Cathodic and anodic biofilms in Single Chamber Microbial Fuel Cells P. Cristiani a, ⁎, M.L. Carvalho a , E. Guerrini a , M. Daghio b , C. Santoro c, d , B. Li c, d a RSE — Ricerca sul Sistema Elettrico S.p.A., Environment and Sustainable Development Department, Via Rubattino 54, 20134 Milan, Italy b Department of Earth and Environmental Science, University of Milano-Bicocca DISAT, Piazza della Scienza, 1-20126 Milan, Italy c Department of Civil and Environmental Engineering, University of Connecticut, 261 Glenbrook Rd., Unit 2037, Storrs, CT 06269-2037, USA d Center Clean Energy Engineering (C2E2), University of Connecticut, 44 Weaver Rd., Unit 5233, Storrs, CT 06269-5233, USA abstract article info Article history: Received 5 October 2012 Received in revised form 28 January 2013 Accepted 29 January 2013 Available online 8 February 2013 Keywords: Microbial fuel cell Single chamber Membraneless Biocathode Anodic overpotential The oxygen reduction due to microaerophilic biofilms grown on graphite cathodes (biocathodes) in Single Chamber Microbial Fuel Cells (SCMFCs) is proved and analysed in this paper. Pt-free cathode performances are compared with those of different platinum-loaded cathodes, before and after the biofilm growth. Membraneless SCMFCs were operating in batch-mode, filled with wastewater. A substrate (fuel) of sodium acetate (0.03 M) was periodically added and the experiment lasted more than six months. A maximum of power densities, up to 0.5 W m -2 , were reached when biofilms developed on the electrodes and the cathodic potential decreased (open circuit potential of 50–200 mV vs. SHE). The power output was almost constant with an acetate concentration of 0.01–0.05 M and it fell down when the pH of the media exceeded 9.5, independently of the Pt-free/Pt-loading at the cathodes. Current densities varied in the range of 1–5 Am -2 (cathode area of 5 cm 2 ). Quasi-stationary polarization curves performed with a three-electrode configuration on cathodic and anodic electrodes showed that the anodic overpotential, more than the cathodic one, may limit the current density in the SCMFCs for a long-term operation. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Microbial Fuel Cells (MFCs) represent an innovative electrochem- ical bio-technology capable of generating electricity from organic substances. The application of microbial electrogenic phenomena in wastewater plants as well as to specific industrial biomass substrates (e.g. corn stover, landfill leachate, lignocellulosic biomass) have been already investigated [1–3]. Nevertheless, this technology still lacks in systematic laboratory studies aimed to develop simple and cost- effective systems [4,5]. Many MFC studies use the components derived from low temperature hydrogen fuel cell devices, such as polymeric electrolyte membrane (PEM) [6] and abiotic, chemically catalysed cathodes based on platinum-loaded materials [7]. These components are the most expensive parts of MFCs, and act as the major bottleneck for developing large-scale MFC systems. The membraneless SCMFC is a promising simplified system, where both cathode and anode are directly exposed to a microbial consor- tium [8]. Bacteria colonize the electrodes forming biofilms which are good ionic conductors, since they contain more than 90% of water [9]. Furthermore, cathodic biofilms can contribute to preserve the anaerobic conditions in the media in the absence of a membrane, consuming oxygen incoming from the porous cathode. The aerobic biofilm was demonstrated to be able to catalyse the oxygen reduction to water on stainless steel. This phenomenon was studied in lab-scale marine MFCs [10–13] and already exploited in biofilm sensors for industrial cooling waters [14] as well. From brackish water/sediments MFC tests it was underlined also the capability of carbon biocathodes to catalyse the oxygen reduction reaction [15]. Be- cause of the previous studies, it was reasonable to suppose that cathodic biofilms have the ability to transform inorganic cathodes into more active microbial catalysed “biocathodes” also in SCMFCs fed with wastewater, thus avoiding the use of expensive Pt catalysts and reducing the MFC costs. There is a specific issue for Pt-loaded cathodes directly in contact with organic substances in SCMFCs [16], beside the cost. The oxidation by-products generated from the degradation of organic substances could cover the Pt catalyst on cathodes. This phenomenon substantially reduces the Pt efficiency [17]. Finally, Pt has high catalyst capability at low pH [18]. Neutral or alkaline conditions (typical of wastewaters) decrease the Pt's electrocatalytic activity [19]. In this study, electrochemical performances of membraneless SCMFCs with different Pt-loaded and Pt-free graphite based cathodes, before and after the anaerobic biofilm growth, were compared. During the six months of the experimentation, it was demonstrated that biocathodes can work better than inorganic platinum-based cathodes in wastewaters in addition with sodium acetate. Some as- pects, related to the power enhancement, the pH modification and Bioelectrochemistry 92 (2013) 6–13 ⁎ Corresponding author. Tel.: +39 0239924655; fax: +39 0239924608. E-mail addresses: pierangela.cristiani@rse-web.it (P. Cristiani), marialeonor.carvalho@rse-web.it (M.L. Carvalho), edoardo.guerrini@rse-web.it (E. Guerrini), m.daghio@campus.unimib.it (M. Daghio), carlo.santoro@uconn.edu (C. Santoro), baikun.li@uconn.edu (B. Li). 1567-5394/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.bioelechem.2013.01.005 Contents lists available at SciVerse ScienceDirect Bioelectrochemistry journal homepage: www.elsevier.com/locate/bioelechem