DOI: 10.1002/cssc.201100720 Linking Bacterial Metabolism to Graphite Cathodes: Electrochemical Insights into the H 2 -Producing Capability of Desulfovibrio sp. Federico Aulenta,* [a, b] Laura Catapano, [a] Laura Snip, [a, c] Marianna Villano, [a] and Mauro Majone [a] Introduction The possibility of converting and storing electrical energy pro- duced from renewable sources (e.g., sunlight, wind, or organic wastes) into chemical fuels such as H 2 is a major scientific and technological challenge that could have, in the future, a re- markable impact on our energy systems. [1–3] In this respect, the discovery that electricity can be directly fed to bacteria that use it to produce reduced (value-added) compounds is attract- ing considerable attention. The electricity-driven and microbial- ly catalyzed synthesis of (gaseous and liquid) fuels or chemicals is an emerging field of research, which is commonly referred to as “microbial electrosynthesis”. [4–6] The idea of using electrodes as electron donors for metabo- lite production is not completely new since it was initially pro- posed by Park and Zeikus, who demonstrated that fumarate can be reduced to succinate at a high efficiency by providing Actinobacillus succinogenes with electrical current and dissolved neutral red (NR) as an electron shuttle. [7] Similarly, electrically reduced NR was successfully used to stimulate growth and methane production (from carbon dioxide reduction) by a mixed anaerobic culture enriched from an anaerobic sludge. [8] A major breakthrough in the field of microbial electrosynthe- sis was the discovery that electron transfer from a polarized electrode (cathode) to living cells of the Geobacter species could be achieved even in the absence of externally supplied redox mediators. [9] Cells of Geobacter metallireducens attached onto a graphite cathode poised at À300 mV vs. the standard hydrogen electrode (SHE), were shown to reduce nitrate to ni- trite with the expected stoichiometry of electron consump- tion. [9] Recently, published studies have suggested that extra- cellular electron transfer (to electrodes, minerals, or other mi- croorganisms) in Geobacter species is linked to the capacity of this microorganism to form highly conductive networks of fila- ments that transfer electrons along their length with organic metallic-like conductivity. [10] It remains unclear, whether in Geo- bacter spp. similar mechanisms mediate the electron transfer in the reverse direction, that is, from electrodes to microbes, which is the basis for microbial electrosynthesis. In a recent literature review, a key role of hydrogenases in the uptake of electrons in hydrogenophilic bacteria, and there- fore also possibly in certain species of Geobacter , has been pro- posed. [11] This latter hypothesis is consistent with the ability of Microbial biocathodes allow converting and storing electricity produced from renewable sources in chemical fuels (e.g., H 2 ) and are, therefore, attracting considerable attention as alterna- tive catalysts to more expensive and less available noble metals (notably Pt). Microbial biocathodes for H 2 production rely on the ability of hydrogenase-possessing microorganisms to catalyze proton reduction, with a solid electrode serving as direct electron donor. This study provides new chemical and electrochemical data on the bioelectrocatalytic activity of De- sulfovibrio species. A combination of chronoamperometry, cyclic voltammetry, and impedance spectroscopy tests were used to assess the performance of the H 2 -producing microbial biocathode and to shed light on the involved electron transfer mechanisms. Cells attached onto a graphite electrode were found to catalyze H 2 production for cathode potentials more reducing than À900 mV vs. standard hydrogen electrode. The highest obtained H 2 production was 8 mmol L À1 per day, with a Coulombic efficiency close to 100 %. The electrochemical per- formance of the biocathode changed over time probably due to the occurrence of enzyme activation processes induced by extended electrode polarization. Remarkably, H 2 (at least up to 20% v/v) was not found to significantly inhibit its own production. [a] Dr. F. Aulenta, L. Catapano, L. Snip, Dr. M. Villano, Prof. M. Majone Department of Chemistry Sapienza University of Rome P.Le Aldo Moro 5, 00185 Rome (Italy) Fax: (+ 39) 06-490631 E-mail : federico.aulenta@uniroma1.it [b] Dr. F. Aulenta Water Research Institute National Research Council (CNR-IRSA) Via Salaria km 29.300 C.P. 10, 00015 Monterotondo (RM) (Italy) E-mail: aulenta@irsa.cnr.it [c] L. Snip Sub-Department of Environmental Technology Wageningen University Bornse Weilanden 9, 6700 AA Wageningen (The Netherlands) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201100720. 1080  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemSusChem 2012, 5, 1080 – 1085