Layer-by-Layer Assembly of Molecular Metal Oxide Catalysts for Photoelectrochemical Water Splitting

Department of Energy EngineeringArtificial photosynthesis is considered one of the most promising solutions to modern energy and environmental crises. Considering that it is enabled by multiple components through a series of photoelectrochemical processes, the key to successful development of a photosynthetic device depends not only on the development of novel individual components but also on the rational design of an integrated photosynthetic device assembled from them. However, most studies have been dedicated to the development of individual components due to the lack of a general and simple method for the construction of the integrated device. In the present study, we report a versatile and simple method to prepare an efficient and stable photoelectrochemical device via controlled assembly and integration of functional components using the layer-by-layer (LbL) assembly technique. As a proof of concept, we could successfully build a photoanode for photocatalytic water oxidation by modifying the surface of various photoelectrode materials (e.g., Fe2O3, BiVO4, and TiO2) with diverse cationic polyelectrolytes and anionic polyoxometalate (molecular metal oxide) water oxidation catalysts. It was found that the performance of photoanodes was significantly improved after the deposition in terms of stability as well as photocatalytic properties, regardless of types of photoelectrodes and polyelectrolytes employed. Considering the simplicity and universal nature of LbL assembly techniques, we believe that our approach can provide a general and simple method for the design and realization of a novel photosynthetic device.ope

Amine???Rich Hydrogels Enhance Solar Water Oxidation via Boosting Proton???Coupled Electron Transfer

Photoelectrochemical (PEC) water oxidation is a highly challenging task that acts as a bottleneck for efficient solar hydrogen production. It is because each cycle of water oxidation is composed of four proton-coupled electron transfer (PCET) processes and conventional photoanodes and cocatalysts have limited roles in enhancing the charge separation and storage rather than in enhancing catalytic activity. In this study, a simple and generally applicable strategy to improve the PEC performance of water oxidation photoanodes through their modification with polyethyleneimine (PEI) hydrogel is reported. The rich amine groups of PEI not only allow the facile and stable modification of photoanodes by crosslinking but also contribute to improving the kinetics of PEC water oxidation by boosting the PCET. Consequently, the PEC performance of various photoanodes, such as BiVO4, Fe2O3, and TiO2, is significantly enhanced in terms of photocurrent densities and onset potentials even in the presence of notable cocatalyst, cobalt phosphate. The present study provides new insights into and strategies for the design of efficient photoelectrodes and PEC devices

Superaerophobic hydrogels for enhanced electrochemical and photoelectrochemical hydrogen production

The efficient removal of gas bubbles in (photo)electrochemical gas evolution reactions is an important but underexplored issue. Conventionally, researchers have attempted to impart bubble-repellent properties (so-called superaerophobicity) to electrodes by controlling their microstructures. However, conventional approaches have limitations, as they are material specific, difficult to scale up, possibly detrimental to the electrodes' catalytic activity and stability, and incompatible with photoelectrochemical applications. To address these issues, we report a simple strategy for the realization of superaerophobic (photo)electrodes via the deposition of hydrogels on a desired electrode surface. For a proof-of-concept demonstration, we deposited a transparent hydrogel assembled from M13 virus onto (photo)electrodes for a hydrogen evolution reaction. The hydrogel overlayer facilitated the elimination of hydrogen bubbles and substantially improved the (photo)electrodes' performances by maintaining high catalytic activity and minimizing the concentration overpotential. This study can contribute to the practical application of various types of (photo)electrochemical gas evolution reactions

Phloretin Exerts Anti-Tuberculosis Activity and Suppresses Lung Inflammation

An increase in the prevalence of the drug-resistant Mycobacteria tuberculosis necessitates developing new types of anti-tuberculosis drugs. Here, we found that phloretin, a naturally-occurring flavonoid, has anti-mycobacterial effects on H37Rv, multi-drug-, and extensively drug-resistant clinical isolates, with minimum inhibitory concentrations of 182 and 364 μM, respectively. Since Mycobacteria cause lung inflammation that contributes to tuberculosis pathogenesis, anti-inflammatory effects of phloretin in interferon-γ-stimulated MRC-5 human lung fibroblasts and lipopolysaccharide (LPS)-stimulated dendritic cells were investigated. The release of interleukin (IL)-1β, IL-12, and tumor necrosis factor (TNF)-α was inhibited by phloretin. The mRNA levels of IL-1β, IL-6, IL-12, TNF-α, and matrix metalloproteinase-1, as well as p38 mitogen-activated protein kinase and extracellular signal-regulated kinase phosphorylation, were suppressed. A mouse in vivo study of LPS-stimulated lung inflammation showed that phloretin effectively suppressed the levels of TNF-α, IL-1β, and IL-6 in lung tissue with low cytotoxicity. Phloretin was found to bind M. tuberculosis β-ketoacyl acyl carrier protein synthase III (mtKASIII) with high affinity (7.221 × 107 M−1); a binding model showed hydrogen bonding of A-ring 2′-hydroxy and B-ring 4-hydroxy groups of phloretin with Asn261 and Cys122 of mtKASIII, implying that mtKASIII can be a potential target protein. Therefore, phloretin can be a useful dietary natural product with anti-tuberculosis benefits

Tailoring of molecular catalysts for photoelectrochemical and electrochemical water splitting

Department of Energy Engineering (Energy Engineering)clos

Interfacial engineering of hematite photoanodes through layer-by-layer assembly for solar water splitting

Solar to chemical conversion is considered as a promising solution to energy and environmental problems because various chemicals (e.g., hydrogen, formate, and syngas) can be produced from wasted carbon dioxide and abundant water in a carbon-neutral manner. It can be enabled by a series of photoelectrochemical processes with various functional materials, which include semiconducting materials for exciton generation, conducting materials for exciton dissociation and charge transport, and redox catalysts for target-chemical reactions. For the development of efficient and stable solar to chemical energy conversion devices, it is imperative to precisely assembly these components. Here, we report that an efficient and stable photoanode for solar water oxidation can be readily fabricated by layer-by-layer (LbL) assembly. In particular, cationic graphene oxide (GO) nanosheets and anionic molecular metal oxide catalysts were readily deposited on hematite without alteration of their properties using the LbL method. It was found that their sequential deposition significantly improves the photocatalytic performance and stability of hematite for solar water oxidation. In addition, the deposition of multilayers of cationic and anionic polymer electrolyte prior to the GO and catalyst layers improve the photoanode performance even further by allowing the engineering of the flat band potential of the underlying hematite photoanode. We believe that the present study opens a new avenue for an efficient photosynthetic device, as well as an academic insight to scientists and engineers for designing novel electrochemical/photoelectrochemical devices

Interfacial Engineering of Hematite through Layer-by-Layer Assembly for Solar Water Oxidation

Artificial photosynthesis has a great attention as a promising energy solution to environmental problems. In principle, valuable chemicals can be produced from wasted carbon dioxide and abundant water, instead of using fossil fuels, through a series of photoelectrochemical processes in a carbon-neutral manner. For the successful development of efficient and stable photosynthetic devices, it is significantly required to assemble various functional materials for efficient exciton generation, exciton dissociation, charge transport, and electrocatalytic charge transfer reactions. Here, we develop an efficient and stable photoanode for solar water oxidation through deposition of artificial nacre film on hematite by layer-by-layer assembly of cationic graphene oxide nanosheets and anionic molecular metal oxide catalysts. The deposition of the film greatly improved both the photocatalytic activity and stability of hematite photoanodes. It was found that deposition of alternating layers of cationic and anionic polymers prior to the artificial nacre film allowed fine-tuning of the work-function of the hematite electrode, enhancing the photoelectrochemical performance even further

Bioinspired Materials Science: Mimicking Nature's Strategies to Build Functional Materials

One of most fascinating features of biological system is that their excellent physical and chemical properties stem from their unique structure where various organic and inorganic components are precisely assembled at nanoscale precision. They have developed their own strategies to build functional materials and systems in response to external stimuli (or environment) through evolution over millions of years. For example, excellent mechanical properties of natural bone is resulted from their unique structure where organic peptide nanofibers and calcium phosphate nanocrystals are hierarchically organized at nano- and micro-scales. Another good example is photosynthetic machinery of plants, which can produce sugars and biological fuels with sustainable resources. Spatiotemporal arrangement of light-harvesting chlorophyl dyes and redox catalysts allows efficient separation of charges and directional flow of electrons (i.e. redox power), enabling photocatalytic splitting of water and production of carbohydrates from CO2. In this presentation, we report the development of functional materials and systems, especially for energy storage and conversion devices, by mimicking Mother Nature'ss stretegies. Following topics will be covered in this presentation: 1) Synthesis of functional materials by using biological templates such as peptides and viruses, 2) Development of artiticial photosynthetic system for the production of valuable chemicals