Chemical Storage Of Solar Energy Research Articles

Chlorophyll(a)/Carbon Quantum Dot Bio-Nanocomposite Activated Nano-Structured Silicon as an Efficient Photocathode for Photoelectrochemical Water Splitting.

Solar-driven water splitting is considered as a futuristic sustainable way to generate hydrogen and chemical storage of solar energy. Further, considering the technological competence, silicon is one of the potential materials for developing large-scale and cost-effective photocathodes (PCs), but it lacks efficacy and stability. Here, we show that chlorophyll(a)/carbon quantum dots (Chl/CQDs) bio-nanocomposite (b-NC)-decorated Si-nanowires (SiNWs) as PC can surpass the reported efficiency for photoelectrochemical (PEC) hydrogen generation along with stability. The optimized heterojunction (Chl/CQDs_SiNW) significantly enhances broad-band solar absorption and protects Si surface from corrosion. Further, the appropriate band alignment enforces efficient photogenerated charge separation and possesses directional exciton transport property via the Förster resonance energy transfer (FRET) mechanism. This synergic effect demonstrates an ∼18 times increase in photocurrent density (26.36 mA/cm2) compared to pristine SiNW PC at 1.07 V vs reversible hydrogen electrode (RHE). The efficiency reaches ∼7.86%, which is comparably the highest reported for hybrid Si-based photocathodes. Hydrogen evaluation rate was measured to be ∼113 μmol/h at 0.8 V vs RHE under 1 sun illumination. With Si-process line compatibility, this new finding opens a new direction toward the development of Si-based efficient and stable PCs at a large scale for commercial applications.

Understanding Charge Transport in Carbon Nitride for Enhanced Photocatalytic Solar Fuel Production.

Photocatalytic solar fuel production, for example, production of hydrogen via water-splitting, is an effective means of chemical storage of solar energy and provides a potential option for achieving a zero-emissions energy system. Conveniently, hydrogen can be converted back to electricity either via fuel cells or through combustion in gas turbines, or it can be mixed in low concentrations with natural gas or biogas for combustion in existing power plants. The cornerstone of a practical solar fuel production process is a stable, efficient, and scalable photocatalyst (a semiconductor material that accommodates photon absorption, charge carrier generation and transport, and catalytic reactions). Therefore, the quest for suitable photocatalyst materials is an ongoing process. Recently, carbon nitride (CN) has attracted widespread interest as a metal-free, earth-abundant, and highly stable photocatalyst. However, the catalytic efficiency of CN is not satisfactory because of its poor charge transport attributes. There is a direct relation between the photocatalytic efficiency and charge transport because the basic principle of light-promoted overall photodecomposition of water into H2 and O2 molecules (or, generally speaking, photoredox reactions) relies on separation and subsequent transfer of excited-state electron-hole pairs to relative redox couples. However, the excited states last for a very short time, typically nanoseconds to microseconds in liquids, and unless they are separated within this time frame, the excited-state electron-hole pairs undergo recombination with release of the captured light energy as heat or photon emission. To utilize light in a form other than heat or emitted photons by avoiding the recombination of excited-state electron-hole pairs, charged excitons must be scavenged before the absorption of subsequent photons to sustain a multielectron photoredox reaction. Otherwise, the extraction of charges becomes more difficult. This imposes a potential efficiency-limiting factor. An enhancement in water to hydrogen conversion efficiency in CN therefore requires the use of precious-metal cocatalysts (e.g., Pt) and sacrificial electron donor/acceptors to facilitate multielectron/multiproton transfers to overcome the high kinetic barriers. The use of Pt and sacrificial agents is not consistent with the notion of low-cost and sustainable hydrogen production from water. CN must overcome this dependence to stand out as a truly scalable photocatalyst. To make progress, the foremost requirement is to attain an in-depth understanding of the fundamental charge transport phenomena needed for the rational design of CN-based photocatalysts. In this Account, therefore, our aim is to provide a synopsis of current understanding and progress regarding charge-transport-related phenomena (e.g., recombination, trapping, transfer of charge carriers, etc.) and to discuss the effects of charge transport in enhancing the apparent quantum yield of hydrogen production in CN. This understanding is necessary to broaden the scope of CN for other catalytic applications, for example, efficient CO2 reduction to methanol or methane, fixation of nitrogen to ammonia, and use as an active material in solar cells. We also identify research gaps and issues to be addressed for a more clear elucidation of charge-transport-related phenomena in CN. Thus, this Account may inspire new research opportunities for tuning the extrinsic/intrinsic photophysicochemical properties of CN by rational design to attain the most favorable properties for improved catalytic efficiency.

Morphology regulation and surface modification of hematite nanorods by aging in phosphate solutions for efficient PEC water splitting

Solar hydrogen production via photoelectrochemical water splitting using hematite thin films is a promising approach for the chemical storage of solar energy. Nanorod structured hematite photoanodes provide a direct path for electron collection and hole transport, which have been attracting growing interest. In this study, efficient hematite thin films were synthesized though dissolution and recrystallization of FeOOH nanorods in phosphate solutions. It is found that the morphology and surface characteristic, and PEC photoelectrochemical properties of the hematite films are strongly affected by the aging conditions. The phosphate (NaH2PO4) mediated hematite film exhibits 2.1 times higher photocurrent density than that of bare α-Fe2O3. The influences of phosphate solutions including Na3PO4, Na2HPO4 and NaH2PO4, pH values, and aging time on the morphology regulation, isoelectric point, and PEC photoelectrochemical properties of the hematite films are investigated.

State of the art on reactor designs for solar gasification of carbonaceous feedstock

The association of concentrated solar energy and biomass gasification has often been suggested as an interesting alternative to conventional autothermal processes where a significant portion of the biomass has to be used for heat generation to drive endothermic reactions. It is a clean process able to produce high quality synthesis gas with a higher output per unit of feedstock and that allows for the chemical storage of solar energy in the form of a readily transportable fuel, among other advantages. The present paper describes the latest advances in solar thermochemical reactors for gasification of carbonaceous feedstocks. This work is categorized in this paper into patents and research/journal papers.

Photoelectrochemical Water Splitting with Mesoporous Hematite Prepared by a Solution-Based Colloidal Approach

Sustainable hydrogen production through photoelectrochemical water splitting using hematite (alpha-Fe(2)O(3)) is a promising approach for the chemical storage of solar energy, but is complicated by the material's nonoptimal optoelectronic properties. Nanostructuring approaches have been shown to increase the performance of hematite, but the ideal nanostructure giving high efficiencies for all absorbed light wavelengths remains elusive. Here, we report for the first time mesoporous hematite photoelectodes prepared by a solution-based colloidal method which yield water-splitting photocurrents of 0.56 mA cm(-2) under standard conditions (AM 1.5G 100 mW cm(-2), 1.23 V vs reversible hydrogen electrode, RHE) and over 1.0 mA cm(-2) before the dark current onset (1.55 V vs RHE). The sintering temperature is found to increase the average particle size, and have a drastic effect on the photoactivity. X-ray photoelectron spectroscopy and magnetic measurements using a SQUID magnetometer link this effect to the diffusion and incorporation of dopant atoms from the transparent conducting substrate. In addition, examining the optical properties of the films reveals a considerable change in the absorption coefficient and onset properties, critical aspects for hematite as a solar energy converter, as a function of the sintering temperature. A detailed investigation into hematite's crystal structure using powder X-ray diffraction with Rietveld refinement to account for these effects correlates an increase in a C(3v)-type crystal lattice distortion to the improved optical properties.

Methane reforming with CO 2 in molten salt using FeO catalyst

Methane dry reforming with CO 2 using FeO powder in molten salt has been investigated at various flow rates of CH 4/CO 2 mixed gases (CH 4/CO 2=1) between 50 and 400 ml/min at 1223 K in an infrared furnace. This work is carried out to determine the usefulness of this method for the chemical storage of solar energy. The CH 4/CO 2 mixed gases passing through the molten salt (Na 2CO 3/K 2CO 3=1) containing the FeO powder were catalytically decomposed into CO, H 2 and H 2O. The product gas mole ratios, CO/H 2/H 2O, were shown to be 3:1:1 for a high flow rate of 200 ml/min and to be CO/H 2=2:1 for a low flow rate of 50 ml/min. The results were explained in terms of the kinetics of the CH 4-reforming reaction and the thermodynamics of the redox process of FeO powder mixed in the molten salt; CH 4+2FeO⇒2Fe+H 2+CO+H 2O Fe+CO 2⇒FeO+CO for a high flow rate, and FeO+CH 4⇒Fe+2H 2+CO Fe+CO 2⇒FeO+CO for a low flow rate.

Light-induced hydrogen production using waste compounds as sacrifical electron donors

Systems for the conversion and chemical storage of solar energy are usually based on photo-induced electron transfer reactions from an excited sensitizer to an electron acceptor (i.e. an electron relay compound). We have investigated the photo- and electrochemical properties of two novel electron relay compounds: l,l″,r″′-trimethyl[4,2′; 4′,4″; 6′,4″′]quaterpyridinium trichloride (1) and 1,1′,1″,1″′-tetramethyl[4,2′; 4′,4′’; 6′,4″] quaterpyridinium tetrachloride (2). When solutions containing Ru(bpy)3Cl2 or Zn-porphyrin (as photosensitizer), compound1 or2 and EDTA (as sacrificial electron donor) are irradiated by visible light (λ > 400 nm), only the formation of reduced relay compound 1 occurs. Addition of platinum catalyst to such solutions with compound 1 leads to the formation of hydrogen. Quantum yields are in the range of 5%, calculated for absorbed light. Using other sacrificial electron donors such as alcohols or glucose (or waste compounds like 4-chlorophenol) did not result in hydrogen evolution. However,1 and2 are reduced by these sacrificial electron donors in the absence of an additional photosensitizer, when near UV irradiation light (λ > 280 nm) is used. Quantum yields for hydrogen production with compound1 are about 2%, calculated for absorbed light out of GC-measurements from H2 in the gas phase above the irradiated solution. The photo- and electrochemical properties of compounds1 and2 are discussed.

Computer modelling of solar gasification of oil shale; comparison with experiments

A detailed computer model that incorporates the principal optical and thermal parameters of the system used in the gasification of oil shale by concentrated solar flux has been developed. The results of the calculations agree reasonably well with the experimental data. This model can serve as a powerful predictive tool in the optimal design of solar-driven endothermic reactions for chemical storage of solar energy and for increasing the energy content of carbonaceous materials.

UV/VIS/IR-induced heterogenous processes of transition metal carbonates and transition metal oxides

Mechanism and energetics of heterogenous solid state processes of relevance for the chemical storage of solar energy have been investigated by means of a recently developed experimental set-up consisting of the combination of a UV/VIS light source with a thermobalance as well as by means of X-ray diffraction and electron microscopic techniques. As model reactions for these studies, the decomposition of siderite, FeCO 3, as well as reversible reduction/reoxidation processes in the systems FeO x/Fe 0 and RuO 2/Ru 0 are presented.

Application of quantum chemical methods to problems of chemical storage of solar energy: The dissociation of LiH and LiB

Quantum chemical calculations on the dissociation of LiH and LiB in the gas phase under the influence of highly concentrated solar radiation and high temperature are presented. These two molecules possess low lying excited electronic states. Thermochemical and photochemical contributions to the reaction rate are compared. With these two examples we would like to introduce some methods of quantum chemistry to the field of chemical conversion and storage of solar energy and illustrate how the mechanism and rate of a reaction can depend on molecular structure on the hand and on temperature and radiation intensity on the other hand.

Light-assisted transport of nitric oxide across membranes containing nitrosyl chloride solutions

Experimental evidence for the light-assisted concentration of nitric oxide taking part in a reversible photochemical reaction in a solution is presented. For the system, nitrosyl chloride-nitric oxide, a gradient of light energy across the membrane sandwich containing nitrosyl chloride solution results in a gradient of nitric oxide concentration across the membrane. For the experimental conditions employed, nitric oxide concentration ratios of up to 15 were obtained. The experimental results are explained using an “equilibrium-facilitation” model. The photodiffusion membrane configuration of the kind discussed can be used for the chemical storage of solar energy

Chemical storage of solar energy: hydrogen generation by visible light with Cr(Ox) 33H 2O −3 containing ferrous sulphate in acidic solution

Hydrogen gas is generated continuously by visible light irradiation of aqueous H 2SO 4 solution at pH 2–4 containing (5 × 10 −3M) K 3Cr(Ox) 3 · 3H 2O and (10 −2 M) FeSO 4. The rate of formation of hydrogen has been recorded. Hydrogen is about 21% of the total gases evolved. The reaction is markedly pH dependent. The chromium is the photoactive species and the chromium or the iron forms the storage system for electrons and protons. It appears that the generation of hydrogen is taking place by indirect photodecomposition of water. Hydrogen was generated when Fe(CN) 6 −4 was substituted for FeSO 4. Control experiments have been performed and the mechanism and proposed cycle for the processes are discussed.

Thermodynamique de composes azotes. VIII. Etude thermochimique de la diethanolamine et de la triethanolamine et de la reaction de reduction de l'eau par celle-cl

The enthalpies of combustion of diethanolamine (DEA) and triethanolamine (TEA) in the condensed state were determined by means of a rotary bomb isoperibol calorimeter. We found: DEA: Δ H o c(c.298.15 K)=-2652.3±2.5 kJ mole −1 TEA: Δ H o c(c.298.15 K)=-3840.6±1.5 kJ mole −1 The enthalpies of sublimation or vaporization of these two substances were obtained by calorimetry. We found: DEA: Δ H o sub(298.15 K)=96.7±1.2 kJ mole −1 TEA: Δ H o vap(298.15 K)=105.9±2.2 kJ mole −1 The experimental enthalpy of atomization for these two molecules is in excellent agreement with the calculated value derived from the energetical contributions. previously obtained in the laboratory. In another connection the enthalpy of reduction reaction of water by triethanolamine could be determined. It is endothermic, which allows it to be considered among the reactions which could possibly be used for chemical storage of solar energy.

Chemical Storage of Solar Energy and Photochemical Fuel Formation

AbstractRecent advances in the quantum utilization of solar energy will be surveyed. The efficiency of photovoltaic devices in combination with electrical storage will be compared with photogalvanic and photochemical systems. Photochemical formation of fuel (including hydrogen) in homogeneous and heterogeneous devices will be discussed in detail.

Industrial applications of photochemistry

Abstract