Energy harvest with mangrove benthic microbial fuel cells

Benthic microbial fuel cells (BMFCs) are continuous electricity generators using electroactive microorganisms and organic matter from aquatic environment, respectively, as catalysts and substrate. In this paper, first a low‐cost PVC‐made structure is constructed to harvest electricity from mangrove environment located in French Guiana. An in situ BMFC has given power density of 30 mW/m² of the anodic surface area. This performance has been confirmed by experience in laboratory where inter‐electrode distance and electrode surface area appeared to be power increasing factors. However, the output power of one BMFC is not used to supply real devices such as autonomous sensors. Second, to meet this expectation, in parallel and in series associations were considered. These associations were made in order to increase the output voltage and consequently the power, to reach levels that can supply small sensors (about 3 V). Finally, to improve the performance of the series association and to avoid the voltage reversal phenomenon, a voltage balancing circuit was simulated and added to the series connections. With balancing method, the cell voltage of BMFCs can be equalized, and the performances can be improved. This allows an optimal energy harvesting and a better global efficiency of the set. Copyright © 2014 John Wiley & Sons, Ltd.     

Arginine of Chlamydomonas reinhardtii [Fe–Fe] hydrogenase HydA1 plays a crucial role in electron transfer to its catalytic center

[Fe–Fe] hydrogenases, with hydrogen evolution activities outperforming [Ni–Fe] hydrogenases by 3–4 orders of magnitude, are still the most promising enzyme class for hydrogen production purposes. For Chlamydomonas reinhardtii [Fe–Fe] hydrogenase HydA1 the question of catalytic activity and electron transport is of main importance. Here we report the characterization of two mutant forms of C. reinhardtii HydA1. An aspartic acid in place of arginine¹⁷¹ leads to a six-fold increase of the catalytic activity in comparison to the wild type protein during methyl viologen-dependent hydrogen production. Tryptophan in position 171 does not result in any change in methyl viologen-induced activity. At the same time these mutations lead to a strong decrease in ferredoxin-dependent hydrogen production while the catalytic center of mutant forms stays intact. The localization of this amino acid (arginine¹⁷¹) in the environment of CrHydA1 H-cluster indicates that the limitation of the catalytic activity of this hydrogenase is due to the electron transfer step to the catalytic center where the reduction of protons takes place.     

Multi-scale coupling between two dynamical models for PEMFC aging prediction

In this paper, an approach allowing connecting two numerical models for the simulation of the PEMFC operation and durability at different physical scales is presented. After explaining the interest of coupling them to study the interactions between the fuel cell system and the fuel cell itself, along with lifetime concerns, the feasibility of the task is assessed. Then the numerical approach to achieve this coupling is presented. Finally the response of the coupled models is examined to check its validity, and first results are presented. Predicted fuel cell lifetime trends when changing the stack operation conditions are shown, which highlight the presence of optima concerning temperature, demanded current, pressure and O₂ stoichiometry. Two operation modes are then compared in terms of their impact on the fuel cell performance decay, showing that power cycles are more damaging the fuel cell than nominal operation.     

Combined Experimental and Numerical Flow Field Study of Inclined Louvered Fins

In this study the flow behavior within an interrupted fin design, the inclined louvered fin, is investigated experimentally through visualization and numerically through computational fluid dynamics (CFD) simulation. The inclined louvered fin is a hybrid of the offset strip fin and standard louvered fin, aimed at improved performance at low Reynolds numbers for compact heat exchangers. The flow behavior is studied in six geometrically different configurations over a range of Reynolds numbers and quantified using the concept of “fin angle alignment factor,” which is related to the flow efficiency in louvered fins. The experimental data resulted in a discrete data set of local fin angle alignment factor values, which were used to validate the simulations. Using these validated cases it is shown that the graphical measurement method can be distorted by recirculation zones, resulting in erroneous values. Care should thus be taken when performing graphical measurement of the mean flow angle based on dye injection images. The transition from steady laminar to unsteady flow in inclined louvered fins is geometrically triggered and occurs at lower Reynolds numbers compared to slit fins and standard louvered fins. This property can potentially be used to further improve on the performance of interrupted fin surfaces.     

Investigation of the combined effects of acetate and photobioreactor illuminated fraction in the induction of anoxia for hydrogen production by Chlamydomonas reinhardtii

In the context of hydrogen production by microalgae, the growth of Chlamydomonas reinhardtii was characterized under autotrophic and mixotrophic conditions in a fully controlled photobioreactor (PBR). The combined effect of light transfer conditions, as represented by the illuminated fraction γ, with acetate consumption was observed upon establishment of anoxia. Anoxia was reached in batch cultures when γ was close to 1 (almost fully illuminated culture) in mixotrophic conditions while a value of γ ≈ 0.46 in autotrophic conditions was not sufficient. Based on these results, continuous hydrogen production was established in a cylindrical PBR operated in luminostat with constant illumination and in mixotrophic conditions. Maximum hydrogen gas production was equal to 1.4 ± 0.1 ml_H2 l⁻¹ h⁻¹ for photon flux density of 110 μmol m⁻² s⁻¹ and reactor illuminated fraction of γ = 0.5. Carbon mass balance was realized, emphasizing the necessity to work in strictly autotrophic conditions for hydrogen production with no concomitant CO₂ release.     

Transition metal-catalyzed dehydrogenation of hydrazine borane N2H4BH3via the hydrolysis of BH3 and the decomposition of N2H4

Hydrazine borane N₂H₄BH₃ (denoted HB) is a novel candidate in hydrogen generation by catalytic hydrolysis. The challenge with this material is the dehydrogenation of the N₂H₄ moiety, which occurs after the hydrolysis of the BH₃ group. This challenge requires the utilization of a reactive and selective metal-based catalyst. In this work, we considered various transition metal salts as precursors of in situ forming catalysts by reduction in the presence of HB. According to their reactivity, the metals studied can be classified into 3 groups: (1) Fe- and Re-based catalysts, showing a limited reactivity in the hydrolysis of the BH₃ group; (2) Co-, Ni-, Cu-, Pd-, Pt- and Au-based catalysts, only active in the hydrolysis of BH₃ (3 mol H₂ per mol HB generated); (3) Ru-, Rh, and Ir-based catalysts, being also active in the decomposition of N₂H₄. With the Rh-based catalyst, characterized as agglomerated Rh⁰ nanorods (10 × 4 nm) by XRD, TEM, SAED and XPS, 4.1 mol H₂ + N₂ per mol HB can be produced at 50 °C. Rhodium is thus a possible candidate for synthesizing nanosized particles and bimetallic nanoalloys in order to tune its reactivity and increase its selectivity up to the targeted conversion of 100%. Our main results are reported herein and the behavior of the metals is discussed.     

Numerical simulation of the resistance braze welded assembly of a copper Inconel 601 ground electrode and a steel shell

Abstract

The ground electrode of spark plugs are assembled to a steel shell through a resistance braze-welding technique. Two types of currents can be used in that aim: AC or DC. Based on the current type, two different kinds of models were built. The first one is a 3-D magnetodynamic-thermal model, specially suited for AC current. The magnetodynamic and thermal FE analyses are weakly coupled to calculate the temperature distribution during the process. For the second model dedicated to DC currents, the temperature distribution during the process is obtained through a fully coupled 3-D electrokinetic-thermal modeling. The temperature distributions are then used to simulate the mechanical phenomena. The results of the different models are compared. The effects on the welded zone of the frequency (50 Hz and 5000 Hz), the regulation mode (current or voltage), and the spacing between copper and Inconel 601 coating are discussed.     

Multiple transient point heat sources identification in heat diffusion: application to experimental 2D problems

This paper deals with an inverse problem, which consists of the experimental identification of line heat sources in a homogeneous solid in transient heat conduction. The location and strength of the line heat sources are both unknown. For a single source we examine the case of a source which moves in the system during the experiment. The identification procedure is based on a boundary integral formulation using transient fundamental solutions. The discretized problem is non-linear if the location of the line heat sources is unknown. In order to solve the problem we use an iterative procedure to minimize a cost function comparing the modelled heat source term and the measurements. The proposed numerical approach is applied to experimental 2D examples using measurements provided by an infrared scanner for surface temperatures and heat fluxes. In some particular examples, internal thermocouples can be used. A time regularization procedure associated to future time-steps is used to correctly solve the ill-posed problem.     

Promising anode candidates for direct ethanol fuel cell: Carbon supported PtSn-based trimetallic catalysts prepared by Bönnemann method

To find an efficient anode catalyst for ethanol electrooxidation, several trimetallic PtSnM/C (M = Ni, Co, Rh, Pd) and their corresponding bimetallic PtX/C (X = Sn, Ni, Co, Rh, Pd) catalysts were synthesized by Bönnemann's colloidal precursor method and evaluated by comparing their electrocatalytic activity using conventional electrochemical techniques. For better understanding of the catalyst deactivation during the ethanol electrooxidation, chronoamperometric test was also combined to X-ray photoelectron spectroscopy (XPS) analysis. A significant finding is that trimetallic compositions PtSnCo/C and PtSnNi/C have enhanced activity compared to that of PtSn/C, with lower onset potential for ethanol electrooxidation and notably improved peak current densities. Thus the presence of Ni and Co heteroatom seems to promote C–C bond cleavage and facilitate the removal from the catalyst surface of adsorbed intermediates. These trends are satisfactorily confirmed by testing in a direct ethanol fuel cell (DEFC), since trimetallic PtSnNi/C and PtSnCo/C anode catalysts have significantly higher overall performance and peak power density than Pt/C, PtSn/C or other trimetallic catalyst compositions PtSnRh/C or PtSnPd/C. Furthermore, the presence of Ni or Co helps to improve the weak stability of PtSn/C by providing a stronger Pt–carbon support interaction. XPS results revealed that the surface Pt/Sn atomic ratio of PtSnNi/C catalyst only slightly decreased even after 12 h at 500 mV. On the other hand, a higher concentration of oxide species appeared on the treated PtSn/C surface as a result of a high degradation of carbon support.     

Emetic toxin-producing strains of Bacillus cereus show distinct characteristics within the Bacillus cereus group

One hundred representative strains of Bacillus cereus were selected from a total collection of 372 B. cereus strains using two typing methods (RAPD and FT-IR) to investigate if emetic toxin-producing hazardous B. cereus strains possess characteristic growth and heat resistance profiles. The strains were classified into three groups: emetic toxin (cereulide)-producing strains (n=17), strains connected to diarrheal foodborne outbreaks (n=40) and food-environment strains (n=43), these latter not producing the emetic toxin. Our study revealed a shift in growth limits towards higher temperatures for the emetic strains, regardless of their origin. None of the emetic toxin-producing strains were able to grow below 10 degrees Celsius. In contrast, 11% (9 food-environment strains) out of the 83 non-emetic toxin-producing strains were able to grow at 4 degrees Celsius and 49% at 7 degrees Celsius (28 diarrheal and 13 food-environment strains). non-emetic toxin-producing strains. All emetic toxin-producing strains were able to grow at 48 degrees Celsius, but only 39% (16 diarrheal and 16 food-environment strains) of the non-emetic toxin-producing strains grew at this temperature. Spores from the emetic toxin-producing strains showed, on average, a higher heat resistance at 90 degrees Celsius and a lower germination, particularly at 7 degrees Celsius, than spores from the other strains. No difference between the three groups in their growth kinetics at 24 degrees Celsius, 37 degrees Celsius, and pH 5.0, 7.0, and 8.0 was observed. Our survey shows that emetic toxin-producing strains of B. cereus have distinct characteristics, which could have important implication for the risk assessment of the emetic type of B. cereus caused food poisoning. For instance, emetic strains still represent a special risk in heat-processed foods or preheated foods that are kept warm (in restaurants and cafeterias), but should not pose a risk in refrigerated foods.