Artificial Photosynthesis System Research Articles

Water‐Soluble Conjugated Molecule for Solar‐Driven Hydrogen Evolution from Salt Water

AbstractPhotocatalytic hydrogen evolution is an attractive method for the acquisition of clean and sustainable energy with the use of solar power. Most reported studies have been carried out in scarce pure water. Therefore, the development of an artificial photosynthesis system that works perfectly with the earth's abundant seawater would be attractive. Herein, a supramolecular strategy for photocatalytic hydrogen production from the simulated seawater under sunlight irradiation (AM 1.5G, 100 mW cm−2) is presented using a water‐soluble, conjugated molecule as the photosensitizer and the photodeposited Pt nanoparticles as the catalyst. Inspired by the natural photosynthesis system, unprecedented advantage of the chloride ions in seawater is taken and the formation of supramolecular structure is promoted by electrostatic interactions between chloride ions and the fine‐designed PorFN, which further facilitates the loading of Pt nanoparticles and multielectron transfer. As a result, a hydrogen evolution rate of 10.8 mmol h−1 g−1 is achieved in the simulated seawater. Moreover, the photocatalytic activity shows relatively low dependence on the light intensity, which is of great importance for practical applications.

Size Controllable Metal Nanoparticles Anchored on Nitrogen Doped Carbon for Electrocatalytic Energy Conversion

AbstractMetal nanoparticles (NPs) are an important class of materials for electrocatalysis. Synthesis of metal NPs with uniform particle size below 10 nm without a capping agent is challenging due to the tendency of particle aggregation to minimize surface energy. Here we demonstrate that pyrolysis of a metal‐TCNQ (TCNQ−=tetracyanoquinodimethane radical anion) compound can produce metal NPs with controllable particle sizes anchored on nitrogen doped carbon (denoted as MetalNC). NiNC and CoNC derived from Ni‐TCNQ and Co‐TCNQ with Ni and Co particle sizes below 10 nm were successfully prepared. NiNC, with a particle size of 8.8 nm, showed excellent catalytic activity for hydrogen evolution in an alkaline medium, reaching a catalytic current density of 10 mA cm−2 at an overpotential of 230 mV. CoNC, with a particle size of 1.8 nm, exhibited the capability of producing syngas by electrocatalytic CO2 reduction over a wide potential range in an acetonitrile medium containing 0.3 M H2O. An artificial photosynthesis system based on CoNC achieved faradaic efficiencies of over 70 % for production of syngas and 22 % for formate. This work demonstrates a general strategy to synthesize size controllable metal NPs supported on carbon materials for electrocatalytic energy conversion.

Strongly Coupled Phenazine-Porphyrin Dyads: Light-Harvesting Molecular Assemblies with Broad Absorption Coverage.

The development of light-harvesting architectures with broad absorption coverage in the visible region continues to be an important research area in the field of artificial photosynthesis. Here, we introduce a new class of ethynyl-linked panchromatic dyads composed of dibenzophenazines coupled ortho and meta to tetrapyrroles with an anchoring group that can be grafted onto metal oxide surfaces. Quantum chemical calculations and photophysical measurements of the synthesized materials reveal that both of the dibenzophenazine dyads absorb broadly from 300 to 636 nm and exhibit absorption bands different from those of the constituent chromophore units. Moreover, the different points of attachment of dibenzophenazines to tetrapyrroles give different absorption profiles which computations suggest result from differences in the planarity of the two dyads. Applicability of the dyads in artificial photosynthesis systems was assessed by their incorporation and characterization of their performance in dye-sensitized solar cells.

Colloidal FeIII , MnIII , CoIII , and CuII Hydroxides Stabilized by Starch as Catalysts of Water Oxidation Reaction with One Electron Oxidant Ru(bpy)33.

Colloidal catalysts for oxidation of water to dioxygen, which are stable on storage and under the reaction conditions, are synthesized based on CoIII , MnIII , FeIII and CuII hydroxides. Stabilization of the colloids with dextrated starch allows the process of hydroxide ageing to be stopped at the stage of the formation of primary nuclei (ca. 2-3 nm from transmission electron microscopy data). Molecular mechanics and dynamic light scattering studies indicate a core-shell type structure of the catalysts, where the hydroxide core is stabilized by the molecular starch network (ca. 5-7 nm). The colloidal catalysts are highly efficient in oxidizing water with one electron oxidant Ru(bpy)33+ at pH 7 to 10. The influence of pH, catalyst concentration, and buffer nature on the oxygen yield is studied. The maximal yields are 72, 53, and 78 % over Fe-, Mn- and Co-containing catalysts, respectively, and turnover numbers are 7.8; 54 and 360, respectively. The Cu-containing catalyst is poorly effective to the water oxidation (the maximal yield is 28 % O2 ). The synthesized catalysts are of interest for stopped-flow kinetic studies of the mechanism of the water oxidation and as precursors for anchoring nanosized hydroxides onto various supports in order to develop biomimetic systems for artificial photosynthesis.

A quadruple-band metal–nitride nanowire artificial photosynthesis system for high efficiency photocatalytic overall solar water splitting

First demonstration of a quadruple-band InGaN nanowire photocatalyst for overall water splitting with an STH efficiency >5%.

Principles and Advances in Supramolecular Catalysis

Highly efficient aqueous artificial-light-harvesting systems (ALHSs) were successfully fabricated based on the supramolecular assembly of naphthalenyl-phenylacrylonitrile derivative (NPT), water-soluble pillar [5]arene (WP5), and three kinds of pigments (4,7-di(2-thienyl)-2,1,3-benzothiadiazole (DBT), Eosin Y (ESY), and sulforhodamine-101 (SR101)). The assembled ALHSs perform a high energy-transfer-efficiency (ΦETE) and antenna effect (90.9% and 40.6 for WP5⊃NPT-DBT, 81.5% and 39.1 for WP5⊃NPT-ESY as well as 71.3% and 38.4 for WP5⊃NPT-SR101), suggesting that the energy of WP5⊃NPT complex has been effectively transferred to pigment acceptors (DBT, ESY, and SR101). Notably, during the energy-transfer process of WP5⊃NPT-SR101 ALHS, a white light emission (ΦQY = 24.21%) could be achieved by tuning the molar-ratio of [NPT]/[SR101] to 250:1, which is close to that of natural light-harvesting system, displaying a promising application in simulating natural light-harvesting system. Furthermore, the WP5⊃NPT-SR101 ALHS was successfully utilized as nanoreactors to catalyze the free-radical dehalogenation reactions of 2-bromo-acetophenone, 2-bromo-4′-methylacetophenone, and 2-bromo-4′-nitroacetophenone with the yields of 92%, 90% as well as 95%, which realized the energy transformation from solar-energy to chemical-energy, displaying a potential prospect in the field of artificial photosynthesis systems.

Theory of chemical bonds in metalloenzymes XXII: a concerted bond-switching mechanism for the oxygen–oxygen bond formation coupled with one electron transfer for water oxidation in the oxygen-evolving complex of photosystem II

ABSTRACTQM(UB3LYP)/MM(AMBER) calculations were performed for the locations of the transition structure (TS) of the oxygen–oxygen (O–O) bond formation in the S4 state of the oxygen-evolving complex (OEC) of photosystem II (PSII). The natural orbital (NO) analysis of the broken-symmetry (BS) solutions was also performed to elucidate the nature of the chemical bonds at TS on the basis of several chemical indices defined by the occupation numbers of NO. The computational results revealed a concerted bond switching (CBS) mechanism for the oxygen–oxygen bond formation coupled with the one-electron transfer (OET) for water oxidation in OEC of PSII. The orbital interaction between the σ-HOMO of the Mn(IV)4–O(5) bond and the π*-LUMO of the Mn(V)1=O(6) bond plays an important role for the concerted O–O bond formation for water oxidation in the CaMn4O6 cluster of OEC of PSII. One electron transfer (OET) from the π-HOMO of the Mn(V)1=O(6) bond to the σ*-LUMO of the Mn(IV)4–O(5) bond occurs for the formation of electron transfer diradical, where the generated anion radical [Mn(IV)4–O(5)]-• part is relaxed to the •Mn(III)4 … O(5)- structure and the cation radical [O(6)=Mn(V)1]+ • part is relaxed to the +O(6)–Mn(IV)1• structure because of the charge-spin separation for the electron-and hole-doped Mn–oxo bonds. Therefore, the local spins are responsible for the one-electron reductions of Mn(IV)4->Mn(III)4 and Mn(V)1->Mn(IV)1. On the other hand, the O(5)- and O(6)+ sites generated undergo the O–O bond formation in the CaMn4O6 cluster. The Ca(II) ion in the cubane- skeleton of the CaMn4O6 cluster assists the above orbital interactions by the lowering of the orbital energy levels of π*-LUMO of Mn(V)1=O(6) and σ*-LUMO of Mn(IV)4–O(5), indicating an important role of its Lewis acidity. Present CBS mechanism for the O–O bond formation coupled with one electron reductions of the high-valent Mn ions is different from the conventional radical coupling (RC) and acid-base (AB) mechanisms for water oxidation in artificial and native photosynthesis systems. The proton-coupled electron transfer (PC-OET) mechanism for the O–O bond formation is also touched in relation to the CBS-OET mechanism.

Encapsulation of Organic Dyes within an Electron‐Deficient Redox Metal‐Organic Tetrahedron for Photocatalytic Proton Reduction

AbstractThe design of artificial systems that mimic highly evolved and finely tuned natural photosynthetic systems is a subject of intensive research. By incorporating electron‐deficient anthraquinone within the ligand backbone, a redox‐active Ni‐based tetrahedron was developed as a redox vehicle for the construction of an artificial photosynthesis system. The tetrahedron can encapsulate fluorescein within its cavity for light‐driven H2 evolution, with the turnover number reaching 1200 moles H2 per mole redox catalyst. This well‐designed supramolecular system displayed a significantly superior activities compared with the reference mononuclear compound or introducing an inactive inhibitor (ATP), which confirmed this enzymatic photocatalytic behaviour.

Highly Improved Solar Energy Harvesting for Fuel Production from CO2 by a Newly Designed Graphene Film Photocatalyst

Our growing energy demands must be met by a sustainable supply with reduced carbon intensity. One of the most exciting prospects to realize this goal is the photocatalyst-biocatalyst integrated artificial photosynthesis system which affords solar fuel/chemicals in high selectivity from CO2. Graphene based photocatalysts are highly suitable for the system, but their industrial scale use requires immobilization for improved separation and recovery of the photocatalyst. Therefore for practical purposes, design and fabrication of film type graphene photocatalyst with higher solar energy conversion efficiency is an absolute necessity. As a means to achieve this, we report herein the successful development of a new type of flexible graphene film photocatalyst that leads to >225% rise in visible light harvesting efficiency of the resultant photocatalyst-biocatalyst integrated artificial photosynthesis system for highly selective solar fuel production from CO2 compared to conventional spin coated graphene film photocatalyst. It is an important step towards the design of a new pool of graphene film based photocatalysts for artificial photosynthesis of solar fuels from CO2.

Structural Variations in Chlorosomes from Wild-Type and a bchQR Mutant of Chlorobaculum tepidum Revealed by Single-Molecule Spectroscopy.

Green sulfur bacteria can grow photosynthetically by absorbing only a few photons per bacteriochlorophyll molecule per day. They contain chlorosomes, perhaps the most efficient light-harvesting antenna system found in photosynthetic organisms. Chlorosomes contain supramolecular structures comprising hundreds of thousands of bacteriochlorophyll molecules, which are properly positioned with respect to one another solely by self-assembly and not by using a protein scaffold as a template for directing the mutual arrangement of the monomers. These two features-high efficiency and self-assembly-have attracted considerable attention for developing light-harvesting systems for artificial photosynthesis. However, reflecting the heterogeneity of the natural system, detailed structural information at atomic resolution of the molecular aggregates is not yet available. Here, we compare the results for chlorosomes from the wild type and two mutants of Chlorobaculum tepidum obtained by polarization-resolved, single-particle fluorescence-excitation spectroscopy and theoretical modeling with results previously obtained from nuclear-magnetic resonance spectroscopy and cryo-electron microscopy. Only the combination of information obtained from all of these techniques allows for an unambiguous description of the molecular packing of bacteriochlorophylls within chlorosomes. In contrast to some suggestions in the literature, we find that, for the chlorosomes from the wild type as well as for those from mutants, the dominant secondary structural element features tubular symmetry following a very similar construction principle. Moreover, the results suggest that the various options for methylation of the bacteriochlorophyll molecules, which are a primary source of the structural (and spectral) heterogeneity of wild-type chlorosome samples, are exploited by nature to achieve improved spectral coverage at the level of individual chlorosomes.

A photochemical diode artificial photosynthesis system for unassisted high efficiency overall pure water splitting

The conversion of solar energy into chemical fuels can potentially address many of the energy and environment related challenges we face today. In this study, we have demonstrated a photochemical diode artificial photosynthesis system that can enable efficient, unassisted overall pure water splitting without using any sacrificial reagent. By precisely controlling charge carrier flow at the nanoscale, the wafer-level photochemical diode arrays exhibited solar-to-hydrogen efficiency ~3.3% in neutral (pH ~ 7.0) overall water splitting reaction. In part of the visible spectrum (400–485 nm), the energy conversion efficiency and apparent quantum yield reaches ~8.75% and ~20%, respectively, which are the highest values ever reported for one-step visible-light driven photocatalytic overall pure water splitting. The effective manipulation and control of charge carrier flow in nanostructured photocatalysts provides critical insight in achieving high efficiency artificial photosynthesis, including the efficient and selective reduction of CO2 to hydrocarbon fuels.

Charge Transport and Stability of a Semiconductor-Solution Interface Under Electrical Bias from First Principles

Solar energy is the most abundant energy source available to humankind; this energy cannot be harnessed on demand, however, due to the variability of sunlight. Artificial photosynthesis offers a sustainable way to overcome that variability through the photocatalytic conversion of solar power into chemical fuels at a semiconductor–electrolyte interface. Although considerable progress has been made in simulating the bulk properties of semiconductors from first principles, much less has been done to address the electrochemical response of semiconductor–electrolyte interfaces under realistic environmental conditions. We present broadly applicable and highly transferable computational techniques to simulate semiconductor–electrolyte interfaces. By introducing a continuum model of the semiconductor and electrolyte regions surrounding the quantum-mechanical interfacial layer, our model enables the self-consistent determination of the electrical response of a semiconductor-solution interface, including the atomistic effects of charge trapping at interfacial surface states. Using this, we develop a new description of the semiconductor-solution interface allowing us to predict the electrical response, stability, and equilibrium Schottky barrier of a photoelectrode as a function of different surface chemistries. This allows researchers to optimize materials selection for both charge transport and stability, leading to more efficient and practical artificial photosynthesis systems. Reference: Campbell and Dabo, Physical Review B 95, 205308 (2017).

Transition-Metal Single Atom Catalysts for Highly Efficient Artificial Photosynthesis

Utilizing solar energy to fix CO2 with water into chemical fuels and oxygen, a mimic process of photosynthesis in nature, is becoming increasingly important but still challenged by low selectivity and activity, especially in CO2 electrocatalytic reduction. Here, we report transition-metal atoms coordinated in a graphene shell as active centers for aqueous CO2 reduction to CO with high Faradaic efficiencies over 90% under significant currents up to ∼60 mA/mg 1 or a CO evolution rate of 3.81 mmol/h.2 We employed three-dimensional atom probe tomography to directly identify the single Ni atomic sites in graphene vacancies. Theoretical simulations suggest that compared with metallic Ni, the Ni atomic sites present different electronic structures that facilitate CO2-to-CO conversion and suppress the competing hydrogen evolution reaction dramatically. Coupled with Li+-tuned Co3O4 oxygen evolution catalyst and powered by a triple-junction solar cell, our artificial photosynthesis system achieves a peak solar-to-CO efficiency of 12.7% by using earth-abundant transition-metal electrocatalysts in a pH-equal system. References (1) Jiang, K.; Siahrostami, S.; Akey, A.J.; Li, Y.; Lu, Z.; Lattimer, J; Hu, Y.; Stokes, C.; Gangishetty, M.; Chen, G.; Zhou, Y.; Hill, W.; Cai, W.B.; Bell, D.C.; Chan, K.; Nørskov, J.K.; Cui, Y.; Wang, H. Chem 2017 https://doi.org/10.1016/j.chempr.2017.09.014. (2) Jiang, K.; Siahrostami, S.; Zheng, T.; Hu, Y.; Hwang, S.; Stavitski, E.; Peng, Y; Dynes, J.; Gangishetty, M.; Su, D.; Attenkofer, K.; Wang, H. submitted.

Metal‐Free Artificial Photosynthesis of Carbon Monoxide Using N‐Doped ZnTe Nanorod Photocathode Decorated with N‐Doped Carbon Electrocatalyst Layer

AbstractAn artificial photosynthesis system based on N‐doped ZnTe nanorods decorated with an N‐doped carbon electrocatalyst layer is fabricated via an all‐solution process for the selective conversion of CO2 to CO. Substitutional N‐doping into the ZnTe lattice decreases the bandgap slightly and improves the charge transfer characteristics, leading to enhanced photoelectrochemical activity. Remarkable N‐doping effects are also demonstrated by the N‐doped carbon layer that promotes selective CO2‐to‐CO conversion instead of undesired water‐to‐H2 reduction by providing active sites for CO2 adsorption and activation, even in the absence of metallic redox centers. The photocathode shows promising performance in photocurrent generation (−1.21 mA cm−2 at −0.11 VRHE), CO selectivity (dominant CO production of ≈72%), minor H2 reduction (≈20%), and stability (corrosion suppression). The metal‐free electrocatalyst/photocatalyst combination prepared via a cost‐effective solution process exhibits high performance due to synergistic effects between them, and thus may find application in practical solar fuel production.

Challenging the [Ru(bpy)3]2+ Photosensitizer with a Triazatriangulenium Robust Organic Dye for Visible-Light-Driven Hydrogen Production in Water

Photosensitizers used in homogeneous photocatalytic systems for artificial photosynthesis, such as hydrogen production, are typically based on expensive transition metal complexes such as d6 ruthenium(II) or iridium(III). In this work, we demonstrate efficient H2 production in acidic water by using an organic dye derived from the triazatriangulenium (TATA+) family as a visible-light-absorbing photosensitizer (PS). By associating the hydrosoluble tris(ethoxyethanol)triazatriangulenium with an efficient H2-evolving cobalt catalyst and ascorbic acid as sacrificial electron donor (SD), remarkable photocatalytic performances were reached in aqueous solution at pH 4.5, under visible-light irradiation, with up to 8950 catalytic cycles versus catalyst. The performances of this dye largely exceed those of the benchmark Ru tris-bipyridine in the same experimental conditions when low concentrations of catalyst are used. This higher efficiency has been clearly ascribed to the remarkable robustness of the reduced form...

Photocatalytic water oxidation over BiVO4 with interface energetics engineered by Co and Ni-metallated dicyanamides

Photocatalytic water oxidation based on semiconductors usually suffers from poor charge transfer from the bulk to the interface, which is necessary for oxygen generation. Here, we construct a hybrid artificial photosynthesis system for photocatalytic water oxidation. The system consists of BiVO4 as the light harvester, a transitional metal complex (M(dca)2, M = Co, Ni, dca: dicyanamide) as the water oxidation catalyst, and S2O82− as a sacrificial electron acceptor. The system exhibits enhanced oxygen evolution activity when M(dca)2 is introduced. The BiVO4/Co(dca)2 and BiVO4/Ni(dca)2 systems exhibit excellent oxygen evolution rates of 508.1 and 297.7 μmol/(h·g) compared to the pure BiVO4 which shows a photocatalytic oxygen evolution rate of 252.2 μmol/(h·g) during 6 h of photocatalytic reaction. Co(dca)2 is found to be more effective than Ni(dca)2 as a water oxidation catalyst. The enhanced photocatalytic performance is ascribed to the M(dca)2-engineered BiVO4/electrolyte interface energetics, and to the M(dca)2-catalyzed surface water oxidation. These two factors lead to a decrease in the energy barrier for hole transfer from the bulk to the surface of BiVO4, which promotes the water oxidation kinetics.

Graphene Oxide and Polyelectrolyte Composed One-Way Expressway for Guiding Electron Transfer of Integrated Artificial Photosynthesis

A novel photocatalyst/biocatalyst integrated artificial photosynthesis system (APS) based on polyurethane hollow nanofibers doped with graphene oxide (GO) and poly(allylamine hydrochloride) (PAH) was developed and employed for selective methanol conversion from CO2. The biocatalysts, including formate, formaldehyde, and alcohol dehydrogenases, as well as NAD+, were in situ coencapsulated inside the lumen of the GO-PAH-doped PU nanofibers (G-Fiber) by simply predissolving them in the core-phase solution for coaxial electrospinning, while the precise assembling of the photocatalyst parts involving visible light active photosensitizer (PS) and electron mediator (M) on the surface of the G-Fiber was realized by their π–π interactions with the GO doped in the shell of fibers. By using this highly integrated APS, about 10-times higher methanol yield was accomplished as compared with the solution-based system. The significantly enhanced reaction efficiency of the G-Fiber-based APS is considered predominately due...

Mimicking the Key Functions of Photosystem II in Artificial Photosynthesis for Photoelectrocatalytic Water Splitting.

It has been anticipated that learning from nature photosynthesis is a rational and effective way to develop artificial photosynthesis system, but it is still a great challenge. Here, we assembled a photoelectrocatalytic system by mimicking the functions of photosystem II (PSII) with BiVO4 semiconductor as a light harvester protected by a layered double hydroxide (NiFeLDH) as a hole storage layer, a partially oxidized graphene (pGO) as biomimetic tyrosine for charge transfer, and molecular Co cubane as oxygen evolution complex. The integrated system exhibited an unprecedentedly low onset potential (0.17 V) and a high photocurrent (4.45 mA cm-2), with a 2.0% solar to hydrogen efficiency. Spectroscopic studies revealed that this photoelectrocatalytic system exhibited superiority in charge separation and transfer by benefiting from mimicking the key functions of PSII. The success of the biomimetic strategy opened up new ways for the rational design and assembly of artificial photosynthesis systems for efficient solar-to-fuel conversion.

Review on optofluidic microreactors for artificial photosynthesis.

Artificial photosynthesis (APS) mimics natural photosynthesis (NPS) to store solar energy in chemical compounds for applications such as water splitting, CO2 fixation and coenzyme regeneration. NPS is naturally an optofluidic system since the cells (typical size 10 to 100 µm) of green plants, algae, and cyanobacteria enable light capture, biochemical and enzymatic reactions and the related material transport in a microscale, aqueous environment. The long history of evolution has equipped NPS with the remarkable merits of a large surface-area-to-volume ratio, fast small molecule diffusion and precise control of mass transfer. APS is expected to share many of the same advantages of NPS and could even provide more functionality if optofluidic technology is introduced. Recently, many studies have reported on optofluidic APS systems, but there is still a lack of an in-depth review. This article will start with a brief introduction of the physical mechanisms and will then review recent progresses in water splitting, CO2 fixation and coenzyme regeneration in optofluidic APS systems, followed by discussions on pending problems for real applications.

Applications of Synthetic Biology in Materials Science

Materials are the basis for human being survival and social development. To keep abreast with the increasing needs from all aspects of human society, there are huge needs in the development of advanced materials as well as high-efficiency but low-cost manufacturing strategies that are both sustainable and tunable. Synthetic biology, a new engineering principle taking gene regulation and engineering design as the core, greatly promotes the development of life sciences. This discipline has also contributed to the development of material sciences and will continuously bring new ideas to future new material design. In this paper, we review recent advances in applications of synthetic biology in material sciences, with the focus on how synthetic biology could enable synthesis of new polymeric biomaterials and inorganic materials, phage display and directed evolution of proteins relevant to materials development, living functional materials, engineered bacteria-regulated artificial photosynthesis system as well as applications of gene circuits for material sciences.