Microbial electrochemical energy storage and recovery in a combined electrotrophic and electrogenic biofilm

Authors: YATES, MATHEW - Naval Research Laboratory; MA, LI - University Of California; SACK, JOSHUA - Dickinson College; GOLDEN, JOEL - Naval Research Laboratory; STRYCHARZ-GLAVEN, SARAH - Naval Research Laboratory; Yates, Scott; TENDER, LEONARD - Naval Research Laboratory

Submitted to: Environmental Science and Technology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/23/2017
Publication Date: 8/23/2017
Citation: Yates, M.D., Ma, L., Sack, J., Golden, J.P., Strycharz-Glaven, S.M., Yates, S.R., Tender, L.M. 2017. Microbial electrochemical energy storage and recovery in a combined electrotrophic and electrogenic biofilm. Environmental Science and Technology Letters. 4:374-379. https://pubs.acs.org/doi/ipdf/10.1021/acs.estlett.7b00335.
DOI: https://doi.org/10.1021/acs.estlett.7b00335

Interpretive Summary: Energy storage is needed for on-demand power systems to accommodate variable rates of power usage. Batteries are the primary method to store energy because they are capable of high energy and current densities and are relatively inexpensive. While battery technology has improved during the past decade, there are still challenges associated with their use. Batteries are often made from refined, finite materials, suffer from significant performance degradation with repeated charging-discharging over a period of months, and contain potentially hazardous materials. Storing the energy obtained from renewable energy sources presents a challenge for traditional battery-based systems because the power generated from solar, wind, tides, hydro-, or geo-thermal energy is often produced during off-peak hours and must be stored for use during on-peak hours. Bioelectrochemical systems provides an alternative by utilizing microorganisms in a system that is able to store and convert energy. This approach holds promise as an alternative to traditional battery storage because the materials (i.e., catalysts) naturally occur and regenerate. Biofilms harboring electroactive microorganisms on electrodes are able to convert different forms of energy to useful end products. For example, microbial fuel cells are able to convert chemical energy into electrical energy. To date, lasting bi-directional electrodes have only been observed in phototrophic systems, where battery currents (charge or discharge) can be generated by cycling photosynthetic end products (oxygen and fixed carbon). In these systems, significant anodic currents are only produced in the dark and cathodic currents in the light and these photosynthetic systems have limited current densities. This manuscript describes research to address these limitations by enriching an electroactive biofilm capable of microbial electro-synthesis and power production on a single electrode by repeated switching of the electrode potential. Furthermore, the current densities were found to be an order of magnitude higher than photosynthetic bi-directional electrodes. This research indicates it may be feasible to produce a self-sustaining, light-independent biofilm capable of energy conversion and storage through the interconversion of chemical and electrical energy. While this exploratory research will require further development before practical application is achieved, it is hoped that this technology will one day enable inexpensive energy production in remote locations, such as farms and ranches; and in a more environmentally benign manner since there is no need for catalysts/acids found in traditional batteries.

Technical Abstract: Electroactive biofilms, used as biocatalysts in bioelectrochemical systems (BESs), are usually operated either as electrogenic (the electrode is the electron acceptor) or electrotrophic (the electrode is the electron donor). Here, we enriched a non-photosynthetic bifunctional electroactive biofilm capable of both electrogenic and electrotrophic processes. By operating the electrode sequentially as an anode (+0.0V vs SHE) and a cathode (–0.4V vs SHE), we enriched a single community capable of interconverting between generating electrical and chemical energy with a maximum current density of ±1.4 ± 0.4 A/m2 with a coulombic efficiency of ~91%. Cyclic voltammograms exhibited a sigmoidal shape and square wave voltammograms exhibited reversible peaks at –0.15V and –0.05V, suggesting surface bound redox mediators facilitated electron transport to/from the electrode surface. Hydrogen, carbon monoxide, and methane were detected in the headspace of most reactors and acetate in the medium of some reactors. Cells and cell clusters were spread across the electrode surface, as seen by confocal laser scanning microscopy. These results indicate that a light-independent electroactive biofilm is capable producing relatively high current densities using vastly different potential-dependent metabolic processes on a single electrode, furthering the potential relevance of BESs as alternative biotechnologies in energy storage and conversion applications.