High-Temperature Oxidized Mo2CTx MXene for a High-Performance Supercapacitor

In situ oxidized Mo2CTx MXene film via electrochemical activation for smart electrochromic supercapacitors

Mo2CTx MXenes have great potential for multifunctional energy storage applications because of their outstanding electrical conductivity, superior cycling stability, and high optical transmittance. In this study, we fabricate Mo2CTx film electrodes (referred to as Mo2C) on fluorine-doped tin oxide (FTO) substrates using the layer-by-layer (LbL) self-assembly technique. To improve the energy-storage performance of Mo2CTx film electrodes, we develop a convenient electrochemical activation process to prepare in situ oxidized Mo2CTx/MoO3 film electrodes (referred to as EA-Mo2C). The Mo2CTx/MoO3 hybrid film benefits from the addition of MoO3, which introduces extra redox sites and enhances the charge-storage capacity. Furthermore, the unique layered structure of Mo2CTx significantly reduces the diffusion energy barrier for cations. The synergistic interaction between Mo2CTx and MoO3 results in superior electrochemical performance, and the EA-Mo2C displays a remarkable increase in areal specific capacitance, achieving 23.29 mF cm-2 at a current density of 1.5 mA cm-2, which is 518 % higher than that of Mo2C. The electrochromic supercapacitor, assembled using EA-Mo2C as the ion-storage layer and polyaniline (PANI) as the electrochromic layer, enables power visualization and quantitative display. In summary, this study utilizes in situ electrochemical activation to derive high-performance electrode materials, offering an innovative strategy for advancing MXene-based energy-storage materials.

Ambient energy harvesters in wearable electronics: fundamentals, methodologies, and applications

In recent years, wearable sensor devices with exceptional portability and the ability to continuously monitor physiological signals in real time have played increasingly prominent roles in the fields of disease diagnosis and health management. This transformation has been largely facilitated by materials science and micro/nano-processing technologies. However, as this technology continues to evolve, the demand for multifunctionality and flexibility in wearable devices has become increasingly urgent, thereby highlighting the problem of stable and sustainable miniaturized power supplies. Here, we comprehensively review the current mainstream energy technologies for powering wearable sensors, including batteries, supercapacitors, solar cells, biofuel cells, thermoelectric generators, radio frequency energy harvesters, and kinetic energy harvesters, as well as hybrid power systems that integrate multiple energy conversion modes. In addition, we consider the energy conversion mechanisms, fundamental characteristics, and typical application cases of these energy sources across various fields. In particular, we focus on the crucial roles of different materials, such as nanomaterials and nano-processing techniques, for enhancing the performance of devices. Finally, the challenges that affect power supplies for wearable electronic products and their future developmental trends are discussed in order to provide valuable references and insights for researchers in related fields.

Super-Stretchable and High-Energy Micro-Pseudocapacitors Based on MXene Embedded Ag Nanoparticles

The advancement of aqueous micro-supercapacitors offers an enticing prospect for a broad spectrum of applications, spanning from wearable electronics to micro-robotics and sensors. Unfortunately, conventional micro-supercapacitors are characterized by low capacity and slopy voltage profiles, limiting their energy density capabilities. To enhance the performance of these devices, the use of 2D MXene-based compounds has recently been proposed. Apart from their capacitive contributions, these structures can be loaded with redox-active nanowires which increase their energy density and stabilize their operation voltage. However, introducing rigid nanowires into MXene films typically leads to a significant decline in their mechanical properties, particularly in terms of flexibility. To overcome this issue, super stretchable micro-pseudocapacitor electrodes composed of MXene nanosheets and in situ reconstructed Ag nanoparticles (Ag-NP-MXene) are herein demonstrated, delivering high energy density, stable operation voltage of ≈1 V, and fast charging capabilities. Careful experimental analysis and theoretical simulations of the charging mechanism of the Ag-NP-MXene electrodes reveal a dual nature charge storage mechanism involving ad(de)sorption of ions and conversion reaction of Ag nanoparticles. The superior mechanical properties of synthesized films obtained through in situ construction of Ag-NP-MXene structure show an ultra stretchability, allowing the devices to provide stable voltage and energy output even at 100% elongation.

Highly Sensitive and Stable Multifunctional Self-Powered Triboelectric Sensor Utilizing Mo2CTx/PDMS Composite Film for Pressure Sensing and Non-Contact Sensing

Sensors based on triboelectric nanogenerators (TENGs) are increasingly gaining attention because of their self-powered capabilities and excellent sensing performance. In this work, we report a Mo2CTx-based triboelectric sensor (Mo-TES) consisting of a Mo2CTx/polydimethylsiloxane (PDMS) composite film. The impact of the mass fraction (wt%) and force of Mo2CTx particles on the output performance of Mo-TES was systematically explored. When Mo2CTx particles is 3 wt%, Mo-TES3 achieves an open-circuit voltage of 86.89 V, a short-circuit current of 578.12 nA, and a power density of 12.45 μW/cm2. It also demonstrates the ability to charge capacitors with varying capacitance values. Additionally, the Mo-TES3 demonstrates greater sensitivity than the Mo-TES0 and a faster recovery time of 78 ms. Meanwhile, the Mo-TES3 also demonstrates excellent stability in water washing and antifatigue testing. This demonstrates the effectiveness of Mo-TES as a pressure sensor. Furthermore, leveraging the principle of electrostatic induction, the triboelectric sensor has the potential to achieve non-contact sensing, making it a promising candidate for disease prevention and safety protection.