Direct Electron Transfer Mechanism Research Articles

Novel Composite Electrode of the Reduced Graphene Oxide Nanosheets with Gold Nanoparticles Modified by Glucose Oxidase for Electrochemical Reactions

Graphene-based composites have been widely explored for electrode and electrocatalyst materials for electrochemical energy systems. In this paper, a novel composite material of the reduced graphene oxide nanosheets (rGON) with gold nanoparticles (NPs) (rGON-AuNP) is synthesized, and its morphology, structure, and composition are characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopic (FTIR), Raman, and UV-Vis techniques. To confirm this material’s electrochemical activity, a glucose oxidase (GOD) is chosen as the target reagent to modify the rGON-AuNP layer to form GOD/rGON-AuNP/glassy carbon (GC) electrode. Two pairs of distinguishable redox peaks, corresponding to the redox processes of two different conformational GOD on AuNP, are observed on the cyclic voltammograms of GOD/rGON-AuNP/GC electrode. Both cyclic voltammetry and electrochemical impedance spectroscopy are employed to study the mechanism of direct electron transfer from GOD to GC electrode on the rGON-AuNP layer. In addition, this GOD/rGON-AuNP/GC electrode shows catalytic activity toward glucose oxidation reaction.

Investigation of the effects of different conductive materials on the anaerobic digestion

In recent years, the efforts of enhancement of the transformation of organic matter into methane have intensified and direct interspecies electron transfer (DIET) mechanisms have great importance in this regard. In this study, magnetite, graphite powder, activated carbon and iron (II) sulfate were used to investigate DIET mechanisms during the conversion of glucose into methane. Obtained methane gas measurements at the end of the 30-day incubation period (37 ± 1 °C) were evaluated with the modified Gompertz model, first-order kinetic model and two-stage first-order kinetic model. Maximum total and soluble COD removal efficiencies were observed in the magnetite-added R2 reactor (73.75% and 90.68%, respectively). While there was no significant difference in terms of cumulative methane gas measurements, a significant decrease was observed in the lag phase time for the magnetite-added R2 reactor (reduced by half) with regard to the modified Gompertz model. According to the first-order kinetic model, the maximum conversion rate of glucose into methane and the peak methane production rate were observed in the graphite powder-added R3 reactor (k = 0.1744 day−1 and 93 mL/day). According to the two-stage kinetic model, the maximum methanation rate was observed in the magnetite-added R2 reactor (k2 = 0.7223 day−1). The sludge in the magnetite-added R2 reactor has best settleability (SVI = 53.4 mL/g).

Electrochemical Valorization of Glycerol on Ni-Rich Bimetallic NiPd Nanoparticles: Insight into Product Selectivity Using in Situ Polarization Modulation Infrared-Reflection Absorption Spectroscopy

Glycerol partial electrooxidation was studied on NixPd1–x (x = 100, 95, 90, and 80 atom %) nanoparticles synthesized using a polyol method. The shape-controlled urchin-like monometallic Ni and spherical NixPd1–x catalysts were synthesized. The morphology, crystal structure, and composition of Ni-rich catalysts were characterized using a number of physicochemical techniques. Detailed electrochemical characterizations showed that Ni and NixPd1–x NPs are active for GEOR and that the reaction follows either the direct electron transfer mechanism at low glycerol concentrations or the indirect electron transfer mechanism at high concentration. Among all investigated electrocatalysts, Ni80Pd20 exhibited the highest current density at lower overpotentials due to both a synergetic effect of Ni and Pd and the smaller particle size of Ni80Pd20. In situ polarization modulation infrared-reflection absorption spectroscopy (PM-IRRAS) at various anodic potentials allowed discriminating the reaction products and intermediates directly on the electrode surface and in the electrolyte solution. PM-IRRAS showed that the main reaction products on NixPd1–x are glyceraldehyde, carbonyl groups for mesoxalate and tartronate ions, carboxylate ions, and traces of carbon dioxide. NixPd1–x catalysts are promising anode materials for glycerol oxidation to value added products and could be potentially combined with cathodic hydrogen production or CO2 electro-reduction processes in alkaline media.

(Invited) Current Understanding and Future Aspects of Direct Electron Transfer Mechanism of Fad Dependent Glucose Dehydrogenase Complex

Direct electron transfer (DET) between enzyme molecule and electrode provides the ideal principle for the enzyme based sensing system. In DET principle the electrons are transferred from enzyme active site to electrode directly in the absence of any additional electron acceptors, or mediators. This intriguing reaction is useful for various biodevices such as biosensors and biofuel-cells, especially by focusing anodic reactions, such as the oxidation of glucose, fructose, and ethanol. The absence of redox mediators in the system enables the operation of the sensor in redox potential closer to the co-factor in the enzyme, reducing the effect of interfering reactions by electroactive compounds in the sample. However, only a limited number of redox enzymes are capable of DET-reaction with electrodes. Among these, several dehydrogenases harboring a redox center in the catalytic subunit/domain and haem which is not involved in catalysis but act as a built-in mediator for electron transfer between enzyme and electrode are reported. One of the representative groups of DET enzymes is the oligomeric dehydrogenases composed of catalytic subunit harboring FAD as a co-factor, and an electron transfer subunit with haem c, the FAD dependent dehydrogenase complexes. Our research group have been engaged in the isolation, characterization, application and engineering of one of the representative FAD-dependent dehydrogenase complexes. FAD glucose dehydrogenase complex (FADGDH). FADGDH is comprised the three distinct subunits: the catalytic subunit (α subunit) that has an FAD cofactor in its redox center, shows catalytic activity, and oxidizes the first hydroxyl group of glucose; the small subunit (γ subunit), a hitch-hiker protein of the bacterial TAT secretion system, which is necessary for the proper folding and secretion of the α subunit; and the three heme-cytochrome c subunit (β subunit) that is in responsible for the transfer of electrons between the active-site cofactor and external electron acceptors. Thanks to the presence of β subunit, FADGDH is capable to transfer electrons directly to an electrode, making FADGDH as the ideal molecule for the 3rd Gen glucose sensors.This paper focuses on biomolecular aspects on DET mechanism of FAD dependent dehydrogenase complexes, considering current increasing number of applicational researches, and recent remarkable progress in understanding their DET mechanism, especially about the recent progress in understanding inter- and intra-molecular electron transfer of FADGDH are introduced. These studies included protein engineering approaches of these molecules, thereby led to construct engineered GDH. Finally, the future prospect of the FAD dependent dehydrogenase complexes will be addressed.

Degradation kinetics and structure-reactivity relation of naphthenic acids during anodic oxidation on graphite electrodes

Naphthenic acids (NAs) are refractory carboxylic acids that are believed to be one of the main causes of the oil sands process water (OSPW) toxicity. Understanding the kinetics, selectivity and structure-reactivity relation is a key factor to evaluate any process proposed for NAs degradation. Anodic oxidation (AO) using graphite anode was investigated for model NA compounds degradation. The degradation of cyclohexane carboxylic acid (CHA) increased with increasing the applied current density from 0.25 to 20 mA/cm2 and followed pseudo first-order degradation kinetics with rates increased from 0.00091 to 0.01 min−1, respectively. Carbonate species in the electrolyte medium had a scavenging effect on the degradation rate. The main oxidation mechanism for CHA during AO using graphite was through oxygenated species generated on the surface of graphite anode. Direct electron transfer (DET) mechanism had no contribution in the degradation of CHA. Structure-reactivity analysis by using different model NA compounds showed that NAs with higher carbon number were preferentially degraded by AO. Branched NAs were more reactive than non-branched NAs only if the branch existed far enough from the carboxylate group. Monocyclic NAs were more reactive than linear NAs but any increase in the cyclicity beyond one ring resulted in reduced reactivity. Aliphatic compounds were found to be more reactive than aromatic compounds and the existence of more than one carboxylate group in the structure hindered the reactivity. The kinetics and structure-reactivity of anodic oxidation for NAs shown that AO using graphite electrodes can be an attractive option for OSPW treatment.

Quantum confinement chemistry of CdS QDs plus hot electron of Au over TiO2 nanowire protruding to be encouraging photocatalyst towards nitrophenol conversion and ciprofloxacin degradation

Solar light harvesting science is ascertained to be the topmost effective green technique in alleviating environmental pollutants. In this respect, we report a visible light active TiO2/Au/CdS QDs nanocomposite which manifested upgraded photocatalytic activity towards the transformation of 2-nitrophenol, 4-nitrophenol, and degradation of ciprofloxacin. Here, TiO2 nanowire is synthesized by a molten flux method with high product yield and crystallinity with organized dimensions. Au nanoparticles are successfully integrated in between TiO2-CdS composite by Reverse Turkevich method. The prepared composites are meticulously characterized by different physical and optoelectronic techniques to inspect the crystal structure, phase purity, optical properties, nanostructured morphology and electrochemical properties. The plasmonic direct hot electron transfer (DET) mechanism is confirmed from UV-Vis DRS spectra. The prepared composite produces 2.98 mA/cm2 of current density under light irradiation. A Longer lifetime of electrons is found from Bode phase plot i.e. 97.4 μs for TiO2/1%Au/3%CdS QDs owing to the integrative cooperation effect of high aspect ratio of TiO2 nanowire, quantum size effect of CdS and the direct hot electron transfer by Au nanoparticle.

Evaluation of Inlet Design and Flow Rate Effect on Current Density Distribution in a Microbial Electrolysis Cell Using Computational Simulation Techniques, Coupling Hydrodynamics and Bioanode Kinetics.

Abstract A theoretical model that describe the effect of design and operational conditions on current density distribution in a bioelectrochemical reactor used as microbial electrolysis cell (MEC) is described in this study. This model is proposed considering an approach where a direct electron transfer mechanism from the biofilm to the electrode surface takes place (mechanism present in most of microbial systems) and is governed by a dual donor-acceptor Nernst-Monod bioelectrochemical kinetic expression. The bioelectrochemical reactor is modelled considering two flow electrochemical reactor designs (a reactor design based in literature reports and a modified system proposed by the authors) operating at different flow inlet velocities and electrical overpotentials. Results obtained from the numerical solution shows that flow distribution is an essential aspect that impact the reactor performance, since concentration profiles and electrical potential-current distributions are strongly dependent on flow regime. Modified inlet configuration displays a more homogeneous fluid distribution and this behavior directly affects the mass transport and current density performance, as a result higher current density values are obtained for such configuration. Finally, it is expected that the information obtained from the analysis carried out in this report will provide us with a theoretical basis to realize the construction of a bioelectrochemical reactor prototype to develop the MEC concept.

Enhancing the Electricity Generation and Nitrate Removal of Microbial Fuel Cells With a Novel Denitrifying Exoelectrogenic Strain EB-1.

Microbial fuel cells (MFCs) have been tentatively applied for wastewater treatment, but the presence of nitrogen, especially nitrate, induces performance instability by changing the composition of functional biofilms. A novel denitrifying exoelectrogenic strain EB-1, capable of simultaneous denitrification and electricity generation and affiliated with Mycobacterium sp., was isolated from the anodic biofilm of MFCs fed with nitrate containing medium. Polarization curves and cyclic voltammetry showed that strain EB-1 could generate electricity through a direct electron transfer mechanism with a maximum power density of 0.84 ± 0.05 W m−2. Additionally, anodic denitrification, as a concurrent metabolism, was demonstrated with an efficient removal rate of 0.66 ± 0.01 kg N m−3 d−1 at a COD/N ratio of 3.5 ± 0.3. Importantly, voltage output was not negatively influenced by nitrate, indicating that the concurrent process of nitrate removal and electricity generation was a limitation of the electron donor rather than an inhibition of the system. Furthermore, various organic materials were successfully utilized as anode donors for strain EB-1, and demonstrated the exciting performances in terms of simultaneous denitrification and electricity generation. Mycobacterium sp. EB-1 thus expands the diversity of exoelectrogens and contributes to the potential applications of MFC for simultaneous energy recovery and wastewater treatment.

Insights into direct interspecies electron transfer mechanisms for acceleration of anaerobic digestion of wastes

Anaerobic digestion of waste organic biomass is a well-known process for conversion of biomass to bioenergy. However, global acceptability of anaerobic digestion process for renewable energy has often been undermined because of its inconsistent or lower rate of biogas production. The overall success of the anaerobic digestion process considerably depends on the interactions between the microbial communities within the digester. The electron transfer through interspecies hydrogen transfer between acetogens and methanogens is a major bottleneck for successful anaerobic digestion process. Recent studies have reported the role of biotic (pili and cytochromes) as well as abiotic (conductive materials) components to accelerate direct interspecies electron transfer between microbial communities in the digester. These transfer mechanisms via biotic components of exoelectrogenic bacteria and methanogenic archaea is thermodynamically more favorable over indirect interspecies electron transfer. However, the use of conductive materials in promoting anaerobic digestion process has been an area of research in the last few years. The process of direct interspecies electron transfer promoting anaerobic digestion process has been investigated evidently in pure microbial cultures; however, there are scanty reports on existence of direct interspecies electron transfer in mixed microbial consortia. The present review highlights the fundamentals and applications of direct interspecies electron transfer-promoted anaerobic digestion process at laboratory scale studies used to improve kinetics of methanogenesis.

A DFT Study on the Radical-Scavenging Properties of Ferruginol-Type Diterpenes

Ferruginol-type diterpenes have been identified in extracts from numerous plant species. These secondary metabolites are characterized by the multifaceted bioactivity and beneficial impact on the human health. Unfortunately, the antioxidant properties and function of these foods components is not well recognized so far. Therefore, in the current study the theoretical calculations based on the Density Functional Theory (DFT) method were undertaken to investigate in details the radical-scavenging mechanism of ferruginol (1) and its derivatives such as hinokiol (2) and sugiol (3) for the first time. According to these results the direct hydrogen atom transfer (HAT) and sequential proton loss electron transfer (SPLET) mechanism was exhibited by the ferruginol-type abietanes in the non-polar media and polar solvents, respectively. Ferruginol (1) and hinokiol (2) were found to be the most promising free radical scavengers with activity comparable to that of butylated hydroxytoluene (BHT), a synthetic antioxidant commonly used in the food industry.

Direct electron transfer (DET) mechanism of FAD dependent dehydrogenase complexes ∼from the elucidation of intra- and inter-molecular electron transfer pathway to the construction of engineered DET enzyme complexes∼

Summary Direct electron transfer (DET) reaction is intriguing for application to biodevices such as biosensors and biofuel-cells. However, for improvement of DET for application to electrochemical devices, the understanding of its mechanism is essential. This review focuses on the recent progress on studies of biomolecular aspects of DET mechanism of flavin adenine dinucleotide (FAD) dependent dehydrogenase complex, especially, glucose dehydrogenase (GDH) and fructose dehydrogenase (FDH). These enzymes are hetero-trimeric membrane bound dehydrogenases, comprised of three distinctive subunits: a catalytic subunit, a small subunit, and an three haem c containing electron transfer subunit. The catalytic subunit was recently elucidated to harbor 3Fe-4S cluster as the FAD primary electron acceptor, and presumably to transfer electron from catalytic subunit to electron transfer subunit. The small subunit is a hitch-hiker protein, which is essential for proper folding and secretion of catalytic subunit into the periplasmic space. The electron transfer subunit has three haem binding motif, which make these enzyme complexes possible for DET. First, application studies of these enzymes to DET-based electrochemical devices are overviewed to address the challenges faced. Next, the recent progress in elucidation of inter- and intra-molecular electron transfer pathway of these enzymes were summarized. Finally, the future prospect of the application of FAD dependent dehydrogenase complexes was addressed.

Direct Electron Transfer of Dehydrogenases for Development of 3rd Generation Biosensors and Enzymatic Fuel Cells.

Dehydrogenase based bioelectrocatalysis has been increasingly exploited in recent years in order to develop new bioelectrochemical devices, such as biosensors and biofuel cells, with improved performances. In some cases, dehydrogeases are able to directly exchange electrons with an appropriately designed electrode surface, without the need for an added redox mediator, allowing bioelectrocatalysis based on a direct electron transfer process. In this review we briefly describe the electron transfer mechanism of dehydrogenase enzymes and some of the characteristics required for bioelectrocatalysis reactions via a direct electron transfer mechanism. Special attention is given to cellobiose dehydrogenase and fructose dehydrogenase, which showed efficient direct electron transfer reactions. An overview of the most recent biosensors and biofuel cells based on the two dehydrogenases will be presented. The various strategies to prepare modified electrodes in order to improve the electron transfer properties of the device will be carefully investigated and all analytical parameters will be presented, discussed and compared.

Enhanced antibacterial activity through the controlled alignment of graphene oxide nanosheets

The cytotoxicity of 2D graphene-based nanomaterials (GBNs) is highly important for engineered applications and environmental health. However, the isotropic orientation of GBNs, most notably graphene oxide (GO), in previous experimental studies obscured the interpretation of cytotoxic contributions of nanosheet edges. Here, we investigate the orientation-dependent interaction of GBNs with bacteria using GO composite films. To produce the films, GO nanosheets are aligned in a magnetic field, immobilized by cross-linking of the surrounding matrix, and exposed on the surface through oxidative etching. Characterization by small-angle X-ray scattering and atomic force microscopy confirms that GO nanosheets align progressively well with increasing magnetic field strength and that the alignment is effectively preserved by cross-linking. When contacted with the model bacterium Escherichia coli, GO nanosheets with vertical orientation exhibit enhanced antibacterial activity compared with random and horizontal orientations. Further characterization is performed to explain the enhanced antibacterial activity of the film with vertically aligned GO. Using phospholipid vesicles as a model system, we observe that GO nanosheets induce physical disruption of the lipid bilayer. Additionally, we find substantial GO-induced oxidation of glutathione, a model intracellular antioxidant, paired with limited generation of reactive oxygen species, suggesting that oxidation occurs through a direct electron-transfer mechanism. These physical and chemical mechanisms both require nanosheet penetration of the cell membrane, suggesting that the enhanced antibacterial activity of the film with vertically aligned GO stems from an increased density of edges with a preferential orientation for membrane disruption. The importance of nanosheet penetration for cytotoxicity has direct implications for the design of engineering surfaces using GBNs.

Development of biocathode during repeated cycles of bioelectrochemical conversion of carbon dioxide to methane

Functioning biocathodes are essential for electromethanogenesis. This study investigated the development of a biocathode from non-acclimated anaerobic sludge in an electromethanogenesis cell at a cathode potential of −0.7V (vs. standard hydrogen electrode) over four cycles of repeated batch operations. The CO2-to-CH4 conversion rate increased (to 97.7%) while the length of the lag phase decreased as the number of cycles increased, suggesting that a functioning biocathode developed during the repeated subculturing cycles. CO2-resupply test results suggested that the biocathode catalyzed the formation of CH4 via both direct and indirect (H2-mediated) electron transfer mechanisms. The biocathode archaeal community was dominated by the genus Methanobacterium, and most archaeal sequences (>89%) were affiliated with Methanobacterium palustre. The bacterial community was dominated by putative electroactive bacteria, with Arcobacter, which is rarely observed in biocathodes, forming the largest population. These electroactive bacteria were likely involved in electron transfer between the cathode and the methanogens.

Quorum sensing signals enhance the electrochemical activity and energy recovery of mixed-culture electroactive biofilms

The impacts of exogenous or endogenous quorum sensing (QS) signaling molecules on mixed-culture electroactive biofilms (EABs), especially extracellular polymeric substances (EPS) and exoelectrogens using direct electron transfer mechanism inside EABs are poorly understood. This research focuses on the influence of acylhomoserine lactones (AHLs), the most common QS signaling molecules for gram negative bacteria, on mixed-culture EABs. Results indicated that both exogenous and endogenous AHLs played the role as regulators to improve the electrochemical activities of EABs. The energy recovery of MFCs increased from 20.5% ± 3.9% to 28.3% ± 4.1% with endogenous AHLs and further rose to 36.2% ± 5.1% with exogenous AHLs, and the start-up period of MFCs shortened from 13 days to 10 days with endogenous AHLs and further reduced to 4 days in the presence of exogenous AHLs. The influences of exogenous and endogenous AHLs were non-instantaneous. They improved some intrinsic properties, i.e. the electrode-associated biomass, the biofilm compactness and the ratio of live/dead cells to obtain superior EABs. Meanwhile, both endogenous and exogenous AHLs increased the concentration and redox activities of EPS. Besides, endogenous AHLs enhanced the diversity of EPS components. Noteworthily, the relative abundance of Geoboacter sp. which is the typical microbe using direct electron transfer mechanism is raised by exogenous AHLs, though so far neither known chemical QS-related gene nor protein has been reported in this genus. These findings will increase the current understanding of QS in EABs and open up an opportunity for regulating mixed-culture MFCs via QS.

The influence of sludge retention time on mixed culture microbial fuel cell start-ups

In this work, the start-ups of air-cathode microbial fuel cells (MFCs) seeds with conventional activated sludge cultivated at different solid retention times (SRTs) are compared. A clear influence of the SRT of the inoculum was observed, corresponding to an SRT of 10days to the higher current density exerted, about 0.2Am−2. This observation points out that, in this type of electrochemical device, it is recommended to use high SRT seeds. The work also points out that in order to promote an efficient start-up, it is not only necessary to use high SRT seeds, but also to feed a high COD concentration. When feeding 10,000ppm COD and keeping SRT of 10 d differences of current densities up to 0.1Am−2 were observed within a cycle. Additionally it was observed that SRT influences direct and indirect electron transfer mechanisms, being the direct mechanisms the most relevant ones, accounting for more than 95% of the total electricity production.

Cooperative growth of Geobacter sulfurreducens and Clostridium pasteurianum with subsequent metabolic shift in glycerol fermentation

Interspecies electron transfer is a common way to couple metabolic energy balances between different species in mixed culture consortia. Direct interspecies electron transfer (DIET) mechanism has been recently characterised with Geobacter species which couple the electron balance with other species through physical contacts. Using this mechanism could be an efficient and cost-effective way to directly control redox balances in co-culture fermentation. The present study deals with a co-culture of Geobacter sulfurreducens and Clostridium pasteurianum during glycerol fermentation. As a result, it was shown that Geobacter sulfurreducens was able to grow using Clostridium pasteurianum as sole electron acceptor. C. pasteurianum metabolic pattern was significantly altered towards improved 1,3-propanediol and butyrate production (+37% and +38% resp.) at the expense of butanol and ethanol production (−16% and −20% resp.). This metabolic shift was clearly induced by a small electron uptake that represented less than 0.6% of the electrons consumed by C. pasteurianum. A non-linear relationship was found between G. sulfurreducens growth (i.e the electrons transferred between the two species) and the changes in C. pasteurianum metabolite distribution. This study opens up new possibilities for controlling and increasing specificity in mixed culture fermentation.

Direct oxygen atom transfer versus electron transfer mechanisms in the phosphine oxidation by nonheme Mn(iv)-oxo complexes.

Direct oxygen atom transfer from a nonheme Mn(iv)-oxo complex, [(Bn-TPEN)MnIV(O)]2+, to triphenylphosphine (Ph3P) derivatives occurs with a significant steric effect resulting from the ortho-substituents on the phenyl group of the Ph3P derivatives, whereas the phosphine oxygenation by a Mn(iv)-oxo complex in the presence of HOTf occurs via an electron transfer mechanism without the substrate-steric effect.

Modification of Gold Electrodes with Bacterial Reaction Centres Immobilized by Laser Induced Forward Transfer (LIFT) Technique for Amperometric Herbicide Detection

The functionalization of screen-printed electrodes (SPEs) with a thin film of reaction centre (RC) proteins from the phototrophic bacterium Rhodobacter (R.) sphaeroides, by means of laser induced forward transfer (LIFT) technique, allowed the fabrication of robust and sensitive bio-hybrid devices for terbutryn detection and analysis. The optimal wiring between RCs and the gold electrode surface, achieved by LIFT, led to the generation of cathodic photocurrents sustained by a direct electron transfer (DET) mechanism, which were attenuated by addition of the herbicide inhibitor.

Cathodic biofilm activates electrode surface and achieves efficient autotrophic sulfate reduction

Recent evidence suggests that autotrophic sulfate reduction could be driven by direct and indirect electron transfer mechanisms in bioelectrochemical systems. However, much uncertainty still exists about the electron fluxes from the electrode to the final electron acceptor sulfate during autotrophic sulfate reduction.In this study, linear sweep voltammetry and chronamperometry coupled to off-gas measurement demonstrates that autotrophic sulfate reduction (0.9±0.1mol SO42−-S m−2 d−1) is driven by electron fluxes from the cathode to sulfate via hydrogen as intermediate, with 95±0.04% Coulombic efficiency towards sulfide production. Moreover, the biofilm-forming sulfate-reducing bacteria (SRBs) enriched on the cathode showed the remarkable ability to consume hydrogen at a rate of 3.9±0.5mol H2 m−2 d−1, outcompeting methanogens and homoacetogens for the hydrogen without the need to add chemical inhibitors.Furthermore, quantitative DAIME-FISH of the microbial communities in z-stack images confirmed that SRBs were more abundant (46.1±3.9%) across the 16±2μm-thick biofilm than Methanobacteriales (13.9±1.8%) and other bacteria (24.8±2.6%) were.Finally, exposing the biofilm to biocidal conditions (pH 3.0, air drying and autoclaving) led to a 27% reduction of the hydrogen production rate, which was nevertheless 5.3 times higher than a bare electrode. Energy dispersive x-ray spectroscopy (EDS) and protein electrode surface analyses revealed the presence of metallic and proteinaceous materials deposited on the surface after biocidal conditions, suggesting that the biofilm was able to modify the electrode surface towards more efficient hydrogen evolution reaction (HER).