Dissertations / Theses on the topic 'Green hydrogen production'

This thesis concerns two aspects of microorganism behaviour. Firstly, the phenomenon of bioconvection is explored, where suspensions of motile microorganisms that are denser than the fluid in which they swim spontaneously form concentrated aggregations of cells that drive fluid motion, forming intricate patterns. The cells considered herein orientate by gyrotaxis, a balance between a gravitational torque due to uneven starch deposits causing cells to be bottom heavy and a viscous torque due to fluid flow gradients, and phototaxis, biased movement towards or away from a light source. In Chapters 2 and 3, a stochastic continuum model for gyrotaxis is extended to include phototaxis using three physically diverse and novel methods. A linear stability analysis is performed for each model and the most unstable wavenumber for a range of parameter values is predicted. For two of the models, sufficiently strong illumination is found to stabilize all wavenumbers compared to the gyrotaxis only case. Phototaxis is also found to yield non-zero critical wavenumbers under such strong illumination. Two mechanisms that lead to oscillatory solutions are presented. Dramatically different results are found for the third model, where instabilities arise even in the absence of fluid flow. In Chapter 4, an experimental study of pattern formation by the photo-gyrotactic unicellular green alga species Chlamydomonas nivalis is presented. Fourier analysis is used to extract the wavelength of the initial dominant mode. Variations in red light illumination are found to have no significant effect on the initial pattern wavelength. However, fascinating trends for the effects of cell concentration and white light intensity on cells illuminated either from above or below are described. This work concludes with comparisons between theoretical predictions and experimental results, between which good agreement is found. Secondly, we investigate the intracellular pathways and processes that lead to hydrogen production upon implementation of a two-stage sulphur deprivation method in the green alga C. reinhardtii. In Chapter 5, a novel model of this system is constructed from a consideration of the main cellular processes. Model results for a range of initial conditions are found to be consistent with published experimental results. In Chapter 6, a parameter sensitivity of the model is performed and a study in which different sulphur input functions are used to optimize the yield of hydrogen gas over a set time is presented, with the aim of improving the commercial and economic viability of algal hydrogen production. One such continuous sulphur input function is found to significantly increase the yield of hydrogen gas compared to using the discontinuous two-stage cycling of Ghirardi et al. (2000).

Philosophiae Doctor - PhD
Today fossil fuels such as oil, coal and natural gas are providing for our ever growing energy needs. As the world’s fossil fuel reserves fast become depleted, it is vital that alternative and cleaner fuels are found. Renewable energy sources are the way of the future energy needs. A solution to the looming energy crisis can be found in the energy carrier hydrogen. Hydrogen can be produced by a number of production technologies. One hydrogen production method explored in this study is electrolysis of water.

Hydrogen production and storage play a critical role in energy transformation from fossil fuels to green energy. To realize the carbon neutralization target by increasing the competitiveness of hydrogen as an energy vector, production and storage of hydrogen must be made more efficient, safer, and cheaper, which is essential for future energy security and economic development. Water splitting via electrolysis holds great promise for hydrogen production, due to its simplicity, sustainability, and high purity for industrial hydrogen production. Recently, despite tremendous efforts have been devoted, platinum (Pt)-based catalysts are still considered to be the most effective electrocatalysts for hydrogen evolution reaction (HER). However, the high cost and low reserves of platinum-based catalysts greatly limit their commercial application. To make hydrogen derived from water splitting more cost-competitive, it is thus highly desirable to exploit low-cost, highly efficient electrocatalysts to replace the expensive Pt-based catalysts. Furthermore, after hydrogen production, the gaseous hydrogen needs to be stored safely and efficiently for utilization by end-users. The current mainstream methods of solid-state hydrogen storage including molecular physisorption and atomic chemisorption, both possess either too high or too low enthalpy of hydrogen adsorption, which are not suitable for practical application. The ideal hydrogen storage materials should be reversibly ab-/desorbing hydrogen under mild temperatures with high hydrogen capacities. To this end, it is extremely essential to design and construct new solid-state hydrogen storage materials at atomic levels. Recently, the atomic metal-site (AMS) nanomaterials are found to be promising catalysts and solid-state media for both the H2 production and storage, which is not only ascribed to the maximized atomic metals utilization but also the unique electronic structure of various metal-site coordination motifs at atomic scales. The aim of this project is to develop efficient and inexpensive AMS nanomaterials that are expected to create new knowledge of atomic interface catalysis and develop practical applications of solid-state hydrogen storage materials, reducing carbon dioxide emissions and alleviating the air pollution. In summary, this thesis mainly focusses on designing and fabricating cost-effective, efficient , and scalable AMS nanomaterials for both hydrogen production and storage, and the reaction mechanisms of atomic metal sites in hydrogen production and storage are also systematically studied.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text

The modernized world is over-consuming low-cost energy sources that strongly contributes to pollution and environmental stress. As a consequence, the interest for environmentally friendly alternatives has increased immensely. One such alternative is the use of solar energy and water as a raw material to produce biohydrogen through the process of photosynthetic water splitting. In this work, the relation between H2-production and photosynthesis in the green algae Chlamydomonas reinhardtii was studied with respect to three main aspects: the establishment of prolonged H2-production, the involvement of PSII in H2-production and the electron pathways associated with PSII during H2-production. For the first time, this work reveals that PSII plays a crucial role throughout the H2-producing phase in sulfur deprived C. reinhardtii. It further reveals that a wave-like fluorescence decay kinetic, before only seen in cyanobacteria, is observable during the H2-producing phase in sulfur deprived C. reinhardtii, reflecting the presence of cyclic electron flows also in green algae.

Recently, the increasing level of atmospheric CO₂ has been widely noticed due to its association with global warming, provoking a growth in environmental concerns toward the continued use of fossil fuels. To mitigate the concentration of atmospheric CO₂, various strategies have been implemented. Among options to turn waste CO₂ into useful fuels and chemicals, carbon capture and utilisation along with renewable hydrogen production as the source materials for methanol production is more preferable. In the 1960s, the highly active and economic Cu/ZnO/Al₂O₃ catalyst was developed for CO₂ hydrogenation reaction to methanol, since then, metal nanoparticles and nanocomposites have been extensively investigated and applied. Especially, bimetallic catalysts have emerged as an important class of catalysts due to their unique properties and superior catalytic performances compared to their monometallic counterparts. This thesis presents the evolution of the catalyst development for CO₂ hydrogenation to methanol: Firstly, we introduced the CuZn-based catalysts with Zn content increased in the bimetallic CuZn system via a heterojunction synthesis approach. Secondly, we increased the active CuZn sites via introducing ultra-thin layered double hydroxide as the catalyst precursor for methanol production from CO₂ and H₂. Thirdly, a new class of Rh-In bimetallic catalysts were studied, which shows high methanol yield and selectivity under thermodynamically unfavourable methanol synthesis conditions owing to the strong synergies of Rh-In bimetallic system. Fourthly, for the renewable methanol production from H₂ and CO₂, the hydrogen source must come from the green production routes. Therefore, an in-depth study of a nanocomposite system, CdS-carbon nanotubes-MoS₂, for photocatalytic hydrogen production from water has been demonstrated. Finally, the conclusion of this thesis is given and an outlook is presented for the future development in this research area.

The present Ph.D. thesis deals with the hydrogen production via a novel process involving a biogas autothermal reforming (ATR) unit with the adoption of a catalytic wall-flow filter located downstream from the ATR processor to effectively filter and in-situ gasify the carbon emissions eventually generated. This work was aimed to produce 50 Nm3/h of green hydrogen from the ATR of a model biogas (60:40 Vol ratio) by using catalytic structured supports. Moreover, a solution for the eventual carbon formation during the biogas ATR was addressed. A nanostructured delafossite catalyst to ensure the gasification of soot in absence of O2 was synthesized. In addition, a Life Cycle Assessment (LCA) and a techno-economic analysis for the hydrogen production from biogas were also carried out. Concerning the identification of the suitable support structure to improve the coupling of exothermic and endothermic reactions during the hydrogen production from biogas ATR, homogenous SiSiC lattices composed of Cubic, Octet and Kelvin cells and the Conventional Foam structure coated with Ni based catalysts doped with noble metals were investigated. The different catalytic geometries were tested using a model biogas composed of clean methane and carbon dioxide (60:40 Vol ratio) with a steam to carbon ratio (S/C) fixed at 2.0. The effect of the space velocity, inlet temperature and oxygen to carbon ratio (O/C) on methane conversion and hydrogen yield were studied for each catalytic support. The O/C ratios evaluated was equal to 1.0, 1.1 and 1.2. Space velocity (GHSV) values from 2000 to 20000 h-1 in standard conditions (equivalent to 5000- 85000 h-1 in operating conditions), and, inlet temperatures of 500, 600 and 700°C were employed. The combined effect of chemical reaction and some properties and parameters such as: pressure drop and specific surface area on the steady-state performances of an adiabatic reactor at high flow rates has been analyzed. ASPEN simulations were performed to calculate the thermodynamic equilibrium at the different boundary conditions to validate the data and to determine the hydrodynamic properties. This study has demonstrated that the rotated cubic cell support shows the best performance in transforming the biogas into hydrogen with high CH4 conversion (<95%) and an H2 yield higher of 2.1 using an O/C ratio of 1.0, 1.1 and 1.2, S/C ratio of 2 and GHSV of 20000 h-1. Besides, this support can ensure a high reliability of the ATR process due to its lower pressure drop (6-40 Pa/m) with the lower specific surface area comparing to the other structures tested. The conventional foam has presented also good performances for all the GHSV values in terms of CH4 conversion but it is less selective for hydrogen production. With respect to the catalyst for gasification of carbon in a reducing atmosphere (H2, CO, H2O, CO2), nano-materials based on transition metal were synthesized via a solution combustion synthesis (SCS) method. LiFeO2 catalyst was selected as the most promising candidate for the soot gasification catalyst on the soot trap application close coupled to the ATR reactor for syngas post-treatment process. Afterwards, some issues in mixed atmosphere, i.e., when simultaneous carbon gasification with CO2 and steam in the presence of H2 and CO take place, were studied. It was demonstrated that the carbon gasification is inhibited during an isothermal reaction at 650°C for 40 minutes when CO and H2 are used as co-reagents. But even in these extreme reduced conditions, the LiFeO2-catalyst gasified 32.9% of the initial carbon, compared to 8% for the non-catalytic case. when H2 is used as co-reagent in the steam carbon gasification, the reaction is inhibited, the carbon conversion decreases from 73.1% to 46.6%. Analogously, when CO is a co-reactant in the carbon gasification with CO2, the reaction is inhibited, the soot conversion declines from 70.2% to 31.6 %. However, it was observed that in mixed atmosphere gasification reactions, when CO2 and H2O simultaneously reacts with carbon, there is a passive combination of steam and carbon dioxide in the gasification reaction. This means that the two gases operate on separated active sites without influencing each other. LiFeO2 was also coated on the monoliths (15/20 μm mean pore size and 45% porosity) and the coated filters’ performance was evaluated during the soot particles loading. The pressure drop across the filters was very low (<8 mbar) during loading showing that the applied coated method on the filters was successfully. On the other hand, the catalytic filter coupled with the rotated cube cell was tested at the pilot plant to examine their interaction, the effect of the coating method and the penalty in pressure drop of all system. A pressure drop of 0 – 68 mbar obtained during the test proves that the coating method did not alter the operation of the plant. As for testing at the demonstration plant, firstly, a monolith (Rh/Pt) was tested close coupled with an uncoated filter using an O/C ratio from 0.9 to 1.3, S/C ratio equal to 2.0, an inlet temperature (Tin) of 450°C with a GHSV from 5000 to 14000 h-1. The overall result fully agrees with the prediction from the simulation. The thermodynamic equilibrium was reached during the testing time with a methane conversion of 98% and hydrogen yield of 2.0. Moreover, tests with the integration of the catalyzed conventional foam and the catalytic trap downstream of the reforming reactor were performed. The boundary conditions were a space velocity of 4000, S/C= 2 and O/C=1.1. A thermodynamic equilibrium and a methane conversion higher than 98% were achieved. The plant was able to reach the predicted conversions and concentrations at nominal capacities corresponding to 50 Nm3/h (100 Kg/day) of pure hydrogen, creating a negligible pressure drop during the operation time of the processor. Finally, this thesis also deals with a comparative LCA of three different hydrogen production process from biogas. The investigated processes are: the biogas ATR, the biogas steam reforming (SR) and the water hydrolysis (a biogas-fueled internal combustion engine (ICE) followed by an electrolyzer). They were compared using environmental (GWP) and energetic (GER) impacts in order to highlight their weaknesses and strengths. H2 from biogas ATR has been demonstrated to be the most promising process in terms of the emissions reduction and energetic efficiency considering its life cycle from the extraction and processing of raw materials to the production of high purity hydrogen. The ICE + Electrolyzer process require a large amount of energy and biogas to sustain the electrochemical reactions. This feature makes such system the least energetically efficient with the most negative environmental impact. With a process efficiency of 65%, 63% and 25% for ATR, steam reforming and electrolysis process, respectively. Lastly, the economic analysis was performed to evaluate the H2 final cost. On the one hand, it was found that the process is economically favorable for H2 production higher than 100 Nm3/h. On the other hand, in 10 years of amortization using this technology, the final cost for H2 production of 100 Nm3/h from biogas is 3€/Kg H2, lower than the European target (5€/kg H2). The longer the plant life is, the more affordable the initial investment is.

L'objectif principal de cette thèse est de concevoir, mettre en œuvre et comparer différentes stratégies de gestion de l'énergie et approches d'optimisation pour un système hybride impliquant l'intégration de l'énergie marémotrice flottante avec la production de l'hydrogène vert. Pour atteindre les objectifs, les composants individuels du système sont d'abord modélisés. Les capacités annuelles de performance du système de la centrale d'énergie marémotrice ont ensuite été obtenues à l'aide des profils quotidiens fréquents au poste d'amarrage de Fall of Warness dans les îles Orcades. Les modes de fonctionnement transitoires des électrolyseurs à membrane échangeuse de protons, lorsqu'elles sont soumises à l'énergie de la centrale hydrolienne, ont été analysés sur la base d'une (RBA) stratégie de gestion de l'énergie basée sur des règles. Plus tard, une évaluation préliminaire du coût de production d'hydrogène est effectuée sur la base de différentes conditions de demande quotidienne d'hydrogène et de profils de marée quotidiens. En outre, une approche d'optimisation dans le but de maximiser le profit d'exploitation du système tout en assurant un fonctionnement optimal et suffisant des deux électrolyseurs sous des contraintes réelles du système, est formulée en donnant la priorité à la production d'hydrogène par l'énergie marémotrice. Le problème d'optimisation est résolu à l'aide d'un algorithme génétique basé sur un problème non linéaire à entiers mixtes. Une analyse coûts-avantages complète basée à la fois sur les coûts fixes-variables et sur les facteurs de coûts actualisés est réalisée pour analyser le fonctionnement technico-environnemento-économique optimal d'un système hybride d'énergie marémotrice-éolienne-hydrogène connecté au réseau. Les résultats ont été comparés aux résultats de l'approche basée sur des règles. Les bénéfices annuels dans l'approche d'optimisation ont été estimés supérieurs de 41,5 % par rapport à ceux de la RBA. De plus, d'un point de vue environnemental, les meilleurs résultats d'optimisation étaient supérieurs d’environ 47 % par rapport aux résultats de la RBA en termes de réduction des émissions de carbone. Un électrolyseur dynamique capable de fonctionner à deux fois sa puissance nominale pendant une durée limitée s'avère particulièrement avantageux lorsqu'il est couplé à l'énergie marémotrice qui est de nature cyclique avec des périodes prévisibles de production d'énergie élevée et faible. Enfin, il est conclu que l'approche d'optimisation des coûts fixes-variables est relativement simple dans l'estimation des coûts. Au contraire, bien que des résultats légèrement meilleurs soient obtenus dans le cas de l'approche par coût actualisé, il est nécessaire d'avoir une meilleure connaissance préalable du fonctionnement du système pour estimer finement les facteurs de coût actualisé. Le modèle proposé peut être utilisé comme un outil générique pour l'analyse de la production d'hydrogène dans différents contextes et il est particulièrement applicable dans les sites à fort potentiel d'énergie verte avec des installations de réseau limitées
The overarching aim of this thesis is to design, implement and compare different energy management strategies and optimisation approaches for a hybrid system involving floating tidal stream energy integration with green hydrogen production. Towards reaching the objectives, the individual system components are modelled initially. The annual system performance capabilities of the tidal stream energy plant are then obtained using frequently occurring daily profiles at the Fall of Warness berth in the Orkney Islands, Scotland. The transitionary operating modes of two polymer electrolyte membrane electrolyser units, when subjected to the energy from the tidal stream plant are analysed based on a rule-based approach energy management strategy. Later, a preliminary evaluation of the hydrogen production cost is assessed based on different daily hydrogen demand and daily tidal profile conditions. Further, an optimisation approach with the objective to maximise the system operating profit ensuring optimal and sufficient operations of both the electrolyser units under real system constraints, is formulated with priority for tidal energy powered hydrogen production. The optimisation problem is solved using a genetic algorithm based on the mixed integer non-linear problem. A comprehensive cost-benefit analysis based on fixed-variable costs and levelised costs factors is performed to analyse the optimal techno-enviro-economic operation of a hybrid grid connected tidal-wind-hydrogen energy system. The outcomes are compared against the rule-based approach results. The annualised profits in the optimisation approach are estimated to be 41.5% higher compared to the rule-based approach. Further, from an environmental view, the best optimisation results are approximately 47% higher than the rule-based approach results in terms of carbon emission reductions. A dynamic electrolyser capable of working at twice of its nominal power rating for limited duration, resulted particularly advantageous when coupled with tidal energy which is cyclic in nature with predictable periods of high and low power generation. Finally, it was determined that the fixed cost (FC) optimisation approach is relatively simple in terms of cost estimation. On the contrary, while the levelised cost (LC) approach yields slightly better results, it necessitates a greater prior knowledge of system operations to reasonably estimate the cost factors. The proposed method can be used as a generic tool for electrolytic hydrogen production analysis under different contexts, with preferable application in high green energy potential sites with constrained grid facilities

The hydrogen production in the green microalga Chlamydomonas reinhardtii was evaluated by means of a detailed physiological and biotechnological study. First, a wide screening of the hydrogen productivity was done on 22 strains of C. reinhardtii, most of which mutated at the level of the D1 protein. The screening revealed for the first time that mutations upon the D1 protein may result on an increased hydrogen production. Indeed, productions ranged between 0 and more than 500 mL hydrogen per liter of culture (Torzillo, Scoma et al., 2007a), the highest producer (L159I-N230Y) being up to 5 times more performant than the strain cc124 widely adopted in literature (Torzillo, Scoma, et al., 2007b). Improved productivities by D1 protein mutants were generally a result of high photosynthetic capabilities counteracted by high respiration rates. Optimization of culture conditions were addressed according to the results of the physiological study of selected strains. In a first step, the photobioreactor (PBR) was provided with a multiple-impeller stirring system designed, developed and tested by us, using the strain cc124. It was found that the impeller system was effectively able to induce regular and turbulent mixing, which led to improved photosynthetic yields by means of light/dark cycles. Moreover, improved mixing regime sustained higher respiration rates, compared to what obtained with the commonly used stir bar mixing system. As far as the results of the initial screening phase are considered, both these factors are relevant to the hydrogen production. Indeed, very high energy conversion efficiencies (light to hydrogen) were obtained with the impeller device, prooving that our PBR was a good tool to both improve and study photosynthetic processes (Giannelli, Scoma et al., 2009). In the second part of the optimization, an accurate analysis of all the positive features of the high performance strain L159I-N230Y pointed out, respect to the WT, it has: (1) a larger chlorophyll optical cross-section; (2) a higher electron transfer rate by PSII; (3) a higher respiration rate; (4) a higher efficiency of utilization of the hydrogenase; (5) a higher starch synthesis capability; (6) a higher per cell D1 protein amount; (7) a higher zeaxanthin synthesis capability (Torzillo, Scoma et al., 2009). These information were gathered with those obtained with the impeller mixing device to find out the best culture conditions to optimize productivity with strain L159I-N230Y. The main aim was to sustain as long as possible the direct PSII contribution, which leads to hydrogen production without net CO2 release. Finally, an outstanding maximum rate of 11.1 ± 1.0 mL/L/h was reached and maintained for 21.8 ± 7.7 hours, when the effective photochemical efficiency of PSII (ΔF/F'm) underwent a last drop to zero. If expressed in terms of chl (24.0 ± 2.2 µmoles/mg chl/h), these rates of production are 4 times higher than what reported in literature to date (Scoma et al., 2010a submitted). DCMU addition experiments confirmed the key role played by PSII in sustaining such rates. On the other hand, experiments carried out in similar conditions with the control strain cc124 showed an improved final productivity, but no constant PSII direct contribution. These results showed that, aside from fermentation processes, if proper conditions are supplied to selected strains, hydrogen production can be substantially enhanced by means of biophotolysis. A last study on the physiology of the process was carried out with the mutant IL. Although able to express and very efficiently utilize the hydrogenase enzyme, this strain was unable to produce hydrogen when sulfur deprived. However, in a specific set of experiments this goal was finally reached, pointing out that other than (1) a state 1-2 transition of the photosynthetic apparatus, (2) starch storage and (3) anaerobiosis establishment, a timely transition to the hydrogen production is also needed in sulfur deprivation to induce the process before energy reserves are driven towards other processes necessary for the survival of the cell. This information turned out to be crucial when moving outdoor for the hydrogen production in a tubular horizontal 50-liter PBR under sunlight radiation. First attempts with laboratory grown cultures showed that no hydrogen production under sulfur starvation can be induced if a previous adaptation of the culture is not pursued outdoor. Indeed, in these conditions the hydrogen production under direct sunlight radiation with C. reinhardtii was finally achieved for the first time in literature (Scoma et al., 2010b submitted). Experiments were also made to optimize productivity in outdoor conditions, with respect to the light dilution within the culture layers. Finally, a brief study of the anaerobic metabolism of C. reinhardtii during hydrogen oxidation has been carried out. This study represents a good integration to the understanding of the complex interplay of pathways that operate concomitantly in this microalga.

The hydrogen production in the green microalga Chlamydomonas reinhardtii was evaluated by means of a detailed physiological and biotechnological study. First, a wide screening of the hydrogen productivity was done on 22 strains of C. reinhardtii, most of which mutated at the level of the D1 protein. The screening revealed for the first time that mutations upon the D1 protein may result on an increased hydrogen production. Indeed, productions ranged between 0 and more than 500 mL hydrogen per liter of culture (Torzillo, Scoma et al., 2007a), the highest producer (L159I-N230Y) being up to 5 times more performant than the strain cc124 widely adopted in literature (Torzillo, Scoma, et al., 2007b). Improved productivities by D1 protein mutants were generally a result of high photosynthetic capabilities counteracted by high respiration rates. Optimization of culture conditions were addressed according to the results of the physiological study of selected strains. In a first step, the photobioreactor (PBR) was provided with a multiple-impeller stirring system designed, developed and tested by us, using the strain cc124. It was found that the impeller system was effectively able to induce regular and turbulent mixing, which led to improved photosynthetic yields by means of light/dark cycles. Moreover, improved mixing regime sustained higher respiration rates, compared to what obtained with the commonly used stir bar mixing system. As far as the results of the initial screening phase are considered, both these factors are relevant to the hydrogen production. Indeed, very high energy conversion efficiencies (light to hydrogen) were obtained with the impeller device, prooving that our PBR was a good tool to both improve and study photosynthetic processes (Giannelli, Scoma et al., 2009). In the second part of the optimization, an accurate analysis of all the positive features of the high performance strain L159I-N230Y pointed out, respect to the WT, it has: (1) a larger chlorophyll optical cross-section; (2) a higher electron transfer rate by PSII; (3) a higher respiration rate; (4) a higher efficiency of utilization of the hydrogenase; (5) a higher starch synthesis capability; (6) a higher per cell D1 protein amount; (7) a higher zeaxanthin synthesis capability (Torzillo, Scoma et al., 2009). These information were gathered with those obtained with the impeller mixing device to find out the best culture conditions to optimize productivity with strain L159I-N230Y. The main aim was to sustain as long as possible the direct PSII contribution, which leads to hydrogen production without net CO2 release. Finally, an outstanding maximum rate of 11.1 ± 1.0 mL/L/h was reached and maintained for 21.8 ± 7.7 hours, when the effective photochemical efficiency of PSII (ΔF/F'm) underwent a last drop to zero. If expressed in terms of chl (24.0 ± 2.2 µmoles/mg chl/h), these rates of production are 4 times higher than what reported in literature to date (Scoma et al., 2010a submitted). DCMU addition experiments confirmed the key role played by PSII in sustaining such rates. On the other hand, experiments carried out in similar conditions with the control strain cc124 showed an improved final productivity, but no constant PSII direct contribution. These results showed that, aside from fermentation processes, if proper conditions are supplied to selected strains, hydrogen production can be substantially enhanced by means of biophotolysis. A last study on the physiology of the process was carried out with the mutant IL. Although able to express and very efficiently utilize the hydrogenase enzyme, this strain was unable to produce hydrogen when sulfur deprived. However, in a specific set of experiments this goal was finally reached, pointing out that other than (1) a state 1-2 transition of the photosynthetic apparatus, (2) starch storage and (3) anaerobiosis establishment, a timely transition to the hydrogen production is also needed in sulfur deprivation to induce the process before energy reserves are driven towards other processes necessary for the survival of the cell. This information turned out to be crucial when moving outdoor for the hydrogen production in a tubular horizontal 50-liter PBR under sunlight radiation. First attempts with laboratory grown cultures showed that no hydrogen production under sulfur starvation can be induced if a previous adaptation of the culture is not pursued outdoor. Indeed, in these conditions the hydrogen production under direct sunlight radiation with C. reinhardtii was finally achieved for the first time in literature (Scoma et al., 2010b submitted). Experiments were also made to optimize productivity in outdoor conditions, with respect to the light dilution within the culture layers. Finally, a brief study of the anaerobic metabolism of C. reinhardtii during hydrogen oxidation has been carried out. This study represents a good integration to the understanding of the complex interplay of pathways that operate concomitantly in this microalga.

Hydrogen is considered one of the means by which to store energy coming from renewable and intermittent power sources. With the growing capacity of renewable energy sources, a storage system is required to not waste energy. PEM electrolysis provides a sustainable solution for the production of hydrogen and is well suited to couple with energy sources such as solar and wind. This work reports the development of simulation software to estimate the performance of a proton exchange membrane electrolyzer working at atmospheric or low pressure conditions connected to a solar energy source. The electrolyzer is defined from a validated reference semi-empirical model, which allows for simulating the electrochemical, thermal and H2 output flow behaviours with enough precision for engineering applications. An algorithm for a fitting procedure to characterize commercial products, and functions for power modulation have been implemented. A series of simulations have been carried on, starting from real photovoltaic data of input power, and the output values have been discussed, with particular attention to output flow rate, thermal behaviour and the cooling demand in order to preserve the operation of the electrolyzer.

The energy transition taking place in various parts of the world will have many effects on the current energy systems as an increasing amount of intermittent power supply gets installed every year. In Sweden, just as many other countries, this will cause both challenges and opportunities for today´s energy producers. Challenges that may arise along with an increasingly fluctuating electricity production include both power deficits at certain times and regions but also hours of over-production which can cause electricity prices to drop significantly. Such challenges will have to be met by both dispatchable power generation and dynamic consumption. Conversely, actors prepared to adapt to the new climate by implementing new technologies or innovative business models could benefit from the transition towards a fully renewable energy system.  This thesis evaluates the techno-economic potential of green hydrogen production at a combined heat and power plant with the objective to provide decision support to a district heat and electricity producer in Sweden. It was in the company’s interest to investigate how hydrogen production could help reduce the production cost of district heat as well as contribute to the reduction of greenhouse gases.  In the project, two separate business models: Power-to-gas and Power-to-power were evaluated on the basis of technical and economic performance and environmental impact. To do this, a mathematical model of the CHP plant and the hydrogen systems was developed in Python which optimizes the operation based on costs. The business models were then simulated for two different years with each year representing a distinctly different electricity market situation.  The main conclusions of the study show that Power-to-gas could already be profitable at a hydrogen retail price of 40 SEK per kg, which is the projected retail price for the transportation sector. The demand today is however limited but is expected to grow fast in the near future, especially within heavy transportation. Another limiting factor for hydrogen production showed to be the availability of storage space, as hydrogen gas even at pressures up to 200 bar require large volumes.  Power-to-power for frequency regulation was found to not be economically justifiable as the revenue for providing grid services could not outweigh the high investment costs for any of the simulated years. This resulted in a high levelized cost of energy at over 3000 SEK per MWh which was mostly due to the low capacity factor of the power-to-power system.  Finally, green hydrogen has the potential of replacing fossil fuels in sectors that is difficult to reach with electricity, for example long-haul road transport or the shipping industry. Therefore, green hydrogen production in large scale could help decarbonize many of society’s fossil-heavy segments. By also serving as a grid-balancer, hydrogen production in a power-to-gas process has the potential of becoming an important part of a renewable energy system.
Energiomställningen som äger rum i olika delar av världen kommer att ha många effekter på de nuvarande energisystemen eftersom en ökande mängd väderberoende kraftproduktion installeras varje år. I Sverige, precis som många andra länder, kommer detta att medföra både utmaningar och möjligheter för dagens energiproducenter. Utmaningar som kan uppstå tillsammans med en alltmer fluktuerande elproduktion inkluderar både kraftunderskott vid vissa tider och regioner men också timmar av överproduktion som kan få elpriserna att sjunka avsevärt. Sådana utmaningar måste mötas av både planerbar kraftproduktion och dynamisk konsumtion. Omvänt kan aktörer som är beredda att anpassa sig till det nya klimatet genom att implementera ny teknik eller innovativa affärsmodeller dra nytta av övergången till ett helt förnybart energisystem.  Denna rapport utvärderar den tekno-ekonomiska potentialen för produktion av grön vätgas vid ett kraftvärmeverk med målet att ge beslutsstöd till en fjärrvärme- och elproducent i Sverige. Det var i företagets intresse att undersöka hur vätgasproduktion kan bidra till att sänka produktionskostnaden för fjärrvärme samt bidra till att minska växthusgaser.  I projektet utvärderades två separata affärsmodeller: Power-to-gas och Power-to-power baserat på teknisk och ekonomisk prestanda samt miljöpåverkan. För att kunna göra detta utvecklades en matematisk modell i Python av kraftvärmeverket och vätgassystemen som optimerar driften baserat på kostnader. Affärsmodellerna simulerades sedan för två olika års elpriser för att undersöka modellens prestanda i olika typer av elmarknader.  De viktigaste slutsatserna i studien visar att Power-to-gas redan kan vara lönsamt till ett vätgaspris på 40 SEK per kg, vilket är det förväntade marknadspriset på grön vätgas for transportsektorn. Efterfrågan är idag begränsad men förväntas växa snabbt inom en snar framtid, särskilt inom tung transport. En annan begränsande faktor för vätgasproduktion visade sig vara tillgången på lagringsutrymme, eftersom vätgas även vid tryck upp till 200 bar kräver stora volymer.  Power-to-power för frekvensreglering visade sig inte vara ekonomiskt försvarbart, eftersom intäkterna för att tillhandahålla nättjänster inte kunde uppväga de höga investeringskostnaderna under några av de simulerade åren. Detta resulterade i en hög LCOE på över 3000 SEK per MWh, vilket främst berodde på Power-to-power-systemets låga utnyttjandegrad.  Slutligen kan det sägas att grön vätgas har stor potential att ersätta fossila bränslen i sektorer som är svåra att elektrifiera, exempelvis tunga vägtransporter eller sjöfart. Därför kan storskalig grön vätgasproduktion hjälpa till att dekarbonisera många av samhällets fossiltunga segment. Genom att dessutom fungera som balansering har väteproduktion i en Power-to-gas-process potential att bli en viktig del av ett system med stor andel förnybar energi.

With increasing global populations and demand for energy, greater strain is placed on the limited supply of fossil derived fuels, which in turn drives the need for development of alternative energy sources. The discovery of biophotolysis in Chlamydomonas reinhardtii and the development of a spectral-selective photosystem I activating/photosystem II deactivating light (PSI-light) method provides a promising platform for commercial hydrogen production systems. The PSI-light method allows electrons to pass through the photosynthetic electron transport chain while reducing radiation available for photosynthetic oxygen evolution that inactivates hydrogenase. Exploring the physiology of photohydrogen production using the PSI-light method can provide insight on how to optimize conditions for maximum hydrogen production. Through the use of photosynthetic mutant strains of C. reinhardtii, it was possible to suppress photosynthetic oxygen evolution further than using photosystem I light alone to extend photohydrogen production longevity and total yield. A preliminary investigation of an iterating light treatment revealed that longevity and yield could be increased further by providing a period of darkness to allow cells to consume evolved oxygen and resynthesize hydrogenase. Work with these mutants provided understanding that a balance of radiation was required to provide electrons to hydrogenase while limiting oxygen evolution, and that when no light was provided, fermentation of stored starch was the major contributor of electrons to hydrogen production. To determine the role of starch during hydrogen production, wild type cells were exposed to different media and light treatments and monitored for starch consumption and hydrogen production. The results indicated that starch was required for hydrogen production in the dark, but for photohydrogen production, starch likely played a minor role in contributing electrons to hydrogenase. The experiments also showed the importance of acetate in the medium during the hydrogen production phase to allow any significant photohydrogen production. The role of acetate was further investigated as a growth medium constituent that stimulates metabolic activity while reducing photosynthetic oxygen evolution when added to cells grown auto- or mixotrophically. By exposing cells to CO₂ during growth, photohydrogen production was significantly increased over cells grown only in the presence of acetate.

With a surge in future demand for hydrogen as a renewable fuel, the specific aim of this study was to develop a novel strategy in photosynthetic hydrogen production from green algae, which is one of the cleanest processes among existing hydrogen-production methodologies currently being explored. The novel strategy designed was a spectral-selective PSI-activation/PSII-deactivation protocol that would work to maintain a steady flow of electrons in the electron transport system in the light-dependent part of photosynthesis for delivery of electrons to hydrogenase for photo-hydrogen production. The strategy would work to activate PSI to assist in driving the electron flow, while partially deactivating PSII to a degree that it would still supply electrons, but would limit its photosynthetic oxygen production below the respiratory oxygen consumption so that an anoxic condition would be maintained as required by hydrogenase. This study successfully showed that the implementation of the spectral-selective PSIactivation/ PSII-deactivation strategy resulted in actual and relatively sustained photohydrogen production in Chlamydomonas reinhardtii cells, which had been dark-adapted for three hours immediately prior to exposure to a PSI-spectral selective radiation, which had a spectral peak at 692 nm, covering a narrow waveband of 681-701 nm, and was applied at 15 W m⁻². The optimal condition for the PSI-spectral-selective radiation (692 nm) corresponded with low cell density of 20 mg chlorophyll L⁻¹ ("chl" henceforth) with cells grown at 25⁰C. At this condition, the PSI-spectral-selective radiation induced the maximal initial hydrogen production rate of 0.055 mL H² mg⁻¹ chl h⁻¹ which statistically the same as that achieved under white light of 0.044 mL H² mg⁻¹ chl h⁻¹, a maximal total hydrogen production of 0.108 mL H² mg⁻¹ chl which significantly exceeded that under white light of 0.066 mL H² mg⁻¹ chl, and a maximal gross radiant energy conversion efficiency for hydrogen production of 0.515 μL H² mg⁻¹ chl L⁻¹ that statistically matched that under white light of 0.395 μL H² mg⁻¹ chl L⁻¹. The study also successfully demonstrated the reversibility feature of the novel strategy, allowing for the cells to alternately engage in photo-hydrogen production and to recover by simply switching on or off the PSI-spectral-selective radiation.

L’hydrogène vert est le vecteur d’énergie du futur le plus prometteur car il est d’une part capté par des sources renouvelables et inépuisables qui sont les énergies éolienne et/ou solaire et d’autre part permet de meilleurs transport et stockage de l’énergie sur le long terme en bouteilles haute pression par un électrolyseur pour produire ensuite de l’électricité par des piles à combustible sans émission d’aucun polluant. La nature intermittente des SER dégrade la performance et le fonctionnement dynamique des électrolyseurs PEM et leur couplage doit être étudié afin d’assurer la disponibilité opérationnelle et la pérennité du fonctionnement des équipements par une détection précoce des défauts et l’estimation de leurs durées de vie mais aussi le suivi en ligne des performances technico économiques.L’objectif de la thèse réalisé dans le cadre du projet Européen Interreg-2 Mers E2C est de développer un modèle dynamique multi-physique d’un électrolyseur PEM, basé sur une approche Bond-Graph pour une utilisation générique pour d’autres types d’électrolyseur non seulement pour l’analyse mais aussi pour la conception de systèmes de supervision en ligne pour la détection et localisation de défauts. La modélisation des divers composants de l’électrolyseur a été réalisée sous forme de capsules Bond-Graph. Ces capsules peuvent être connectées en tenant compte de la structure du diagramme d’instrumentation pour obtenir un modèle dynamique global. Ce modèle est capable de représenter différentes configurations, du pilote de laboratoire jusqu’à l’échelle industrielle, et également de suivre l’efficacité en temps réel. Le modèle a été converti en MATLAB® Simulink pour implémentation, puis validé expérimentalement sur une cellule alimentée par une Plateforme Multi-Source Hybride comprenant des sources d’énergie solaire et éolienne. Le modèle a été adapté pour représenter et étudier la performance d’un électrolyseur à Membrane Echangeuse d’Anions, dont la configuration et l’architecture sont similaires, en collaboration avec l’Université d’Exeter. Le modèle permet également de développer des algorithmes de commande, diagnostic et pronostic ; ainsi, un diagnostic robuste des défauts est présenté dans ce travail. Une Interface Utilisateur Graphique pour la supervision en ligne incorpore le modèle et les algorithmes de diagnostic
Renewable Energy Sources (RES) have emerged as a sustainable alternative to carbon-based energy sources as the world is struggling in limiting the greenhouse effect in the coming years. The use of RES, such as solar and wind, alone is non-reliable due to their intermittent nature. The surplus electricity generated during off-peak hours must be stored to tackle the problem of the unavailability of energy. Green Hydrogen (GH$_2$) generation using electrolyser running on RES has seen an increase in recent years for the storage of this surplus energy due to its advantages over conventional methods (such as batteries and ultra-capacitors) for long term storage and transport. Proton Exchange Membrane (PEM) based electrolysers are better suited for the coupling with RES as compared to the alkaline electrolysers due to their faster start-up times and fast dynamic load changing capability. The intermittent nature of RES affects the performance and operation dynamics of the PEM electrolyser and must be analysed and studied in order to make these systems more reliable and safer to use. Mathematical modelling is one of the possible solutions for studying their behavior and developing supervision algorithms.Under the framework of the E2C project of the European Interreg 2-Seas program, a generic dynamic multi-physics model of a PEM electrolyser has been proposed in this work based on Bond Graph (BG) approach. Various components of the PEM electrolyser have been modelled in the form of BG capsules. These capsules can be connected based on the piping and instrumentation diagram of the PEM electrolyser system to have a global model of the system. The developed model is capable of representing different configurations of PEM electrolysers ranging from laboratory scale to industrial scale. The model is also capable of facilitating efficiency tracking in real-time. The developed model in the BG form has been converted into MATLAB® Simulink block diagram from the implementation point of view.The model was then validated using a single cell PEM electrolyser powered by a Hybrid Multi-source Platform (HMP) running on solar and wind energy at the University of Lille. The proposed model was also extended for the modelling and performance study of Anion Exchange Membrane (AEM) electrolysis cell, in collaboration with the University of Exeter of England, which shares a similar configuration and architecture.The developed model for the PEM electrolysis system is also suitable for the development of control, diagnosis, and prognosis algorithms. Therefore, a model-based robust fault diagnosis for PEM water electrolyser has been proposed in this work. The proposed diagnosis algorithms and model have been then utilized for developing the graphical user interface for online supervision

The exigent need to address climate change and its adverse effects is felt all around the world. As pioneers in tackling carbon emissions, the European Union continue to be head and shoulders above other continents by implementing policies and keeping a tab on its carbon dependence and emissions. However, being one of the largest importers of Natural Gas in the world, the EU remains dependent on a fossil fuel to meet its demands.  The aim of the research is to investigate the barriers and constraints in the EU policies and framework that affects the natural gas decarbonization and to investigate the levelized cost of hydrogen production (LCOH) that would be used to decarbonize the natural gas sector. Thus a comprehensive study, based on existing academic and scientific literature, EU policies, framework and regulations pertinent to Natural gas and a techno economic analysis of possible substitution of natural gas with Hydrogen, is performed. The motivation behind choosing hydrogen is based on various research studies that indicate the importance and ability to replace to natural gas. In addition, Portugal provides a great environment for cheap green hydrogen production and thus chosen as the main region of evaluation.  The study evaluates the current framework based on a SWOT ((Strength, Weakness, and Opportunities & Weakness) analysis, which includes a PESTEL (Political, Economic, Social, Technological, Environmental & Legal) macroeconomic factor assessment and an expert elicitation. The levelized cost of hydrogen is calculated for blue (SMR - Steam Methane Reforming with natural gas as the feedstock) and green hydrogen (Electrolyzer with electricity from grid, solar and wind sources). The costs were specific to Portuguese conditions and for the years 2020, 2030 and 2050 based on availability of data and the alignment with the National Energy and Climate Plan (NECP) and the climate action framework 2050. The sizes of Electrolyzers are based on the current Market capacities while SMR is capped at 300MW. The thesis only considers production of hydrogen. Transmission, distribution and storage of hydrogen are beyond the scope of the analysis.  Results show that the barriers are mainly related to costs competitiveness, amendments in rules/regulations, provisions of incentives, and constraints in the creation of market demand for low carbon gases. Ensuring energy security and supply while being economically feasible demands immediate amendments to the regulations and policies such as incentivizing supply, creating a demand for low carbon gases and taxation on carbon.  Considering the LCOH, the cheapest production costs continue to be dominated by blue hydrogen (1.33 € per kg of H2) in comparison to green hydrogen (4.27 and 3.68 € per kg of H2) from grid electricity and solar power respectively. The sensitivity analysis shows the importance of investments costs and the efficiency in case of electrolyzers and the carbon tax in the case of SMR. With improvements in electrolyzer technologies and increased carbon tax, the uptake of green hydrogen would be easier, ensuring a fair yet competitive gas market.
Det starka behovet av att ta itu med klimatförändringarna och deras negativa effekter är omfattande världen över. Den europeiska unionen utgör en pionjär när det gäller att såväl hantera sina koldioxidberoende och utsläpp som att implementera reglerande miljöpolitik, och framstår därmed som överlägsen andra stater och organisationer i detta hänseende. Unionen är emellertid fortfarande mycket beroende av fossilt bränsle för att uppfylla sina energibehov, och kvarstår därför som en av världens största importörer av naturgas.  Syftet med denna forskningsavhandling är att undersöka befintliga hinder och restriktioner i EU: s politiska ramverk som medför konsekvenser avkolningen av naturgas, samt att undersöka de utjämnande kostnaderna för väteproduktion (LCOH) som kan användas för att avkolna naturgassektorn. Därmed utförs en omfattande studie baserad på befintlig akademisk och vetenskaplig litteratur, EU: s politiska ramverk och stadgar som är relevanta för naturgasindustrin. Dessutom genomförs en teknisk-ekonomisk analys av eventuella ersättningar av naturgas med väte. Valet av väte som forskningsobjekt motiveras olika forskningsstudier som indikerar vikten och förmågan att ersätta till naturgas. Till sist berör studien Portugal. som tillhandahåller en lämplig miljö för billig och grön vätgasproduktion. Av denna anledning är Portugal utvalt som den viktigaste utvärderingsregionen.  Studien utvärderar det nuvarande ramverket baserat på en SWOT-analys ((Strength, Weakness, and Opportunities & Weakness), som inkluderar en PESTEL (Political, Economical, Social, Technological, Environmental och Legal) makroekonomisk faktoranalys och elicitering. Den utjömnade vätekostnaden beräknades i blått (SMR - Ångmetanreformering med naturgas som råvara) och grönt väte (elektrolyser med el från elnät, sol och vindkällor). Kostnaderna var specifika för de portugisiska förhållandena under åren 2020, 2030 och 2050 baserat på tillgänglighet av data samt anpassningen till den nationella energi- och klimatplanen (NECP) och klimatåtgärdsramen 2050. Storleken på elektrolyserar baseras på den nuvarande marknadskapaciteten medan SMR är begränsad till 300 MW. Avhandlingen tar endast hänsyn till produktionen av vätgas. Transmission, distribution och lagring av väte ligger utanför analysens räckvidd.  Resultaten visar att hindren är främst relaterade till kostnadskonkurrens, förändringar i stadgar och bestämmelser, incitament och begränsningar i formerandet av efterfrågan på koldioxidsnåla gaser på marknaden. Att säkerställa energiförsörjning och tillgång på ett ekonomiskt hållbart sätt kräver omedelbara ändringar av reglerna och politiken, såsom att stimulera utbudet, att skapa en efterfrågan på koldioxidsnåla gaser och genom att beskatta kol.  När det gäller LCOH dominerar blåväte beträffande produktionskostnaderna (1,33 € per kg H2) jämfört med grönt väte (4,27 respektive 3,68 € per kg H2) från elnät respektive solenergi. Osäkerhetsanalysen visar vikten av investeringskostnader och effektiviteten vid elektrolysörer och koldioxidskatten för SMR. Med förbättringar av elektrolys-tekniken och ökad koldioxidskatt skulle upptagningen av grön vätgas vara enklare och säkerställa en rättvis men konkurrenskraftig gasmarknad.

碩士
國立臺灣科技大學
化學工程系
103
It is well-known that hydrogen peroxide is a highly versatile environmentally friendly industrial oxidant. Recently, palladium and bimetallic palladium gold catalysts have come to prominence, due to their high selectivity and activity. However, the high cost of gold both limits their wide application in industry and at the same time fuels research into alternative catalytic metals able to replace gold in bimetallic catalysts. This study focuses on PdxNiy bimetallic nanocatalysts for green production of hydrogen peroxide. In this work a new supported catalyst for the direct synthesis of hydrogen peroxide was developed. Nickel has been adopted as the catalytic candidate due to its low cost compared to gold. Two main approaches were taken to synthesize PdxNiy nanocatalysts. NaBH4 and H2 were applied as a reductive agent to reduce Pd2+ and Ni2+ in precursors to form bimetallic PdxNiy on pretreated-carbon, respectively. However, the analysis results show that NaBH4 was not able to reduce Ni2+, and the H2 reduction method cannot achieve desired interaction between nanocatalysts and support. Thus, mesoporous carbon support and the organic agent reduction method were further developed for the synthesis of bimetallic nanocatalysts which were characterized by the crystallographic face-centered-cubic structure. Next, it is demonstrated that the alloy crystal structure of PdxNiy alloy can be arranged into the face-centered tetragonal (fct) structure after hydrogen treatment. Attributed to the ordered structure, the fct- PdxNiy catalyst found in this study enhances not only structural stability but also productivity with respect to the direct synthesis of hydrogen peroxide.

碩士
國立臺灣科技大學
化學工程系
99
The purpose of this study is to develop a new green process for production of H2O2 through the direct synthesis route, of which the hydrogen and oxygen contacts each other during the reaction. An electrochemical approach with the rotating ring disk electrode (RRDE) had been systematically explored and developed accordingly to measure the produced H2O2. Two different methods – co-reduction and successive reduction prepared in the microwave were adopted to prepare bimetallic Pd-Au/C nanocatalysts. The relationship between the structure of prepared nanocatalysts and their catalytic activity in the direct synthesis process were investigated. As synthesized bimetallic Pd-Au/C were characterized by ICP-AES, XRD, SEM, TEM, and XAS for better understanding in the catalytic activity of direct synthesis of H2O2. The approach in the electrochemical to measure H2O2 produced from direct synthesis has been successfully done with the detection method 2, where the catalyst is dispersed homogenously in the solution. The calibration curve of the different concentration of H2O2 is made in the parameter of 0.891 V (vs Ag/AgCl) and with the scan rate 50 mV/s. The optimum loading of samples prepared by co reduction was observed in CR Pd3%-Au2%/C with the productivity of H2O2 is 65.8 mol.kgcat-1h-1. This productivity is higher than the other prepared catalysts, such as monometallic Pd0%-Au5% & Pd5%-Au0% and bimetallic SR Pd-Au/C that is prepared by successive reduction. The higher or the lower productivity of one sample to another was explained by the parameter of the particle size, the structure of the bimetallic Pd-Au/C, the selective crystalline plane, and the role of palladium and gold. The smaller the particle size tends to Pd rich, while the larger one tends to Au rich. The smaller particle size yielded in the high surface area, thus the productivity increases. However, if the particle size is too small, the active site or selective crystalline plane may be slightly appeared (as can be seen in SR Pd-Au/C), thus the productivity decreases. From XAS analysis, the structure CR Pd-Au/C is Au rich in core and Pd rich in shell. The structure of SR PdAu at some part of catalyst is Au rich in core and Pd rich in shell, while at the other part, the structure is Pd in core and Au in shell. The Q value of SR PdAu (0.638) is higher than that of CR PdAu (0.605), which indicates that the existence of Au atoms in the shell of SR PdAu is more than that of CR PdAu. The difference in their structure is one reason why the H2O2 productivity of CR PdAu is higher than SR PdAu. The role of Pd is to provide the surface area for the selective oxidation of hydrogen and the role of Au is to provide inactive site for the reaction of decomposition and hydrogenation of H2O2.

碩士
國立臺灣科技大學
化學工程系
102
Hydrogen Peroxide is a valuable chemical with wide spread uses in industry; its demand is recently increasing due to its utilization. The modified reduced graphene oxide supported PdAu nanocatalysts were prepared for direct synthesis of hydrogen peroxide at ambient conditions in this work. The various atomic ratios of PdAu nanocatalysts on reduced graphene oxides were synthesized and characterized by XRD, SEM, TEM, Raman, FTIR and electrochemical analysis. It is found that the Pd07Au03 nanocatalyst shows the highest productivity of hydrogen peroxide due to its higher alloying extent. The graphene oxides were further modified by sulfonation. The results indicate the productivity can be further improved when Pd07Au03 nanocatalysts were prepared on the modified reduced graphene oxide. The high productivity of hydrogen peroxide was successfully achieved on the developed PdAu/mrGO nanocatalysts at ambient conditions. The method developed for preparation of PdAu nanocatalysts on modified reduced graphene oxide opens a new and interesting direction for increasing productivity hydrogen peroxide.

碩士
東海大學
環境科學與工程學系
105
The silver nanoparticles were successfully doped on a titanium dioxide nanotube arrays (TNAs) by green synthesis. Tea and coffee extract were used as reducing agent in green synthesis, and the synthesized photocatalysts were denoted as Ag/ TNAs-t and Ag/TNAs-c, respectively. The synthesized Ag/TNAs were used as electrodes in photoelectrochemical (PEC) systems to degrade ibuprofen and produce hydrogen in the anode and cathode, respectively. Ag/TNAs-t and Ag/TNAs-c showed that silver nanoparticles were successfully deposited on titanium dioxide nanotube arrays with a diameter of about 10 nm observed by scanning electron microscope (SEM). The results of XPS showed that the amount of silver contained in Ag/TNAs-t and Ag/TNAs-c were 1.7% and 1.6%, respectively. Similar results were obtained with EDX, confirming that silver nanoparticles were successfully deposited on the surface of TNAs. The bandgap energy of Ag/TNAs-t and Ag/TNAs-c decreased from 3.2 eV to 2.7-2.8 eV after doping silver nanoparticles. In the photoelectric current measurement, Ag/TNAs-t and Ag/TNAs-c showed the photogenerated current of 2.29 and 2.50 mA/ cm2, respectively, which was 1.45 mA /cm2 higher than that of TNAs. The degradation rates of Ag/TNAs-t by electrochemical (EC), light (P), photocatalysis (PC) and photoelectrochemical (PEC) were 0.004 min-1, 0.0148 min-1, 0.0950 min-1, and 0.2132 min-1, respectively. On the other hand, the degradation rates of Ag/TNAs-c were 0.0022 min-1, 0.0639 min-1, 0.0937 min-1 and 0.2180 min-1, respectively. The results showed that the highest degradation performance were achieved in photoelectrochemical system.

Nano-structures were investigated for the advancement of energy conversion technology because of their enhanced catalytic, thermal, and physiochemical interfacial properties and increased solar absorption. Hydrogen is a widely investigated and proven fuel and energy carrier for promising "green" technologies such as fuel cells. Difficulties involving storage, transport, and availability remain challenges that inhibit the widespread use of hydrogen fuel. For these reasons, in-situ hydrogen production has been at the forefront of research in the renewable and sustainable energy field. A common approach for hydrogen generation is the reforming of alcoholic and hydrocarbon fuels from fossil and renewable sources to a hydrogen-rich gas mixture.

Unfortunately, an intrinsic byproduct of any fuel reforming reaction is toxic and highly reactive CO, which has to be removed before the hydrogen gas can be used in fuel cells or delicate chemical processes. In this work, Au/alpha-Fe2O3 catalyst was synthesized using a modified co-precipitation method to generate an inverse catalyst model. The effects of introducing CO2 and H2O during preferential oxidation (PROX) of CO were investigated. For realistic conditions of (bio-)fuel reforming, 24% CO2 and 10% water the highest document conversion, 99.85% was achieved. The mechanism for PROX is not known definitively, however, current literature believes the gold particle size is the key. In contrast, we emphasize the tremendous role of the support particle size. A particle size study was performed to have in depth analysis of the catalysts morphology during synthesis. With this study we were also able to modify how the catalyst was made to further reduce the particle size of the support material leading to ~99.9% conversion. We also showed that the resulting PROX output gas could power a PEM fuel cell with only a 4% drop in power without poisoning the membrane electrode assembly.

The second major aim of this study is to develop an energy-efficient technology that fuses photothermal catalysis and plasmonic phenomena. Although current literature has claimed that the coupling of these technologies is impossible, here we demonstrate the fabrication of reaction cells for plasmon-induced photo-catalytic hydrogen production. The localized nature of the plasmon resonance allows the entire system to remain at ambient temperatures while a high-temperature methanol reformation reaction occurs at the plasmonic sites. Employing a nanostructured plasmonic substrate, we have successfully achieved sufficient thermal excitement (via localized surface plasmon resonance (LSPR)) to facilitate a heterogeneous chemical reaction. The experimental tests demonstrate that hydrogen gas can indeed be generated in a cold reactor, which has never been done before. Additionally, the proposed method has the highest solar absorption out of several variations and significantly reduces the cost, while increasing the efficiency of solar fuels.

Dissertation

博士
國立臺灣科技大學
材料科學與工程系
107
Energy and environmental issues have been the most concern of the worldwide in this recent decade. Due to extremely utilization of fossil energy have been causing the environmental issues like global warming and energy crisis. In the near future, the global energy needs must be obtained from the renewable and sustainable resources. Hydrogen is as a great candidate fuel to replace fossil fuels in the future since it has high energy density, zero-emission, and renewability. Unfortunately, the major hydrogen production still obtained from fossil by using steam reforming and gasification techniques. These techniques not only use unrenewable resource but also emit the carbon dioxide as the waste product. Therefore, in this particular research the green and sustainable hydrogen production is performed using photocatalytic method. This research also provides green chemical conversion of 4-nitrophenol to 4-aminophenol without using any sacrificial reagents. The first chapter of this dissertation briefly gives the introduction including background of study, hydrogen production techniques and 4-nitrophenol reduction. Then, the next chapter provides the basic theory and clear literature review of present progress in this particular research topic. This dissertation includes four works as follows. In the first work, we apply the doping concept to enhance the hydrogen production rate of Zn(O,S) with nickel as a dopant. High efficient hydrogen evolved Ni-doped Zn(O,S) photocatalyst with different Ni amounts had been successfully synthesized with a simple method at low temperature of 90C. Our Ni-doped Zn(O,S) catalyst reached the highest hydrogen generation rate of 14,800 µmole g-1·h-1, which was 2.3 times higher compared to the TiO2/Pt used as a control in this work. It was found that a small amount of Ni doped into Zn(O,S) nanoparticles could increase the optical absorbance, lower the charge transfer resistance, accordingly decrease the electron-hole recombination rate, and significantly enhance the photocatalytic hydrogen evolution reaction (HER). The as-prepared catalyst has the characteristics of low cost, low power consumption for activating the catalytic HER, abundant and environmental friendly constituents, and low surface oxygen bonding for forming oxygen vacancies. The photocatalytic performance of Ni-doped Zn(O,S) was demonstrated with a proposed kinetic mechanism in this work. In the second work, we design surface modification of Zn(O,S) by coating thin layers of graphene oxide (GO). This work demonstrates a feasible synthesis method of Zn(O,S)/GO nanocomposite with graphene oxide (GO) to serve as an inexpensive cocatalyst. Raman spectra and transmission electron microscopy (TEM) images clearly verified that GO was successfully loaded on the surface of Zn(O,S). This GO layer could effectively decrease the charge transfer resistance and promote the charge carrier separation for enhancing hydrogen production rate. By optimizing the GO content, the best hydrogen production rate of 6,400 µmol/g·h was achieved under 16W 352 nm UV lamp with Zn(O,S)/0.5 wt% GO catalyst, which showed about two times higher than GO-free Zn(O,S). The effect of sacrificial reagent on the hydrogen production rate of Zn(O,S)/0.5 wt% GO catalyst was also evaluated. The sacrificial reagent showed the efficiency with the following trend: ethanol > methanol > isopropanol > ethylene glycol. We consider the simple synthesis method of Zn(O,S)/GO and its low cost have a great potential for practical application. In the third work, the p-type Ag2O and n-type Zn(O,S) were loaded on mesoporous silica to form SiO2/Ag2O/Zn(O,S) with the nano p-n heterojunction to improve the efficiency of photocatalytic hydrogen evolution reaction (HER). The photocatalysts were systematically characterized to identify their properties. Through the optimization of the Zn(O,S)-loaded amount and position of p-Ag2O, the highest hydrogen production rate of 9,200 µmol. g-1cat.h-1 was achieved by SiO2/Ag2O/Zn(O,S)-0.6 catalyst, which was about 2.7 times higher than pure Zn(O,S). By placing n-Zn(O,S) of diodes outwards was proposed for the electron-rich part to enhance the reduction reaction, while placing p-Ag2O inwards for the hole-rich part to modulate the electron concentration and establish the built-in electrical nano field. Our design reveals that p-n heterojunction was superior and efficient for enhancing its properties and generating hydrogen. In the fourth work, the conversion of 4-nitrophenol as toxic pollutant and hazardous waste to be 4-aminophenol as non-toxic and useful compound by photocatalytic reduction was conducted. The solid solution and doping concept was combined to synthesis earth- abundant and green material Mn-doped Zn(O,S) by a simple and facile method. Different Mn contents doped Zn(O,S) was easily synthesized at low temperature of 90C for 4-NP reduction without using the reducing agent NaBH4. The Mn-doped Zn(O,S) catalyst exhibited the enhancement optical and electrochemical properties of un-doped Zn(O,S). It was found that 10% Mn doped Zn(O,S) had the best properties and it could totally reduce 4-NP after 2h photoreaction under low UV illumination. The hydrogen ion was proposed for reduction 4-NP to involved for the 4-NP reduction to 4-AP which is the hydrogen ion and electron replaced the oxygen in amino group to form the nitro group. We proposed the incorporation of Mn in Zn side in the Zn(O,S) host lattice could make the oxygen surface bonding weak to easily form the oxygen vacancy. As more oxygen vacancy, more hydrogen ion would be generated to consume for 4-NP reduction.

There has recently been an increased interest in hydrogen, both as a solution for seasonal energy storage but also for implementations in various industries and as fuel for vehicles. The transition to a society less dependent on fossil fuels highlights the need for new solutions where hydrogen is predicted to play a key role. This project aims to investigate technical and economic outcomes of different strategies for production and storage of hydrogen based on hydrogen demand and source of electricity. This is done by simulating the operation of different systems over a year, mapping the storage level, the source of electricity, and calculating the levelized cost of hydrogen (LCOH). The study examines two main cases. The first case is a system integrated with offshore wind power for production of hydrogen to fuel the operations in the industrial port Gävle Hamn. The second case examines a system for independent refueling stations where two locations with different electricity prices and traffic flows are analyzed. Factors such as demand, electricity prices, and component costs are investigated through simulating cases as well as a sensitivity analysis. Future potential sources of income are also analyzed and discussed. The results show that using an alkaline electrolyzer (AEL) achieves the lowest LCOH while PEM electrolyzer is more flexible in its operation which enables the system to utilize more electricity from the offshore wind power. When the cost of wind electricity exceeds the average electricity price on the grid, a higher share of wind electricity relative to electricity from the grid being utilized in the production results in a higher LCOH. The optimal design of the storage depends on the demand, where using vessels above ground is the most beneficial option for smaller systems and larger systems benefit financially from using a lined rock cavern (LRC). Hence, the optimal design of a system depends on the demand, electricity source, and ultimately on the purpose of the system. The results show great potential for future implementation of hydrogen systems integrated with wind power. Considering the increased share of wind electricity in the energy system and the expected growth of the hydrogen market, these are results worth acknowledging in future projects.