Light Energy Storage Research Articles

Ultrafast internal conversion in a low band gap polymer for photovoltaics: experimental and theoretical study

Ultrafast dynamics upon photoexcitation in a low band gap polymer for photovoltaics is investigated both experimentally and theoretically. Our work sheds light on the excess energy relaxation processes occurring immediately after photon absorption and responsible for dissipation in the photovoltaic process of light harvesting and energy storage. A peculiar non-adiabatic decay path through a conical intersection (CI) between the higher excited state S(2) and the first singlet state S(1) is identified by ultrafast spectroscopy and theoretical calculations. Ultrafast twisting of the initially flat conformation in S(2) drives the system to the CI connecting the two potential energy surfaces, actually eliciting an internal conversion within 60 femtoseconds, followed by planarization along the adiabatic surface in S(1). Relaxed potential energy profiles (PEPs) of ground and lowest excited states along a dihedral coordinate, calculated within the time dependent density functional theory (TDDFT) approach, support the S(2)/S(1) CI mechanism. Furthermore a screening of the widely used hybrid and range separated exchange-correlation (XC) DFT functionals has been carried out finding different descriptions of S(2)/S(1) PEPs and good agreement between experimental data and long-range corrected DFT.

Bacterial Chimeras and Reversible Phosphorylation: The Work of Walther Stoeckenius

In 1971, Walther Stoeckenius discovered that Halobacterium halobium contains a purple pigment that is chemically similar to rhodopsin and works as a light-driven proton pump. This discovery set Stoeckenius on a research path centered on bacteriorhodopsin, which included the creation of a bovine-soybean-halobacteria chimera that was able to produce ATP when exposed to light and the discovery of a class of proteins that are phosphorylated in a light-dependent manner.

Single-Molecule-Resolved Structural Changes Induced by Temperature and Light in Surface-Bound Organometallic Molecules Designed for Energy Storage

We have used scanning tunneling microscopy, Auger electron spectroscopy, and density functional theory calculations to investigate thermal and photoinduced structural transitions in (fulvalene)tetracarbonyldiruthenium molecules (designed for light energy storage) on a Au(111) surface. We find that both the parent complex and the photoisomer exhibit striking thermally induced structural phase changes on Au(111), which we attribute to the loss of carbonyl ligands from the organometallic molecules. Density functional theory calculations support this conclusion. We observe that UV exposure leads to pronounced structural change only in the parent complex, indicative of a photoisomerization reaction.

Influence of carbon nanotubes on chlorophyll fluorescence parameters of green algae Chlamydomonas reinhardtii

It has been shown that carbon nanotubes are capable of decreasing the development speed of Chlamydomonas reinhardtii algae culture and significantly changing the parameters of chlorophyll fluorescence that characterize the prime processes of light energy storage throughout photosynthesis. The quantum yield reduction of photochemical light energy transformation during photosynthesis and the relative speed of noncycle electron transfer calculated using the fluorescence parameters have been observed. The inhibition of the electrochemical proton gradient involved in ATP synthesis has been determined using delayed fluorescence. A conclusion on the prospects of implementing highly sensitive fluorescent methods for evaluating the toxic effect of modern nonmaterials on water objects is made.

Solar fuels: thermodynamics, candidates, tactics, and figures of merit

Inorganic chemistry has been and continues to be a central discipline in the field of renewable energy and solar fuels. A fundamental approach to storing solar energy is artificial photosynthesis, whereby uphill chemical reactions are driven by light, e.g. the water gas shift reaction, halogen acid splitting, or water splitting. This article endeavors to define a common context for these research topics, particularly by analyzing the thermodynamic boundaries of photosynthesis. Specifically, the generalized efficiency restrictions on both light absorption and energy storage are expounded, the analogous limitations for several individual photosynthetic strategies are stated, several synthetic catalyst architectures are highlighted, the advantages of molecular and macroscopic approaches are discussed, and key figures of merit are presented.

Molecules: Nanotech powers up paper battery: New technology would offer easy, light energy storage

Molecules: Nanotech powers up paper battery: New technology would offer easy, light energy storage

Light energy storage and photoelectrochemical behavior of the titanate nanotube array/Ni(OH) 2 electrode

A new kind of TiO 2 nanotube array/Ni(OH) 2 (TiO 2/Ni(OH) 2) composite electrode with the storage ability of light energy was prepared by the deposition of Ni(OH) 2 on the TiO 2 nanotube array, which was synthesized by anodizing Ti foils in an HF aqueous solution. SEM and XRD results showed that Ni(OH) 2 particles were well distributed on high density, well-ordered and uniform TiO 2 nanotube arrays. The photoelectrochemical properties of the TiO 2/Ni(OH) 2 electrode were investigated in NaHCO 3/NaOH buffer solution (pH 10) by means of UV–vis absorption spectra, cyclic voltammogram (CV) and photocurrent measurements. It was found that the TiO 2/Ni(OH) 2 electrode was highly sensitive to light and exhibited excellent photoelectrochromic properties. Upon UV irradiation, the photogenerated holes by TiO 2 nanotube arrays can oxidize Ni(OH) 2 to NiOOH, and thus the TiO 2/Ni(OH) 2 electrode can be photo-charged by light.

Photo-chargeable titanium/vanadium oxide composites

Titanium and vanadium oxides were prepared by a sol–gel technique and supercritical drying and evaluated for light energy conversion and storage in a wet-type photoelectrochemical cell. Ultraviolet light irradiation to the nanocrystalline titania aerogel (anatase) produced significant photocurrents, and the maximum incident photon-to-current conversion efficiency (IPCE) attained 37.1%. From cyclic voltammetry, the vanadium oxide gel was shown capacitive for charge storage, associated with the shcherbinaite structure and V4+/V5+ redox pair. Photopotential responses revealed that coupled TiO2/V2O5 composites not only were photo-chargeable but also exhibited a greater discharging capacity than the TiO2 or V2O5 alone. The discharging capacity was remarkably reduced in the presence of dissolved oxygen. Results demonstrate that in the hybrid TiO2/V2O5 system the V2O5 serves to accumulate photoelectrons generated by the illuminated TiO2 during the photo-charging process. A schematic energy diagram that describes the band structure of the composite semiconductor is proposed.

Light Energy Conversion and Storage with Soft Carbonaceous Materials that Solidify Mesoscopic Electrochemical Interfaces

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Light Energy Conversion and Storage with Soft Carbonaceous Materials that Solidify Mesoscopic Electrochemical Interfaces

Abstract Photoactive interfaces created by mesoscopic materials realize high-efficiency light to electric conversion as achieved by dye-sensitized photoelectrodes. Combinaiton of soft carbon composite materials with the mesoscopic interfaces enables solidification of the electrochemical charge-transfer interfaces and incorporation of energy storage function. New approaches for solid-state photoelectrochemistry are described.

UV light energy storage and thermoluminescence in AlN ceramics

AbstractAlN ceramics, untreated and subjected to oxygen ion implantation, are studied for potential application in TL dosimetry of UV light. Based on photoluminescence and thermoluminescence measurements there are shown advantages of the selection of the 480 emission band for TL signal recording instead of the previously used 400 nm band: higher intensity of the TL signal, lower fading rate of the accumulated TL signal, excitation region (270‐340 nm) corresponding to UV‐B range, monitoring of which is actual in UV dosimetry. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Biocalorimetric monitoring of photoautotrophic batch cultures

Cultivations of photoautotrophic microorganisms show a rather distinct behavior from the cultivations of microorganisms on chemical energy. This is caused by the fact that light energy is the limiting substrate. Light supply is characterized by a constant photon flux which cannot be stored within the culture broth. In this study batch cultivations of Chlorella sorokiniana were closely followed in a bench-scale biocalorimeter (1.63 L, Ø 11.6 cm) illuminated with red light emitting diodes. Calorimetry provided the rate of light energy storage inside biomass representing chemical energy. Normalized to the total input of light energy this yielded the photosynthetic efficiency. It was highest in the beginning of the batch cultures: 14% at a cell density of less than 1 mL cells L −1. Efficiency decreased to 5.4% as cell density increased further to 5 mL cells L −1 (=2.5 g L −1). Efficiency was highest at low cell density when light penetrates far inside the reactor. Our results support previous findings that the presence of an increasing dark zone leads to reduced photosynthetic efficiency. The same trend was detected using measurements of carbon dioxide and ammonium consumption. The carbon dioxide consumption rate was used to calculate the enthalpy increase in the culture broth during photoautotrophic growth. The maximum photosynthetic efficiency calculated from the enthalpy increase was higher than the one measured directly in the biocalorimeter: 16% as opposed to 14%. This discrepancy probably is related to a combination of factors which are discussed opening up possibilities for further improvement of this technique.

Near-field gap effects on small microcavity whispering-gallery mode resonators

The near-field gap effects are investigated in planar dielectric microdisc and waveguide coupling structures, emphasizing miniaturization of integrated sensor systems. The simulation results show that the resonance frequency is not obviously affected by the gap dimension when the gap between a microcavity and its coupler is larger than 300 nm. However, the resonance frequency shifts observably with a further decreasing gap to the nanometre level. This shift is generally larger than the cavity resonance linewidth in the 10 µm diameter microdisc system, but is comparable to the cavity resonance linewidth in the 2 µm diameter microdisc system. With increasing gap, the cavity Q increases exponentially until it is saturated at a limit Q factor. An optimal gap dimension exists for maximum light energy transfer and storage. The concept of optimum gap is introduced and defined at the gap dimension where half-maximum energy storage capability is achieved; meanwhile, the cavity Q is high and the resonance frequency remains stable.

A photoacoustic method for rapid assessment of temperature effects on photosynthesis

The photosynthetic and photoacoustic properties of leaf samples were studied using a photoacoustic system modified for precise temperature control. Data were collected over a temperature range of -10 degrees C to +60 degrees C. A distinct acoustic noise transient marked the freezing temperature of the samples. A positive absorption transient and a brief period of oxygen uptake marked the thermal denaturing temperature of the samples. Between these extremes, the effects of temperature on light absorption, oxygen evolution, and photochemical energy storage were quantified quickly and easily. Oxygen evolution could be measured as low as -5 degrees C and showed a broad temperature peak that was 10 degrees C lower under limiting light intensity than under saturating light intensity. Photochemical energy storage showed a narrower temperature peak that was only slightly lower for limiting light intensities than for saturating light intensities. In a survey of diverse plants, temperature response curves for oxygen evolution were determined readily for a variety of leaf types, including ferns and conifer needles. These results demonstrate that temperature-controlled photoacoustics can be useful for rapid assessment of temperature effects on photosynthesis and other leaf properties.

Application of bench-scale biocalorimetry to photoautotrophic cultures

Bench-scale biocalorimetry (≥1 L) allows for the determination of the metabolic heat flow during bioprocesses under complete control of all process conditions for extended periods of time. It can be combined with a number of on-line and off-line measurement techniques. This combination can significantly improve insight into the metabolism of microorganisms and the optimization of bioprocesses. In this study it is demonstrated that bench-scale biocalorimetry can also be applied to phototrophic microorganisms. The green microalga Chlorella vulgaris CCAP 211/11B was cultivated in a Mettler-Toledo RC1 calorimeter adapted for high-sensitivity biological calorimetry (BioRC1). Heat production was monitored in 1.5 L batch cultures. In the linear phase of growth, inhibitors of photosynthetic electron transport (DCMU, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, and DBMIB, 2,5-dibromo-3-methyl-6-isopropyl- p-benzoquinone), were used to stop photosynthesis and to monitor the resulting increase in the energy dissipating heat flux. This resulted in a calculated storage of light energy as chemical energy, i.e. biomass, of 141 ± 12.2 mW L −1 (±S.D.). In addition, it was demonstrated that calorimetric determination of the total amount of light energy absorbed within the reactor was accurate by comparing two different calorimetric techniques. Using both the value of the total light input and the quantity stored as chemical energy, the photosynthetic efficiency could be calculated as 10.5% in this example.

The photocapacitor: An efficient self-charging capacitor for direct storage of solar energy

A light-driven self-charging capacitor was fabricated as an efficient solar energy storage device. The device, which we name the photocapacitor, achieves in situ storage of visible light energy as an electrical power at high quantum conversion efficiency. The photocapacitor was constructed on a multilayered photoelectrode comprising dye-sensitized semiconductor nanoparticles/hole-trapping layer/activated carbon particles in contact with an organic electrolyte solution, in which photogenerated charges are stored at the electric double layer. Repeated charge-discharge cycles with a charging voltage of >0.45V yielded a capacitance of 0.69Fcm−2.

Synthesis of a Pyrene-Labeled Polyanion and Its Adsorption onto Polyelectrolyte Hollow Capsules Functionalized for Electron Transfer

A multilayer system is built up that enables vectorial electron transfer along a polarity gradient. For this, pyrene is covalently coupled to a polyeclectrolyte that can then be incorporated into polyelectrolyte multilayers by layer-by-layer technology. High pyrene labeling (1:30) allows for high chromophore density in the film (1/10 nm3), which is necessary for efficient electron transfer. The photophysical properties of the covalently coupled dye do not differ much from those of the well-known free pyrene, except that the high local pyrene concentration yields considerable excimer emission. The multilayer is built in the form of the wall of hollow capsules of micrometer dimensions. This enables kinetic studies due to the high specific area and also gives perspectives for further development of the system for light harvesting and energy storage in the inside, in analogy to natural photosynthesis. Quantitative charge transfer across the capsule shell is demonstrated by means of fluorescence quenching studies.

Celebrating the Millennium: Historical Highlights of Photosynthesis Research, Part 3

This paper introduces the third and final part of the 'millennium celebrations of historical highlights of photosynthesis research.' Part 1 (308 pages) was published in October 2002 as Vol. 73 of the journal Photosynthesis Research, and Part 2 (458 pages) was published in July 2003 as Vol. 76. Here, we recognize particularly the work of three major contributors to our understanding of photosynthesis: Roger Stanier (1916-1982); Germaine Cohen-Bazire (Stanier) (1920-2001); and William Arnold (1904-2001). We also introduce the historical papers contained in this volume; consider the legacy of Alfred Nobel (1833-1896); and identify Nobel prizes of special relevance to understanding the capture, conversion, and storage of light energy in both anoxygenic and oxygenic photosynthesis.

Fracture toughness and microhardness of a composite: do they correlate?

Objectives. Chipping and bulk fracture are major contributors in clinical failures of composite restorations. Fracture toughness ( K Ic) quantifies susceptibility for fracture, but experimental determination is complicated. It would be beneficial for the dental community if a relatively simple experiment, such as microhardness (HK), could be used to screen composites for fracture resistance. This study explores a possible correlation between K Ic and HK. Methods. Composite cylinders (4 mm diameter and ∼7 mm long) were cured for five combinations of light intensity ( I, mW/cm 2) and curing time ( T, s) to achieve a range of different total light energy densities ( I× T=100×10, 100×20, 300×20, 300×40, and 700×60 mW s/cm 2). A chevron-notch was cut in the median plane of the cylinders for the fracture toughness test, which was executed in a displacement control mode at 6 μm/s cross-head speed (sample size 4). Knoop hardness was determined at the median plane of the cylinders (sample size 6). The tests were performed 15 min and 24 h after curing. Results. Both the K Ic and HK increased with increased light energy density and storage time. Linear regression analysis indicated a strong correlation between HK and K Ic tested at the same time period ( R 2=0.97 and 0.90 for 15 min and 24 h, respectively). The correlation became weaker between the different storage times ( R 2=0.71), indicating a change in fracture toughness and/or microhardness mechanisms. Conclusion. Fracture toughness of a composite cannot be simply extrapolated from microhardness.

Cyclic Electron Flow around Photosystem I in C3 Plants. In Vivo Control by the Redox State of Chloroplasts and Involvement of the NADH-Dehydrogenase Complex

Cyclic electron flow around photosystem (PS) I has been widely described in vitro in chloroplasts or thylakoids isolated from C3 plant leaves, but its occurrence in vivo is still a matter of debate. Photoacoustic spectroscopy and kinetic spectrophotometry were used to analyze cyclic PS I activity in tobacco (Nicotiana tabacum cv Petit Havana) leaf discs illuminated with far-red light. Only a very weak activity was measured in air with both techniques. When leaf discs were placed in anaerobiosis, a high and rapid cyclic PS I activity was measured. The maximal energy storage in far-red light increased to 30% to 50%, and the half-time of the P700 re-reduction in the dark decreased to around 400 ms; these values are comparable with those measured in cyanobacteria and C4 plant leaves in aerobiosis. The stimulatory effect of anaerobiosis was mimicked by infiltrating leaves with inhibitors of mitochondrial respiration or of the chlororespiratory oxidase, therefore, showing that changes in the redox state of intersystem electron carriers tightly control the rate of PS I-driven cyclic electron flow in vivo. Measurements of energy storage at different modulation frequencies of far-red light showed that anaerobiosis-induced cyclic PS I activity in leaves of a tobacco mutant deficient in the plastid Ndh complex was kinetically different from that of the wild type, the cycle being slower in the former leaves. We conclude that the Ndh complex is required for rapid electron cycling around PS I.