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.

Highly sensitive and stable fructose self-powered biosensor based on a self-charging biosupercapacitor.

Herein, we present an alternative approach to obtain a highly sensitive and stable self-powered biosensor that was used to detect D-fructose as proof of concept.In this platform, we perform a two-step process, viz. self-charging the biosupercapacitor for a constant time by using D-fructose as fuel and using the stored charge to realize the detection of D-fructose by performing several polarization curves at different D-fructose concentrations. The proposed BSC shows an instantaneous power density release of 17.6 mW cm-2 and 3.8 mW cm-2 in pulse mode and at constant load, respectively. Moreover, the power density achieved for the self-charging BSC in pulse mode or under constant load allows for an enhancement of the sensitivity of the device up to 10 times (3.82 ± 0.01 mW cm-2 mM-1, charging time = 70 min) compared to the BSC in continuous operation mode and 100 times compared to the normal enzymatic fuel cell. The platform can potentially be employed as a self-powered biosensor in food or biomedical applications.

Pastes and hydrogels from carboxymethyl cellulose sodium salt as supporting electrolyte of solid electrochemical supercapacitors.

Different carboxymethyl cellulose sodium salt (NaCMC)-based pastes and hydrogels, both containing a salt as supporting electrolyte, have been prepared and characterized as potential solid state electrolyte (SSE) for solid electrochemical supercapacitors (ESCs).The characteristics of the NaCMC-based SSEs have been optimized by examining the influence of five different factors in the capacitive response of poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes: i) the chemical nature of the salt used as supporting electrolyte; ii) the concentration of such salt; iii) the concentration of cellulose used to prepare the paste; iv) the concentration of citric acid employed during NaCMC cross-linking; and v) the treatment applied to recover the supporting electrolyte after washing the hydrogel. The specific capacitance of the device prepared using the optimized hydrogel as SSE is 81.5 and 76.8 F/g by means of cyclic voltammetry and galvanostatic charge/discharge, respectively, these values decreasing to 60.7 and 75.5 F/g when the SSE is the paste.

An Intrinsic Self-Charging Biosupercapacitor Comprised of a High-Potential Bioanode and a Low-Potential Biocathode.

An intrinsic self-charging biosupercapacitor built on a unique concept for the fabrication of biodevices based on redox polymers is presented. The biosupercapacitor consists of a high-potential redox polymer based bioanode and a low-potential redox polymer based biocathode in which the potentials of the electrodes in the discharged state show an apparent potential mismatch Eanode >Ecathode and prevent the use of the device as a conventional biofuel cell. Upon charging, the potentials of the electrodes are shifted to more positive (cathode) and more negative (anode) values because of a change in the aox -to-ared ratio within the redox polymer matrix. Hence, a potential inversion occurs in the charged state (Eanode 0.4 V is achieved and the biodevice acts as a true biosupercapacitor. The bioanode consists of a novel specifically designed high-potential Os complex modified polymer for the efficient immobilization and electrical wiring of glucose converting enzymes, such as glucose oxidase and flavin adenine dinucleotide (FAD)-dependent glucose dehydrogenase. The cathodic side is constructed from a low-potential Os complex modified polymer integrating the O2 reducing enzyme, bilirubin oxidase. The large potential differences between the redox polymers and the prosthetic groups of the biocatalysts ensure fast and efficient charging of the biodevice.