In this communication we discuss, by means of the metal reducing bacterium Geobacter sulfurreducens, a strategy to use cyclic voltammetry for the study of anodic bioelectrocatalytic electron transfer in microbial fuel cells.

Microbial electrochemistry is the study and application of interactions between living microbial cells and electrodes (i.e. electron conductors, capacitive materials). For a long time this subfield of bioelectrochemistry has been the interest of mainly fundamental researchers. This has considerably changed during the last decade and microbial electrochemistry gained interest from applied researchers and engineers. These researchers took the microbial fuel cell (MFC), which is a system that converts the chemical energy of organic material in wastewater into electric power, from a concept to a technology. In addition, a plethora of derivative technologies, such as microbial electrolysis cells (MECs), microbial desalination cells (MDCs), photomicrobial fuel cells (photoMFCs), microbial electrosynthesis (MES), and biocomputing have been developed. The growing number of systems is often referred to in literature under the termini bioelectrochemical system (BES), microbial electrochemical technology (MET), or electrobiotechnology. Within this article we introduce a classification of technologies based on interfacing microbiology and electrochemistry. We argue that BESs comprise all systems based on bioelectrochemistry, with a further layer of termini through the use of METs. Primary METs are based on extracellular electron transfer (direct or mediated), whereas secondary METs include systems in which electrochemistry is connected – at least through ionic contact – with a microbial process via the electrochemical control or adaptation of environmental parameters, such as pH or metabolite concentration level.

Microbial fuel cells (MFC) are the archetype microbial bioelectrochemical system (BES), producing electricity from microbially catalyzed anodic oxidation processes. The greatest potential of MFC lies in the use of wastewater as a substrate (fuel), which allows combining waste treatment and energy recovery. Recently, a development has been initiated that expands the scope of these bioelectrochemical systems from power generation to an increasing number of further applications. This development has become possible by the introduction of new cathode catalyst concepts. The corresponding devices, here summarized as MXCs—the X standing for the different types and applications—share one common element: the microbial anode. The cathode, however, has to fulfil rather different tasks and thus differs quite remarkably across these systems. In this critical review we analyze the different cathode tasks and the resulting requirements for the respective cathode and discuss the available catalyst options in the light of their major advantages and weaknesses. These catalyst options comprise inorganic, biomolecular as well microbial catalyst systems. Hereby, special emphasis is put on a comparative analysis of chemical and biological cathodes and their individual potentials and limitations. For this purpose, criteria are defined based on relevant properties (performance, price, longevity, etc.) and are evaluated by means of a multi-factor analysis, based on the individual target reaction and catalyst. This analysis is exemplarily elaborated for the oxygen reduction reaction (typical for MFCs) and for the hydrogen production (in MECs) (91 references).