Supercapacitors in bioelectrochemical systems

Bioelectrochemical systems (BESs) are devices composed of two electrodes: (1) an anode and a cathode and a (2) separator that can be a solid (e.g., membrane) or a liquid (e.g., electrolyte) [1, 2]. At the anode, the oxidation reaction occurs while at the cathode reduction reaction takes place. Different from classical abiotic electrochemical systems such as fuel cells, batteries, and supercapacitors, BESs have biotic components and features in at least one of the two electrodes [1, 2]. It may happen that both of the electrodes experience and interact with the biotic matter. The biotic components are generally microorganisms and enzymes that categorize fuel cells called microbial fuel cells (MFCs) [1, 2] and enzymatic fuel cells (EFCs) [3]. The latter are also known as a general term, that is, biofuel cells (BFCs). BESs dealing with microorganisms can also be exploited for the following: (i) generating hydrogen at the cathode under an external voltage supply in a microbial electrolysis cell (MEC); (ii) reducing carbon dioxide to methane, acetate, or other valuable compounds in a microbial electrosynthesis cell (MEC); (iii) desalinate water while producing electricity (MDC) [2].