Constructing Flexible Film Electrode with Porous Layered Structure by MXene/SWCNTs/PANI Ternary Composite for Efficient Low-Grade Thermal Energy Harvest

Thermal energy, constituting the majority of the energy lost through various inefficiencies, is abundant and ubiquitous. With thermogalvanic effect, thermocells (TECs) can directly convert thermal energy into electricity without producing vibration, noise or other waste emissions. This work presents a rational design of flexible film electrodes constructed on a ternary composite of Ti₃C₂T_x MXene (T_x represents surface terminations), polyaniline (PANI) and single-wall carbon nanotubes for TECs, which exhibit notably enhanced thermoelectrochemical performance compared to the widely adopted noble platinum electrodes. The ternary composite electrodes form a porous layered structure with a large electrochemical-active surface area. Experiment and simulation results reveal that synergistic effects of Ti₃C₂T_x and PANI are induced for promoting both mass and charge transport at the electrolyte-electrode interface, resulting in a TEC with an output power of 13.15 µW cm⁻² at the ΔT of 40 K. The TEC also shows a rapid response to the small temperature difference between the human body and the ambient, demonstrating high potential in harvesting low-grade heat to power small electronics.     

Controlled Assembly of MXene Nanosheets as an Electrode and Active Layer for High-Performance Electronic Skin

MXenes are an emerging class of 2D transition metal carbides and nitrides. They have been widely used in flexible electronics owing to their excellent conductivity, mechanical flexibility, and water dispersibility. In this study, the electrode and active layer applications of MXene materials in electronic skins are realized. By utilizing vacuum filtration technology, few-layer MXene electrodes are integrated onto the top and bottom surfaces of the 3D polyacrylonitrile (PAN) network to form a stable electronic skin. The fabricated flexible device with Ti₃C₂T_x MXene electrodes outperforms those with other electrodes and exhibits excellent device performance, with a high sensitivity of 104.0 kPa⁻¹, fast response/recovery time of 30/20 ms, and a low detection limit of 1.5 Pa. Furthermore, the electrode and the constructed MXene/PAN-based flexible pressure sensor exhibit robust mechanical stability and can survive 240 bending cycles. Such a robust, flexible device can be enlarged or folded like a jigsaw puzzle or origami and transformed from 2D to 3D structures; moreover, it can detect tiny movements of human muscles, such as movements corresponding to sound production and intense movements during bending of fingers.     

Flexible Transparent Bifunctional Capacitive Sensors with Superior Areal Capacitance and Sensing Capability based on PEDOT:PSS/MXene/Ag Grid Hybrid Electrodes

Flexible transparent supercapacitors (FTSs) have aroused considerable attention. Nonetheless, balancing energy storage capability and transparency remains challenging. Herein, a new type of FTSs with both excellent energy storage and superior transparency is developed based on PEDOT:PSS/MXene/Ag grid ternary hybrid electrodes. The hybrid electrodes can synergistically utilize the high optoelectronic properties of Ag grids, the excellent capacitive performance of MXenes, and the superior chemical stability of PEDOT:PSS, thus, simultaneously demonstrating excellent optoelectronic properties (T: ≈89%, R_s: ≈39 Ω sq⁻¹), high areal specific capacitance, superior mechanical softness, and excellent anti-oxidation capability. Due to the excellent comprehensive performances of the hybrid electrodes, the resulting FTSs exhibit both high optical transparency (≈71% and ≈60%) and large areal specific capacitance (≈3.7 and ≈12 mF cm⁻²) besides superior energy storage capacity (P: 200.93, E: 0.24 µWh cm⁻²). Notably, the FTSs show not only excellent energy storage but also exceptional sensing capability, viable for human activity recognition. This is the first time to achieve FTSs that combine high transparency, excellent energy storage and good sensing all-in-one, which make them stand out from conventional flexible supercapacitors and promising for next-generation smart flexible energy storage devices.