Residences require electricity for lights, appliances, and space cooling and thermal energy for space and domestic water heating. Total energy systems (TES) which provide both electricity and thermal energy can meet these needs more effectively than conventional systems because thermal energy rejected during the on-site production of electricity can be recovered to meet the heating loads. TESs based on fuel cell systems are particularly attractive because of their high efficiencies, quiet operation, and small size. This research evaluates a TES consisting of a fuel cell sub-system (FCS), an electric heat pump (HP), and a thermal storage tank (TS). A model of a grid-independent, electric load following TES is developed to determine the energy required to meet the hourly average electric and thermal loads of the residence. The TES uses a heat pump to provide space cooling. Electricity for air conditioning, lights, and appliances is provided by the FCS. Space heating and water heating of the residence are provided by the thermal energy available from the FCS. The TES is designed so that, heating requirements that exceed the heat available from the FCS can be satisfied by the HP and an electric water heater. A thermal storage tank is used to store and transfer thermal energy from the FCS to the residence. The results of the research include a comparison of the energy use by the TES to the energy use by conventional residential energy systems; an evaluation of the effects of climatic conditions on system performance and energy use; and a comparison of the life-cycle cost of the TES and conventional residential energy systems. The results indicate that total energy systems can reduce primary energy use by as much as 40 percent, but that to be economically attractive, the FCS cost must be reduced to approximately $500/kWe. / Master of Science

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第19090号 / エネ博第314号 / 新制||エネ||64(附属図書館) / 32041 / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 萩原 理加, 教授 佐川 尚, 教授 野平 俊之 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19729号 / 工博第4184号 / 新制||工||1645(附属図書館) / 32765 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 江口 浩一, 教授 安部 武志, 教授 陰山 洋 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Renewable energy applications (i.e. fuel cells, flow batteries, electrolyzers) have been at the forefront of green energy and environmental research over the past couple of decades and the research associated with them has skyrocketed due to changes in funding and incentives. The extensive research over the years have resulted in higher efficiency and longer lasting devices for renewable energy applications, but there is still a major bottleneck that all these devices share; the ion-exchange membrane (IEM). The development of polymer ion-exchange membranes has been very beneficial for these devices as they allow for higher working temperatures and increase the longevity and efficiency of said devices. IEM research can be summed up into two major types of membranes; proton- and anion-exchanging. Of these materials, proton-exchanging membrane (PEM) are well established and studied due to how long they have been manufactured and the ease of manufacturing. There has been a variety of different PEMs developed and tested, but none have been commercialized as heavily or used as universally as Nafion® (developed by DuPont in the 1960s) although it still suffers from setbacks like its high cost, low working temperatures and its low tolerance for fuel impurities. On the other hand, anion-exchange membranes (AEM) have become popular in this field of study as they boast a non-acidic substitute as well as more efficient oxygen reduction reactions allowing for operation without the use of expensive catalysts. AEMs are first in line to replace commercial PEMs like Nafion®, the major bottleneck being their ionic conductivities. Pairing the structural characteristics of PEMs with the efficient and more cost effective AEMs we sought out to design and synthesize new IEMs to compete with current commercial membranes. By using ring opening metatheses polymerization (ROMP) we have designed and developed numerous hydrocarbon polynorbornene derivative membranes with the intention of incorporating amino-phosphine ion exchange groups (IEG) to compete with current IEMs in both efficiency and cost with the major application of fuel cells and flow batteries in mind. We also performed different modifications to the initial membranes such as crosslinking and alkyl chain addition to increase the mechanical strength and mitigate the degradation of the membranes. Using results gathered from developing polynorbornene IEMs, we pivoted to another multitude of membranes, this time focusing on the PEM capabilities of fluorinated polymers instead of their hydrocarbon alternatives for use in redox flow batteries with the main goal of decreasing electrolyte crossover, therefore increasing the longevity of the devices. Several new IEMs were designed as composite membranes of Nafion® and aromatic organic IEGs and synthesized to compete with the current commercial IEMs while testing the effect of different aromatic IEGs on the salt permeability and mechanical strength of the membrane. Synthesis of a stable IEM with good electrolyte crossover and conductivity properties was achieved by combining a grafted Nafion® backbone with 2-phenylbenzimidazole side chains containing a long hydrocarbon chain to facilitate hydrophobicity and increase mechanical strength. These composite membranes take advantage of the imidazole’s highly stable chemical backbone and proton exchanging properties allowing it to withstand highly acidic and oxidative environments as well as relying on benzimidazoles tight packing to reduce electrolyte permeability throughout the membrane.

No description available.

Master Thesis, Department of Mechanical Engineering / A comprehensive analytical model of an indirect internal reforming type tubular Solid Oxide Fuel Cell (IIR-T-SOFC) has been developed. Two-dimensional axisymmetric multicomponent gas flow fields and quasi-three-dimensional electric potential/current fields in the tubular cell are simultaneously treated in the model with consideration of the involved phenomena such as internal reforming, electrochemical reactions and radiative heat transfer. By using this model, the characteristics of the operating state of an IIR-T-SOFC were numerically examined. As a result, it was shown how the thermal field and power generation characteristics of the cell were affected by the gas inlet temperature, air flow rate, steam-methane ratio, reforming catalyst distribution and thickness of the electrodes. In particular, the optimized catalyst distribution greatly reduced both the maximum temperature and temperature gradients of the cell with little negative impact on the power generation performance of the cell. / 京都大学 / 0048 / 修士 / 修士(工学) / Kyoto University / TFtmp

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23577号 / 工博第4932号 / 新制||工||1770(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 江口 浩一, 教授 阿部 竜, 教授 岩井 裕 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Deriving electrical energy from glucose and other carbohydrates under mild conditions is an important research objective because these biomolecules are abundant, renewable, and can provide 12 to 24 electrons per molecule, yielding substantial electrical power. It was previously observed that disubstituted viologens, salts of N,N'-disubstituted 4,4'-bipyridine, are able to oxidize glucose under alkaline conditions. Building on that initial result, the objective of this work was to understand and quantify the effectiveness and utility of viologens as catalysts for use in direct carbohydrate fuel cells.The extent that viologens oxidize carbohydrates, the conditions under which that oxidation occurs, and the mechanism for the oxidation were examined using oxygen-uptake and other methods. Viologens were found to catalytically oxidize carbohydrates extensively in alkaline solution. Viologens were also found to react with the enediol form of the carbohydrate, initiating carbohydrate oxidation with subsequent reduction of the viologen. If the viologen/carbohydrate ratio is low, electron transfer from the carbohydrate to the viologen becomes limiting and the carbohydrates undergoing oxidation rearrange into unreactive intermediates such as carboxylic acids and alcohols. At high catalyst ratios, excess viologen more rapidly oxidizes the carbohydrate and minimizes formation of unreactive intermediates. We also found that viologen polymers were more efficient than an equivalent concentration of monomers, suggesting that the higher localized concentration in polymeric viologen acts to efficiently oxidize carbohydrates and simulates high viologen/carbohydrate ratios.Monoalkyl viologens, aminoviologens, indigo carmine, and methylene blue were investigated by the method of cyclic voltammetry to inform their use as catalysts in the oxidation of carbohydrates. Redox potentials, diffusion coefficients, and heterogeneous electron-transfer rate constants were determined. Stability in alkaline solution and aqueous solubility were also examined in a semi-quantitative fashion. A comparison between the catalysts was made and viologens were found to be superior based on the examined parameters.The catalytic oxidation of carbohydrates by viologen was also examined using a fuel cell-like device. For the conditions in which a test cell was operated, oxidation efficiencies of up to 33% were observed, compared to previously reported values from about 2.5% to 80%. Anode polarization curves were obtained and used to determine the behavior of the viologen-controlled anode as a function of pH, viologen and carbohydrate concentration, and carbohydrate identity. pH was found to have a stronger effect on the performance at the anode for carbohydrates with a higher number of carbons than those with a lower number.

Membrane durability is one of the limiting factors for proton exchange membrane fuel cell (PEMFC) commercialisation by limiting the lifetime of the membrane via electrochemical / mechanical / thermal degradation. Lower internal humidity in the membrane at high temperature ( > 100 °C) and low relative humidity (25-50 %RH) operating conditions leads to increased resistance, lowering of performance and higher degradation rate. One of the promising candidates is composite proton exchange membranes (CPEMs) which have heteropoly acid (HPA) e.g. Phosphotungstic acid (PTA) doped throughout the Nafion® matrix. HPA is primarily responsible for carrying intrinsic water which reduces the external water dependence. The role of relative humidity during membrane casting was studied using surface analysis tools such as Xray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Thermo-gravimetric analysis (TGA), and Scanning electron microscopy (SEM) / Energy dispersive spectrometer (EDS). Membrane casting at lower relative humidity (30% approx.) results in finer size, and better PTA incorporation in the composite membrane. The effect of increase in PTA concentration in the Nafion matrix was studied with regards to conductivity, performance and durability. In-plane conductivity measurements were performed at 80 oC and 120 oC. During theses measurements, relative humidity was varied from 20% to 100% RH. Membrane conductivity invariably increases on increasing the relative humidity or operating temperature of the cell. Membrane conductivity increases with increasing PTA content from 3% to 25% PTA but never reaches the conductivity of membrane with 0% PTA. Possible explanation might be the role of cesium in PTA stabilisation process. Cesium forms a complex compound with PTA inside host matrix, rendering the PTA incapable of holding water. In plane conductivity measurements only measure surface conductivity, hence another reason might be the existence of a PTA skin on the membrane surface which is not truly representative of the whole membrane. XRD revealed that the structure of the composite membrane changes significantly on addition of PTA. Membrane with 3% PTA has structure similar to Nafion® and does not exhibit the characteristic 25o and 35o 2Ө peaks while membrane with 15% PTA and 25% PTA have strong characteristic PTA peaks. Also the membrane structure with 25% PTA matches well with that of PTA.6H2O. By applying the Scherer formula, PTA particle size was calculated from Full width half maximum (FWHM) studies at 17o 2Ө peak of the membranes. Particles coalesce on increasing the PTA concentration in the membrane leading to larger particles but still all particles were in nanometer range. Also the FWHM of membranes decreased at 17o 2Ө peak on increasing the PTA concentration, leading to higher crystallinity in the membrane. Structure analysis by FTIR indicated increase in PTA signature intensity dips, as the PTA concentration in membrane increases from 0-25%. Also by FTIR studies, it was found that some PTA is lost during the processing step as shown by comparison of as cast and protonated spectra. Possible reasoning might be that some amount of PTA does not gets cesium stabilized which gets leached away during processing. TGA studies were performed which showed no signs of early thermal degradation (temperature > 300 °C); hence the assumption that all membranes are thermally robust for intended fuel cell applications. The membranes with different amounts of PTA were then catalyst coated and tested for 100-hour at open circuit voltage (OCV), 30% RH and 90 oC. By increasing the PTA in the host Nafion® matrix, the percent change in fuel crossover decreases, percent change in ECA increases, cathode fluoride emission rate decreases, and percent change in OCV decreases after the 100 hour test. Possible reasons for decreasing percentage of fuel crossover might be the increased internal humidity of the membrane due to increasing PTA incorporation. It is reported that during higher relative humidity operation, there is decrease in fuel crossover rate. Increasing ECA percentage loss might be due to the fact that HPA in the membrane can get adsorbed on the catalyst sites, rendering the sites inactive for redox reaction. Decrease in cathode fluorine emission rate (FER) might be due to the fact that there is more water available internally in the membrane as compared to Nafion®. It is reported that at higher relative humidity, FER decreases. ECA and crossover both contribute to the OCV losses. Higher component of OCV is crossover loss, which results in mixed potentials. Hence decreasing percentage of crossover might be the reason behind the decreasing OCV loss. Initial performance of fuel cell increases with increasing PTA concentration, but after the 100 hour test, higher PTA membrane exhibited highest performance loss. Increasing initial fuel cell performance can be due to the lowering of resistance due to PTA addition. Increasing ECA losses might be responsible for the increasing performance losses on adding more PTA to host membrane.

<p> Today' s commercial proton exchange membranes for fuel cell applications use a liquid electrolyte such as water to facilitate the conduction process. The vapour pressure of water limits the operating temperature of a fuel cell, resulting in a decrease in efficiency as the electrolyte evaporates. Anhydrous electrolytes such as acidified polybenzimidazole or poly(vinyl-4-imidazole) are able to transport ions without using water as an electrolyte. </p> <p> The mechanism of ion transport involves the structural diffusion of the ions through the solid-state lattice. Compounds modeling the basic modes of the ionic conductivity are used in the solid-state nuclear magnetic resonance (NMR) investigation. The hydrogen-bonding structures of model compounds are established using diffraction paired with 1H solid-state double quantum NMR. The structural studies of the compounds reveal a continuous network of hydrogen bonded molecules. The structural motif is based on strong N-H••O and 0-H••O hydrogen bonds between the ions of the material. The dynamics of the hydrogen bonds observed in the 1H NMR and the multinuclear studies using the CODEX (Centerband Only Detection of EXchange) pulse sequence define the mechanism of ionic conductivity in these model compounds. </p> <p> These solid-state NMR techniques are then applied to a novel electrolyte material consisting of a solid electrolyte inside the pores of a host polymer material. This new material is able to transport protons at high temperatures without the use of an aqueous electrolyte. The properties and mechanism of ion transport is investigated using solid­ state NMR and impedance spectroscopy. </p> / Thesis / Doctor of Philosophy (PhD)