Integration of supercapacitors with enzymatic biobatteries toward more effective pulse-powered use in small-scale energy harvesting devices

Abstract

Effective integration of electrochemical devices consisting of enzyme-based biobatteries together with high power double-layer type capacitors is discussed here. An ultimate goal is to overcome a typical drawback of enzymatic power sources (biofuel cells and biobatteries): although their energy is potentially high enough to fulfill the needs of small electronic devices, their power is often too low. It is demonstrated that properly selected capacitor can support operation of such a low power device simply by supplying appropriate power pulses with fast dynamic response that is required for many applications involving fluctuating loads. Our model integrated system is obtained by coupling a series of double-layer capacitors with well-behaved zinc/oxygen biobattery. The biobattery utilizes a stable cathodic material composed of covalently phenylated single-walled carbon nanotubes and the oxygen reduction enzyme, laccase, together with the hopeite-covered zinc rod acting as the anode. The enzymatic power source was characterized by the maximum power density of 1.8 mW cm-2, the open circuit voltage of 1.6 V. Nevertheless, under the 50 Ω loading, the voltage of biobattery (electrode surface areas of ca. 0.3 cm2) drops to 0 V after 2 s. The practical performance (power stability) of a biobattery has significantly improved by its parallel connection to electrochemical capacitor. The importance of such capacitor's parameters as low resistance (not more than a few hundred of milliohms), proper capacitance, and leakage current (not higher than a few microamperes) is emphasized here. The potential utility of the optimized biobattery/supercapacitor system is discussed in terms of use as a source of power to operate a digital watch. © 2014 The Author(s).