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Platinum group metal nanoparticles (Pt, Pd, and Rh) were synthesized in aqueous NaCl solutions using, as reducing agent, H2/CO electrogenerated in situ by the reduction of CO2 and water.

As a result of their unique physical, chemical and/or biological properties, the use of engineered nanoparticles (ENPs) is growing very rapidly. Iron oxide nanoparticles (IONPs) are of particular interest owing to their magnetic properties, and thus the development of suitable methods for their characterization is essential. Inductively coupled plasma-mass spectrometry (ICP-MS) operated in single-particle (SP) mode provides different types of relevant information, such as size distribution and particle number and mass concentrations. However, the use of SP-ICP-MS becomes less straightforward when the analyte signal is subject to spectral overlap. In the case of IONPs, characterization by means of SP-ICP-MS is hindered by the occurrence of ArO+ polyatomic ions with the same nominal mass-to-charge (m/z) ratio as the most abundant Fe isotope. In this work, different approaches relying on either chemical or physical (mass) resolution, to avoid this spectral interference otherwise jeopardizing accurate results, were assessed. In the case of chemical resolution, the performance of on-mass and mass-shift approaches was evaluated using different types of quadrupole-based ICP-MS instrumentation, including single-quadrupole (SQ) and tandem ICP-MS (ICP-MS/MS) units. Physical resolution was accomplished using a new generation of sector field (SF) ICP-MS instrumentation, capable of dealing with transient signals of extremely short duration (10–100 μs dwell time), even when operated at higher mass resolution (pseudo-resolution mode). Based on the figures-of-merit obtained for the different approaches evaluated, an on-mass approach using NH3 as the reaction gas in SQ-ICP-MS, an on-mass approach using H2 as the collision/reaction gas in ICP-MS/MS and pseudo-medium resolution in SF-ICP-MS were found to be the best-suited approaches for fast interference-free monitoring of the ion signals generated by IONPs in SP mode. While the use of chemical (H2/on-mass) and physical (pseudo-medium) resolutions also provided accurate and precise results for custom-made Fe3O4 (magnetite) NPs of ≈50 nm, the use of NH3 was less successful, as it leads to an extension of the SP pulse profile and a lower signal-to-background ratio. Finally, SF-ICP-MS operated in pseudo-medium resolution mode was used for the characterization of Fe3O4 NPs synthesized electrochemically (batch and continuous operation mode).

The electrosynthesis of iron oxide nanoparticles offers a green route, with significant energy and environmental advantages. Yet, this is mostly restricted by the oxygen solubility in the electrolyte. Gas-diffusion electrodes (GDEs) can be used to overcome that limitation, but so far they not been explored for nanoparticle synthesis. Here, we develop a fast, environmentally-friendly, room temperature electrosynthesis route for iron oxide nanocrystals, which we term gas-diffusion electrocrystallization (GDEx). A GDE is used to generate oxidants and hydroxide in-situ, enabling the oxidative synthesis of a single iron salt (e.g., FeCl2) into nanoparticles. Oxygen is reduced to reactive oxygen species, triggering the controlled oxidation of Fe2+ to Fe3+, forming Fe3−xO4−x (0 ≤ x ≤ 1). The stoichiometry and lattice parameter of the resulting oxides can be controlled and predictively modelled, resulting in highly-defective, strain-heavy nanoparticles. The size of the nanocrystals can be tuned from 5 nm to 20 nm, with a large saturation magnetization range (23 to 73 A m2 kg−1), as well as minimal coercivity (~1 kA m−1). Using only air, NaCl, and FeCl2, a biocompatible approach is achieved, besides a remarkable level of control over key parameters, with a view on minimizing the addition of chemicals for enhanced production and applications.

Lithium is a critical raw material for developing current lithium-ion batteries and prospective next-generation batteries. Its reserves are concentrated in a handful of countries. It is primarily extracted from continental brines, wherein Li+ is relatively concentrated (0.3 –1.5 wt%) in a complex mixture of many more components with relatively large water solubilities. Current practices to extract lithium from continental brines involve evaporation, i.e., >90% of water. Eventually, the concentration of Li+ intensifies up to 6–7%, in a brine which follows numerous chemical processing steps, to ultimately produce battery-grade lithium chemicals. Despite being the easiest and currently most cost-effective practices, these are inefficient and unsustainable (chemical-intensive, requires extensive land use and time, and delivers large volumes of waste), especially in the context of the sharp increase in the demand for lithium that is already happening and is expected to endure in the coming decades. To sustainably meet the future demand for lithium, it is imperative to develop more efficient extraction methods, which are faster, less climate/weather reliant, minimize waste production, and especially deal with water differently than current industrial processing (i.e., circumventing evaporation). Besides being applicable to concentrated lithium brines, characteristic of primary extraction, these methods should especially be applicable to dilute brines (i.e., geothermal, oilfield, seawater, wastewater,—which contain 0.01–0.3 mg of Li+ per L of brine), as these have more recently prospected for Li recovery. Together with lithium recycling from spent batteries, these hold the promise of delocalizing raw lithium sourcing. New extraction technologies have emerged within the past decade, including adsorption and the use of membranes. In addition to being insufficient for an effective recovery, some alternatives seem to imply a harsher environmental impact than current practices, whereas others would be disadvantageous to treat the large volumes of fluid associated with lithium extraction. Especially, electrochemical methods for Li+ recovery are (re)surging.[1] The use of Li+ insertion electrodes coupled to membranes and membrane electrolysis are notoriously thriving.[1,2] However, the first approach bears the limitation of requiring extremely thin and large area electrodes to process large brine volumes, and the second one suffers from being energy-intensive, plus current investigations show the constant addition of chemicals for pH adjustment, and produce chloride- and hypochlorite-anions rich solutions which are neither economic nor sustainable.[2] Furthermore, in membrane electrolysis swelling of the ion exchange membrane could be an issue[3] that has not been addressed in Li+ recovery studies; if excessive, this could lead to membrane deformations and ultimately to the blockage of the flow channels within the reactor. Despite the aforementioned limitations, electrochemical methods are a more sustainable and versatile option, with latent competitiveness vs. current industrial practices. Thus, ideal solutions should have the added value of circumventing the limitations of the state-of-the-art electrochemical approaches mentioned above. This aim was pursued in the present work. Gas diffusion electrodes (GDEs) are broadly used in electrochemical energy-conversion devices, such as fuel cells and metal-air batteries, as well as in electrolyzers aiming at chemical synthesis, like in the chlor-alkali industry, hydrogen peroxide production, CO2 conversions to fuels and fine chemicals, or N2 reduction to ammonia. Recently, the use of GDEs was pioneered for metal recovery in a process named gas-diffusion electrocrystallization (GDEx).[4–7] This talk will explain the underlying principles of GDEx and its successful application in the recovery of highly dilute lithium (-1) in synthetic brines containing up to 150 mg L-1 NaCl, as well as in real geothermal brines with Li+ concentrations below 50 mg L-1. Up to 50% of direct lithium extraction from the brine can be achieved, selectively, forming solid materials with lithium concentrations >0.5%, which are promising as a starting material for the direct conversion into battery-grade lithium hydroxide or carbonate. References: [1] Battistel A., et al. (2020) Adv Mater 32, 1905440. [2] Torres W.R., et al. (2020) J Membrane Sci, 615, 118416. [3] Paidar, M., Faleev V., Bouzek K. (2016) Electrochim Acta, 209, 737. [4] Prato et al. (2019) Sci Rep https://doi.org/10.1038/s41598-019-51185-x [5] Prato et al. (2020) J Mat Chem A https://doi.org/ 10.1039/D0TA00633E [6] Pozo et al. (2020) Nanoscale https://doi.org/10.1039/C9NR09884D [7] Eggermont et al. (2021) React Chem Eng https://doi.org/10.1039/D0RE00463D Acknowledgements: This research has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654100 (CHPM2030 project). Support from the Flemish SIM MaRes programme, under grant agreement No 150626 (Get-A-Met project) is also acknowledged. The author thanks Elisabet Andres Garcia, Luis Fernando Leon Fernandez and Erwin Maes for their valuable contributions to this work.

Metal oxide nanoparticles become increasingly important as functional materials because their diversity in composition and structure allow the control of their physical properties. This work investigates gas-diffusion electrocrystallization (GDEx) as a method to synthesize metal (oxy)(hydr)oxide nanoparticles (NPs) via oxidation-assisted alkaline precipitation (Ox-AP) by using gas-diffusion electrodes. GDEx was benchmarked against alkaline titration (AT). NPs were synthesized from ZnCl2, MnCl2, or FeCl2 precursor solutions at room temperature. Using AT, Zn(OH)2, Mn3O4, and FeO NPs were synthesized, respectively. Using GDEx, Zn(OH)2, Mn3O4, and Fe3O4 NPs were synthesized, respectively. The AT and GDEx process of the ZnCl2 and MnCl2 solutions demonstrated very similar pH behavior during precipitation and the Zn(OH)2 and Mn3O4 NPs synthesized with either technique were similar in size, morphology, and composition. For these cases, AT and GDEx both elicited alkaline precipitation and were considered equivalent processes for NP synthesis. In contrast, the AT and GDEx process of the FeCl2 solution demonstrated very different pH behavior during precipitation. Moreover, the FeO NPs, synthesized with AT, were much larger and of different shape and composition than the Fe3O4 NPs, synthesized with GDEx. The smaller sizes obtained with GDEx are suggested to result from an Ox-AP mechanism caused by the oxidation of Fe(II) to Fe(III) by H2O2 or HO2− during precipitation which presumably improves condensation kinetics and increases the supersaturation, both well-known size-determining factors. ispartof: Reaction Chemistry & Engineering vol:6 issue:6 pages:1031-1041 status: published

In recent years, interest in using unsupported catalysts, especially Pt-based nanomaterials, has resurged in direct methanol fuel cells (DMFC). Unsupported catalysts eliminate the problems related to the corrosion of carbon catalyst supports, thus improving the long-term stability of DMFC. In addition, the design of catalyst synthesis protocols to tailor nanostructured materials with high surface area and catalytic activity improves catalyst performance.1 Consequently, we recently reported a method for the synthesis of platinum group metal (PGM, i.e., Pt, Pd, Rh) nanoparticles (NPs), using a process called Gas Diffusion Electrocrystallization (GDEx) (Fig. 1a).2 The simultaneous electrochemical reduction of CO2 and water occurs at the triple-phase boundary of uncatalyzed gas-diffusion electrodes, producing H2 and CO. Both gases, but especially H2, are reducing agents for water-soluble noble metal ions leading to the formation of small metal nanoclusters. CO can also act as a capping agent. Furthermore, the presence of CO2 stabilizes the pH, avoiding the formation of metal (hydr)oxides. In this work, we used the GDEx process to synthesize unsupported Pt NPs using polyvinyl pyrrolidone (PVP, 55000 Mw) as a stabilizer and evaluated their electrocatalytic activity for methanol oxidation. The synthesis was performed at -30 mA cm-2, using 3.0 mM Pt4+ (as H2PtCl4) as metal precursor and different concentrations of PVP (i.e., 0.0, 0.01, 0.1 and 1.0 g L-1). We chose low concentrations of stabilizer to facilitate its removal after synthesis, as clean surface catalysts are required for electrocatalytic applications. The size distribution of the Pt NPs, measured using Scanning Electron Microscopy (SEM), was 64 ± 22, 60 ± 22, 42 ± 18, and 38 ± 12 nm for PVP 0.0, PVP 0.01, PVP 0.1, and PVP 1.0, respectively. For comparison, the reduction of 3.0 mM Pt4+ using 1.0 g L-1 PVP with only H2 (either electrogenerated or bubbled) produced bigger and much more polydisperse particles (100 nm–1000 nm), highlighting the importance of the GDEx process and the presence of CO to synthesize small NPs using low concentrations of stabilizer. Furthermore, Transmission Electron Microscopy (TEM) images (Fig. 1b) revealed that the NPs are nanoclusters of single crystals of 2 nm–4 nm in diameter. The synthesized Pt NPs were cleaned using NaOH,3 and their electrocatalytic activity was evaluated in acidic media. The CV curves of Pt NPs in 0.5 M H2SO4 are shown in Fig. 1c. All catalysts showed hydrogen adsorption-desorption peaks from -0.2 to 0.1 VAg/AgCl. The calculated electrochemical surface area (ECSA), obtained by integrating the charge in the hydrogen adsorption-desorption region, was 7.6 ± 0.7, 14.1 ± 1.2, 33.6 ± 1.2, and 30.3 ± 1.0 m2 g-1 Pt for PVP 0.0, PVP 0.01, PVP 0.1 and PVP 1.0 respectively. The MeOH electro-oxidation experiments were performed in 0.5 M H2SO4 containing 1.0 M MeOH, and the CV curves are shown in Fig. 1d. The forward anodic peak (If) at about 0.7 VAg/AgCl corresponds to MeOH oxidation, while the backward anodic peak (Ib) at about 0.5 VAg/AgCl corresponds to the oxidation of the incompletely oxidized carbonaceous species formed in the forward sweep. The mass activity (MA), defined by the forward peak current density per unit of catalyst loading, was 71 ± 2, 136 ± 7, 463 ± 28, and 341 ± 25 mA mg-1 Pt for PVP 0.0, PVP 0.01, PVP 0.1, and PVP 1.0 g L-1, respectively. Hence, the MA scale with the ECSA . Besides, ECSA (and hence MA) increases when the PVP concentration during synthesis increases. However, this trend is not followed for a PVP concentration of 1.0 g L-1. Even though all catalysts were cleaned using the same protocol, residual PVP might still be left on the surface of Pt NPs synthesized using 1.0 g L-1 PVP, lowering their electrocatalytic activity. Overall, the GDEx process was a useful tool for synthesizing unsupported Pt NPs using low concentrations of stabilizer and with high electrocatalytic activity. This project has received funding from the European Union's Horizon 2020 Research and Innovation program under Grant Agreements n° 730224 (PLATIRUS) and n° 958302 (PEACOC) 1. E. Antolini, J. Perez, J. Mat. Sci, 2011, 46, 4435–4457. 2. X. Dominguez-Benetton, O. Martinez-Mora, J. Fransaer, EP21165681, 2021. 3. A. Zalineeva, S. Baranton, C. Coutanceau, G. Jerkiewicz, Langmuir, 2015, 31, 1605–1609. Figure 1

PLATInum group metals Recovery Using Secondary raw materials (PLATIRUS), a European Union (EU) Horizon 2020 project, aims to address the platinum group metal (pgm) supply security within Europe by developing novel and greener pgm recycling processes for autocatalysts, mining and electronic wastes. The initial focus was on laboratory-scale research into ionometallurgical leaching, microwave assisted leaching, solvometallurgical leaching, liquid separation, solid phase separation, electrodeposition, electrochemical process: gas-diffusion electrocrystallisation and selective chlorination. These technologies were evaluated against key performance indicators (KPIs) including recovery, environmental impact and process compatibility; with the highest scoring technologies combining to give the selected PLATIRUS flowsheet comprising microwave assisted leaching, non-conventional liquid-liquid extraction and gas-diffusion electrocrystallisation. Operating in cascade, the PLATIRUS flowsheet processed ~1.3 kg of spent milled autocatalyst and produced 1.2 g palladium, 0.8 g platinum and 0.1 g rhodium in nitrate form with a 92‐99% purity. The overall recoveries from feedstock to product were calculated as 46 ± 10%, 32 ± 8% and 27 ± 3% for palladium, platinum and rhodium respectively. The recycled pgm has been manufactured into autocatalysts for validation by end users. This paper aims to be a project overview, an in‐depth technical analysis into each technology is not included. It summarises the most promising technologies explored, the technology evaluation, operation of the selected technologies in cascade, the planned recycled pgm end user validation and the next steps required to ready the technologies for implementation and to further validate their potential. PLATIRUS project has received funding from the European Union’s Horizon 2020 Research and Innovation programme under Grant Agreement n° 730224.

Carbon-supported iron complexes were investigated as electrocatalysts for the reduction of nitric oxide (NO) in a H-2-NO fuel cell conceived for the production of hydroxylamine (NH2OH) with concomitant generation of electricity. Two types of iron complexes with tetradentate ligands, namely bis(salicylidene)ethylenediimine (Salen) and phthalocyanine (Pc), supported on activated carbon or graphite were prepared and evaluated as electrocatalysts, either without further treatment or after pyrolysis at 700 degrees C. The performance in the reduction of NO of gas diffusion cathodes based on these electrocatalysts was investigated in an electrochemical half cell (3-electrode configuration) using linear sweep voltammetry (LSV). The most promising electrocatalysts were studied further by chronoamperometric experiments in a H-2-NO fuel cell, which allowed comparison in terms of power output and hydroxylamine production. Depending on the concentration of the NO feed (6 or 18%), the best electrocatalytic performance was delivered either by FePc or FeSalen. The gas diffusion electrode based on FeSalen supported on activated carbon with 0.3 wt% Fe-loading provided the highest current density (86 A/m(2)) and the best current efficiency (43%) towards the desired NH2OH when operating at the higher NO concentration (18%). Moreover, FeSalen offers the advantage of being cheaper than FePc. The experimental work was complemented by density functional theory (DFT) calculations, which allowed to shed more light on the reaction mechanism for the reduction of nitric oxide at the atomistic level.

Gas diffusion electrocrystallization (GDEx) was explored for the synthesis of iron oxide nanoparticles (IONPs). A gas-diffusion cathode was employed to reduce oxygen, producing hydroxyl ions (OH−) and oxidants (H2O2 and HO2−), which acted as reactive intermediates for the formation of stable IONPs. The IONPs were mainly composed of pure magnetite. However, their composition strongly depended on the presence of a weak acid, i.e., ammonium chloride (NH4Cl), and on the applied electrode potential. Pure magnetite was obtained due to the simultaneous action of H2O2 and the buffer capacity of the added NH4Cl. Magnetite and goethite were identified as products under different operating conditions. The presence of NH4Cl facilitated an acid–base reaction and, in some cases, led to cathodic deprotonation, forming a surplus of hydrogen peroxide, while adding the weak acid promoted gradual changes in the pH by slightly enhancing H2O2 production when increasing the applied potential. This also resulted in smaller average crystallite sizes as follows: 20.3 ± 0.6 at −0.350 V, 14.7 ± 2.1 at −0.550 and 12.0 ± 2.0 at −0.750 V. GDEx is also demonstrated to be a green, effective, and efficient cathodic process to recover soluble iron to IONPs, being capable of removing >99% of the iron initially present in the solution. ispartof: Nanoscale Advances vol:2 issue:5 pages:2052-2062 ispartof: location:England status: published

To provide a good reference for many metal ion removal processes, we developed an analytical model (AM) and used the PHREEQC computer program to numerically model (NM) arbitrary metal hydroxide precipitation titration curves (PTCs). For validation, these models were compared to slow titration experiments of ZnCl₂ with NaOH to precipitate Zn(OH)₂. The AM effectively demonstrates how initial pH, metal ion concentration and -valence and metal hydroxide equilibrium constant affect the shape of the PTCs. Comparison of AM and NM exposed AM limitations that include the effect of NaCl concentration, activity coefficients, and multi-species ions, on the shape of the PTCs. The experimental results agree well with either model for different concentrations of ZnCl₂ at slow titration rates. However, the models and experiments deviated at higher titration rates. These deviations were attributed to inhomogeneities in the solution concentration, which caused precipitation at a bulk pH below the theoretical precipitation pH (i.e., pre-precipitation). ispartof: Journal of Environmental Chemical Engineering vol:8 issue:1 status: published

Materials displaying novel magnetic ground states signify the most exciting prospects for nanoscopic devices for nanoelectronics and spintronics. Spin transition materials, e.g., spin liquids and spin glasses, are at the forefront of this pursuit; but the few synthesis routes available do not produce them at the nanoscale. Thus, it remains an open question if and how their spin transition nature persists at such small dimensions. Here we demonstrate a new route to synthesize nanoparticles of spin transition materials, gas-diffusion electrocrystallization (GDEx), wherein the reactive precipitation of soluble metal ions with the products of the oxygen reduction reaction (ORR), i.e., in situ produced H2O2, OH−, drives their formation at the electrochemical interface. Using mixtures of Cu2+ and Zn2+ as the metal precursors, we form spin transition materials of the herbertsmithite family—heralded as the first experimental material known to exhibit the properties of a quantum spin liquid (QSL). Single-crystal nanoparticles of ∼10–16 nm were produced by GDEx, with variable Cu/Zn stoichiometry at the interlayer sites of ZnxCu4−x(OH)6Cl2. For x = 1 (herbertsmithite) the GDEx nanoparticles demonstrated a quasi-QSL behavior, whereas for x = 0.3 (0.3 < x < 1 for paratacamite) and x = 0 (clinoatacamite) a spin-glass behavior was evidenced. Finally, our discovery not only confirms redox reactions as the driving force to produce spin transition nanoparticles, but also proves a simple way to switch between these magnetic ground states within an electrochemical system, paving the way to further explore its reversibility and overarching implications. ispartof: Nanoscale vol:12 issue:9 pages:5412-5421 ispartof: location:England status: published

The safe immobilization of arsenic present in liquids is a key environmental challenge due to the inherent toxicity of arsenic. This immobilization is mostly restricted by the application of chemicals and several stages of oxidation and precipitation. Although the formation of bioscorodite is a greener alternative, it is intensive in the use of energy for aeration, and it is costly due to nutrient addition. The electrochemically-driven crystallization of arsenic into scorodite is proposed here to overcome these limitations. We disclose gas-diffusion electrocrystallization (GDEx) for the immobilization of arsenic into highly crystalline scorodite (FeAsO4·2H2O) by the in situ production of oxidizing substances (i.e., H2O2) on gas-diffusion electrodes. GDEx yielded an exceptional arsenic immobilization efficiency of up to 70% without the use of any primary minerals or seed crystals. At 70 °C and using As3+ as the precursor, polydisperse micrometric scorodite particles were obtained (from fine particles of

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H2O2 was demonstrated to narrow the size distribution and decrease the size of CuO and hydrous FeOOH (2-line ferrihydrite) nanoparticles under conditions of high supersaturation. We introduce oxidation-assisted alkaline precipitation (Ox-AP) and compare it to traditional alkaline precipitation (AP). While for AP, a metal salt solution (e.g., CuCl2) is mixed with an alkali (e.g., NaOH), for Ox-AP, the more reduced form of that metal salt solution (e.g., CuCl) is simultaneously mixed with that alkali and an oxidant (e.g., H2O2). The resulting precipitates were characterized with SEM, XRD, DLS and single particle ICP-MS and shown to be nanoparticles (NPs). Ox-AP CuO NPs were up to 3 times smaller than AP NPs. Ox-AP FeOOH NPs were up to 22.5% smaller than AP NPs. We discuss and propose a possible mechanism of Ox-AP through careful consideration of the known reaction chemistry of iron and copper. We propose that an increased monomer formation rate enhances the nucleation rate, which ultimately results in smaller particles with a more narrow distribution. The more distinct effect of Ox-AP on copper, was attributed to the fast formation of the stable CuO monomer, compared to AP, where the Cu(OH)2 and/or Cu2(OH)3Cl monomers are more likely formed. Although, the exact mechanism of Ox-AP needs experimental confirmation, our results nicely demonstrate the potential of using Ox-AP to produce smaller NPs with a more narrow distribution in comparison to using AP. ispartof: RSC ADVANCES vol:9 issue:51 pages:29902-29908 ispartof: location:England status: published

The electrode material is one of the key components of a bioelectrochemical system (BES), serving as substratum for the electroactive biofilm development and hence playing a pivotal role in regulating the type and rate of electron transfer processes and bioelectrochemical conversions. Microbial electrosynthesis (MES) requires biocompatible electrode materials with a large surface area, that can support the effective development of microbial biomass at high current densities to provide significant product titers. Carbon-based materials are the most employed and constitute the best available option to grow electroactive biofilms; yet, resolving which of their properties are truly relevant to achieve these goals remains elusive. The present study shows that biofilm coverage and the relative abundance of cell-bound polymeric filaments are directly proportional to the total charge consumed over time. The combination of high biofilm coverage and high relative abundance of the cell-bound polymeric filaments resulted in low charge transfer resistances, as determined by electrochemical impedance spectroscopy. Although a wide variety of physicochemical parameters of the supporting carbon electrode materials (electric conductivity, specific surface area, porosity, roughness, thermogravimetric mass spectrometry, etc.) were characterized in this study, the only one that showed a consistent correlation with the total charge consumed by the electroactive biofilms was the contact angle. This suggests that the hydrophilic moieties and surface tension are two fundamental parameters to consider for an effective design of microbial electrosynthesis biocathodes. Among the carbon electrode materials used in the present study, an activated carbon-based VITO CORE™ electrode was considered the most suitable electrode material to provide such desired features, while other electrodes exhibited roughnesses much higher than those amenable for the microbiological range. The superior wetting characteristics of the VITO CORE™ electrode seem highly reliant on the roughness provided by the manufacturing method (i.e., cold-rolling).

Benthic microbial fuel cells (BMFC) are devices that remove organic matter (OM) and generate energy from sediments rich in organic nutrients. They are composed of electrodes with adequate different distances and floating air cathodes in an aqueous medium with saturated oxygen. In this study we proposed to design, build, analyze and evaluate a set of BMFCs with floating air cathodes to test the optimal distance between the electrodes, using sediment from the Bay of Campeche as a substrate. For the analysis of OM removal, COD tests, volatile solids (VS), E4/E6 study and FTIR analysis were performed. Power generation was evaluated through polarization curves, cyclic voltammetry and electrochemical impedance spectroscopy (EIS). We achieved a current density and power density at 10 cm depth of 929.7 &plusmn, 9.5 mA/m2 and 109.6 &plusmn, 7.5 mW/m2 respectively, with 54% removal of OM from the sediment, obtaining formation of aliphatic structures. BMFCs are proposed as adequate systems for bioremediation and power generation. The system at 10 cm depth and 100 cm distance between sediment and the floating air cathode had a good performance and therefore the potential for possible scaling.

The aim of the present work was to characterize the impedance response of an air-cathode MFC operating in a continuous mode and to determine intrinsic properties that define its performance which are crucial to be controlled for scalability purposes. The limiting step on electricity generation is the anodic electrochemically-active biofilm, independently of the external resistance, Rext, utilized. However, for Rext below 3k? the internal impedance of the bioanode remained invariable, in good correspondence to the power density profile. The hydraulic retention time (HRT) had an effect on the impedance of both the bioanode and the air-cathode and especially on the overall MFC. The lowest HRT at which the MFC was operable was 3h. Yet, the variation on the HRT did not have a significant impact on power generation. A two constant phase element-model was associated with the EIS response of both bioanode and air-cathode, respectively. Consistency was found between the CPE behaviour and the normal power-law distribution of local resistivity with a uniform dielectric constant, which represented consistent values with the electrical double layer, the Nernst diffusion layer and presumably the biofilm thickness. These results have future implications on MFC monitoring and control, as well as in providing critical parameters for scale-up. Grant 180B12A7 from the Environmental and Energy Technology Innovation Platform (MIP2), under the project �Sewage Plus: second life of sewage as a matrix for dilution of organic waste streams�. Surajbhan Sevda gratefully acknowledges a scholarship from the Flemish Government, Department of Higher Education and Scientific Research (Vlaamse Gemeenschap) under the framework of Indo-Belgium fellowship (Academic year 2011�2012) Scopus

Raw metals are fundamental to the global economy as they are essential to maintain the quality of our life as well as industrial performance. A number of metal-bearing aqueous matrices are appealing as alternative supplies to conventional mining, like solid industrial and urban waste leachates, wastewaters and even some natural extreme environments (e.g. deep marine sediments, geothermal brines). Some of these sources are already managed for recovery, while others are not suitable either because they are too low in content of recoverable metals or they contain too many impurities that would interfere with classical recovery processes or would be cost-prohibitive. Microbial electro-metallurgy, which results from the interactions between microorganisms, metals and electrodes, in which the electron transfer chain associated with microbial respiration plays a key role, can contribute to overcome these challenges. This review provides the state of the art on this subject, and summarizes the general routes through which microbes can catalyse or support metal recovery, leading to nano- and macro-scale materials. Competing sorption and electrochemical technologies are briefly revisited. The relevant sources of metals are highlighted as well as the challenges and opportunities to turn microbial electro-metallurgy into a sustainable industrial technology in the near future. Finally, an outlook to pursue functional materials through microbial electrometallurgy is provided.

BACKGROUND Upscaling microbial fuel cells (MFCs) to make them energy-competitive systems requires a systematic understanding of their operating conditions. This study emphasizes the operation of a new MFC design with two gas diffusion cathodes under three different operational modes (batch mode (MFC-BM), semi-continuous mode (MFC-SCM) and continuous mode (MFC-CM)), towards increasing the power density, substrate utilization, bioelectrochemical kinetics and energy conversion efficiencies. RESULTS Higher power density was recorded with MFC-SCM (20.54 mW m−2) followed by MFC-CM (17.22 mW m−2) and MFC-BM (0.75 mW m−2). Such power density magnitudes were obtained with high anode projected surface area 220 cm2, which is about 10–100 times larger than frequently used in laboratory-scale MFCs. On the contrary, susbtrate utilization was higher with MFC-BM (91–96%) followed by MFC-SCM (74–84%) and MFC-CM (53–81%). A higher coulombic efficiency (CE) was obtained with the MFC-CM (7.5–11.2%), followed by MFC-SCM (5.4–5.6%) and MFC-BM (0.5–4%). This is of interest due to its dependence on both current generation as well as substrate utilization. Cyclic voltammograms along with derived bioelectro-kinetic parameters, i.e. redox Tafel's slopes (βa/βc) and electron transfer co-efficients (αa/αc), also explained the higher performance of MFC-CM and MFC-SCM. CONCLUSION Output from this study demonstrates clearly that the new MFC design can be effectively operated under continuous mode operation with high retention time to enhance wastewater treatment along with good amounts of power output. © 2014 Society of Chemical Industry

This study focuses on the effect of operational and physiochemical factors on a stable sulfate reducing bacteria biocathode and their effect on the electrochemical response thereof. Two carbon-based electrode materials i.e. VITO CORE™ and Paxitech® electrodes were evaluated. The electrochemical performance was assessed by changing both organic and inorganic components of the synthetic feed, which included carbon substrates (acetic and butyric acid), ionic strength (concentration of sodium chloride) and weak electrolytes acting as buffering agents (potassium dihydrogen phosphate and ammonium chloride). The concentration of sodium chloride (0.34 M) and acetate (0.1 M) plays a crucial role in determining the performance as well as the bioelectrochemical mechanism of the sulfate reducing bacteria (SRB) biocathode. Butyrate did not significantly influence the performance of the biocathode but showed a synergistic effect when given along with acetate. The developed biocathode was also successfully tested for dark fermentation based effluent treatment application. Concentrations higher than 10% of effluent were found to be detrimental to the electrochemical performance of the biocathode. This study essentially highlights the significance of optimization studies on bioelectrochemical system (BES) at lab scale before its potential upscaling for industrial wastewater processing.

Recovery of valuable metals from wastewaters containing both metals and organics is challenging with current technologies, in part due to their interactions. Typical approaches are chemical intensive. Here, we developed a membrane electrolysis system coupled to an acidic and alkaline crystallizer to enable separate precipitation of the organics and metals without additional chemicals. The target industrial wastewater contained mainly purified terephthalic acid (PTA), benzoic acid (BA), p-Toluic acid (PA), cobalt (Co), and manganese (Mn). We examined the removal and recovery efficiency of PTA and cobalt from two types of synthetic stream and the real process stream using several configurations. The acidic crystallizer reached a removal efficiency of PTA of 98.7 +/- 0.2% (Coulombic efficiency 99.71 +/- 0.2%, pH 3.03 +/- 0.18) in batch tests of the simple synthetic stream. The alkaline crystallizer achieved a cobalt recovery efficiency of 94.51 +/- 0.21% (Coulombic efficiency 87.67 +/- 0.31%, pH 11.37 +/- 0.21) in batch tests of the simple synthetic stream (TPA and Co). Then, the system was operated continuously with complex synthetic stream (TPA, BA, PA, Co and Mn). The alkaline crystallizer achieved a cobalt recovery efficiency of 97.78 +/- 0.02% (Coulombic efficiency 90.45 +/- 0.17%)at pH 11.68 +/- 0.02. The acidic crystallizer obtained a PTA removal efficiency of 61.2 +/- 0.1% (Coulombic efficiency 62.3 +/- 0.2%) over 144 h (pH 3.71 +/- 0.03). A real stream was tested over 5 h runs in batch showing 31.1 +/- 1.0% PTA (Coulombic efficiency 26.5 +/- 0.2%) and 82.92 +/- 0.22% cobalt removal (Coulombic efficiency 75.27 +/- 0.31%) at pH 2.71 +/- 0.12 and 8.07 +/- 0.02, respectively. However, micron-scale precipitates were generated from real stream tests. To conclude, the membrane electrolysis cell coupled with acidic and alkaline crystallizers enabled simultaneous separation of PTA and cobalt as solid precipitates from a complex stream with no chemical addition. The efficiencies were lower with the real stream than the synthetic streams, showing the impact of matrix effects and the need to optimize the performance of the crystallizers.

The present study evaluates the performance of air-cathode microbial fuel cells (MFCs) under alternating open circuit/closed circuit (OC/CC) modes and its effect on independent-electrode and full-cell potentials, power output (at different external resistances) and the polarization behaviour of the electrodes. Three different types of feeds were evaluated using this approach: (1) phosphorus buffer solution (PBS) with acetate as carbon source, (2) glucose-rich synthetic wastewater, and (3) sewage from wastewater treatment plant enriched with fermented molasses. When MFCs were suddenly switched to CC from OC and then again back to OC from CC, the behaviour of the anodes vs reference electrode (Ag/AgCl, 3 M KCl) was monitored. When electric circuit of the MFCs was switched from open to closed circuit, for all cases: (a) the anode potential-shift (vs Ag/AgCl) reallocated in the positive direction in about 200–400 mV, (b) the air-cathode potential-shift (vs Ag/AgCl) reallocated in the negative direction in about 10–25 mV, and (c) the cell-potential difference started at around 0 mV and progressively increased as the MFC reached stability. This behaviour was consistently reproduced during different OC/CC cycles. The systems studied delivered good performance with both controlled media and industrial wastewater. Additionally, this study provides insightful characterization of the independent-electrode behaviours.

Mixed culture of sulphate reducing bacteria named TERI-MS-003 was used for development of biocathode on activated carbon fabric fastened to stainless steel mesh for conversion of volatile fatty acids to reduced organic compounds under chronoamperometric conditions of -0.85V vs. Ag/AgCl (3.5M KCl). A range of chemicals were bioelectrosynthesized, however the gases present in headspace environment of the bioelectrochemical reactor governed the product profile. Succinate, ethanol, hydrogen, glycerol and propionate were observed to be the predominant products when the reactor was hermetically sealed. On the other hand, acetone, propionate, isopropanol, propanol, isobutyrate, isovalerate and heptanoate were the predominant products when the reactor was continuously sparged with nitrogen. This study highlights the importance of head space composition in order to manoeuvre the final product profile desired during a microbial electro-synthesis operation and the need for simultaneously developing effective separation and recovery strategies from an economical and practical standpoint.

Bioelectrochemical system (BES) was operated using the enzyme formate dehydrogenase as catalyst at cathode in its free form for the reduction of CO2 into formic acid. Electrosynthesis of formic acid was higher at an operational voltage of -1V vs. Ag/AgCl (9.37mgL(-1) CO2) compared to operation at -0.8V (4.73mgL(-1) CO2) which was strongly supported by the reduction catalytic current. Voltammograms also depicted a reversible redox peak throughout operation at -1V, indicating NAD(+) recycling for proton transfer from the source to CO2. Saturation of the product was observed after 45min of enzyme addition and then reversibility commenced, depicting a lower and stable formic acid concentration throughout the subsequent time of operation. Stability of the enzyme activity after immobilization on the electrode and product yield will be studied further.

Background Metals react chemically/electrochemically in electrolytic solutions, such as that present in the oral cavity, which leads to corrosion of metal dental implants. Corrosion can increase the failure rate of dental implants. Purpose This study evaluated the corrosion behavior of nicotine on Ti-6Al-4V under physiological conditions. It was hypothesized that nicotine in artificial saliva would have an adverse effect on the corrosion of Ti-6Al-4V. Methods Ti-6Al-4V discs were electrochemically analyzed using a three-electrode electrochemical cell. The disks were immersed in an electrolytic artificial saliva with varying pH (3.0 and 6.5) and nicotine concentration (control, 1 mg/mL, 5 mg/mL, and 20 mg/mL). Open circuit potential, cyclic polarization, and electrochemical impedance spectroscopy (EIS) tests were conducted. Results Electrochemical parameters indicated that the presence of nicotine significantly reduced (p

Microbial fuel cells (MFCs) which are operated in continuous mode are more suitable for practical applications than fed batch ones. The aim of the present study was to characterize an air-cathode MFC operating in continuous mode and to determine the intrinsic properties for suitable performance and scalability. Air-cathode MFCs were constructed from plexiglass with a total working volume of 220 mL. Zirfon® separator used in this MFC had cross section area of 100 cm2. The air cathode MFCs were operated in fed-batch mode and then shifted to the continuous mode. To determine the behavior of anode and cathode in long term operation (274 days), their contribution in MFC performance was evaluated over time. Once the active biofilm was formed, power production and substrate consumption rate were significantly higher. The internal resistance increased with the passage of time. After stabilization of biofilm when the MFC was placed in close circuit by connecting an external resistance, the anode-reference ...

Semi-solid flow batteries (SSFBs) provide a highly scalable energy storage alternative for the reliable use of intermittent renewable energy sources. In this work, a new pseudo three-dimensional (P3D), multi-scale and multi-physics approach to the modeling of SSFBs is presented which includes the correct way to model flowing active particles. Two coupled continuum domains; one representing the battery and another representing the electrochemically active particles, are used as the computational solution strategy, to resolve the characteristic multi-scale electrochemical phenomena. In modeling the flowing particles, solid-state diffusion is applied as the single transport mechanism, contrary to previous investigations which included convection/advection. Time dependent voltage profiles, as well as spatial distributions of the state of charge in the SSFB active particles are herein examined and a Ragone plot for a SSFB is unveiled for the first time. Although presented in the case of a nickel-metal hydride SSFB, this P3D model framework is adaptable to any other SSFB chemistry, based on Li-ion or Na-ion active materials for example.

The efficiency of microbial fuel cells (MFCs) is affected by several factors such as activation overpotentials, ohmic losses and concentration polarization. These factors are handled in micro-sized MFCs using special electrodes with physically or chemically modified surfaces constructed with specified materials. Most of the existing μLscale MFCs show great potential in rapid screening of electrochemically-active microbes and electrode performance; although they generate significantly lower volumetric power density compared with their mL counterparts because of their high internal resistance. This review presents the development of microfluidic MFCs, with summarization of their advantages and challenges, and focuses on the efforts done to minimize the adverse effects of internal resistance (ohmic and non-ohmic) on their performance.

Bioelectricity production from microbial fuel cell (MFC), fed with synthetic wastewater can achieve both wastewater treatment and energy production. Two different types of separators were used in this study to compare their performance in an air cathode MFC. Power generation and substrate utilization from the wastewater was compared for these membranes. The maximum power density obtained with Zirfon® was 424.50 mW/m 2 and of 16.98 W/m 3 (volumetric) while with Fumasep® was 38.03 mW/m 2 and 1.52 W/m 3 (volumetric). The internal resistance obtained with Zirfon® increased from initial 0.38 Ω cm 2 to 1.72 Ω cm 2 while with Fumasep® increased from 2.57 Ω cm 2 to 10.92 Ω cm −2 at the end of the experiment. The results showed that the MFC with Zirfon® stabilized early and the anodic and cathodic cell potentials reached maximum earlier as compared to Fumasep®. Impedance spectra confirmed the lower resistance of the Zirfon® as compared to Fumasep® and this may be the reason for its better performance. Zirfon® might be a good option for the future scale up of MFCs because of its low cost and low internal resistance in comparison to other membranes.

Microbial fuel cells (MFCs) present a novel method for simultaneous bioelectricity generation and wastewater treatment. In this study, an air–cathode MFC with membrane-electrode assembly was operated over three batch cycles (total of 160 days) and results indicated that molasses mixed sewage wastewater (high strength wastewater) containing 9978 mg/L of chemical oxygen demand (COD) could be used as substrate to produce bioelectricity with this system. Three different compositions of wastewater were used as substrate. The original wastewater, half-diluted wastewater and centrifuged wastewater were used as substrate in MFCs. Maximum voltage output of 762 mV and maximal power density of 382.5 mW/m 2 (5.06 W/m 3 ) were obtained with the original wastewater by the 14 th day of operation. During this time the system evolved to 0.93 Ω cm −2 internal resistance and 59% removal of the total COD were achieved. Centrifuged wastewater showed poor performance in terms of power production (0.12 mW/m 2 or 4.2 mW/m 3 ), presumably due to organic substrate limitations. The MFC running on diluted wastewater showed a power density of 56.17 mW/m 2 (2.25 mW/m 3 ), with 70% COD removal. Energy-Dispersive X-ray spectroscopy (EDX) analysis, together with other characterization methods, confirmed the breakdown of organic compounds in the wastewater, EDX and Scanning Electron Microscopy (SEM) revealed the surface morphology of the materials utilized and showed the evolution in electrode and membrane composition after the long term MFC processes. Denaturing Gradient Gel Electrophoresis (DGGE) profiles showed the presence of mixed populations enclosing the electrochemically-active bacteria that established a biofilm on the anode surface and as such differed from the suspended bacterial community in the anode medium. These results demonstrate that complex wastewater can be used as a substrate for power generation in MFCs and also can be treated with high COD removal efficiencies.

International audience; One of the greatest challenges in the development of Microbial Electrochemical Technologies (METs) is the achievement of efficient bioanodes, which not only can operate for long term but which can also be effectively and promptly regenerated for the sustained and successive production of electricity out of waste organics contained in aqueous streams. Simple strategies that facilitate the engineering of these systems are then pursued. Sustainable electricity generation was here achieved using electrochemically-active marine biofilms, which reached up to 6.8 A m−2 in the best case. These biofilms showed deteriorated current generation after successive transfers in fresh natural media. The electricity-generation functionality of these marine biofilms was recuperated after their relocation into synthetic minimal media (i.e. up to about 3.8 A m−2 after a decay down to about 1–2 A m−2). Upon this relocation, the overall electrochemical mechanisms were preserved. Fluctuating nutrient stress intensified the effect of minimal media on current generation. The change from natural to minimal media showed an important impact on the selection and adaptation of microbial communities, characterized by CE-SSCP profiles; yet, robust bioanodes in which some microbial species were preserved were obtained in synthetic minimal media, these being sufficient for a reproducible electrochemical functionality. The systematic cycling between natural media and minimal media, regarded as periodic stress conditioning, is therefore proposed as a convenient strategy to boost current generation in robust electrochemically-active marine bioanodes.

This study reports the development and evaluation of gas diffusion electrodes (GDEs) for application in a fuel cell reactor aimed at the production of hydroxylamine. Electrode materials manufactured by two different methods are reported. The composition of the active layer of these electrodes has been tailored for application as gas diffusion cathodes for a NO-H 2 fuel cell. The results on physico-chemical characterization of the catalyst layers (density, water porosity, total porosity and BET surface area) are discussed in relation with the differences in their composition (carbonaceous powder and binder used, ratios carbon to binder). The gas porous electrodes were first tested in an electrochemical half cell configuration (3-electrode configuration) for their ability to reduce diluted nitric oxide (6% in nitrogen). Later, the performance in a NO-H 2 fuel cell was evaluated for the promising electrodes in a single cell set-up (2-electrode configuration). It was observed that non-platinized electrodes offer an acceptable performance for NO reduction. In the single cell set-up, current densities of −12 mA cm −2 for a non-platinized electrode and −10 mA cm −2 for a non-catalyzed activated charcoal electrode were obtained at 50 mV cell voltage, vs. 17 mA cm −2 for a platinized charcoal electrode.

Electrochemical evolution of the interface formed by carbon steel exposed to artificial seawater with nutrients in the presence and absence of mixed cultures that contain sulfate-reducing bacteria (SRB) is characterized by electrochemical impedance spectroscopy (EIS). The artificial seawater in sterile conditions progressively covered the surface of the steel sample with two different layers after 30 days of exposure. An outer layer is formed by a mixture of chlorides and phosphorus-based iron corrosion products with organic compounds from the culture media, and an inner layer is formed by corrosion products mixture constituted mainly by phosphorus-base products. Alternatively, under biotic conditions there was one heterogeneous layer composed by a mixture of phosphorous and sulfur-based corrosion products and biofilm. Three time constants were observed with EIS for sterile conditions. At low frequencies one constant is associated with the charge transfer resistance related to the iron dissolution reaction and inversely proportional to the active area; the porous resistance magnitudes at medium frequencies characterized the physicochemical properties of the inner layer, and high frequency described the electrical properties of the outer mixture layer. Low carbon steel in the presence of SRB (halophilic hydrogenotrophic) showed the impedance distribution after the formation of a corrosion product thick black layer mixed with organic composites and bio-entities. The SRB-biofilm enhanced the corrosion rate and influenced the appearance of diffusion controlled mechanism process. Electrical passive analogs in terms of constant phase elements characterized the evolution of the cover films formed and the impedance of the layers with time. The mechanisms are characterized based on the impedance response for three time constants in the absence of SRB and one time constant with a finite Warburg element when SRB are present in the electrolyte. The validation of the theoretical approximation with electrical analogs was in good agreement with the experimental results.

Petroleum, gas, shipping and water treatment and distribution industries are significantly affected by microbial activity-environments in which biofilms might cause or serious problems such as biofouling, biodeterioration and biocorrosion, which are usually associated with great human, environmental and financial losses. The present work has as a main objective the biological and electrochemical characterization using electrochemical impedance spectroscopy of the anaerobic microorganisms present in gasoline distribution pipelines that might have an influence in corrosion processes, specifically focusing on those biofilm-developers. Several microorganisms have been isolated and their metabolic activities monitored, as well as their electrochemical influence over carbon steel in laboratory conditions.

The present work is based on the biocomplexity analysis and the electrochemical influence of anaerobic biofilms obtained from gasoline distribution pipelines. Microbial populations were grown in anaerobic media using either of the following carbon sources: lactate, acetate, benzene, toluene, xilene, pentane, TBA or MTBE. The cultured microorganisms developed complex biofilms either in pure cultures or in consortia. An analysis of some possible microbial interactions in which the cultured biofilms might impact corrosion is presented as a biocomplexity analysis. The electrochemical activity of the biofilms is monitored using electrochemical impedance spectroscopy, from which it is determined that diffusion is a strong limiting factor under biofilm presence and active sites influence under abiotic conditions, for corrosion control. A simplified 2-dimensional transmission line approach is used to describe the current distribution along a biofilm growing over a carbon steel surface and its influence in corrosion, according to the EIS results obtained.

Carbon dioxide (CO2) reduction to multi-carbon compounds at the cathode using chemolithoautotrophs is an emerging application of microbial electrosynthesis (MES). In this study, CO2 reduction in MES was investigated at hydrogen evolving potentials, separately by a mixed culture and Clostridium ljungdahlii, using a graphite felt and stainless steel assembly as cathode. The mixed culture reactor produced acetate at the maximum rate of 1.3 mM d(-1), along with methane and hydrogen at -1.1 V/Ag/AgCl. Over 160 days of run-time in four fed-batches, 26% of bicarbonate was converted to acetate between day 28 and 41, whereas in the late batches, methane production prevailed. Out of 45 days of run-time in the C. ljungdahlii reactor, 2.4 mM d(-1) acetate production was achieved at -0.9 V/Ag/AgCl in Batch 1. Simultaneous product degradation occurred when the mixed culture was not selectively enriched. Hydrogen evolution is potentially the rapid way of transferring electrons to the biocatalysts for higher bioproduction rates.

Diverse areas of electrochemistry are greatly impacted by nanoscale materials. In return, electrochemistry is demonstrating a fast-growing impact on their synthesis. This slipstream conveys a vibrant ecosystem for electrochemical breakthroughs that bring about advanced nanomaterials. Gas-diffusion electrocrystallization (GDEx), a new electrochemical process that we have developed, allows the synthesis of crystalline nanomaterials with well controlled and narrowly distributed properties that relate to specific functionalities. Gas-diffusion electrocrystallization is a one-pot rapid process involving a porous cathode with surface functionalities, an aqueous electrolyte containing metal or metalloid ions, and an oxidant gas, in which colloidal dispersions of nanomaterials or solid nanoparticles are synthesized. The general principles and mechanism through which GDEx operates will be introduced. Furthermore, examples of nanomaterials we have produced and their functionality or industrial relevance will be disclosed. For instance, cerium oxide nanoparticles with controlled crystallite sizes in the range of 2 to 10 nm as well as varying content of Ce3+ and Ce4+ sites, which result in different degrees of oxygen sorption capacities and kinetics were synthesized using GDEx. Due to this feature, these cerium oxide particles can be tailored for pro-oxidant or anti-oxidant applications of interest for electronic packaging, oxidative stress alleviation, or cancer therapy. Likewise, lanthanum carbonate hydroxides formed by GDEx may find a niche as phosphate scavengers. GDEx was also used to produce iron oxide nanoparticles in the range of 40 to 100 nm in which the ratio of heamatite (Fe2O3) and magnetite (Fe3O4) can be tweaked, providing the possibility to regulate their magnetic susceptibility. These materials are studied for molecular diagnostics. Solid nanoparticles of herbertsmithite, have been obtained through GDEx when applied to electrolytes containing Cu2+, Zn2+ and Cl– ions, by manipulating the redox potential. These Cu/Zn-based nanoparticles may have applications in data storage, high-temperature superconductors and for so-called ‘‘quantum-entangled’’ batteries. Finally, when operating GDEx with Mn(III/IV), compositions with birnessite and hausmannite—which may intercalate water and alkali metals— were synthesized, providing promising materials for batteries electrodes or catalysts. In conclusion, GDEx is revealed as a new route to synthesize a wide range of nanoparticles, flexibly and with versatile control of composition, morphology, and physicochemical parameters such as crystallite size, lattice parameter and particle size, which in turn tailor specific functionalities. The authors acknowledge the grant from the Flemish SIM MaRes programme for SBO project Get-A-Met.

Background A laboratory-scale two-chamber microbial fuel cell employing an aerated cathode with no catalyst was inoculated with mixed inoculum and acetate as the carbon source. Electrochemical impedance spectroscopy (EIS) was used to study the behavior of the MFC during initial biofilm (week 1) and maximum power density (week 20). EIS were performed on the anode chamber, biofilm (without anolyte) and anolyte (without biofilm). Nyquist plots of the EIS data were fitted with two equivalent electrical circuits to estimate the contributions of intrinsic resistances to the overall internal MFC impedance at weeks 1 and 20, respectively. Results The results showed that the system tended to increase power density from 15 ± 3 (week 1) to 100 ± 15 mW/m2 (week 20) and current density 211 ± 7 (week 1) to 347 ± 29 mA/m2 (week 20). The Samples were identified by pyrosequencing of the 16S rRNA gene and showed that initial inoculum (week 1) was constituted by Proteobacteria (40%), Bacteroidetes (22%) and Firmicutes (18%). At week 20, Proteobacterial species were predominant (60%) for electricity generation in the anode biofilm, being 51% Rhodopseudomonas palustris. Meanwhile on anolyte, Firmicutes phylum was predominant with Bacillus sp. This study proved that under the experimental conditions used there is an important contribution from the interaction of the biofilm and the anolyte on cell performance. Table 1 presents a summary of the specific influence of each element of the system under study. Conclusions The results showed certain members of the bacterial electrode community increased in relative abundance from the initial inoculum. For example, Proteobacterial species are important for electricity generation in the anode biofilms and Firmicutes phylum was predominant on anolyte to transfer electron. R1 is the same in the three systems and no variation is observed over time. The biofilm makes a significant contribution to the charge transfer processes at the electrode (R2 and Cdl) and, consequently, on the performance of the anode chamber. The biofilm can act as a barrier which reduces diffusion of the anolyte towards the electrode, all the while behaving like a porous material. The anolyte and its interaction with the biofilm exert a considerable influence on diffusion processes, given that it presents the highest values for Rd which increased at week 20.

Increasing the conductivity of the electrolytes used in microbial electrochemical systems is an essential prerequisite to the large-scale success of these technologies. Microbial bioanodes formed from a salt marsh inoculum under constant acetate feeding generated up to 85 A·m−2 in media containing 776 mM NaCl (45 g·L−1, 1.5 times the salinity of seawater). These values were the highest salinities accepted by a microbial anode so far and the highest current densities reported with felt graphite electrodes. Keywords: Bioanode, Microbial anode, Salinity, Microbial fuel cell, Bioelectrochemical system

Sulfate-reducing bacteria (SRB) developed biocathodes efficient for reduction of acetic and butyric acids to alcohols and acetone via direct electron transfer reaching current densities of 160-210 A m(-2).

The present critical review aims to portray the principles and theoretical foundations that have been used for the application of electrochemical impedance spectroscopy (EIS) to study electron-transfer mechanisms, mass transfer phenomena and distribution of the heterogeneous properties of microbial electrochemical systems (MXCs). Over the past eight years, the application of this method has allowed major breakthroughs, especially in the field of microbial fuel cells (MFCs); however, it is still most widely extended only to the calculation of internal resistances. The use and interpretation of EIS should greatly improve since the intrinsic knowledge of this field, and efforts and current trends in this field have already allowed its understanding based on rather meaningful physical properties and not only on fitting electrical analogues. From this perspective, the use, analysis and interpretation of EIS applied to the study of MXCs are critically examined. Together with the revision of more than 150 articles directly devoted to this topic, two examples of the correct and improved analysis of EIS data are extensively presented. The first one focuses on the use of graphical methods for improving EIS analysis and the other one concentrates on the elucidation of the constant phase element (CPE) parameters. CPEs have been introduced in equivalent circuit models, sometimes without solid justification or analysis; the effective capacitance has been obtained from CPE parameters, following an unsuitable theory for the case of microbial–electrochemical interfaces. The use of CPE is reviewed in terms of meaningful physical parameters, such as biofilm thickness. The use of a finite-diffusion element is reviewed throughout estimation of accurate values for obtaining the dimensionless numbers, Schmidt and Sherwood, in the context of a dioxygen-reducing-biocathode, under different flow-rate conditions. The use and analysis of EIS in this context are still emerging, but because of the promising potential of MXCs in renewable power generation, wastewater treatment and energy-positive biorefining, among other applications, it becomes necessary to boost our global capacities for the application of EIS—and especially its interpretation—so that we achieve a better understanding and optimization of these systems.

Recent interest in the field of biocommodities production through bioelectrochemical systems has generated interest in the enzyme catalyzed redox reactions. Enzyme catalyzed electrodes are well established as sensors and power generators. However, a paradigm shift in recent science towards the production of useful chemicals has changed the face of biofuel cells, keeping the fuels or chemicals production in the upfront. This review article comprehensively presents the progress in the field of enzyme-electrodes for the production of electricity, fuels and chemicals with an aim to represent a practical outline for understanding the use of single or multiple redox enzymes as electrocatalysts for their electron transfer onto electrodes. It also provides the state-of-the-art information regarding the different existing processes to fabricate enzyme electrodes. Successfully-achieved electroenzymatic anodic and cathodic reactions are further discussed, together with their potential applications. Particular focus was made on the novel single/multiple enzyme systems towards product synthesis and other applications. Finally, techno-economic and environmental elements for industrial processing with enzyme catalyzed bioelectrochemical system (e-BES) are anticipated, in order to provide useful strategies for further development of this technology.

One of the most intriguing renewable energy production methods being explored currently is electrical power generation by microbial fuel cells (MFCs). However, to make MFC technology economically feasible, cost efficient electrode manufacturing processes need to be proposed and demonstrated. In this context, VITO has developed an innovative electrode manufacturing process based on film casting and phase inversion. The screening and selection process of electrode compositions was done based on physicochemical properties of the active layer, which in turn maintained a close relation with their composition A dual hydrophilic-hydrophobic character in the active layer was achieved with values of εhydrophilic up to 10% while εTOTAL remained in the range 65 wt % to 75 wt %. Eventually, selected electrodes were tested as air cathodes for MFC in half cell and full cell modes. Reduction currents, up to −0.14 mA·cm2− at −100 mV (vs. Ag/AgCl) were reached in long term experiments in the cathode half-cell. In full MFC, a maximum power density of 380 mW·m−2 was observed at 100 Ω external load.