Doctoral dissertation for PhD degree in Chemical and Biological Engineering; Microbial Fuel Cell (MFC) technology is a novel approach for the production of bioelectricity. In
MFC, electroactive bacteria oxidize organic matter and have the particularity to transfer the
electrons, directly to external electron acceptors producing electricity. Geobacter species are
one of the most effective microorganisms known to use electrodes as the sole electron
acceptor. In that regard, the present work was focused on the study of the parameters which
influence the bacterial electron transfer process to electrodes and on the advancement of
wastewater valorization and monitoring technologies based on the MFC concept.
The electrochemical behavior of Geobacter sulfurreducens in different stages of the biofilm
formation in MFC anodes was assessed by cyclic voltammetry in a three-electrode glass cells
with two compartments separated by an ion exchange membrane at room temperature and
35 ºC. Cyclic voltammograms showed that the presence of G. sulfurreducens biofilm results
in an increase of current intensities between - 0.5 V and 0.89 V vs. SCE with three well
defined oxidation peaks at 0.16 V, 0.6 V and 0.8 V vs. SCE respectively. In mature biofilm the
current intensity were higher. The current intensities for both cases were dependent on
operating temperature (≈ 22 °C and 35ºC). In every stage of the biofilm formation...
TiO2 porous films were prepared on ITO coated glass slides by the sol-gel dip-coating method assisted with Polyethylene glycol (PEG). The films were used as photo-anodes in the photo-assisted electrolytic removal of cuprous ions in cyanide media. These were characterized by SEM, UV-Visible spectroscopy and XRD. The PEG modified films were free of cracks and developed a porous structure after heat treatment at 500 ºC, due to the thermal decomposition of the structure associated PEG. It was demonstrated that the photo-assisted electrochemical reduction of copper is promoted by the use of modified TiO2 films as photo-anodes, thanks to the greater surface area given by the PEG decomposition. However, the film thickness was found to be a critical factor in the process, to such an extent that films composed of 5 layers were completely inefficient, meaning that despite the open porosity, multilayered films acted as a barrier within the photo-electrolytic process.
The electrical performance of indium tin oxide (ITO) coated glass was improved by including a controlled layer of carbon nanotubes directly on top of the ITO film. Multiwall carbon nanotubes (MWCNTs) were synthesized by chemical vapor deposition, using ultrathin Fe layers as catalyst. The process parameters (temperature, gas flow and duration) were carefully refined to obtain the appropriate size and density of MWCNTs with a minimum decrease of the light harvesting in the cell. When used as anodes for organic solar cells based on poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM), the MWCNT-enhanced electrodes are found to improve the charge-carrier extraction from the photoactive blend, thanks to the additional percolation paths provided by the CNTs. The work function of as-modified ITO surfaces was measured by the Kelvin probe method to be 4.95 eV, resulting in an improved matching to the highest occupied molecular orbital level of the P3HT. This is in turn expected to increase the hole transport and collection at the anode, contributing to the significant increase of current density and open-circuit voltage observed in test cells created with such MWCNT-enhanced electrodes.
Aluminum based amorphous metallic glass powders were produced and tested as the anode materials for the lithium ion rechargeable batteries. Ground Al₈₀Ni₁₀La₁₀ was found to have a low first cycle capacity of about 100 Ah/Kg. The considerable amount of intermetallic formed in the amorphous glass makes the aluminum inactive towards the lithium. The ball milled Al₈₈Ni₉Y₃ powders contain pure aluminum crystalline particles in the amorphous matrix and have first cycle capacity of about 500 Ah/Kg. Nevertheless, polarization was caused by oxidation introduced by the ball-milling process. The electrochemical performances of these amorphous metallic glasses need to be further investigated. Their full lithium insertion capacities cannot be confirmed until the compositions and particle size inside the metallic glass anodes, the conformation of the electrodes and the mechanical milling processes are optimized.; Singapore-MIT Alliance (SMA)
We have investigated the use of aluminum based amorphous metallic glass as the anode in lithium ion rechargeable batteries. Amorphous metallic glasses have no long-range ordered microstructure; the atoms are less closely packed compared to the crystalline alloys of the same compositions; they usually have higher ionic conductivity than crystalline materials, which make rapid lithium diffusion possible. Many metallic systems have higher theoretical capacity for lithium than graphite/carbon; in addition irreversible capacity loss can be avoided in metallic systems. With careful processing, we are able to obtain nano-crystalline phases dispersed in the amorphous metallic glass matrix. These crystalline regions may form the active centers with which lithium reacts. The surrounding matrix can respond very well to the volume changes as these nano-size regions take up lithium. A comparison study of various kinds of anode materials for lithium rechargeable batteries is carried out.; Singapore-MIT Alliance (SMA)
peer-reviewed; Robust nanoporous gold electrodes were fabricated by sputtering a gold-silver
alloy onto a glass support and subsequent dealloying of the silver component. Alloys
were prepared with either a non-uniform or uniform distribution of silver alloy which
showed clear differences in morphology on characterization with scanning electron
microscopy. The surface area of these electrodes was up to 28 times that of the
geometric surface area. The surface area accessible to modification by redox proteins
was determined using cyt c as a model system. Covalent immobilization of cyt c at
SAMs modified planar and nanoporous gold electrodes resulted in ca. 9 and 11 times
higher surface coverages at uniform and non-uniform nanoporous gold, respectively,
than at planar gold electrodes.
Well defined mediatorless bioelecytrocatalytic reduction of oxygen was
obtained on nanoporous gold electrodes prepared using a vacuum method and
subsequently modified with Myrthecium verrucaria bilirubin oxidase (MvBOD).
Diffusion limited faradaic response, with current densities of 0.8 mA/cm2, was observed
when the enzyme modified electrode was stabilized with a layer the P017-epoxy
polymer. The enzyme, Trametes hirsuta laccase (ThLc) also displayes direct electron
transfer at unmodified nanoporous gold electrodes. The observed current densities of
ca. 0.03 mA/cm2 were 10 times higher than the current densities at the ThLc modified
electrode made by drop-casting and are in contrast to the absence of a response at
unmodified polycrystalline gold electrodes.
Nanoporous and planar gold electrodes modified with Aspergillus niger glucose
oxidase (GOx) and Corynascus thermophilus cellobiose dehydrogenase (CtCDH)
together with Os redox mediators and PEGDGE as a cross-linking agent resulted in
glucose and lactose detecting biosensors. The sensors had (Imax...
Microchannel plates are vacuum-based electron multipliers for particle—in particular, photon— detection, with applications ranging from image intensifiers to single-photon detectors. Their key strengths are large signal amplification, large active area, micrometric spatial resolution and picosecond temporal resolution. Here, we present the first microchannel plate made of hydrogenated amorphous silicon (a-Si:H) instead of lead glass. The breakthrough lies in the possibility of realizing amorphous silicon-based microchannel plates (AMCPs) on any kind of substrate. This achievement is based on mastering the deposition of an ultra-thick (80–120 μm) stress-controlled a-Si:H layer from the gas phase at temperatures of about 200°C and micromachining the channels by dry etching. We fabricated AMCPs that are vertically integrated on metallic anodes of test structures, proving the feasibility of monolithic integration of, for instance, AMCPs on application-specific integrated circuits for signal processing. We show an electron multiplication factor exceeding 30 for an aspect ratio, namely channel length over aperture, of 12.5:1. This result was achieved for input photoelectron currents up to 100 pA, in the continuous illumination regime...
A smooth, ultra-flexible, and transparent electrode was developed from silver nanowires (AgNWs) embedded in a colorless polyimide (cPI) by utilizing an inverted film-processing method. The resulting AgNW-cPI composite electrode had a transparency of >80%, a low sheet resistance of 8 Ω/□, and ultra-smooth surfaces comparable to glass. Leveraging the robust mechanical properties and flexibility of cPI, the thickness of the composite film was reduced to less than 10 μm, which is conducive to extreme flexibility. This film exhibited mechanical durability, for both outward and inward bending tests, up to a bending radius of 30 μm, while maintaining its electrical performance under cyclic bending (bending radius: 500 μm) for 100,000 iterations. Phosphorescent, blue organic light-emitting diodes (OLEDs) were fabricated using these composites as bottom electrodes (anodes). Hole-injection was poor, because AgNWs were largely buried beneath the composite's surface. Thus, we used a simple plasma treatment to remove the thin cPI layer overlaying the nanowires without introducing other conductive materials. As a result, we were able to finely control the flexible OLEDs' electroluminescent properties using the enlarged conductive pathways. The fabricated flexible devices showed only slight performance reductions of <3% even after repeated foldings with a 30 μm bending radius.
The results of five years of development of the inner tracking system of the
HERA-B experiment and first experience from the data taking period of the year
2000 are reported. The system contains 184 chambers, covering a sensitive area
of about 20 * 20 cm2 each. The detector is based on microstrip gas counters
(MSGCs) with diamond like coated (DLC) glass wafers and gas electron
multipliers (GEMs). The main problems in the development phase were gas
discharges in intense hadron beams and aging in a high radiation dose
environment. The observation of gas discharges which damage the electrode
structure of the MSGC led to the addition of the GEM as a first amplification
step. Spurious sparking at the GEM cannot be avoided completely. It does not
affect the GEM itself but can produce secondary damage of the MSGC if the
electric field between the GEM and the MSGC is above a threshold depending on
operation conditions. We observed that aging does not only depend on the dose
but also on the spot size of the irradiated area. Ar-DME mixtures had to be
abandoned whereas a mixture of 70% Ar and 30% CO2 showed no serious aging
effects up to about 40 mC/cm deposited charge on the anodes. X-ray measurements
indicate that the DLC of the MSGC is deteriorated by the gas amplification
process. As a consequence...
[ES] Como parte de nuestros estudios de nuevos materiales de electrodos para aplicación en celdas reversibles de litio, hemos
abordado el estudio de materiales vítreos e híbridos  como posibles alternativas a los materiales activos cristalinos, que
ven frecuentemente limitada su capacidad como resultado de transiciones de fase irreversibles. Dentro de este trabajo se presentan
aquí los resultados recientes sobre cátodos híbridos de PPi/MnO2 (PPi= polipirrol) y de PAni/V2O5 (PAni= polianilina),
y de ánodos basados en vidrios en el sistema V-Ni-Te-O, así como de su combinación en celdas reversibles de ion litio.
Hemos logrado obtener mediante reacción directa de pirrol con permanganato el híbrido PPi/MnO2, y hemos observado que
en la síntesis de PAni/V2O5 existen factores que influyen positivamente en su comportamiento electroquímico.; [EN] This paper is based on new materials applied as electrodes in rechargeable lithium batteries. We have approached the study
of glassy and hybrid materials as an alternative to crystalline active materials, which capacity is frequently limited by irreversible
phase transitions. We present here our latest results on hybrid cathodes, PPy/MnO2 (PPy= PPi= polypirrol) and
PAni/V2O5 (PAni= polyaniline)...