In situ formation of Co3O4 nanocrystals embedded in laser-induced graphene foam for high-energy flexible micro-supercapacitors

Standalone Stretchable Biophysical Sensing System Based on Laser Direct Write of Patterned Porous Graphene/Co3O4 Nanocomposites

Skin-interfaced wearable sensors can continuously monitor various biophysical and biochemical signals for health monitoring and disease diagnostics. However, such devices are typically limited by unsatisfactory and unstable output performance of the power supplies under mechanical deformations and human movements. Furthermore, there is also a lack of a simple and cost-effective fabrication technique to fabricate and integrate varying materials in the device system. Herein, we report a fully integrated standalone stretchable biophysical sensing system by combining wearable biophysical sensors, triboelectric nanogenerator (TENG), microsupercapacitor arrays (MSCAs), power management circuits, and wireless transmission modules. All of the device components and interconnections based on the three-dimensional (3D) networked graphene/Co3O4 nanocomposites are fabricated via low-cost and scalable direct laser writing. The self-charging power units can efficiently harvest energy from body motion into a stable and adjustable voltage/current output to drive various biophysical sensors and wireless transmission modules for continuously capturing, processing, and wirelessly transmitting various signals in real-time. The novel material modification, device configuration, and system integration strategies provide a rapid and scalable route to the design and application of next-generation standalone stretchable sensing systems for health monitoring and human-machine interfaces.

Fabrication of Flexible Poly(m-aminophenol)/Vanadium Pentoxide/Graphene Ternary Nanocomposite Film as a Positive Electrode for Solid-State Asymmetric Supercapacitors

In this study, poly(m-aminophenol) (PmAP) has been investigated as a multi-functional conductive supercapacitor binder to replace the conventional non-conductive binder, namely, poly(vinylene difluoride) (PVDF). The kye benefits of using PmAP are that it is easily soluble in common organic solvent and has good film-forming properties, and also its chemical functionalities can be involved in pseudocapacitive reactions to boost the capacitance performance of the electrode. A new ternary nanocomposite film based on vanadium pentoxide (V₂O₅), amino-functionalized graphene (amino-FG) and PmAP was fabricated via hydrothermal growth of V₂O₅ nanoparticles on graphene surfaces and then blending with PmAP/DMSO and solution casting. The electrochemical performances of V₂O₅/amino-FG/PmAP nanocomposite were evaluated in two different electrolytes, such as KCl and Li₂SO₄, and compared with those of V₂O₅/amino-FG nanocomposite with PVDF binder. The cyclic voltametric (CV) results of the V₂O₅/amino-FG/PmAP nanocomposite exhibited strong pseudocapacitive responses from the V₂O₅ and PmAP phases, while the faradaic redox reactions on the V₂O₅/amino-FG/PVDF electrode were suppressed by the inferior conductivity of the PVDF. The V₂O₅/amino-FG/PmAP electrode delivered a 5-fold greater specific capacitance than the V₂O₅/amino-FG/PVDF electrode. Solid-state asymmetric supercapacitors (ASCs) were assembled with V₂O₅/amino-FG/PmAP film as a positive electrode, and their electrochemical properties were examined in both KCl and Li₂SO₄ electrolytes. Although the KCl electrolyte-based ASC has greater specific capacitance, the Li₂SO₄ electrolyte-based ASC delivers a higher energy density of 51.6 Wh/kg and superior cycling stability.

Phytosynthesis of Co3O4 Nanoparticles as the High Energy Storage Material of an Activated Carbon/Co3O4 Symmetric Supercapacitor Device with Excellent Cyclic Stability Based on a Na2SO4 Aqueous Electrolyte

The benign preparation of cobalt oxide nanoparticles (Co₃O₄-NPs) was performed using marine red algae extract (Grateloupia sparsa) as a simple, cost-effective, scalable, and one-pot hydrothermal technique. The nominated extract was employed as an environmental reductant and stabilizing agent. The resultant product showed the typical peak of Co₃O₄-NPs around 400 nm wavelength as ascertained by UV-vis spectroscopy. Size and morphological techniques combined with X-ray diffraction (XRD) showed the small size of Co₃O₄-NPs deformed in a spherical shape. The activated carbon (AC) electrode and Co₃O₄-NP electrode delivered a specific capacitance (C _sp) of 125 and 182 F g^-1 at 1 A g^-1, respectively. The energy density of the AC and AC/Co₃O₄ electrodes with a power density of 543.44 and 585 W kg^-1 was equal to 17.36 and 25.27 Wh kg^-1, respectively. The capacitance retention of designed electrodes was 99.2 and 99.5% after 3000 cycles. Additionally, a symmetric AC/Co₃O₄//AC/Co₃O₄ supercapacitor device had a specific capacitance (C _sp) of 125 F g^-1 and a high energy density of 55 Wh kg^-1 at a power density of 650 W kg^-1. Meanwhile, the symmetric device exhibited superior cyclic stability after 8000 cycles, with a capacitance retention of 93.75%. Overall, the adopted circular criteria, employed to use green technology to avoid noxious chemicals, make the AC/Co₃O₄ nanocomposite an easily accessible electrode for energy storage applications.