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Electrodialysis has become a relevant technology in promoting sustainability within the food industry. Bipolar membrane electrodialysis offers an efficient and eco-friendly alternative for skim milk acidification, eliminating the need for added acids that affect milk composition and properties. For the first time, this study presents a comprehensive 2-D computational model to investigate the multi-ionic transport and dynamics of skim milk electro-acidification using bipolar membrane electrodialysis. The model is based on conservation equations for mass-charge transport, coupled with the description of water-splitting through the second Wien effect. The primary focus of the analysis was on the skim milk pH evolution and the concentration profiles of the major ions. The results showed that ion concentration values varied due to concentration polarization and differences in ion mobilities. The simulations were compared with experimental data, showing reasonable agreement, particularly for Ca2+ ion concentration. Despite excluding organic components in its analysis, this model offers a novel and valuable approach to the study of skim milk electro-acidification using bipolar membrane electrodialysis, providing essential insights for process understanding and optimization., Peer Reviewed, Postprint (published version)

Commercialization of photoelectrochemical (PEC) water-splitting devices requires the development of large-area, low-cost photoanodes with high efficiency and photostability. Herein, we address these challenges by using scalable fabrication techniques and porous transport layer (PTLs) electrode supports. We demonstrate the deposition of W-doped BiVO4 on Ti PTLs using successive-ionic-layer-adsorption-and-reaction methods followed by boron treatment and chemical bath deposition of NiFeOOH co-catalyst. The use of PTLs that facilitate efficient mass and charge transfer allowed the scaling of the photoanodes (100 cm2) while maintaining ~90 % of the performance obtained with 1 cm2 photoanodes for oxygen evolution reaction, that is, 2.10 mA cm−2 at 1.23 V vs. RHE. This is the highest reported performance to date. Integration with a polycrystalline Si PV cell leads to bias-free water splitting with a stable photocurrent of 208 mA for 6 h and 2.2 % solar-to-hydrogen efficiency. Our findings highlight the importance of photoelectrode design towards scalable PEC device development.

Electrodialysis has become a relevant technology in promoting sustainability within the food industry. Bipolar membrane electrodialysis offers an efficient and eco-friendly alternative for skim milk acidification, eliminating the need for added acids that affect milk composition and properties. For the first time, this study presents a comprehensive 2-D computational model to investigate the multi-ionic transport and dynamics of skim milk electro-acidification using bipolar membrane electrodialysis. The model is based on conservation equations for mass-charge transport, coupled with the description of water-splitting through the second Wien effect. The primary focus of the analysis was on the skim milk pH evolution and the concentration profiles of the major ions. The results showed that ion concentration values varied due to concentration polarization and differences in ion mobilities. The simulations were compared with experimental data, showing reasonable agreement, particularly for Ca2+ ion concentration. Despite excluding organic components in its analysis, this model offers a novel and valuable approach to the study of skim milk electro-acidification using bipolar membrane electrodialysis, providing essential insights for process understanding and optimization.

Electrodialysis has become a relevant technology in promoting sustainability within the food industry. Bipolar membrane electrodialysis offers an efficient and eco-friendly alternative for skim milk acidification, eliminating the need for added acids that affect milk composition and properties. For the first time, this study presents a comprehensive 2-D computational model to investigate the multi-ionic transport and dynamics of skim milk electro-acidification using bipolar membrane electrodialysis. The model is based on conservation equations for mass-charge transport, coupled with the description of water-splitting through the second Wien effect. The primary focus of the analysis was on the skim milk pH evolution and the concentration profiles of the major ions. The results showed that ion concentration values varied due to concentration polarization and differences in ion mobilities. The simulations were compared with experimental data, showing reasonable agreement, particularly for Ca2+ ion concentration. Despite excluding organic components in its analysis, this model offers a novel and valuable approach to the study of skim milk electro-acidification using bipolar membrane electrodialysis, providing essential insights for process understanding and optimization.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chloro­phyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to di­oxy­gen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O—O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chloro­phyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to di­oxy­gen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O—O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O-O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of O-X from a new water molecule, which disappears on completion of the reaction, implicating it in the O-O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chloro­phyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to di­oxy­gen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O—O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

To meet the demanding requirements for clean energy production, the need to develop advanced electrocatalysts for efficiently catalysing the water splitting reactions attracts a continuously increased attention. However, to meet the anticipated expansion in green hydrogen production from renewable energy sources, the catalysts used for the water splitting reaction not only need to satisfy the required figures of merit but should concurrently be based mainly on abundant, non-critical materials with low environmental impact. In last decades, non-noble metal catalysts, based on transition metals, rare-earth metals, dichalcogenides, and light elements such as phosphorus, nitrogen, and sulphur have shown improved performance. Moreover, in recent years increased interest has been focused on variations of such materials, more specifically on the introduction of defects to further boost their catalytic performance. Through the many studies performed over the last years, it is now possible to summarize, understand and describe the role of these defects for the water splitting reactions, namely the hydrogen and oxygen evolution reactions, and thereby to suggest strategies in the development of next generation electrocatalysts. This is the goal of the current review; we critically summarize the latest progress on the role of introduced defects for catalytic electrolysis applications by scrutinizing the structure–performance correlation as well as the specific catalytic activity. A broad class of nanomaterials is covered, comprising transition metal dichalcogenides, transition metal oxides and carbides, carbon-based materials as well as metal–organic frameworks (MOFs). Finally, the main challenges and future strategies and perspectives in this rapidly evolving field are provided at the end of the review.

To meet the demanding requirements for clean energy production, the need to develop advanced electrocatalysts for efficiently catalysing the water splitting reactions attracts a continuously increased attention. However, to meet the anticipated expansion in green hydrogen production from renewable energy sources, the catalysts used for the water splitting reaction not only need to satisfy the required figures of merit but should concurrently be based mainly on abundant, non-critical materials with low environmental impact. In last decades, non-noble metal catalysts, based on transition metals, rare-earth metals, dichalcogenides, and light elements such as phosphorus, nitrogen, and sulphur have shown improved performance. Moreover, in recent years increased interest has been focused on variations of such materials, more specifically on the introduction of defects to further boost their catalytic performance. Through the many studies performed over the last years, it is now possible to summarize, understand and describe the role of these defects for the water splitting reactions, namely the hydrogen and oxygen evolution reactions, and thereby to suggest strategies in the development of next generation electrocatalysts. This is the goal of the current review; we critically summarize the latest progress on the role of introduced defects for catalytic electrolysis applications by scrutinizing the structure–performance correlation as well as the specific catalytic activity. A broad class of nanomaterials is covered, comprising transition metal dichalcogenides, transition metal oxides and carbides, carbon-based materials as well as metal–organic frameworks (MOFs). Finally, the main challenges and future strategies and perspectives in this rapidly evolving field are provided at the end of the review.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chloro­phyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to di­oxy­gen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O—O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O-O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chloro­phyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to di­oxy­gen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O—O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O-O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O-O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

The water oxidation reaction in photosystem II (PS II) produces most of the molecular oxygen in the atmosphere, which sustains life on Earth, and in this process releases four electrons and four protons that drive the downstream process of CO2 fixation in the photosynthetic apparatus. The catalytic center of PS II is an oxygen-bridged Mn4Ca complex (Mn4CaO5) which is progressively oxidized upon the absorption of light by the chlorophyll of the PS II reaction center, and the accumulation of four oxidative equivalents in the catalytic center results in the oxidation of two waters to dioxygen in the last step. The recent emergence of X-ray free-electron lasers (XFELs) with intense femtosecond X-ray pulses has opened up opportunities to visualize this reaction in PS II as it proceeds through the catalytic cycle. In this review, we summarize our recent studies of the catalytic reaction in PS II by following the structural changes along the reaction pathway via room-temperature X-ray crystallography using XFELs. The evolution of the electron density changes at the Mn complex reveals notable structural changes, including the insertion of OX from a new water molecule, which disappears on completion of the reaction, implicating it in the O-O bond formation reaction. We were also able to follow the structural dynamics of the protein coordinating with the catalytic complex and of channels within the protein that are important for substrate and product transport, revealing well orchestrated conformational changes in response to the electronic changes at the Mn4Ca cluster.

To meet the demanding requirements for clean energy production, the need to develop advanced electrocatalysts for efficiently catalysing the water splitting reactions attracts a continuously increased attention. However, to meet the anticipated expansion in green hydrogen production from renewable energy sources, the catalysts used for the water splitting reaction not only need to satisfy the required figures of merit but should concurrently be based mainly on abundant, non-critical materials with low environmental impact. In last decades, non-noble metal catalysts, based on transition metals, rare-earth metals, dichalcogenides, and light elements such as phosphorus, nitrogen, and sulphur have shown improved performance. Moreover, in recent years increased interest has been focused on variations of such materials, more specifically on the introduction of defects to further boost their catalytic performance. Through the many studies performed over the last years, it is now possible to summarize, understand and describe the role of these defects for the water splitting reactions, namely the hydrogen and oxygen evolution reactions, and thereby to suggest strategies in the development of next generation electrocatalysts. This is the goal of the current review; we critically summarize the latest progress on the role of introduced defects for catalytic electrolysis applications by scrutinizing the structure–performance correlation as well as the specific catalytic activity. A broad class of nanomaterials is covered, comprising transition metal dichalcogenides, transition metal oxides and carbides, carbon-based materials as well as metal–organic frameworks (MOFs). Finally, the main challenges and future strategies and perspectives in this rapidly evolving field are provided at the end of the review.

To meet the demanding requirements for clean energy production, the need to develop advanced electrocatalysts for efficiently catalysing the water splitting reactions attracts a continuously increased attention. However, to meet the anticipated expansion in green hydrogen production from renewable energy sources, the catalysts used for the water splitting reaction not only need to satisfy the required figures of merit but should concurrently be based mainly on abundant, non-critical materials with low environmental impact. In last decades, non-noble metal catalysts, based on transition metals, rare-earth metals, dichalcogenides, and light elements such as phosphorus, nitrogen, and sulphur have shown improved performance. Moreover, in recent years increased interest has been focused on variations of such materials, more specifically on the introduction of defects to further boost their catalytic performance. Through the many studies performed over the last years, it is now possible to summarize, understand and describe the role of these defects for the water splitting reactions, namely the hydrogen and oxygen evolution reactions, and thereby to suggest strategies in the development of next generation electrocatalysts. This is the goal of the current review; we critically summarize the latest progress on the role of introduced defects for catalytic electrolysis applications by scrutinizing the structure–performance correlation as well as the specific catalytic activity. A broad class of nanomaterials is covered, comprising transition metal dichalcogenides, transition metal oxides and carbides, carbon-based materials as well as metal–organic frameworks (MOFs). Finally, the main challenges and future strategies and perspectives in this rapidly evolving field are provided at the end of the review.

To meet the demanding requirements for clean energy production, the need to develop advanced electrocatalysts for efficiently catalysing the water splitting reactions attracts a continuously increased attention. However, to meet the anticipated expansion in green hydrogen production from renewable energy sources, the catalysts used for the water splitting reaction not only need to satisfy the required figures of merit but should concurrently be based mainly on abundant, non-critical materials with low environmental impact. In last decades, non-noble metal catalysts, based on transition metals, rare-earth metals, dichalcogenides, and light elements such as phosphorus, nitrogen, and sulphur have shown improved performance. Moreover, in recent years increased interest has been focused on variations of such materials, more specifically on the introduction of defects to further boost their catalytic performance. Through the many studies performed over the last years, it is now possible to summarize, understand and describe the role of these defects for the water splitting reactions, namely the hydrogen and oxygen evolution reactions, and thereby to suggest strategies in the development of next generation electrocatalysts. This is the goal of the current review; we critically summarize the latest progress on the role of introduced defects for catalytic electrolysis applications by scrutinizing the structure–performance correlation as well as the specific catalytic activity. A broad class of nanomaterials is covered, comprising transition metal dichalcogenides, transition metal oxides and carbides, carbon-based materials as well as metal–organic frameworks (MOFs). Finally, the main challenges and future strategies and perspectives in this rapidly evolving field are provided at the end of the review.

This thesis was a computational study of designing novel catalysts for three main circles involved in electrocatalysis. The method was based on density functional theory to design a series of clean, cheap, and efficient catalysts for water circle, carbon circle, and nitrogen circle reactions. The outcomes of this thesis are expected to provide some theoretical guidance for the global energy shortage and environmental challenges.

This work was supported by the Spanish Ministerio de Ciencia, Universidades e Investigación, Spain (Project No. MAT2017-86616-R), and from Generalitat de Catalunya (Grant No. 2017SGR581). ICMAB acknowledges financial support from MINECO through the Severo Ochoa Program (Grant No. SEV-2015-0496)

[Abstract]: In this document, I analyze the current status of energy landscape and its mid‐term implications on Earth and society, focusing on the need of transitioning to renewables, and emphasizing in artificial photosynthesis as a very interesting approach. Likewise, I review what has been done and researched in the field of artificial photosynthesis and how each stage of the natural photosynthesis has been mimicked; as well, what problems are faced and the solutions found to palliate them. I conclude this work pinpointing what is left to further investigate to finally achieve a viable, durable artificial system, capable of producing and storing chemical energy from water and carbon dioxide., [Resumen]: En este documento, analizo el estado actual del panorama energético y sus implicaciones a medio plazo en la Tierra y en la sociedad, enfocándome en la necesidad de lograr la transición a las energías renovables. En este aspecto, haré especial hincapié en la fotosíntesis artificial, concluyendo que es una de las más prometedoras. Del mismo modo, reviso lo que se ha hecho e investigado en el campo de la fotosíntesis artificial; cómo se ha imitado cada parte de la fotosíntesis natural, a qué problemas se enfrenta y las soluciones encontradas para paliarlos. Finalizo el trabajo señalando qué queda por investigar para lograr un sistema fotosintético artificial viable y duradero, capaz de producir y almacenar energía química a partir de agua y dióxido de carbono., [Resumo]: Neste documento analizo o estado actual do panorama enerxético e as súas implicacións a medio prazo na Terra e na sociedade, centrándome na necesidade de lograr a transición ás enerxías renovables. Neste aspecto, conclúo que a fotosíntese artificial é unha das máis prometedoras. Do mesmo xeito, repaso o que se fixo e investigou no campo da fotosíntese artificial: como se imitou cada parte da fotosíntese natural, que problemas ten e as solucións atopadas para palialos. Finalizo o traballo sinalando que queda por investigar para finalmente acadar completamente un sistema fotosintético artificial viable e duradeiro, capaz de producir e almacenar enerxía química a partir de auga e dióxido de carbono.

Titanium dioxide gel monoliths were synthesized using an organic precursor and 0-30 vol % ethanol in water. The visible-light-activated proton pump, bacteriorhodopsin, in its native purple membrane form, was successfully encapsulated within the titanium dioxide gels. Absorption spectra showed that the folded functional state of the protein remained intact within gels made with 0 and 15 vol % ethanol and retained the ability to make reversible conformational changes associated with the photocycle within the gel made with 0 vol % ethanol. The photocatalytic activity of gels made with no ethanol was significantly detectable and gels made with 0-30 vol % ethanol were comparable to commercial crystalline nanoparticles in similar solution conditions when irradiated with UV light. Our results show that sol-gel-derived photocatalytic titanium dioxide can be made biocompatible for a membrane-associated protein by minimizing the amount of ethanol and maximizing the amount of water in the synthesis procedure. The entrapment of the membrane protein, bacteriorhodopsin, in sol-gel-derived titanium dioxide provides the first step in future explorations of this bionanocomposite for visible light photocatalysis, including hydrogen production.

Titanium dioxide gel monoliths were synthesized using an organic precursor and 0-30 vol % ethanol in water. The visible-light-activated proton pump, bacteriorhodopsin, in its native purple membrane form, was successfully encapsulated within the titanium dioxide gels. Absorption spectra showed that the folded functional state of the protein remained intact within gels made with 0 and 15 vol % ethanol and retained the ability to make reversible conformational changes associated with the photocycle within the gel made with 0 vol % ethanol. The photocatalytic activity of gels made with no ethanol was significantly detectable and gels made with 0-30 vol % ethanol were comparable to commercial crystalline nanoparticles in similar solution conditions when irradiated with UV light. Our results show that sol-gel-derived photocatalytic titanium dioxide can be made biocompatible for a membrane-associated protein by minimizing the amount of ethanol and maximizing the amount of water in the synthesis procedure. The entrapment of the membrane protein, bacteriorhodopsin, in sol-gel-derived titanium dioxide provides the first step in future explorations of this bionanocomposite for visible light photocatalysis, including hydrogen production.

Se-doped g-C3N4 was synthesized from sonicated aqueous suspensions of melamine cyanurate and SeO2. The different thermal condensation temperatures in the 500-650 ºC range were found to influence the photophysical properties and hydrogen evolution rates. H2 evolution increased dramatically by two orders of magnitude when Pt co-catalyst (1 wt.%) was incorporated, reaching an HER of 75 µmol H2/h·gcat

Transmission electron microscopy (TEM) has become an indispensable technique for studying heterogeneous catalysts. In particular, advancements of aberration-corrected electron optics and data acquisition schemes have made TEM capable of delivering images of catalysts with sub-Ångström resolution and single-atom sensitivity. Parallel developments of differentially pumped electron microscopes and of gas cells enable in situ observations of catalysts during the exposure to reactive gas environments at pressures of up to atmospheric levels and temperatures of up to several hundred centigrade. Here, we outline how to take advantage of the emerging state-of-the-art instrumentation and methodologies to study surface structures and dynamics to improve the understanding of structure-sensitive catalytic functionality. The concept of using low electron dose-rates in TEM in conjunction with in-line holography and aberration-correction at low voltage (80 kV) is introduced to allow maintaining atomic resolution and sensitivity during in situ observations of catalysts. Benefits are illustrated by exit wave reconstructions of TEM images of a nanocrystalline Co3O4 catalyst material acquired in situ during their exposure to either a reducing or oxidizing gas environment.

Transmission electron microscopy (TEM) has become an indispensable technique for studying heterogeneous catalysts. In particular, advancements of aberration-corrected electron optics and data acquisition schemes have made TEM capable of delivering images of catalysts with sub-Ångström resolution and single-atom sensitivity. Parallel developments of differentially pumped electron microscopes and of gas cells enable in situ observations of catalysts during the exposure to reactive gas environments at pressures of up to atmospheric levels and temperatures of up to several hundred centigrade. Here, we outline how to take advantage of the emerging state-of-the-art instrumentation and methodologies to study surface structures and dynamics to improve the understanding of structure-sensitive catalytic functionality. The concept of using low electron dose-rates in TEM in conjunction with in-line holography and aberration-correction at low voltage (80 kV) is introduced to allow maintaining atomic resolution and sensitivity during in situ observations of catalysts. Benefits are illustrated by exit wave reconstructions of TEM images of a nanocrystalline Co3O4 catalyst material acquired in situ during their exposure to either a reducing or oxidizing gas environment.

Se-doped g-C3N4 was synthesized from sonicated aqueous suspensions of melamine cyanurate and SeO2. The different thermal condensation temperatures in the 500-650 ºC range were found to influence the photophysical properties and hydrogen evolution rates. H2 evolution increased dramatically by two orders of magnitude when Pt co-catalyst (1 wt.%) was incorporated, reaching an HER of 75 µmol H2/h·gcat

This paper analyzes the thermodynamic feasibility of three reactions, one undesirable side reaction, and a flash separation for a water-splitting cycle. The thermodynamic feasibility of each reaction was analyzed using both an equilibrium constant based approach and through solution of the associated Gibbs free energy minimization problem. The thermodynamic feasibility of each reaction was determined at a variety of feed conditions, temperatures, and pressures. Future research will be conducted to determine optimal conditions at which to run the cycle to produce pure hydrogen and oxygen efficiently.

This paper analyzes the thermodynamic feasibility of three reactions, one undesirable side reaction, and a flash separation for a water-splitting cycle. The thermodynamic feasibility of each reaction was analyzed using both an equilibrium constant based approach and through solution of the associated Gibbs free energy minimization problem. The thermodynamic feasibility of each reaction was determined at a variety of feed conditions, temperatures, and pressures. Future research will be conducted to determine optimal conditions at which to run the cycle to produce pure hydrogen and oxygen efficiently.

The reaction cycles for water-splitting based on redox reactions of alkali metals are composed of four reactions, which are hydrogen generation by solid-liquid reaction, metal separation by thermolysis, oxygen generation by hydrolysis, and phase transition of the metal. Although all the cycles theoretically require more than 1000 °C in thermodynamic equilibrium condition, the reaction temperature are reduced to below 800 °C by non−equilibrium techniques using phase transition of metal vapor. In this work, thermodynamic analyses are performed by using the parameters such as operating temperature and partial pressures of the products obtained by the experiments to determine that the alkali metal redox cycles are potential hydrogen production technique as thermochemical energy storage., Selection and peer review by the scientific conference committee of SolarPACES 2013 under responsibility of PSE AG. Final manuscript published as received without editorial corrections.

The reaction cycles for water-splitting based on redox reactions of alkali metals are composed of four reactions, which are hydrogen generation by solid-liquid reaction, metal separation by thermolysis, oxygen generation by hydrolysis, and phase transition of the metal. Although all the cycles theoretically require more than 1000 °C in thermodynamic equilibrium condition, the reaction temperature are reduced to below 800 °C by non−equilibrium techniques using phase transition of metal vapor. In this work, thermodynamic analyses are performed by using the parameters such as operating temperature and partial pressures of the products obtained by the experiments to determine that the alkali metal redox cycles are potential hydrogen production technique as thermochemical energy storage., Selection and peer review by the scientific conference committee of SolarPACES 2013 under responsibility of PSE AG. Final manuscript published as received without editorial corrections.

A plant was designed that uses a solar sulfur-ammonia thermochemical water-splitting cycle for the production of hydrogen. Hydrogen is useful as a fuel for stationary and mobile fuel cells. The chemical process simulator Aspen Plus® was used to model the plant and conduct simulations. The process utilizes the electrolytic oxidation of aqueous ammonium sulfite in the hydrogen production half cycle and the thermal decomposition of molten potassium pyrosulfate and gaseous sulfur trioxide in the oxygen production half cycle. The reactions are driven using solar thermal energy captured from a heliostat array focused on a receiver. The plant's feed stream is water and the product streams are hydrogen and oxygen; all other materials are contained within the plant. The model is for full-scale operation that would generate 133,333 kg of hydrogen per day, which is equivalent to 370 MW on a lower heating value basis. Thermodynamic properties of chemical species obtained from literature, and from laboratory experiments conducted in another part of this project, were entered into the model to improve its accuracy. Design specifications were placed in strategic areas of the model to aid in its convergence. Model convergence is challenging to obtain because of the many material and energy recycle loops within the plant. Calculator blocks were used to obtain power requirements for the electrolyzer and efficiencies of the entire plant based on definitions from the Department of Energy, which funded this project. Results from this work will aid in the design of a large-scale hydrogen production plant.

A plant was designed that uses a solar sulfur-ammonia thermochemical water-splitting cycle for the production of hydrogen. Hydrogen is useful as a fuel for stationary and mobile fuel cells. The chemical process simulator Aspen Plus® was used to model the plant and conduct simulations. The process utilizes the electrolytic oxidation of aqueous ammonium sulfite in the hydrogen production half cycle and the thermal decomposition of molten potassium pyrosulfate and gaseous sulfur trioxide in the oxygen production half cycle. The reactions are driven using solar thermal energy captured from a heliostat array focused on a receiver. The plant's feed stream is water and the product streams are hydrogen and oxygen; all other materials are contained within the plant. The model is for full-scale operation that would generate 133,333 kg of hydrogen per day, which is equivalent to 370 MW on a lower heating value basis. Thermodynamic properties of chemical species obtained from literature, and from laboratory experiments conducted in another part of this project, were entered into the model to improve its accuracy. Design specifications were placed in strategic areas of the model to aid in its convergence. Model convergence is challenging to obtain because of the many material and energy recycle loops within the plant. Calculator blocks were used to obtain power requirements for the electrolyzer and efficiencies of the entire plant based on definitions from the Department of Energy, which funded this project. Results from this work will aid in the design of a large-scale hydrogen production plant.

Significant insights into plant photosynthesis and respiration have been achieved using membrane inlet mass spectrometry (MIMS) for the analysis of stable isotope distribution of gases. The MIMS approach is based on using a gas permeable membrane to enable the entry of gas molecules into the mass spectrometer source. This is a simple yet durable approach for the analysis of volatile gases, particularly atmospheric gases. The MIMS technique strongly lends itself to the study of reaction flux where isotopic labeling is employed to differentiate two competing processes; i.e., O-2 evolution versus O-2 uptake reactions from PSII or terminal oxidase/rubisco reactions. Such investigations have been used for in vitro studies of whole leaves and isolated cells. The MIMS approach is also able to follow rates of isotopic exchange, which is useful for obtaining chemical exchange rates. These types of measurements have been employed for oxygen ligand exchange in PSII and to discern reaction rates of the carbonic anhydrase reactions. Recent developments have also engaged MIMS for online isotopic fractionation and for the study of reactions in inorganic systems that are capable of water splitting or H-2 generation. The simplicity of the sampling approach coupled to the high sensitivity of modern instrumentation is a reason for the growing applicability of this technique for a range of problems in plant photosynthesis and respiration. This review offers some insights into the sampling approaches and the experiments that have been conducted with MIMS.

Significant insights into plant photosynthesis and respiration have been achieved using membrane inlet mass spectrometry (MIMS) for the analysis of stable isotope distribution of gases. The MIMS approach is based on using a gas permeable membrane to enable the entry of gas molecules into the mass spectrometer source. This is a simple yet durable approach for the analysis of volatile gases, particularly atmospheric gases. The MIMS technique strongly lends itself to the study of reaction flux where isotopic labeling is employed to differentiate two competing processes; i.e., O2 evolution versus O2 uptake reactions from PSII or terminal oxidase/rubisco reactions. Such investigations have been used for in vitro studies of whole leaves and isolated cells. The MIMS approach is also able to follow rates of isotopic exchange, which is useful for obtaining chemical exchange rates. These types of measurements have been employed for oxygen ligand exchange in PSII and to discern reaction rates of the carbonic anhydrase reactions. Recent developments have also engaged MIMS for online isotopic fractionation and for the study of reactions in inorganic systems that are capable of water splitting or H2 generation. The simplicity of the sampling approach coupled to the high sensitivity of modern instrumentation is a reason for the growing applicability of this technique for a range of problems in plant photosynthesis and respiration. This review offers some insights into the sampling approaches and the experiments that have been conducted with MIMS., SpringerLink Date Monday, August 03, 2009

Since the end of the 1950s hydrogencarbonate ('bicarbonate') is discussed as a possible cofactor of photosynthetic water-splitting, and in a recent X-ray crystallography model of photosystem II (PSII) it was displayed as a ligand of the Mn4OxCa cluster. Employing membrane-inlet mass spectrometry (MIMS) and isotope labelling we confirm the release of less than one (approximate to 0.3) HCO3- per PSII upon addition of formate. The same amount of HCO3- release is observed upon formate addition to Mn-depleted PSII samples. This suggests that formate does not replace HCO3- from the donor side, but only from the non-heme iron at the acceptor side of PSII. The absence of a firmly bound HCO3- is corroborated by showing that a reductive destruction of the Mn4OxCa cluster inside the MIMS cell by NH2OH addition does not lead to any CO2/HCO3- release. We note that even after an essentially complete HCO3-/CO2 removal from the sample medium by extensive degassing in the MIMS cell the PSII samples retain 75% of their initial flash-induced O-2-evolving capacity. We therefore conclude that HCO3- has only 'indirect' effects on water-splitting in PSII, possibly by being part of a proton relay network and/or by participating in assembly and stabilization of the water-oxidizing complex. (C) 2008 Elsevier B.V. All rights reserved.

From a chemical point of view methanol is one of the closest analogues of water. Consistent with this idea EPR spectroscopy studies have shown that methanol binds at-or at least very close to-the Mn4OxCa cluster of photosystem II (PSII). In contrast, Clark-type oxygen rate measurements demonstrate that the O-2 evolving activity of PSII is surprisingly unaffected by methanol concentrations of up to 10%. Here we study for the first time in detail the effect of methanol on photosynthetic water-splitting by employing a Joliot-type bare platinum electrode. We demonstrate a linear dependence of the miss parameter for Si state advancement on the methanol concentrations in the range of 0-10% (v/v). This finding is consistent with the idea that methanol binds in PSII with similar affinity as water to one or both substrate binding sites at the Mn(4)OxCa cluster. The possibility is discussed that the two substrate water molecules bind at different stages of the cycle, one during the S-4 -> S-0 and the other during the S-2 -> S-3 transition.

Since the end of the 1950s hydrogencarbonate (‘bicarbonate') is discussed as a possible cofactor of photosynthetic water-splitting, and in a recent X-ray crystallography model of photosystem II (PSII) it was displayed as a ligand of the Mn4OxCa cluster. Employing membrane-inlet mass spectrometry (MIMS) and isotope labelling we confirm the release of less than one (≈ 0.3) HCO3- per PSII upon addition of formate. The same amount of HCO3- release is observed upon formate addition to Mn-depleted PSII samples. This suggests that formate does not replace HCO3- from the donor side, but only from the non-heme iron at the acceptor side of PSII. The absence of a firmly bound HCO3- is corroborated by showing that a reductive destruction of the Mn4OxCa cluster inside the MIMS cell by NH2OH addition does not lead to any CO2/HCO3- release. We note that even after an essentially complete HCO3-/CO2 removal from the sample medium by extensive degassing in the MIMS cell the PSII samples retain ≥ 75% of their initial flash-induced O2-evolving capacity. We therefore conclude that HCO3- has only ‘indirect' effects on water-splitting in PSII, possibly by being part of a proton relay network and/or by participating in assembly and stabilization of the water-oxidizing complex.

From a chemical point of view methanol is one of the closest analogues of water. Consistent with this idea EPR spectroscopy studies have shown that methanol binds at—or at least very close to—the Mn4O x Ca cluster of photosystem II (PSII). In contrast, Clark-type oxygen rate measurements demonstrate that the O2 evolving activity of PSII is surprisingly unaffected by methanol concentrations of up to 10%. Here we study for the first time in detail the effect of methanol on photosynthetic water-splitting by employing a Joliot-type bare platinum electrode. We demonstrate a linear dependence of the miss parameter for S i state advancement on the methanol concentrations in the range of 0–10% (v/v). This finding is consistent with the idea that methanol binds in PSII with similar affinity as water to one or both substrate binding sites at the Mn4O x Ca cluster. The possibility is discussed that the two substrate water molecules bind at different stages of the cycle, one during the S4 → S0 and the other during the S2 → S3 transition.

The influence of co-ion leakage through a bipolar membrane on both I-V response and current efficiency of water dissociation was studied. The monofilm bipolar membrane was synthetized from a pretreated ETFE film functionalized by quaternized ammonium groups on one side and sulphonic groups on the other. The co-ion leakage of this bipolar membrane immersed in NaCl solutions was measured by means of radiotracers. The results showed that the greater the co-ion leakage, the lower was the current efficiency of water dissociation. A theoretical analysis of ion transfer through the bipolar membrane pointing out the effect of boundary layer on the limiting leakage current is presented. © 1994., SCOPUS: ar.j, info:eu-repo/semantics/published

The influence of co-ion leakage through a bipolar membrane on both I-V response and current efficiency of water dissociation was studied. The monofilm bipolar membrane was synthetized from a pretreated ETFE film functionalized by quaternized ammonium groups on one side and sulphonic groups on the other. The co-ion leakage of this bipolar membrane immersed in NaCl solutions was measured by means of radiotracers. The results showed that the greater the co-ion leakage, the lower was the current efficiency of water dissociation. A theoretical analysis of ion transfer through the bipolar membrane pointing out the effect of boundary layer on the limiting leakage current is presented. © 1994., SCOPUS: ar.j, info:eu-repo/semantics/published

In situ generation of hydrogen in photo-electrocatalytic cells shows promise as a portable, efficient, and reliable energy source for expeditionary naval operations. Although several methods are currently used to generate hydrogen, photocatalytic watersplitting stands out due to its ability to provide hydrogen through solar energy conversion, a clean and renewable method. It is believed that the efficiency of the photocatalytic process could be greatly enhanced by doping the surface of the photoanodes with transition metals. This research aimed to generate TiO₂ nanoarrays doped with thin (5–30nm) layers of nickel for future application as the anode in photoelectrocatalytic cells (PEC). Nanoarrays were prepared using anodization in an electrolyte bath, which consisted of ammonium fluoride, ethylene glycol, and deionized water. The Ni-TiO₂ samples were annealed in air or inert atmospheres to produce crystalline structures. Ni-doped TiO₂ nanoarray surface morphology, composition, and microstructure were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy. The annealed nanoarrays consisted of nickel (or nickel oxide) layers on top of a crystalline anatase array. The introduction of Ni/NiO decreased the reflectivity of TiO₂ arrays up to a 40%, and it is expected to significantly enhance the material’s photocatalytic activity., http://archive.org/details/developmentofdop1094556716, Ensign, United States Navy, Approved for public release; distribution is unlimited.