Hydrodynamic energy harvesting using an ionic polymer-metal composite stack for underwater applications

Ionic Polymer Metal Composites (IPMCs) are a class of Electro-Active Polymers (EAPs) consisting of a base polymer (usually Nafion), sandwiched between thin films of electrodes and an electrolyte. Apart from fuel cell like proton exchange process in Nafion, these IPMCs can act both as an actuator and a sensor. Typically, IPMCs have been known for their applications in fuel cell technology and in artificial muscles for robots. However, more recently, sensing properties of IPMC have opened up possibilities of mechanical energy harvesting. In this paper, we consider a bi-layer stack of IPMC membranes where fluid flow induced cyclic oscillation allows collection of electronic charge across a pair of functionalized electrode on the surface of IPMC layers/stacks. IPMCs work well in hydrated environment; more specifically, in presence of an electrolyte, and therefore, have great potential in underwater applications like hydrodynamic energy harvesting. Hydrodynamic forces produce bending deformation, which can induce transport of cations via polymer chains of the base polymer of Nafion or PTFE. In our experimental set-up, the deformation is induced into the array of IPMC membranes immersed in electrolyte by water waves caused by a plunger connected to a stepper motor. The frequency and amplitude of the water waves is controlled by the stepper motor through a micro-controller. The generated electric power is measured across a resistive load. Few orders of magnitude increase in the harvested power density is observed. Analytical modeling approach used for power and efficiency calculations are discussed. The observed electro-mechanical performance promises a host of underwater energy harvesting applications.

Structural Diversity in Multinuclear PdII Assemblies that Show Low- Humidity Proton Conduction

Systematic investigation on synergetic effects of geometry, length, denticity, and asymmetry of donors was performed through the formation of a series of uncommon Pd-II aggregates by employing the donor in a multicomponent self-assembly of a cis-blocked 90 degrees Pd-II acceptor and a tetratopic donor. Some of these assemblies represent the first examples of these types of structures, and their formation is not anticipated by only taking the geometry of the donor and the acceptor building units into account. Analysis of the crystal packing of the X-ray structure revealed several H bonds between the counteranions (NO3-) and water molecules (OHON). Moreover, H-bonded 3D-networks of water are present in the molecular pockets, which show water-adsorption properties with some variation in water affinity. Interestingly, these complexes exhibit proton conductivity (1.87x10(-5)-6.52x10(-4)Scm(-1)) at 296K and low relative humidity (ca. 46%) with activation energies of 0.29-0.46eV. Moreover, the conductivities further increase with the enhancement of humidity. The ability of these assemblies to exhibit proton-conducting properties under low-humidity conditions makes these materials highly appealing as electrolytes in batteries and in fuel-cell applications.

New Insights into Electronic and Geometric Effects in the Enhanced Photoelectrooxidation of Ethanol Using ZnO Nanorod/Ultrathin Au Nanowire Hybrids

Oxidation of small organic molecules in a fuel cell is a viable method for energy production. However, the key issue is the development of suitable catalysts that exhibit high efficiencies and remain stable during operation. Here, we demonstrate that amine-modified ZnO nanorods on which ultrathin Au nanowires are grown act as an excellent catalyst for the oxidation of ethanol. We show that the modification of the ZnO nanorods with oleylamine not only modifies the electronic structure favorably but also serves to anchor the Au nanowires on the nanorods. The adsorption of OH- species on the Au nanowires that is essential for ethanol oxidation is facilitated at much lower potentials as compared to bare Au nanowires leading to high activity. While ZnO shows negligible electrocatalytic activity under normal conditions, there is significant enhancement in the activity under light irradiation. We demonstrate a synergistic enhancement in the photoelectrocatalytic activity of the ZnO/Au nanowire hybrid and provide mechanistic explanation for this enhancement based on both electronic as well as geometric effects. The principles developed are applicable for tuning the properties of other metal/semiconductor hybrids with potentially interesting applications beyond the fuel cell application demonstrated here.

Effect of Manganese (II) Oxide on microstructure and ionic transport properties of nanostructured cubic zirconia

Effect of MnO addition on microstructure and ionic transport properties of nanocrystalline cubic(c)-ZrO2 is reported. Monoclinic (m) ZrO2 powders with 10-30 mol% MnO powder are mechanically alloyed in a planetary ball mill at room temperature for 10 h and annealed at 550 degrees C for 6 h. In all compositions m-ZrO2 transforms completely to nanocrystalline c-ZrO2 phase and MnO is fully incorporated into c-ZrO2 lattice. Rietveld's refinement technique is employed for detailed microstructure analysis by analyzing XRD patterns. High resolution transmission electron microscopy (HRTEM) analysis confirms the complete formation of c-ZrO2 phase. Presence of stoichiometric Mn in c-ZrO2 powder is confirmed by Electron Probe Microscopy analysis. XPS analysis reveals that Mn is mostly in Mn2+ oxidation state. A correlation between lattice parameter and oxygen vacancy is established. A detailed ionic conductivity measurement in the 250 degrees-575 degrees C temperature range describes the effect of MnO on conductivity of c-ZrO2. The ionic conductivity (s) of 30 mol% MnO alloyed ZrO2 at 550 degrees C is 0.04 s cm(-1). Electrical relaxation studies are carried out by impedance and modulus spectroscopy. Relaxation frequency is found to increase with temperature and MnO mol fraction. Electrical characterization predicts that these compounds have potentials for use as solid oxide fuel cell electrolyte material. (C) 2015 Elsevier Ltd. All rights reserved.

Ultrathin Au nanowires supported on rGO/TiO2 as an efficient photoelectrocatalyst

We report the synthesis of stable rGO/TiO2/Au nanowire hybrids showing excellent electrocatalytic activity for ethanol oxidation. Phase-pure anatase TiO2 nanoparticles (similar to 3 nm) were grown on GO sheets followed by the growth of ultrathin Au nanowires leading to the formation of a multidimensional ternary structure (0-D TiO2 and 1-D Au on 2-D graphene oxide). The oleylamine used for the synthesis of the Au nanowires not only leads to stable Au nanowires anchored on the GO sheets but also leads to the functionalization and room temperature reduction of GO. Using control experiments, we delineate the role of the three components in the hybrid and show that there is a significant synergy. We show that the catalytic activity for ethanol oxidation primarily stems from the Au nanowires. While TiO2 triggers the formation of oxygenated species on the Au nanowire surface at a lower potential and also imparts photoactivity, rGO provides a conducting support to minimize the charge transfer resistance in addition to stabilizing the Au nanowires. Compared with nanoparticle hybrids, the nanowire hybrids display a much better electrocatalytic performance. In addition to high efficiency, the nanowire hybrids also show a remarkable tolerance towards H2O2. While our study has a direct bearing on fuel cell technology, the insights gained are sufficiently general such that they provide guiding principles for the development of multifunctional ternary hybrids.

Electronic structure origin of conductivity and oxygen reduction activity changes in low-level Cr-substituted (La, Sr)MnO3

The electronic structure of the (La0.8Sr0.2)(0.98)Mn1-xCrxO3 model series (x = 0, 0.05, or 0.1) was measured using soft X-ray synchrotron radiation at room and elevated temperature. O K-edge near-edge X-ray absorption fine structure (NEXAFS) spectra showed that low-level chromium substitution of (La, Sr)MnO3 resulted in lowered hybridisation between O 2p orbitals and M 3d and M 4sp valance orbitals. Mn L-3-edge resonant photoemission spectroscopy measurements indicated lowered Mn 3d-O 2p hybridisation with chromium substitution. Deconvolution of O K-edge NEXAFS spectra took into account the effects of exchange and crystal field splitting and included a novel approach whereby the pre-peak region was described using the nominally filled t(2g) up arrow state. 10% chromium substitution resulted in a 0.17 eV lowering in the energy of the t(2g) up arrow state, which appears to provide an explanation for the 0.15 eV rise in activation energy for the oxygen reduction reaction, while decreased overlap between hybrid O 2p-Mn 3d states was in qualitative agreement with lowered electronic conductivity. An orbital-level understanding of the thermodynamically predicted solid oxide fuel cell cathode poisoning mechanism involving low-level chromium substitution on the B-site of (La, Sr)MnO3 is presented. (C) 2015 AIP Publishing LLC.

Hetero-atom Doped Carbon Nanotubes for Dye Degradation and Oxygen Reduction Reaction

We report the synthesis of nitrogen doped vertically aligned multi-walled (MWNCNTs) carbon nanotubes by pyrolysis and its catalytic performance for degradation of methylene blue (MB) dye & oxygen reduction reaction (ORR). The degradation of MB was monitored spectrophotometrically with time. Kinetic studies show the degradation of MB follows a first order kinetic with rate constant k=0.0178 min(-1). The present rate constant is better than that reported for various supported/non-supported semiconducting nanomaterials. Further ORR performance in alkaline media makes MWNCNTs a promising cost-effective, fuel crossover tolerance, metal-free, eco-friendly cathode catalyst for direct alcohol fuel cell.

Influencia del diseño de los canales de flujo en el rendimiento de una pila de combustible de membrana de intercambio protónico (PEMFC)

Las pilas de combustible se presentan hoy día como una de las alternativas de generación de energía limpia más adecuadas. En este proyecto de tesis se presenta una visión global de lo que son, de cómo funcionan y de cuáles son las leyes que rigen este funcionamiento, centrándose en las denominadas pilas de combustible de tipo PEM. Además de describir el modelo matemático utilizado para la simulación numérica, también se presenta un procedimiento optimizado para la simulación de prototipos de pila de combustible de tipo PEM. Se incluye una recopilación de los resultados más importantes de los estudios realizados en los últimos años relacionados con la influencia de los diferentes parámetros geométricos de los canales de flujo en el rendimiento global de una pila de combustible de tipo PEM. Esta revisión se ha utilizado como base para un nuevo estudio: Análisis de la influencia de la configuración de la sección transversal del canal de flujo en el funcionamiento de una pila de combustible de tipo PEM con canales de flujo de tipo serpentín. Finalmente, se realiza una propuesta de nueva geometría de canales de flujo que proporcione un rendimiento global óptimo al sistema a través de de la homogeneización de las condiciones de operación a lo largo de toda la superficie reactiva de la pila.

Object oriented simulation of hybrid renewable energy systems focused on supervisor control

EFTA 2009

The electrocatalytic and stoichiometric oxidation chemistry of binuclear ruthenium complexes incorporating the anionic tripod ligand {(η5-C5H5)Co[P(OCH3)2(=O)]3}-

The anionic tripod ligand NaLoMe (L_(oMe) - = [(η^5-C_5H_5)Co{P(O)(OCH_3)_2}_3]^-) reacts with RuO_4 in a biphasic reaction mixture of 1% H_2SO_4 and CCI_4 to afford [(L_(oMe) (HO)Ru^(IV) (µ-O)_2Ru ^(IV)(OH)(L_(oMe)] (1), which is treated with aqueous CF_3S0_3H to generate [(L_(oMe)(H_2O)Ru^(IV) (µ-O)_2R^(IV) (OH_2)(L_(oMe)][CF_3SO_3]_2 ([H_21][CF_3SO_3]_2). Addition of iodosobenzene to an acetonitrile solution of this salt yields [(L_(oMe)(O)Ru^v(µ-0)2Ru^v-(O)(_(LoMe)] (2). The dimer 1 can be reduced chemically or electrochemically to the Ru^(III)- Ru^(III) dimers [(L_(oMe)(H_20)Ru^(III) (µ-OH)_2Ru^(III) (OH_2)(L_(oMe)) ]^2+ and [(L_(oMe)) ^(III) (µ-0Hh(µ-0H2)Ru^(III) (L_(oMe)]^2+ which interconvert in aqueous media. Two electron processes dominate both the bulk chemistry and the electrochemistry of 1. Among these processes are the quasi-reversible Ru^(IV) - Ru^(IV)/Ru^(III)- Ru^(III) and Ru^(III)- Ru^(III)/ Ru^(II)- Ru^(II) reductions and a largely irreversible Ru^(V) - Ru^(V)/ Ru^(IV) - Ru^(IV)/oxidation. The dioxo dimer 2 oxidizes alcohols and aldehydes in organic media to afford 1 and the corresponding aldehydes and acids. Analogously, the Ru^(V) - Ru^(V)/ Ru^(IV)- Ru^(IV) redox wave mediates the electrooxidation of alcohols and aldehydes in aqueous buffer. In this system, substrates can be oxidized completely to CO_2. The kinetic behavior of these oxidations was examined by UV-vis and chronoamperometry, respectively, and the chemistry is typical of metal-oxo complexes, indicating that electronic coupling between two metal centers does not dramatically affect the metal-oxo chemistry. Dimer [H_21]^(2+) also reacts with alcohols, aldehydes, and triphenylphosphine in CH_3CN to afford Ru^(III)- Ru^(III) products including [(L_(oMe))CH_3CN) Ru^(III) (µ-OH)_2 Ru^(III) (NCCH_3)( L_(oMe))][CF_3SO_3]2 (characterized by X-ray crystallography) and the corresponding organic products. Reaction of 1 with formaldehyde in aqueous buffer quantitatively affords the triply bridged dimer [(L_(oMe)Ru^(III) (µ-OH)2- (µ-HCOO) Ru^(III) (L_(oMe)][CF_3SO_3] (characterized by X-ray crystallography). This reaction evidently proceeds by two parallel inner-sphere pathways, one of which is autocatalytic. Neither pathway exhibits a primary isotope effect suggesting the rate determining process could be the formation of an intermediate, perhaps a Ru^(IV) - Ru^(IV) formate adduct. The Ru^(III)- Ru^(III)formate adduct is easily oxidized to the Ru^(IV) - Ru^(IV) analog [(L_(oMe)Ru^(IV)(µ-OH)_2-(µ-HCOO) Ru^(IV) (L_(oMe)][CF_3SO_3], which, after isolation, reacts slowly with aqueous formaldehyde to generate free formate and the Ru^(III)- Ru^(III) formate adduct. These dimers function as catalysts for the electrooxidation of formaldehyde at low anodic potentials (+0.0 V versus SCE in aqueous buffer, pH 8.5) and enhance the activity of Nafion treated palladium/carbon heterogeneous fuel cell catalysts.

Nanostructured tungsten trioxide photoanodes for solar energy conversion

Nanostructured tungsten trioxide (WO₃) photoelectrodes are potential candidates for the anodic portion of an integrated solar water-splitting device that generates hydrogen fuel and oxygen from water. These nanostructured materials can potentially offer improved performance in photooxidation reactions compared to unstructured materials because of enhancements in light scattering, increases in surface area, and their decoupling of the directions of light absorption and carrier collection. To evaluate the presence of these effects and their contributions toward energy conversion efficiency, a variety of nanostructured WO₃ photoanodes were synthesized by electrodeposition within nanoporous templates and by anodization of tungsten foils. A robust fabrication process was developed for the creation of oriented WO₃ nanorod arrays, which allows for control nanorod diameter and length. Films of nanostructured WO₃ platelets were grown via anodization, the morphology of the films was controlled by the anodization conditions, and the current-voltage performance and spectral response properties of these films were studied. The observed photocurrents were consistent with the apparent morphologies of the nanostructured arrays. Measurements of electrochemically active surface area and other physical characteristics were correlated with observed differences in absorbance, external quantum yield, and photocurrent density for the anodized arrays. The capability to quantify these characteristics and relate them to photoanode performance metrics can allow for selection of appropriate structural parameters when designing photoanodes for solar energy conversion.

Development of Metalloenzyme Dioxygen Reduction Cathodes

The prime thrust of this dissertation is to advance the development of fuel cell dioxygen reduction cathodes that employ some variant of multicopper oxidase enzymes as the catalyst. The low earth-abundance of platinum metal and its correspondingly high market cost has prompted a general search amongst chemists and materials scientists for reasonable alternatives to this metal for facilitating catalytic dioxygen reduction chemistry. The multicopper oxidases (MCOs), which constitute a class of enzyme that naturally catalyze the reaction O₂ + 4H⁺ + 4e^- → 2H₂O, provide a promising set of biochemical contenders for fuel cell cathode catalysts. In MCOs, a substrate reduces a copper atom at the type 1 site, where charge is then transferred to a trinuclear copper cluster consisting of a mononuclear type 2 or “normal copper” site and a binuclear type 3 copper site. Following the reduction of all four copper atoms in the enzyme, dioxygen is then reduced to water in two two-electron steps, upon binding to the trinuclear copper cluster. We identified an MCO, a laccase from the hyperthermophilic bacterium Thermus thermophilus strain HB27, as a promising candidate for cathodic fuel cell catalysis. This protein demonstrates resilience at high temperatures, exhibiting no denaturing transition at temperatures high as 95°C, conditions relevant to typical polymer electrolyte fuel cell operation.

In Chapter I of this thesis, we discuss initial efforts to physically characterize the enzyme when operating as a heterogeneous cathode catalyst. Following this, in Chapter II we then outline the development of a model capable of describing the observed electrochemical behavior of this enzyme when operating on porous carbon electrodes. Developing a rigorous mathematical framework with which to describe this system had the potential to improve our understanding of MCO electrokinetics, while also providing a level of predictive power that might guide any future efforts to fabricate MCO cathodes with optimized electrochemical performance. In Chapter III we detail efforts to reduce electrode overpotentials through site-directed mutagenesis of the inner and outer-sphere ligands of the Cu sites in laccase, using electrochemical methods and electronic spectroscopy to try and understand the resultant behavior of our mutant constructs. Finally, in Chapter IV, we examine future work concerning the fabrication of enhanced MCO cathodes, exploring the possibility of new cathode materials and advanced enzyme deposition techniques.

Modificación del sistema energético de la unidad móvil de donantes de osakidetza (CVTT)

[ES]Hoy en día los vehículos usados en la extracción de sangre utilizan un motor de combustión interna, no solamente para sus desplazamientos, sino también para generar electricidad con la que poder utilizar todos los aparatos del interior. Como consecuencia, el autobús es una fuente importante de ruidos y contaminación, ya que el motor diesel está funcionando durante las largas paradas en las que se realiza dicha actividad. El objetivo del proyecto es diseñar un sistema innovador basado en pilas de combustible que sirva para alimentar todos los equipos y dispositivos, evitando el ruido, las vibraciones y los gases contaminantes. Para ello y en primer lugar, será necesario estimar el consumo total del autobús. Tras esto, también se tomarán una serie de decisiones con el fin de mejorar la eficiencia energética del autobús. Finalmente, se hará un diseño del sistema energético, el cual debe incluir una pila de combustible, junto con todos sus sistemas asociados, y todas las especificaciones.