Gérard Perrier

Characterization of a microbial fuel cell with reticulated carbon foam electrodes

A microbial fuel cell with open-pore reticulated vitreous carbon electrodes is studied to assess the suitability of this material in a batch mode, in the perspective of flow-through reactors for wastewater treatment with electricity generation. The cell shows good stability and fair robustness in regards to substrate cycles. A power density of 40 W/m(3) is reached. The cell efficiency is mainly limited by cathodic transfers, representing 85% of the global overpotential in open circuit. Through impedance spectrocopy, equivalent circuit modeling reveals the complex nature of the bioelectrochemical phenomena. The global electrical behavior of the cell seems to result in the addition of three anodic and two cathodic distinct phenomena. On the cathode side, the Warburg element in the model is related to the diffusion of oxygen. Warburg resistance and time are respectively 2.99 kΩ cm(2) and 16.4s, similar to those published elsewhere.

Polystyrene-glass bead composites : Maxwell-Wagner-sillars relaxations and percolation

Dielectric spectrometry experiments are performed on a series of polystyrene-glass bead composites with volume filler content from 0 to 50% and with three particle diameters ( 5μm, 20 μm, and 90 μm) in order to study the Maxwell-Wagner-Sillars (MWS) relaxations and the percolation phenomena. In the high-temperature region (130 to 220°C ), the experimental data give evidence of MWS relaxations for all the composite systems, whatever the bead size and the filler content are. A good agreement is found between the experimental values of the maximum loss factor frequency and the theoretical ones drawn from the van Beek formula, especially for low contents. A percolation phenomenon is shown in the low-temperature region (40 to 120°C for high-content/low-size composites. The percolation threshold, determined by considering the critical interparticle distance, is below 15.0% for the 5 μm glass bead composites and above 47.3% for the 90 μm composites; it lies between 20.5 and 28.6% for the 20 μm composites. Two schematic models, based on a distribution of the sizes and on a random dispersion of the beads, are developed to show how MWS and percolation phenomena can both be observed for the high-content/low-size composites.

Multifactorial evaluation of the electrochemical response of a microbial fuel cell

A lab-scale microbial fuel cell (MFC) with a reticulated vitreous carbon (RVC) anode and a non-catalyzed multi-layered carbon air-cathode was electrochemically characterized under various physicochemical factors: temperature (15–25 °C), phosphate buffer concentration (4–8 mM), acetate concentration (7.1–14.3 mM), and equivalent solution conductivity (2.5–5 mS cm−1). A fundamental step was undertaken to identify and characterize the electrochemical mechanisms through multifactorial evaluation of the simultaneous effect of such factors on the functioning of the MFC. This type of analysis of cyclic voltammetry and impedance spectroscopy parameters revealed complementary features to model the electrochemical response. This multifactorial approach finds broad application in a wide variety of MFC and environmental technology studies.

Maxwell - Wagner - Sillars relaxations in surface-modified glass-bead polystyrene-based composites

Polystyrene-glass-bead and styrene/methacrylic acid copolymer-glass-bead composites were investigated by dielectric spectrometry in order to study the Maxwell-Wagner-Sillars (MWS) interfacial relaxation. Untreated glass beads and glass beads with various surface coatings were both used in the composites. The interfacial relaxation is used to test for the influence of the surface coating on the blocking nature of the interface. A good agreement is found between the van Beek calculated values of the maximum loss frequencies and the experimental ones. Through this analysis, the use of a coupling agent is shown to improve the trapping of the ions at the interface between the polymer matrix and the glass inclusions. This was especially the case in styrene-methacrylic acid copolymer filled with glass beads coated with a methacrylic silane. The presence of water causes the maximum loss frequency to increase dramatically and is also thought to improve the blocking of the electric charges at the matrix-inclusions ...

Bio-electrochemical characterization of air-cathode microbial fuel cells with microporous polyethylene/silica membrane as separator

The aim of this work was to study the behavior over time of a separator made of a low-cost and non-selective microporous polyethylene membrane (RhinoHide®) in an air-cathode microbial fuel cell with a reticulated vitreous carbon foam bioanode. Performances of the microporous polyethylene membrane (RhinoHide®) were compared with Nafion®-117 as a cationic exchange membrane. A non-parametric test (Mann-Whitney) done on the different sets of coulombic or energy efficiency data showed no significant difference between the two types of tested membrane (p<0.05). Volumetric power densities were ranging from 30 to 90 W·m(-3) of RVC foam for both membranes. Similar amounts of biomass were observed on both sides of the polyethylene membrane illustrating bacterial permeability of this type of separator. A monospecific denitrifying population on cathodic side of RhinoHide® membrane has been identified. Electrochemical impedance spectroscopy (EIS) was used at OCV conditions to characterize electrochemical behavior of MFCs by equivalent electrical circuit fitted on both Nyquist and Bode plots. Resistances and pseudo-capacitances from EIS analyses do not differ in such a way that the nature of the membrane could be considered as responsible.

First steps towards a constructal Microbial Fuel Cell

In order to reach real operating conditions with consequent organic charge flow, a multi-channel reactor for Microbial Fuel Cells is designed. The feed-through double chamber reactor is a two-dimensional system with four parallel channels and Reticulated Vitreous Carbon as electrodes. Based on thermodynamical calculations, the constructal-inspired distributor is optimized with the aim to reduce entropy generation along the distributing path. In the case of negligible singular pressure drops, the Hess-Murray law links the lengths and the hydraulic diameters of the successive reducing ducts leading to one given working channel. The determination of generated entropy in the channels of our constructal MFC is based on the global hydraulic resistance caused by both regular and singular pressure drops. Polarization, power and Electrochemical Impedance Spectroscopy show the robustness and the efficiency of the cell, and therefore the potential of the constructal approach. Routes towards improvements are suggested in terms of design evolutions.

Dielectric Spectrometry of Amorphous Thermoplastic/Glass Bead Composites

A series of polystyrene/glass bead and poly (styrene-co-methacrylic acid)/glass bead composites with volumic fractions in the order of 21% is studied by means of dielectric spectrometry. Experimental isochronal data on the pure matrixes show the α relaxation, associated to the glass transition. In the case of the composites, a more intense relaxation appears at a higher temperature compared with that of the α relaxation. This relaxation is attributed to the Maxwell-Wagner-Sillars (MWS) effect. Experimental results are in agreement with the van Beek theory in the case of untreated spherical inclusions. This agreement is more remarkable in the case of coupling agent-treated glass beads.

Maxwell- Wagner- Sillars relaxations and crystallinity in PEEK

Dielectric studies have been carried out on semi-crystalline poly(ether-ether-ketone) at temperatures from 100 to 300°C and at frequencies between 20 Hz and 10 kHz. A relaxation is seen in the isochronal curves and in the Cole-Cole plots, which is attributed to a Maxwell-Wagner-Sillars polarization taking place at the interface between the crystalline inclusions and the amorphous matrix. The intensity of this relaxation is presented in relation to the morphology of the crystalline part which is known to depend on annealing conditions.