A symmetric supercapacitor/biofuel cell hybrid device based on enzyme-modified nanoporous gold: an autonomous pulse generator

The integration of supercapacitors with enzymatic biofuel cells (BFCs) can be used to prepare hybrid devices in order to harvest significantly higher power output. In this study, a supercapacitor/biofuel cell hybrid device was prepared by the immobilisation of redox enzymes with electrodeposited poly(3,4-ethylenedioxythiophene) (PEDOT) and the redox polymer [Os(2,2′-bipyridine)2(polyvinylimidazole)10Cl]+/2+(Os(bpy)2PVI) on dealloyed nanoporous gold. The thickness of the deposition layer can be easily controlled by tuning the deposition conditions. Once charged by the internal BFC, the device can be discharged as a supercapacitor at a current density of 2 mA cm−2 providing a maximum power density of 608.8 μW cm−2, an increase of a factor of 468 when compared to the power output from the BFC itself. The hybrid device exhibited good operational stability for 50 charge/discharge cycles and ca. 7 h at a discharge current density of 0.2 mA cm−2. The device could be used as a pulse generator, mimicking a cardiac pacemaker delivering pulses of 10 μA for 0.5 ms at a frequency of 0.2 Hz.