Electron Communication of Bacillus subtilis in Harsh Environments.

Elucidating the effect of harsh environments on the activities of microorganisms is important in revealing how microbes withstand unfavorable conditions or evolve mechanisms to counteract those effects, many of which involve electron transfer phenomena. Here we show that the non-acidophilic and non-thermophilic Bacillus subtilis is able to maintain activity after being subjected to extreme temperatures (100°C for up to 8 h) and acidic environments (pH = 1.50 for over 2 years). In the process, our results suggest that B. subtilis utilizes an extracellular electron transfer as an electron communication pathway between B. subtilis and the environment that involves the cofactor nicotinamide adenine dinucleotide as an essential participant to maintain viability. Elucidation of the capability of the non-acidophilic and non-thermophilic strain to maintain viability under these extreme conditions could aid in understanding the cell responses to different environments from the perspective of energy conservation pathways.

Core-Shell Co/CoO Integrated on 3D Nitrogen Doped Reduced Graphene Oxide Aerogel as an Enhanced Electrocatalyst for the Oxygen Reduction Reaction.

Here, we demonstrate that Cobalt/cobalt oxide core-shell nanoparticles integrated on nitrogen-doped (N-doped) three-dimensional reduced graphene oxide aerogel-based architecture (Co/CoO-NGA) were synthesized through a facile hydrothermal method followed by annealing treatment. The unique endurable porous structure could provide sufficient mass transfer channels and ample active sites on Co/CoO-NGA to facilitate the catalytic reaction. The synthesized Co/CoO-NGA was explored as an electrocatalyst for the oxygen reduction reaction, showing comparable oxygen reduction performance with excellent methanol resistance and better durability compared with Pt/C.

N-doped crumpled graphene derived from vapor phase deposition of PPy on graphene aerogel as an efficient oxygen reduction reaction electrocatalyst.

Nitrogen-doped crumpled graphene (NCG) is successfully synthesized via vapor phase deposition of polypyrrole onto graphene aerogel followed by thermal treatment. The NCG was explored as an electrocatalyst for the oxygen reduction reaction, showing comparable electrocatalytic performance with the commercial Pt/C in alkaline membrane exchange fuel cells because of the well-regulated nitrogen doping and the robust micro-3D crumpled porous nanostructure.

Anodic microbial community diversity as a predictor of the power output of microbial fuel cells.

The relationship between the diversity of mixed-species microbial consortia and their electrogenic potential in the anodes of microbial fuel cells was examined using different diversity measures as predictors. Identical microbial fuel cells were sampled at multiple time-points. Biofilm and suspension communities were analysed by denaturing gradient gel electrophoresis to calculate the number and relative abundance of species. Shannon and Simpson indices and richness were examined for association with power using bivariate and multiple linear regression, with biofilm DNA as an additional variable. In simple bivariate regressions, the correlation of Shannon diversity of the biofilm and power is stronger (r=0.65, p=0.001) than between power and richness (r=0.39, p=0.076), or between power and the Simpson index (r=0.5, p=0.018). Using Shannon diversity and biofilm DNA as predictors of power, a regression model can be constructed (r=0.73, p<0.001). Ecological parameters such as the Shannon index are predictive of the electrogenic potential of microbial communities.

Bilirubin oxidase bioelectrocatalytic cathodes: the impact of hydrogen peroxide.

Mediator-less, direct electro-catalytic reduction of oxygen to water by bilirubin oxidase (Myrothecium sp.) was obtained on anthracene-modified, multi-walled carbon nanotubes. H2O2 was found to significantly and irreversibly affect the electro-catalytic activity of bilirubin oxidase, whereas similar electrodes comprised of laccase (Trametes versicolor) were reversibly inhibited.

PdNi hollow nanoparticles for improved electrocatalytic oxygen reduction in alkaline environments.

Palladium-nickel (PdNi) hollow nanoparticles were synthesized via a modified galvanic replacement method using Ni nanoparticles as sacrificial templates in an aqueous medium. X-ray diffraction and transmission electron microscopy show that the as-synthesized nanoparticles are alloyed nanostructures and have hollow interiors with an average particle size of 30 nm and shell thickness of 5 nm. Compared with the commercially available Pt/C or Pd/C catalysts, the synthesized PdNi/C has superior electrocatalytic performance towards the oxygen reduction reaction, which makes it a promising electrocatalyst for alkaline anion exchange membrane fuel cells and alkali-based air-batteries. The electrocatalyst is finally examined in a H2/O2 alkaline anion exchange membrane fuel cell; the results show that such electrocatalysts could work in a real fuel cell application as a more efficient catalyst than state-of-the-art commercially available Pt/C.

Hydrogen peroxide produced by glucose oxidase affects the performance of laccase cathodes in glucose/oxygen fuel cells: FAD-dependent glucose dehydrogenase as a replacement.

Hydrogen peroxide production by glucose oxidase (GOx) and its negative effect on laccase performance have been studied. Simultaneously, FAD-dependent glucose dehydrogenase (FAD-GDH), an O2-insensitive enzyme, has been evaluated as a substitute. Experiments focused on determining the effect of the side reaction of GOx between its natural electron acceptor O2 (consumed) and hydrogen peroxide (produced) in the electrolyte. Firstly, oxygen consumption was investigated by both GOx and FAD-GDH in the presence of substrate. Relatively high electrocatalytic currents were obtained with both enzymes. O2 consumption was observed with immobilized GOx only, whilst O2 concentration remained stable for the FAD-GDH. Dissolved oxygen depletion effects on laccase electrode performances were investigated with both an oxidizing and a reducing electrode immersed in a single compartment. In the presence of glucose, dramatic decreases in cathodic currents were recorded when laccase electrodes were combined with a GOx-based electrode only. Furthermore, it appeared that the major loss of performance of the cathode was due to the increase of H2O2 concentration in the bulk solution induced laccase inhibition. 24 h stability experiments suggest that the use of O2-insensitive FAD-GDH as to obviate in situ peroxide production by GOx is effective. Open-circuit potentials of 0.66 ± 0.03 V and power densities of 122.2 ± 5.8 µW cm(-2) were observed for FAD-GDH/laccase biofuel cells.

Low temperature water based electrolytes for MnO2/carbon supercapacitors.

Birnessite nanotubes and activated carbon electrodes have been used in supercapacitor cells to assess the performance of new aqueous based electrolyte systems at temperatures as low as -30 °C. The addition of ethylene glycol to aqueous sodium, lithium, potassium and ammonium sulfates has resulted in electrolytes that are still in liquid phase at such low temperatures. Extensive electrochemical testing showed that in such systems, operation of these aqueous based supercapacitors is possible at -30 °C with a specific capacitance of over 30 F g(-1) and good cycleability.

An optimised glucose oxidase bioelectrode exhibiting high performance direct electron transfer.

A glucose oxidase (GOd) bioelectrode exhibiting high performance, direct electron transfer (DET) has been prepared. Unprecedented redox peak current densities of 1 mA cm(-2) were observed alongside a clear electrochemical response to glucose. This system shows potential as a low cost, high performance enzymatic bioelectrode.

Dynamic changes in the microbial community composition in microbial fuel cells fed with sucrose.

The performance and dynamics of the bacterial communities in the biofilm and suspended culture in the anode chamber of sucrose-fed microbial fuel cells (MFCs) were studied by using denaturing gradient gel electrophoresis (DGGE) of PCR-amplified partial 16S rRNA genes followed by species identification by sequencing. The power density of MFCs was correlated to the relative proportions of species obtained from DGGE analysis in order to detect bacterial species or taxonomic classes with important functional role in electricity production. Although replicate MFCs showed similarity in performance, cluster analysis of DGGE profiles revealed differences in the evolution of bacterial communities between replicate MFCs. No correlation was found between the proportion trends of specific species and the enhancement of power output. However, in all MFCs, putative exoelectrogenic denitrifiers and sulphate-reducers accounted for approximately 24% of the bacterial biofilm community at the end of the study. Pareto-Lorenz evenness distribution curves extracted from the DGGE patterns obtained from time course samples indicated community structures where shifts between functionally similar species occur, as observed within the predominant fermentative bacteria. These results suggest the presence of functional redundancy within the anodic communities, a probable indication that stable MFC performance can be maintained in changing environmental conditions. The capability of bacteria to adapt to electricity generation might be present among a wide range of bacteria.

Spatiotemporal development of the bacterial community in a tubular longitudinal microbial fuel cell.

The spatiotemporal development of a bacterial community in an exoelectrogenic biofilm was investigated in sucrose-fed longitudinal tubular microbial fuel cell reactors, consisting of two serially connected modules. The proportional changes in the microbial community composition were assessed by polymerase chain reaction-denaturing gradient gel electrophoresis (DGGE) and DNA sequencing in order to relate them to the performance and stability of the bioelectrochemical system. The reproducibility of duplicated reactors, evaluated by cluster analysis and Jaccard's coefficient, shows 80-90% similarity in species composition. Biofilm development through fed-batch start-up and subsequent stable continuous operation results in a population shift from γ-Proteobacteria- and Bacteroidetes- to Firmicutes-dominated communities, with other diverse species present at much lower relative proportions. DGGE patterns were analysed by range-weighted richness (Rr) and Pareto-Lorenz evenness distribution curves to investigate the evolution of the bacterial community. The first modules shifted from dominance by species closely related to Bacteroides graminisolvens, Raoultella ornithinolytica and Klebsiella sp. BM21 at the start of continuous-mode operation to a community dominated by Paludibacter propionicigenes-, Lactococcus sp.-, Pantoea agglomerans- and Klebsiella oxytoca-related species with stable power generation (6.0 W/m(3)) at day 97. Operational strategies that consider the dynamics of the population will provide useful parameters for evaluating system performance in the practical application of microbial fuel cells.

A one-compartment fructose/air biological fuel cell based on direct electron transfer.

The construction and characterization of a one-compartment fructose/air biological fuel cell (BFC) based on direct electron transfer is reported. The BFC employs bilirubin oxidase and d-fructose dehydrogenase adsorbed on a cellulose-multiwall carbon nanotube (MWCNT) matrix, reconstituted with an ionic liquid, as the biocathode and the bioanode for oxygen reduction and fructose oxidation reactions, respectively. The performance of the bioelectrode was investigated by chronoamperometric and cyclic voltammetric techniques in a standard three-electrode cell, and the polarization and long-term stability of the BFC was tested by potentiostatic discharge. An open circuit voltage of 663 mV and a maximum power density of 126 microWcm(-2) were obtained in buffer at pH 5.0. Using this regenerated cellulose-MWCNT matrix as the immobilization platform, this BFC has shown a relatively high performance and long-term stability compared with previous studies.

Techniques for the study and development of microbial fuel cells: an electrochemical perspective.

Microbial fuel cells (MFCs) represent a clean and renewable energy resource. To date, power generation in MFCs is severely limited. In order to improve performance, a wide range of techniques have been utilised for a fundamental scientific understanding of the components and processes and also to investigate MFC performance bottlenecks. In this tutorial review, we discuss the electrochemical/electroanalytical techniques employed in recent MFC studies and discusses the principles, experimental implementation, data processing requirements, capabilities, and weaknesses of these techniques.

Direct electron transfer of glucose oxidase immobilized in an ionic liquid reconstituted cellulose-carbon nanotube matrix.

Conductive cellulose-multiwalled carbon nanotube (MWCNT) matrix with a porous structure and good biocompatibility has been prepared using a room temperature ionic liquid (1-ethyl-3-methylimidazolium acetate) as solvent. Glucose oxidase (GOx) was encapsulated in this matrix and thereby immobilized on a glassy carbon surface. The direct electron transfer and electrocatalysis of the encapsulated GOx has been investigated using cyclic voltammetry and chronoamperometry. The GOx exhibited a pair of stable, well defined and nearly symmetric reversible redox peaks. The experimental results also demonstrate that the immobilized GOx retains its biocatalytic activity toward the oxidation of glucose and therefore can be employed in a glucose biosensor. The results show that the bioelectrode modified by the cellulose-MWCNT matrix has potential for use in biosensors and other bioelectronics devices.

Factors affecting the performance of microbial fuel cells for sulfur pollutants removal.

A microbial fuel cell (MFC) has been developed for removal of sulfur-based pollutants and can be used for simultaneous wastewater treatment and electricity generation. This fuel cell uses an activated carbon cloth+carbon fibre veil composite anode, air-breathing dual cathodes and the sulfate-reducing species Desulfovibrio desulfuricans. 1.16gdm(-3) sulfite and 0.97gdm(-3) thiosulfate were removed from the wastewater at 22 degrees C, representing sulfite and thiosulfate removal conversions of 91% and 86%, respectively. The anode potential was controlled by the concentration of sulfide in the compartment. The performance of the cathode assembly was affected by the concentration of protons in the cation-exchanging ionomer with which the electrocatalyst is co-bound at the three-phase (air, catalyst and support) boundary.

Activated carbon cloth as anode for sulfate removal in a microbial fuel cell.

By employing the sulfate-reducing bacterium Desulfovibrio desulfuricans we demonstrate the possibility of electricity generation in a microbialfuel cell (MFC) with concomitant sulfate removal. This approach is based on an in situ anodic oxidative depletion of sulfide produced by D. desulfuricans. Three different electrode materials, graphite foil (GF), carbon fiber veil (CFV), and high surface area activated carbon cloth (ACC), were evaluated for sulfide electrochemical oxidation. In comparison to CFV and GF electrodes, ACC was a superior materialfor sulfide adsorption and oxidation and showed significant potential for harvesting energy from sulfate-rich solutions in the form of electricity. Sulfate (3.03 g dm(-3)) was removed from a bacterial suspension, which represented 99% removal. A maximum power density of 0.51 mW cm(-2) (normalized to geometric electrode area) was obtained with a one-chamber, air-breathing cathode and continuous flow MFC operated in batch mode at 22 degrees C.

Steady-state dc and impedance investigations of H2/O2 alkaline membrane fuel cells with commercial Pt/C, Ag/C, and Au/C cathodes.

The performances of H(2)/O(2) metal-cation-free alkaline anion-exchange membrane (AAEM) fuel cells operated with commercially available Au/C and Ag/C cathodes are reported for the first time. Of major significance, the power density obtained with 4 mg cm(-2) Ag/C (60% mass) cathodes was comparable to that obtained with 0.5 mg cm(-2) Pt/C (20% mass) electrodes, whereas the performance when using the same Ag/C cathode in a Nafion-based acidic membrane electrode assembly (MEA) was poor. These initial studies demonstrate that the oxygen reduction electrokinetics are improved when operating Pt/C cathodes at high pH in AAEM-based fuel cells as compared with operation at low pH (in Nafion-based proton-exchange membrane fuel cells). The results of in situ alternating current impedance spectroscopy were core to the assignment of the source of the limited performances of the AAEM-based fuel cells as being the limited supply of water molecules to the cathode reaction sites. Minimizing the thickness of the AAEM improved the performances by facilitating back-transport of water molecules from the anode (where they are generated) to the cathode. The urgent need for development of electrode architectures that are specifically designed for use in AAEM-based fuel cells is highlighted.

An alkaline polymer electrochemical interface: a breakthrough in application of alkaline anion-exchange membranes in fuel cells.

A novel alkaline polymer has been developed as an interfacial material for use in the preparation of metal-cation-free alkaline membrane electrode assemblies (MEAs) for all-solid-state alkaline fuel cells (AFCs) with long-term performance stability.