9 and 118.7 °C) under quite low power illumination (1.25 W cm^-2) and working voltage (4 V). The Si-MAP pressure sensor exhibited high sensitivity and rapid response time (30-40 ms), which can capture a wide range of human movements. Moreover, the thin PDMS layer not only rendered the textile composites hydrophobic but also improved the stability and adaptation for daily use. Remarkably, the hydrophobic Si-MAPs have maintained the advantages of breathability and washability, which make them suitable for wearing. Thus, this smart Si-MAP textile provides a reference for the study of the next generation of light, portable, and wearable textile-based electronic devices.

Reduced Graphene Oxide/Poly(Pyrrole-co-Thiophene) Hybrid Composite Materials: Synthesis, Characterization, and Supercapacitive Properties

Reduced graphene oxide/poly(pyrrol-co-thiophene) (RGO/COP), prepared by facile in-situ oxidative copolymerization, is reported as a new hybrid composite material with improved supercapacitance performance as compared to the respective homopolymers and their composites with RGO. The as-prepared hybrid materials were characterized with ultraviolet-visible (UV-Vis) spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray (EDX) analysis. The electrochemical behavior and energy storage properties of the materials were tested by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrostatic impedance spectroscopy (EIS) techniques in 0.5 M H2SO4. The specific capacitance (Csp) for RGO/COP calculated from the CV curve was 467 F/g at a scan rate of 10 mV/s. While the Csp calculated from the GCD was 417 F/g at a current density of 0.81 A/g. The energy density calculated was 86.4 Wh/kg with a power density of 630 W/kg. The hybrid composite exhibits good cyclic stability with 65% capacitance retention after 1000 cycles at a scan rate of 100 mV/s. The present work brings a significance development of RGO/COP composites to the electrode materials for pseudocapacitive application.

Fabrication of dual-hollow heterostructure of Ni2CoS4 sphere and nanotubes as advanced electrode for high-performance flexible all-solid-state supercapacitors

High-energy-density and flexible supercapacitors have shown numerous application potential in modern portable electronics. However, the relatively low specific capacity, poor rate retentions, and limited durability have hindered their implement. Herein, a novel hierarchical dual-hollow electrode, composed of a hollow Ni₂CoS₄ sphere and outer hollow Ni₂CoS₄ nanotubes (Ni₂CoS₄HS-HTs), is elaborately constructed. The Ni₂CoS₄HS-HT-5 exhibits a high specific capacity of 817.5 C g^-1 at a current density of 1 A g^-1 with remarkable rate retention of 75.3% at 50 A g^-1. In an all-solid-state asymmetric supercapacitor of Ni₂CoS₄HS-HT-5//CAC, a high capacitance of 1511.5 mF cm^-2 at 5 mA cm^-2 is obtained with an exceptional energy density of 13.6 mWh cm^-3 at a power density of 92.6 mW cm^-3. In addition, the capacity retention reaches 96% over 2000 cycles at 20 mA cm^-3, implying the outstanding durability. The flexibility and mechanical stability are demonstrated by the intact electrochemical performances under different bending angles. As a proof-of-concept, two Ni₂CoS₄HS-HT-5//CACs in series could successfully illuminate 31 LED indicators for more than 8 mins. These fascinating electrochemical performances benefit from the novel electrode structure and depict great potential for modern energy storage applications.