PEDOT:PSS/MnO₂/CNT Ternary Nanocomposite Anodes for Supercapacitive Energy Storage in Cyanobacterial Biophotovoltaics

A high-performance supercapacitive anode integrated into cyanobacterial biophotovoltaics allows the energy produced by the biophotovoltaics to be capacitively stored and delivered through a significant high-power burst. A ternary nanocomposite of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, manganese dioxide (MnO2), and carbon nanotubes was designed to provide unique and critical functions for the development of a fully light-driven biosupercapacitor or a supercapacitive biophotovoltaic device. The nanocomposite on a carbon cloth exhibited a high specific capacitance of 261 F/g in 1 M sodium sulfate (Na2SO4). Even with a thick biofilm of Synechocystis sp. PCC6803 in a BG-11 cyanobacterial growth medium having a low-ionic conductivity, the nanocomposite-covered cloth showed great bioelectrochemical activity under illumination, producing an areal capacitance of 105.2 mF·cm–2 and an energy of 13.2 μW h·cm–2. This nanocomposite integrated in a cyanobacterial biophotovoltaic device serves as a double-function bioanode concurrently exhibiting light-driven bioelectrocatalytic and charge-storage features. It offers the great energy-harvesting capability of biophotovoltaics and the deep power reservoir of an internal supercapacitor through charging and discharging operations. Our hybrid system produced a maximum power density of 162 μW·cm–2 for a 0.1 s pulse at a discharging current density of 300 μA·cm–2, which is about 100 times larger than that of the biophotovoltaic device on an unmodified carbon cloth and about 6 times greater than that of our biophotovoltaic device without the charging–discharging operation. The developed supercapacitive biophotovoltaics represent a revolutionary technological breakthrough that offers a potentially viable long-term and powerful energy source for unattended wireless sensor networks.