Microbial Fuel Cells (MFCs) are commonly developed as organic-matter oxidizing bioanodes with abiotic air cathodes. However, O2 reduction requires active aeration and/or the use of expensive catalysts using noble metals. In this study, 2,7-anthraquinone disulfonate (2,7-AQDS), an organic redox mediator commonly used in aqueous redox flow battery systems (AORFBs), served as a redox-stable intermediate for oxygen reduction. Dual-chamber MFC pilots were developed with 2,7-AQDS in the catholyte under both anoxic and aerobic conditions and compared to pilots with ferricyanide catholytes. In both conditions, cyclic voltammetry studies confirmed similar and efficient electroactivity despite the proximity AQDS formal redox potential to that of acetate oxidation. Mediated air-cathodes achieved open-circuit voltage (OCV) of 510 mV and current densities of 140 μA/cm2, nearly double those of air-only cathodes (72 μA/cm2), while delivering a 33% higher power density (12 mW/m2 vs. 8 mW/m2). Passive catholyte aeration enabled continuous reoxidation of reduced 2,7-AQDS at 8.8 × 10-8 mol/s, exceeding the AQDS reduction rate by the bioanode (2.5 × 10-10 mol/s), thus ensuring effective self-regeneration and stable AQDS concentration. These results demonstrate that AQDS coupled with passive oxygen supply sustains biofilm activity with enhances current and power, and allow long-term / low-maintenance MFC operation and organic-matter oxidation.

Fluorographite is a promising starting material for the synthesis of graphene and graphene oxides via top-down exfoliation routes. C-F bonds in fluorographite can be chemically substituted to form graphene oxides with tuned surface chemistry. However, most defluorination routes reported proceed via fluorographene exfoliation from fluorographite followed by refluxing in organic solvents. Herein a one-pot, biogenic and aqueous route to graphene oxide nanomaterials directly from fluorographite with no pre-exfoliation step is demonstrated. Fluorographite incubation with the electroactive bacterial species Geobacter sulfurreducens yields water-dispersible graphene oxide quantum dots and partially-defluorinated graphene oxides as the main nanomaterial products in a single step. Biocatalysis at ambient temperature and pH proceeds through direct surface contact with bacteria through C-F bond cleavage, with fluorographite serving as the sole electron acceptor for exo-electrogenic respiration. This bioexfoliation strategy presents a sustainable and green synthetic route to functionalised carbon nanomaterials with tuneable size and surface properties under ambient conditions.

This review covers recent advances in the fixing of dinitrogen in microbial bioelectrochemical systems (BES) where bacteria release or accept electron to/from electrodes for their respiratory metabolism, either directly or indirectly. We discuss how BES may be interesting platforms for producing ammonium or biomass from N2 fixation. The potential for N2-fixation in BES is first discussed with a focus on possible metabolism and different mechanism that may lead to an increase of fixed dinitrogen. We then review recent examples where dinitrogen is fixed at the cathodes of BES, either by pure cultures of hydrogenotrophic and/or diazotrophic bacteria using cathodic H2 or reduced redox mediators as the electron, or by mixed enriched consortia. A section is then devoted to the special case of nitrogen fixation at anodic microbial electrode where organic matter oxidation also occurs. Finally, a comparison of the reported current performance of nitrogen fixation in BES with other biotic (anerobic digestion) or abiotic (Haber-Bosch process, electrochemical N2 reduction) is provided together with a perspective on possible optimization and application of this emerging microbial electrochemical and technological process.

Iron is the second most abundant metal in the earth's crust and among the most commonly used metals in industry. Iron is of fundamental importance in electrochemistry due to its rich redox chemistry, which has seen applications in bioelectrochemistry as well as materials in fuel cell electrocatalysts, batteries, and capacitors. This chapter briefly outlines the basic physical and chemical properties of iron including its fundamental thermodynamics and its redox behavior in solution. The electrochemistry of iron is briefly discussed with special emphasis on power sources, including nickel–iron, and iron–air batteries, FeS2 cathodes, iron-nitrogen electrocatalysts for fuel cells and microbial fuel cells based on iron redox proteins.

Electrocatalytic hydrogenation (ECH) of organics of biomass origin represents a promising strategy to enable integration of renewables and circular economy practices. However, most electrocatalysts investigated for ECH remain largely based on precious metals. Nanostructured materials based on transition metals encapsulated in a nitrogenated carbon matrix (M@C:N) offer a promising alternative. Herein, we report on the synthesis of Mo@C:N and W@C:N composites that display the same metal atomic concentrations and thus allow for a comparative study of the effect of the metal centre identity on the properties of such heterostructured materials and their performance in the ECH of benzaldehyde, a diagnostic organic substrate. A combination of structural characterisation methods indicates that the type of metal impacts carbon porosity and metal surface concentration in the synthesised structures. W displays a higher tendency to yield encapsulated nanoparticles compared to Mo, which is instead present with surface excess but at predominantly high oxidation states. Electrolysis studies at varying potentials demonstrate high product rates of benzaldehyde hydrogenation, with good selectivity for the production of the corresponding alcohol vs. the dimerization side product. Turnover frequency (TOF) estimates under the operational conditions tested suggest that replacing Mo-centres with W-centres in M@C:N architectures improves overall performance. A comparison of performance indicators with those for Pt-group metals suggests that W@C:N could be a competitive material for practical implementations of ECH.

Redox flow batteries (RFB) are promising devices for scalable and low-cost energy storage and conversion. Aqueous organic redox flow batteries (AORFBs) employ organic molecules including quinones, flavins and phenazines as active species due to their chemical tuneability, low toxicity and water solubility. However, typical synthetic routes to these molecules involve multiple reaction steps using expensive catalysts and organic solvents, adding significant costs and environmental impact. Organic active species (or redox mediators) with physico-chemical properties similar to synthetic AORFB active species are also ubiquitous in biology, raising the possibility of sustainable biosynthetic strategies for their production. In this perspective we highlight recent progress in the biosynthesis of aqueous organic redox mediators and address challenges for their viable application in AORFBs. We discuss redox mediator secretion by electroactive microorganisms in bioelectrochemical systems as a route to produce AORFB mediators from CO2 and organic waste streams. The unique advantages of applying electroactive microorganisms for mediator biosynthesis are highlighted, while challenges related to scalability, concentration, and stability are addressed. Moreover, we propose Direct coupling of bioelectrochemical/AORFB systems as a single autonomous, hybrid system. Finally, we outline technical, economic and environmental indicators to assess biosynthesised redox mediator applicability in future battery technology.

Carbon porous materials containing nitrogen functionalities and encapsulated iron-based active sites have been suggested as electrocatalysts for energy conversion, however their applications to the hydrogenation of organic substrates via electrocatalytic hydrogenation (ECH) remain unexplored. Herein, we report on a Fe@C:N material synthesized with an adapted annealing procedure and tested as electrocatalyst for the hydrogenation of benzaldehyde. Using different concentrations of the organic, and electrolysis coupled to gas chromatography experiments, we demonstrate that it is possible to use such architectures for the ECH of unsaturated organics. Potential control experiments show that ECH faradaic efficiencies >70 % are possible in acid electrolytes, while maintaining selectivity for the alcohol over the pinacol dimerization product. Estimates of product formation rates and turnover frequency (TOF) values suggest that these carbon-encapsulated architectures can achieve competitive performance in acid electrolytes relative to both base and precious metal electrodes.

We investigate here the ability of N-iodophthalimide (NIPht) to act as a halogen bond (HaB) donor, in comparison with well-known HaB donors N-iodosuccinimide (NISucc) and N-iodosaccharin (NISacc). The structure of NIPht itself is reported, together with those of neutral adducts with 4-dimethylaminopyridine (DMAP), 4,4 '-bipyridine and 2,2 '-bipyridine derivatives. Comparison with analogous adducts involving NISucc and NISacc shows that NIPht behaves essentially like NISucc as a HaB donor, both forming weaker adducts than NISacc with a given Lewis base. A symmetric anionic complex [NPht-I-NPht](-) is isolated in the presence of [K(18-crown-6)](+). It exhibits N-I distances very close to those observed in the known [NSucc-I-NSucc](-) and [NSacc-I-NSacc](-) species (2.24-2.26 & Aring;), confirming the 3-center-4-electron (3c-4e) character of the bonding in these species. This similarity confirms the peculiar character of the only other reported salt of [NPht-I-NPht](-), namely [Me4N][NPht-I-NPht], where the longer N-I distances (2.29 & Aring;) are a consequence of a specific solid-state arrangement and C-H & ctdot;O hydrogen bonds.

A nitrate reducing microbial biocathode was developed through constant polarization at -0.5 V vs SCE using two types of inoculums: a pure culture of Thiobacillus denitrificans and water collected from the artificial wetland of Rampillon (France). The results show a clear increase of the nitrate removal efficiency for the Pilots with the natural water although no catalytic nitrate reduction can be evidenced by cyclic voltammetry. Further studies show a catalytic oxygen reduction through exo-electrogenic metabolism and a correlation between the cathode polarization at -0.5 V vs SCE and the nitrate remediation. 16S rRNA gene amplicon sequencing of the biofilm bacterial DNA shows a very large predominance of Pseudomonas, a genus that includes many species able to reduce nitrate and/or reduce dioxygen (O2) using electrons from a cathode. The increased nitrate reduction performance is hypothesized to arise from an indirect bioelectro-assistance that allows the emergence of local anoxic conditions caused by microbial endo-electrogenic pathway for oxygen reduction.

Bi- and trimetallic platinum(bipyridine)(dithiolene) complexes involving different organic linkers between the redox active platinum(dithiolene) moieties have been synthesized and studied by electrochemistry and spectroelectrochemistry. Cyclic voltammetry experiments carried out on these multinuclear complexes in dichloromethane using [NBu4][PF6] as the supporting salt show only one oxidation process involving the metallacycles. Nevertheless, spectro-electrochemical studies, carried out under the same conditions, show a different evolution of the spectra during oxidation depending on the position of the metallacycles on the phenyl ring. For instance, only the 1,3-disubtituted (Pt21,3-P) and 1,3,5-trisubstituted (Pt31,3,5-P) complexes show the growth of an absorption band in the NIR region upon oxidation while it was not observed for the other complexes. In contrast, electrochemical studies carried out using the poorly coordinating supporting electrolyte, [Na][B(C6H4(CF3)2)4], indicate sequential oxidation of the redox centers with Delta E values varying according to the nature of the bridge and the distance between metal centers. For all the investigated multinuclear complexes, spectro-electrochemical experiments performed in the presence of [Na][B(C6H4(CF3)2)4] show an absorption band in the NIR region consistent with appreciable electrostatic effects and charge delocalization in the mixed valent intermediates.

N-doped graphene oxides (GO) are nanomaterials of interest as building blocks for 3D electrode architectures for vanadium redox flow battery applications. N- and O-functionalities have been reported to increase charge transfer rates for vanadium redox couples. However, GO synthesis typically yields heterogeneous nanomaterials, making it challenging to understand whether the electrochemical activity of conventional GO electrodes results from a sub-population of GO entities or sub-domains. Herein, single-entity voltammetry studies of vanadyl oxidation at N-doped GO using scanning electrochemical cell microscopy (SECCM) are reported. The electrochemical response is mapped at sub-domains within isolated flakes and found to display significant heterogeneity: small active sites are interspersed between relatively large inert sub-domains. Correlative Raman-SECCM analysis suggests that defect densities are not useful predictors of activity, while the specific chemical nature of defects might be a more important factor for understanding oxidation rates. Finite element simulations of the electrochemical response suggest that active sub-domains/sites are smaller than the mean inter-defect distance estimated from Raman spectra but can display very fast heterogeneous rate constants >1 cm s(-1). These results indicate that N-doped GO electrodes can deliver on intrinsic activity requirements set out for the viable performance of vanadium redox flow battery devices.

Microbial Fuel Cells (MFC) convert energy stored in chemicals into electrical energy thanks to exoelectrogenic microorganisms who also play a crucial role in geochemical cycles in their natural environment, including that of iron. In this study, we investigated paleomarine sediments as inoculum for bioanode development in MFCs. These sediments were formed under anoxic conditions ca. 113 million years ago and are rich in clay minerals, organic matter, and iron. The marlstone inoculum was incubated in the anolyte of an MFC using acetate as the added electron donor and ferricyanide as the electron acceptor in the catholyte. After seven weeks of incubation, the current density increased to 0.15 mA.cm(-2) and a stable + 700 mV open circuit potential was reached. Community analysis revealed the presence of two exoelectrogenic bacterial genera, Geovibrio and Geobacter. Development of electroactive biofilms was correlated to bulk chemical transformations of the sediment inoculum with an increase in the Fe(II) to Fe-total ratio. Comparisons to sediments sterilized prior to inoculation confirmed that bioanode development derives from the native microbiota of these paleomarine sediments. This study illustrates the feasibility of developing exoelectrogenic biofilms from iron-rich marlstone and has implications for the role of such bacteria in broader paleoenvironmental phenomena.

Polypyrrole films are commonly prepared as conductive electrode surfaces for a variety of applications. Recently, there has been increasing interest in improving the adhesive properties and biocompatibility of polypyrrole electrodes via the incorporation of bioinspired polydopamine within the polymer scaffold. However, very little is currently known about the structural effects of polydopamine incorporation during the electropolymerisation of hybrid films. In this work, we combine electrochemical quartz crystal microbalance studies, fundamental electrochemical characterisation, atomic force microscopy, and a suite of spectroscopic techniques in order to correlate changes in the structure and performance of polypyrrole–polydopamine films to the structural modifications of the nanostructure induced by polydopamine incorporation. The results indicate that polydopamine incorporation greatly increases the rate of hybrid film deposition, as well as improving adhesion, surface homogeneity, and wettability, with no compromise in charge transfer properties. Polydopamine incorporation is strongly suggested to occur in non-connected domains within a predominantly polypyrrole-like scaffold. We propose a two-step model of co-polymerisation and the subsequent surface adhesion of hybrid films. Results are expected to be of broad general interest to researchers utilizing polypyrrole and polydopamine to prepare tailor-made electrodes for biosensing and catalysis.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Synthesis, X-ray characterization together with ESP calculations of neutral and oxidized tetrathiafulvalenes able to form non-covalent interactions have been explored.

AbstractThis article gives an up‐to‐date (2023) account on the bioinorganic basis for extracellular electron transfer (EET) in electroactive bacteria. These microorganisms connect their respiratory metabolism to extracellular solid electron acceptors or donors, typically metal oxides of iron or manganese. Thanks to this peculiar property, electroactive bacteria can develop as biofilms at electrodes, be studied electrochemically, and form the basis of diverse potential applications termed microbial electrochemical systems (MES). The metalloproteins forming the respiratory chain from NADH oxidation to the reduction of the terminal solid electron acceptor are described in detail for the most studied Gram‐negative electroactive strains developed at anodes:Shewanella oneidensisMR‐1 andGeobacter sulfurreducens. Although less efficient than their Gram‐negative counterpart and sometimes referred to as weak electricigens, an example of electroactive anodophile Gram‐positive bacteria,Thermincolasp., is also discussed. The key cytochromes involved in the electron transport chain are discussed such as outer membranec‐type cytochromes (Omc) and multiheme cytochromes, forming by self‐assembly up to micrometer‐long electron conductive extracellularpilior nanowires. The case of microorganisms that uptake electrons from solid extracellular electron donors is addressed with a highlight on photoferrotrophs and cathodic denitrifying bacteria. Finally, the common strategy developed by different bacteria to electrically connect different types of respiratory metabolism is stressed together with the apparent ubiquity of EET across life domains including archaea.

Bioelectrochemical systems which employ microbes as electrode catalysts to convert chemical energy into electrical energy (or conversely), have emerged in recent years for water sanitation and energy recovery. Mi-crobial biocathodes, and especially those reducing nitrate are gaining more and more attention. The nitrate -reducing biocathodes can efficiently treat nitrate-polluted wastewater. However, they require specific condi-tions and they have not yet been applied on a large scale. In this review, the current knowledge on nitrate -reducing biocathodes will be summarized. The fundamentals of microbial biocathodes will be discussed, as well as the progress towards applications for nitrate reduction in the context of water treatment. Nitrate-reducing biocathodes will be compared with other nitrate-removal techniques and the challenges and opportunities of this approach will be identified.

Exo-electrogenic microorganisms have been extensively studied for their ability to transfer electrons with solid surfaces using a large variety of metabolic pathways. Most of the studies on these microorganisms consist in the replacement of solid electron acceptors such as Fe(III) oxides found in nature by electrodes with the objective of generating harvestable current in devices such as microbial fuel cells. In this study we show how the presence of solid ferric oxide (Fe2O3) particles in the inoculum during bio-anode development influences extracellular electron transfer to the electrode. Amplification and sequencing of the 16S rRNA (V4-V5 region) show bacteria and archaea communities with a large predominance of the Pelobacter genus, which is known to be phylogenetically close to the Geobacter genus, regardless of the presence or absence of ferric oxide in the inoculum. Data indicate that the bacteria at the bio-anode surface can preferentially utilize solid ferric oxide as terminal electron acceptors instead of the anode, though extracellular electron transfer to the anode can be restored by removing the particles. Mixed inoculum commonly used to develop bioanodes may produce similar bacterial communities with divergent electrochemical responses due to the presence of alternate electron acceptors, with direct implications for microbial fuel cell performance.