A Dual-Functional MXene-Based Bioanode for Wearable Self-Charging Biosupercapacitors

As a reliable energy-supply platform for wearable electronics, biosupercapacitors combine the characteristics of biofuel cells and supercapacitors to harvest and store the energy from human's sweat. However, the bulky preparation process and deep embedding of enzyme active sites in bioelectrodes usually limit the energy-harvesting process, retarding the practical power-supply sceneries especially during the complicated in vivo motion. Herein, a MXene/single-walled carbon nanotube/lactate oxidase hierarchical structure as the dual-functional bioanode is designed, which can not only provide a superior 3D catalytic microenvironment for enzyme accommodation to harvest energy from sweat, but also offers sufficient capacitance to store energy via the electrical double-layer capacitor. A wearable biosupercapacitor is fabricated in the "island-bridge" structure with a composite bioanode, active carbon/Pt cathode, polyacrylamide hydrogel substrate, and liquid metal conductor. The device exhibits an open-circuit voltage of 0.48 V and the high power density of 220.9 µW cm-2 at 0.5 mA cm-2 . The compact conformal adhesion with skin is successfully maintained under stretching/bending conditions. After repeatedly stretching the devices, there is no significant power attenuation in pulsed output. The unique bioelectrode structure and attractive energy harvesting/storing properties demonstrate the promising potential of this biosupercapacitor as a micro self-powered platform of wearable electronics.

An Implantable Fiber Biosupercapacitor with High Power Density by Multi-Strand Twisting Functionalized Fibers

Biosupercapacitors (BSCs) that can harvest and store chemical energy show great promise for power delivery of biological applications. However, low power density still limits their applications, especially as miniaturized implants. Here, we report an implantable fiber BSC with maximal power density of 22.6 mW‧cm-2, superior to the previous reports. The fiber BSC was fabricated by integrating anode and cathode fibers of biofuel cell with supercapacitor fibers through multi-strand twisting. This twisting structure endowed many channels inside and high electrochemical active area for efficient mass diffusion and charge transfer among different fibers, benefiting high power output. The obtained thin and flexible fiber BSC operated stably under deformations and performed high biocompatibility after implantation. Eventually, the fiber BSC was implanted subcutaneously in rats and successfully realized electrical stimulation of sciatic nerve, showing promise as a power source in vivo.