Electrochemical capacitive performance of intact anaerobic granular sludge-based 3D bioanode

In search of clean, renewable and efficient supercapacitors, electrogenic microbes have been shown as a promising alternative biomaterial for energy storage. In this study, intact methanogenic granular sludge with a unique spherical structure consisting of dense microbial community was for the first time demonstrated as an efficient exoelectrogenic bioanode of supercapacitor for energy storage. The maximum capacity of 1542.7 ± 203.2 mC is achieved by the exoelectrogenic granular sludge (EGS, 20 g) based bioanode at the anodic potential of +0.2 V VS Ag/AgCl and with 5 min charge and 10 min discharge cycle. The capacitance of the EGS bioanode is 2-3 orders of magnitude higher compared to methanogenic one. The amount of EGS is found critical to the system capacitance. The electrochemical behavior of single EGS suggests the cytochromes, which had close contact with the flat graphite or gold wire electrode, plays an important role as an electron conduit between the electrochemical granule and the electrodes. The superior electron storage capacity of the EGS is probably related to its potential double-layer structure and enrichment of exoelectrogenic bacteria having conductive c-type cytochromes. This proof-of-concept study offers insights into the future development of bio-based sustainable, low cost and environmental-friendly supercapacitor.