Electro-active microorganisms play a pivotal role in Bio-electrochemical systems (BESs). However, their performance in terms of current output is not enough for practical applications. In this project we propose the study of charge storage capabilities of electro-active bacteria (EAB) to understand and tackle this limitation. The influence of intermittent potential and substrate composition on biofilm growth and storing mechanisms will be assessed. To this end, optical and electrochemical techniques will be integrated towards a better understanding of electron flows in EAB. These results will provide valuable information to control and optimize biofilms performances in BES.