Microbial Electrochemical Energy Storage and Recovery in a Combined Electrotrophic and Electrogenic Biofilm

Abstract

Here we report enrichment from a marine-derived inoculum of a nonphotosynthetic electroactive biofilm that is capable of both consuming electricity (electrotrophy) and producing electricity (electrogenesis) from a single electrode. With the alternation of the electrode potential between −0.4 and 0.0 V SHE every 10 min, alternating anodic and cathodic currents increased in lock step (maximum current density of ±1.4 ± 0.4 A/m 2 in both modes, Coulombic efficiency of ∼98% per charge−discharge cycle), which is consistent with alternating between generation and consumption of energy storage compounds by the biofilm. Cyclic voltammetry exhibited a single sigmoid-shaped feature spanning anodic and cathodic limiting currents centered at −0.15 V SHE , a phenomenon not observed to date for an electroactive biofilm, and square wave voltammetry exhibited reversible peaks at −0.15 and −0.05 V SHE , suggesting the same redox cofactor(s) facilitates electron transport at the biofilm−electrode interface in both modes. Hydrogen and carbon monoxide, known energy and/or carbon sources for cellular metabolism, but no volatile fatty acids, were detected in reactors. Cells and cell clusters were spread across the electrode surface, as seen by confocal microscopy. These results suggest that a single microbial electrochemical biofilm can alternate between storing energy and generating power, furthering the potential applicability of bioelectrochemical systems.

Cultivating Electrochemically Active Biofilms at Continuously Changing Electrode Potentials

“…Coulomb efficiencies (CE) in this study refer to the amount of charge ( Q Anode ) passed through the anode versus the theoretical amount of charge which could be gained by the amount of removed COD, in artificial wastewater or real wastewater experiments, respectively. The integration of to determine Q Anode is further calculated as the difference between the areas , as was done and for the reasons explained in another recent study using constant cyclic voltammetry of EAB . The positive falsification of the CE, due to H 2 consumption is to be, in the average worst case, +1.5 % (for calculation see SI).…”

“…The integration of R Idt to determine Q Anode is further calculated as the difference between the areas I < 0 V I > 0 A, as was done and for the reasons explained in another recent study using constant cyclic voltammetry of EAB. [22] The positive falsification of the CE, due to H 2 consumption is to be, in the average worst case, + 1.5 % (for calculation see SI). For the calculations of loading rate, removal rate and removal efficiency the reader is referred to the Supporting Information (SI) to this publication.…”

“…Fast transition or switching between two potentials [19][20][21] 2.2. Slow transition or scanning across a wide range of potentials [22] Maximum power point tracking as method typically falls between 1 and 2.2, [23] however depending on the step (external resistance or potential) width and duration of application (s can rate) varying external resistance, linear sweep/cyclic voltammetry can become equivalent to 2.1. Fast transitions between two potentials yield intermittent enhancement of the current density by exploiting the redox capacitance of electrochemically active biofilms (and their cytochrome pool).…”

Comparison of Two Sustainable Counter Electrodes for Energy Storage in the Microbial Rechargeable Battery

“…These have been reported frequently in biocathodes, but are found in higher relative abundance in bidirectional bioelectrodes, initially operated as anodes before being poised more negative potentiall. Supportive to this hypothesis is the recent report of such an bi-directional electrode by Yates et al, [24] in which growth of electrocatalytic biomass was established by inversion of polarity on a 10 min interval. [21,23] The association of these groups of bacteria specifically with reversed electrodes seems to provide, although not fully, a basis for constructing a bi-directional bioelectrode, in which the biota present can gain energy both by electrogenic oxidation and electrotrophic reduction.…”

“…If successfully established, this could reduce the MRBs footprint by integration of bioanode and biocathode. Supportive to this hypothesis is the recent report of such an bi-directional electrode by Yates et al, [24] in which growth of electrocatalytic biomass was established by inversion of polarity on a 10 min interval. It would be interesting to investigate whether this functionality can be maintained over longer charge/discharge intervals.…”