Electroanalysis of microbial anodes for bioelectrochemical systems: basics, progress and perspectives

Abstract

Over about the last ten years, microbial anodes have been the subject of a huge number of fundamental studies dealing with an increasing variety of possible application domains. Out of several thousands of studies, only a minority have used 3-electrode set-ups to ensure well-controlled electroanalysis conditions. The present article reviews these electroanalytical studies with the admitted objective of promoting this type of investigation. A first recall of basics emphasises the advantages of the 3-electrode set-up compared to microbial fuel cell devices if analytical objectives are pursued. Experimental precautions specifically relating to microbial anodes are then noted and the existing experimental set-ups and procedures are reviewed. The state-of-the-art is described through three aspects: the effect of the polarisation potential on the characteristics of microbial anodes, the electroanalytical techniques, and the electrode. We hope that the final outlook will encourage researchers working with microbial anodes to strengthen their engagement along the multiple exciting paths of electroanalysis.

Increasing the temperature is a relevant strategy to form microbial anodes intended to work at room temperature

“…Conversely, such a system is detrimental to CE values, particularly when non-electrochemical reactions compete for the consumption of the substrate, as was the case here. An electroanalytical device properly designed to characterize a microbial anode under the most favourable conditions should result in low Coulombic efficiencies when complex microbial systems are implemented [50], as observed in the present work. The compost leachate may contain various electron acceptors (nitrates, sulphates, etc.)…”

“…The most likely explanation of the low CE values was the presence of acetoclastic methanogenic Archaea that consumed acetate to produce methane and carbon dioxide [62,63]. Because of the low ratio of the electrode surface area to solution volume, used here to work in suitable electroanalysis conditions [50], the effect of planktonic side-reactions was enhanced.…”

“…CEs increased considerably from the first to the third oxidation peak: from 1.42 ± 0.38% to 38.2 ± 5% at 40 C and from 3.1 ± 0.35% to 47.7 ± 5.2% at 25 C. The fact that CE values remained low had two synergetic causes: the small surface area of the electrodes (10 cm 2 ) in comparison with the relatively large solution volume (650 mL) on the one hand, and the richness of the medium on the other hand. As theorized by Rimboud et al [50], an electroanalysis system must implement a working electrode of small surface area in a large volume of solution in order to favour the highest possible current density. Conversely, such a system is detrimental to CE values, particularly when non-electrochemical reactions compete for the consumption of the substrate, as was the case here.…”

“…Characterizing the behaviour of each of the elements that constitute an electro-microbial reactor, by specific analytical experiments, is a pre-requisite to the launch of an engineering-based strategy for the development of the related technologies [49]. The study was therefore carried out in electroanalytical conditions [50] by using a three-electrode set-up to protect the anode from most interactions due to the other elements of the system, and particularly from variations in the kinetics of the auxiliary electrode. The potential applied to the anode was thus perfectly controlled.…”

Understanding extracellular electron transport of industrial microorganisms and optimization for production application

“…82 Within this study, the focus lies rather on process discovery than process optimization for the highest possible rates. Therefore, the BESs were designed to enable multiple simultaneous fully controlled fermentations with a high level of comparability.…”