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The world's population is constantly growing, leading to a dramatic increase in energy demand. Unfortunately, to meet this growing demand, we have been relying heavily on non-renewable energy sources such as mineral oil, gas, and coal, which have caused severe environmental impacts, leading to detrimental consequences for socioeconomic aspects, human health, and ecological balance. Furthermore, the production of downstream products and industrial processes, such as fuel, plastics, and packaging materials, and processing industries have also contributed significantly to atmospheric greenhouse effects and other environmental impacts such as ozone depletion, acidification, and eutrophication. To mitigate these environmental impacts, there is a dire need for efficient energy conversion technologies that can reduce our reliance on nonrenewable energy sources. Clean energy technologies, where zero waste production is the goal, are the need of the hour. Fuel cells, a technology based on electrochemical oxidation (OER) or reduction (ORR), are an example of clean energy devices used for regular utilities such as transport, stationary, and portable power. The critical component of these technologies is the electrode, which requires the ionic and electronic transport functionalities needed to influence the electrochemical energy barrier of the designed materials, composites, and assemblies, also known as an electrocatalyst. Transition metal electrocatalysts (TMEs) are the most widely used catalysts for clean energy conversion, and activating and optimizing non-noble TMEs for electrocatalysts is an alternative way to produce low-cost technology. Cobalt and nickel, two highly efficient 3d TME metals, have demonstrated excellent performance in OER and ORR. Therefore, developing efficient electrocatalysts based on cobalt and nickel are a promising pathway to clean technologies and reducing our reliance on non-renewable energy sources. […]

An ancient technology of solar-driven water evaporation and distillation has recently been revived due to the concept of interfacial solar evaporation and the development of photothermal materials. There have been many research interests in improving solar light harvesting and solar-to-water evaporation efficiency within these systems, including new photothermal materials search, structural engineering, and thermal management. The application horizon of both solar-driven water evaporation and distillation has been broadly expanded beyond their conventional domain, including now wastewater treatment, seawater desalination, steam sterilization, electric generation, and chemicals/fuels productions. This dissertation focused on designing of photothermal materials and their applications to clean water production. More specifically: (1) a bi-layered porous rGO membrane with a polystyrene (PS) foam as the heat insulator was designed and proved to be effective for reducing heat conduction to the bulk water and to improve the solar-to-water evaporation efficiency, (2) a tandem-structured SiC-C ceramic monolith was prepared and demonstrated to be mechanically and chemically stable to withstand physical or chemical cleaning during long-term use in real seawater and wastewater, (3) in order to simultaneously treat the contaminated water and get clean distillate water, multi-functional SiC foam modified with mesoporous Au/TiO2 nanocomposites has been prepared, which was demonstrated to possess both photocatalytic reduction and oxidation abilities for complex wastewater treatment, and (4) when the water source was contaminated by VOCs, another efficient multi-functional photothermal material was designed with a honeycomb ceramic plate as the matrix material, and a CuFeMnO4 nanocomposite coating layer acting as both photothermal material and Fenton agent for VOCs removal. Therefore, the light absorption property of photothermal material could be improved by using a porous structure, tandem-structure, porous foam or 3D structure. The solar-to-water evaporation efficiency was improved by including a heat insulator and the reduction of the water channels’ dimension. The ceramic-based material showed potential for long-term use with high mechanical strength to endure physical cleaning. Multi-functional photothermal materials were successfully developed for complex wastewater treatment and clean water generation.

The increase of the capacity factor of thermal processes which use renewable energies is closely linked to the implementation of thermal energy storage (TES) systems. Currently, TES systems can be classified depending on the technology for storing thermal: sensible heat, latent heat, and sorption and chemical reactions (usually known as thermochemical energy storage). However, there is no standardized procedure for the evaluation of such technologies, and therefore the development of performance indicators which suit the requisites of the final users becomes an important goal. In the present paper, the authors identified the energy density as an important performance indicator for TES, and evaluated it at both material and system levels. This approach is afterwards applied to prototypes covering the three TES technologies: a two-tank molten salts sensible storage system, a shell-and-tube latent heat storage system, and a magnesium oxide and water chemical storage system. The evaluation of the energy density highlighted the difference of its value at the material value, which presents a theoretical maximum, and the results at system level, which considers all the parts required for operating the TES, and thus presents a significantly lower value. Moreover, the proposed approach captured the effect of the complexity and overall size of the system, showing the relevance of this performance indicator for evaluating technologies for applications in which volume is a limiting parameter. The work was partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER)). The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. Jaume Gasia would like to thank the Departament d'Universitats, Recerca i Societat de la Informació de la Generalitat de Catalunya for his research fellowship (2018 FI_B2 00100). Aran Solé would like to thank Ministerio de Economía y Competitividad de España for Grant Juan de la Cierva, FJCI2015-25741. The authors would also like to thank the participants of IEA ECES Annex 30 for their critical view and feedback during the development of the methodology.

Electrocatalysis contributes to a huge extent in a large array of research fields and applications, including corrosion science, electroanalytical sensors, wastewater treatment, electro-organic synthesis and more importantly, energy conversion applications. Of the many electrocatalytic processes, the oxygen evolution reaction (OER) and triiodide reduction reaction (IRR) are of widespread importance in electrochemical cells and dye-sensitised solar cells (DSSCs). OER is a key half reaction in electrochemical water splitting, direct solar-to-electricity driven water splitting and metal-air batteries. The high cost of efficient benchmark electrocatalysts, such as RuO2 or IrO2, however, is a major drawback of OERs. While, IRR plays a significant role in DSSCs, which must be electrocatalysed at the counter electrode to complete the external circuit in real devices and thereby successfully convert solar energy to electricity. Traditionally, Pt is accepted as an ideal benchmark electrocatalyst for IRR, but its high cost and scarcity limits broad application of DSSCs. Thus, extensive effort has been made to find active alternative electrocatalysts with low-cost, high electrocatalytic activity and excellent stability for OER and IRR to the noble metals (Ru, Ir and Pt). Therefore, a rational design of earth-abundant and low-cost electrocatalysts for OER and IRR maintains a paramount significance for energy conversion applications to meet the constantly growing demand for energy supply.

The connection between astrobiology and green chemistry represents a new approach to sustainability of organic matter on asteroids or similar bodies. Green chemistry is chemistry which is environmentally friendly. One obvious way for chemistry to be green is to use water as a solvent, instead of more toxic organic solvents. Many astrobiological reactions occur in the aqueous medium, for example in the prebiotic soup or during the aqueous alteration period on asteroids. Thus any advances in the green organic reactions in water are directly applicable to astrobiology. Another green chemistry approach is to abolish use of toxic solvents. This can be accomplished by carrying out the reactions without a solvent in the solventless or solid-state reactions. The advances in these green reactions are directly applicable to the chemistry on asteroids during the periods when water was not available. Many reactions on asteroids may have been done in the solid mixtures. These reactions may be responsible for a myriad of organic compounds that have been isolated from the meteorites.

Development of alternative fuel refineries, in order to improve global sustainability through increased biofuel production, has been increasingly supported by both government and private companies. Thermochemical processes such as hydrothermal liquefaction (HTL) and pyrolysis are leading technologies in this area. However, characterization, treatment, and reuse of aqueous by-products produced by such processes have received little attention. This dissertation is focused on aqueous phase characterization and catalytic advanced oxidation processing in novel microscale reactors. Novel char catalysts and improved process design were developed for efficient removal of organic contaminants. Small acids, cyclic pentenes, and carboxylic compounds such as phenol were initially identified. Model compounds were chosen based on these findings, and catalytic wet oxidation (CWO) processes in batch reactors conducted, in order to obtain reaction rate kinetics. The mechanism of compound oxidation was developed and shown through DFT analysis to be a production of hydroxyl free radicals ( ) in the presence of an oxidant and the N-doped char catalyst. The free radicals readily react with the dissolved organic compound, which was further confirmed with a FeO-N-doped char catalysts in a modified Fenton-like reaction system. In order to better develop a treatment processes which could integrate with a biorefinery, all process engineering experiments were conducted in a continuous solid-catalyzed microscale-based reactor utilizing the FeO-N-doped char catalyst. Time scale analysis was used for reactor geometry optimization in an effort to reduce diffusion time. The design led to a parallel plate reactor with channel depth of 500 microns. Thermochemical aqueous phases produced by pilot scale processes were characterized in detailed by extensive analytical methods. Traditional methods of spectroscopic analysis were limited in the ability to identify more complex oligomeric compounds and thus newer methods such as ICR-MS were utilized. The aqueous phases were successfully treated by the novel catalyst in the microreactor with removal of over 70% total organic carbon present at atmospheric pressure and at 90 °C. Some aqueous phase samples were more complex in nature however, successful decontamination was achieved. Catalytic wet oxidation processing in microscale-based reactors proves to be a plausible treatment option for process water in biorefineries.

AbstractDue to the depletion of fossil fuels and their‐related environmental issues, sustainable, clean, and renewable energy is urgently needed to replace fossil fuel as the primary energy resource. Hydrogen is considered as one of the cleanest energies. Among the approaches to hydrogen production, photocatalysis is the most sustainable and renewable solar energy technique. Considering the low cost of fabrication, earth abundance, appropriate bandgap, and high performance, carbon nitride has attracted extensive attention as the catalyst for photocatalytic hydrogen production in the last two decades. In this review, the carbon nitride‐based photocatalytic hydrogen production system, including the catalytic mechanism and the strategies for improving the photocatalytic performance is discussed. According to the photocatalytic processes, the strengthened mechanism of carbon nitride‐based catalysts is particularly described in terms of boosting the excitation of electrons and holes, suppressing carriers recombination, and enhancing the utilization efficiency of photon‐excited electron–hole. Finally, the current trends related to the screening design of superior photocatalytic hydrogen production systems are outlined, and the development direction of carbon nitride for hydrogen production is clarified.

Together with energy harvesting and distribution, energy storage technologies are essential to broadly establish renewable energy sources in a power grid. Chemical energy storage, e.g., through hydrogen, requires two conversion steps. Step one resembles the storage of electrical energy in chemical bonds (electrolyzer), and step two reverses this process (fuel cells). This work will introduce the technology of green hydrogen generation via water electrolysis and illustrate why efficient and sustainable catalyst systems based on non-toxic, abundant, and cost-effective materials are required. For this purpose, the investigations focus on 2D layered materials, which have proven to be a versatile material class to facilitate the oxidative half-reaction of electrochemical water splitting, which is the oxygen evolution reaction (OER). This work will focus on the structure-property relationship in such materials while also paying attention to the ecological aspects of the technology. The aim is to tailor catalytical systems, further improving their capabilities and scalability. In the scope of this work, the influence of composition, specifically iron-content, in layered double hydroxides is investigated concerning the triggering of grafting. That is the chemical bonding of interlayer anions to brucite-like layers. Due to the high importance of bimetallic iron-containing layered double hydroxides, it is crucial to understand which implication its incorporation bears for the structure and, ultimately, the catalytic performance. The systematic variation of Co/Fe composition within the layers showed that the presence of iron favors grafting, thereby inducing structural disorder in the form of random interstratification and planar defects. At the same time, having a minimum amount of Co in the structure is essential to ensure high catalytic activity. From the perspective of the structure-properties relationship, the question remains open as to what kind of effect the extent of grafting has. For this purpose, different brucite-type materials are compared. Three classes are chosen that feature inherently different interlayer constitutions, while the layers have similar compositions. These include metal hydroxides M(OH)2 without interlayer anions, layered double hydroxides with free interlayer anions, and hydroxynitrates with fully grafted interlayer anions. This work shows that an interlayer anion's chemical bonding can alter the metal centers' electronic structure. This is decisive for their oxidation potential, i.e., the potential at which the electrocatalytically active center forms. In the last part of this work, the previously gained knowledge is combined to achieve control of grafting within the same material. The all-iron electrocatalyst mössbauerite is known to exhibit extensive grafting of interlayer anions. By employing a corrosion engineering approach, it is possible to obtain its precursor green rust on a steel plate as a large area electrode and control the ratio of grafted to ungrafted interlayer anions by choice of the oxidation method. This control of grafting in the same material allows for the first systematic study on the influence of grafting in mössbauerite.

Ammonia has been responsible for feeding population growth in the 20th century through synthetic fertilizer, and is poised to become the preferred energy storage medium for a society powered by renewable electricity in the 21st century. However, conventional brown ammonia production through the Haber-Bosch process is optimized for utilization of centralized and steady energy supply from fossil-fuels. When shifting to distributed and intermittent energy supply through wind and solar energy, a re-optimization is required for a low-capital and flexible green ammonia production processes. This thesis re-designs and Haber-Bosch process by targeting the integration of reaction and separation in a single process vessel at low pressures, thereby achieving the simplification and down-scaling of the high pressure recycle loop of the Haber-Bosch process. Materials are developed for this purpose, the feasibility of integration is demonstrated, and mathematical modeling is utilized for assessing the application of the single-vessel process to a range of renewable energy sources in comparison to competing ammonia production processes. Herein, a catalyst with low-temperature (< 350°C) and high-conversion (i.e. near equilibrium) activity is developed using ruthenium nanoparticles as the active metal supported on ceria and promoted with cesium to mitigate hydrogen and ammonia inhibition, respectively. This catalyst is compared to commercial iron-based catalyst from the perspective of the final application. Concurrently, a high-temperature (> 300°C) manganese chloride absorbent is developed that resists decomposition and is stable when supported on silica. These catalyst and absorbent are integrated in a layered reactor configuration to demonstrate the feasibility of the integrated process by exceeding single-pass reaction equilibrium. Mathematical modelling of ammonia production processes illustrates that at small-scales (< 1 t day-1) the single-vessel process is optimal compared to the Haber-Bosch process due to its modular design. In addition, it can achieve simpler ramping because the Haber-Bosch process is constrained by heat-integration in the recycle loop and the potential for runaway reaction. For final application, the pairing of ammonia production processes with examples of intermittent solar and wind sources demonstrates that the flexibility of the production process is essential when considering non-ideal sources of energy with a long-term (e.g. seasonal) oscillations. Flexible ammonia production also expands the economic usage of ammonia as an energy storage vector from the seasonal to the weekly time-scale, with advantage compared to batteries or hydrogen. The work of this thesis provides a framework for advancing the electrification of the chemical industry given the novel constrains of intermittent and distributed renewable energy. A systems level approach is applied from the ground up, starting from material design and progressing to optimized process design and application.