Key advances in the roadmap of bio-electrochemical systems: from past to future

In this review, various key parameters are highlighted keeping in mind the journey of bio-electrochemical systems (BESs), starting from the electrochemical abiotic field, firstly towards the battery and fuel cells, and then towards the fully biotic approach of BESs. To start with, the development of abiotic electrochemical systems and the transition to battery and fuel cell is discussed. Then, the broader range of BESs are discussed, which have a similar as well as multifunctional approach for changing chemical energy into electrical energy or vice versa by using microbes as bio-catalysts. For example, in microbial fuel cells (MFCs) or enzymatic fuel cells (EFCs) organic wastes and biomass can be converted into electricity, but in microbial electrolysis cells (MECs) electrical energy is used to produce hydrogen or other products. Recovery of nutrients, metals or removal of recalcitrant compounds can also be done by shaping BESs as per our desired motive. In recent times the discovery of microbial electro-synthesis (MES) process has widely enhanced the spectrum of BESs. For electricity generation, solar energy can also be used in the case of photosynthetic micro-organisms leading to a concept of microbial solar cells (MSCs). Plant microbial fuel cell (PMFCs) are also gaining attention because of the use of rhizo-deposits. Microbial desalination cells (MDCs) are also discussed which utilize the electric potential difference via MFC technology for making water desalination system. The role of nanomaterials in MFC/EFC technology is also discussed in terms of bio-compatibility, electro-catalytic activity, conductivity, reaction activity, bulk resistance, corrosion resistance, stability etc.