Ion migration has been proposed as a possible cause of photovoltaic current-voltage hysteresis in hybrid perovskite solar cells. A major objection to this hypothesis is that hysteresis can be reduced ...by changing the interfacial contact materials; however, this is unlikely to significantly influence the behaviour of mobile ionic charge within the perovskite phase. Here, we show that the primary effects of ion migration can be observed regardless of whether the contacts were changed to give devices with or without significant hysteresis. Transient optoelectronic measurements combined with device simulations indicate that electric-field screening, consistent with ion migration, is similar in both high and low hysteresis CH
NH
PbI
cells. Simulation of the photovoltage and photocurrent transients shows that hysteresis requires the combination of both mobile ionic charge and recombination near the perovskite-contact interfaces. Passivating contact recombination results in higher photogenerated charge concentrations at forward bias which screen the ionic charge, reducing hysteresis.
Buildings consume about 41.1% of primary energy and 74% of the electricity in the U.S. Better or even optimal building energy control and operation strategies provide great opportunities to reduce ...building energy consumption. Moreover, it is estimated by the National Energy Technology Laboratory that more than one-fourth of the 713GW of U.S. electricity demand in 2010 could be dispatchable if only buildings could respond to that dispatch through advanced building energy control and operation strategies and smart grid infrastructure. Energy forecasting models for building energy systems are essential to building energy control and operation. Three general categories of building energy forecasting models have been reported in the literature which include white-box (physics-based), black-box (data-driven), and gray-box (combination of physics based and data-driven) modeling approaches. This paper summarizes the existing efforts in this area as well as other critical areas related to building energy modeling, such as short-term weather forecasting. An up-to-date overview of research on application of building energy modeling methods in optimal control for single building and multiple buildings is also summarized in this paper. Different model-based and model-free optimization methods for building energy system operation are reviewed and compared in this paper. Agent based modeling, as a new modeling strategy, has made a remarkable progress in distributed energy systems control and optimization in the past years. The research literature on application of agent based model in building energy system control and operation is also identified and discussed in this paper.
Abstract
The exploration of two-dimensional solids is an active area of materials discovery. Research in this area has given us structures spanning graphene to dichalcogenides, and more recently 2D ...transition metal carbides (MXenes). One of the challenges now is to master ordering within the atomic sheets. Herein, we present a top-down, high-yield, facile route for the controlled introduction of ordered divacancies in MXenes. By designing a parent 3D atomic laminate, (Mo
2/3
Sc
1/3
)
2
AlC, with in-plane chemical ordering, and by selectively etching the Al and Sc atoms, we show evidence for 2D Mo
1.33
C sheets with ordered metal divacancies and high electrical conductivities. At ∼1,100 F cm
−3
, this 2D material exhibits a 65% higher volumetric capacitance than its counterpart, Mo
2
C, with no vacancies, and one of the highest volumetric capacitance values ever reported, to the best of our knowledge. This structural design on the atomic scale may alter and expand the concept of property-tailoring of 2D materials.
As the main component of lignocelluloses, cellulose is a biopolymer consisting of many glucose units connected through β-1,4-glycosidic bonds. Breakage of the β-1,4-glycosidic bonds by acids leads to ...the hydrolysis of cellulose polymers, resulting in the sugar molecule glucose or oligosaccharides. Mineral acids, such as HCl and H
2
SO
4
, have been used in the hydrolysis of cellulose. However, they suffer from problems of product separation, reactor corrosion, poor catalyst recyclability and the need for treatment of waste effluent. The use of heterogeneous solid acids can solve some of these problems through the ease of product separation and good catalyst recyclability. This review summarizes recent advances in the hydrolysis of cellulose by different types of solid acids, such as sulfonated carbonaceous based acids, polymer based acids and magnetic solid acids. The acid strength, acid site density, adsorption of the substance and micropores of the solid material are all key factors for effective hydrolysis processes. Methods used to promote reaction efficiency such as the pretreatment of cellulose to reduce its crystallinity and the use of ionic liquids or microwave irradiation to improve the reaction rate are also discussed.
This paper reviews the recent advances in cellulose hydrolysis into glucose over solid acids, which plays an important role in the conversion of biomass derived carbohydrates into useful platform molecules.
Studies of the optical properties and catalytic capabilities of noble metal nanoparticles (NPs), such as gold (Au) and silver (Ag), have formed the basis for the very recent fast expansion of the ...field of green photocatalysis: photocatalysis utilizing visible and ultraviolet light, a major part of the solar spectrum. The reason for this growth is the recognition that the localised surface plasmon resonance (LSPR) effect of Au NPs and Ag NPs can couple the light flux to the conduction electrons of metal NPs, and the excited electrons and enhanced electric fields in close proximity to the NPs can contribute to converting the solar energy to chemical energy by photon-driven photocatalytic reactions. Previously the LSPR effect of noble metal NPs was utilized almost exclusively to improve the performance of semiconductor photocatalysts (for example, TiO
2
and Ag halides), but recently, a conceptual breakthrough was made: studies on light driven reactions catalysed by NPs of Au or Ag on photocatalytically inactive supports (insulating solids with a very wide band gap) have demonstrated that these materials are a class of efficient photocatalysts working by mechanisms distinct from those of semiconducting photocatalysts. There are several reasons for the significant photocatalytic activity of Au and Ag NPs. (1) The conduction electrons of the particles gain the irradiation energy, resulting in high energy electrons at the NP surface which is desirable for activating molecules on the particles for chemical reactions. (2) In such a photocatalysis system, both light harvesting and the catalysing reaction take place on the nanoparticle, and so charge transfer between the NPs and support is not a prerequisite. (3) The density of the conduction electrons at the NP surface is much higher than that at the surface of any semiconductor, and these electrons can drive the reactions on the catalysts. (4) The metal NPs have much better affinity than semiconductors to many reactants, especially organic molecules. Recent progress in photocatalysis using Au and Ag NPs on insulator supports is reviewed. We focus on the mechanism differences between insulator and semiconductor-supported Au and Ag NPs when applied in photocatalytic processes, and the influence of important factors, light intensity and wavelength, in particular estimations of light irradiation contribution, by calculating the apparent activation energies of photo reactions and thermal reactions.
The development and mechanism of new photocatalysts of gold and nanoparticles on insulator supports are reviewed.
Methylene blue (MB) is a carcinogenic pollutant widely known for its hazardous impacts on humans and marine life. Recently, the photocatalysis mediated degradation of MB has been widely reported as ...an advanced approach for the removal of this harmful dye from the aqueous mediums. Numerous scientists have documented the use of nanomaterials (NMs) based photocatalytic assemblies for the degradation of MB. This study highlights the fundamentals and factors involved in the degradation reaction of MB. Furthermore, the detailed kinetics and mechanistic description are also presented for providing essential insights into the light mediated reaction of MB. The vast academic literature is organized by classifying the NMs based photocatalysts based on the utilized stabilization mediums and the advantages/disadvantages of the peculiar stabilization mediums are also discussed for presenting the comparative analysis of the reported stabilization mediums for the preparation of photocatalysts. Future prospects are also discussed for further extending the advancement of scientific research in this field.
Display omitted
In this paper, we present the first attempt at modelling the impact of economic policy uncertainty on renewable energy consumption in the USA using monthly data from 1986 to 2019. By implementing ...recent nonparametric (nonlinear) econometric approaches, we find that our models suffer from nonlinearity and smooth, as well as abrupt structural changes. The nonparametric unit root tests indicate non-stationarity of the model variables while the cointegration suggests the presence of nonlinear cointegration. The Granger causality analyses establish robust nonlinear causation in both directions between the policy uncertainty and renewable energy variables, with one exception: from geothermal energy to the three-component index of uncertainty. The nonparametric regressions exhibit a negative long-run association between policy uncertainty and renewable energy consumption, i.e., higher economic policy uncertainty lowers renewable energy consumptions and vice-versa. These findings have robust policy implications as they underscore the importance of governments, policymakers and concerned agents to maintain uniformity in economic policy to encourage renewable energy consumption in the USA.
Carbon dioxide (CO2) is one of the most important contributors for the increase of the greenhouse effect. CO2 concentrations are increasing in the last decades mainly due to the increase of ...anthropogenic emissions. To reduce the effects caused by this environmental problem, several technologies were studied to capture CO2 from large emission source points: (i) absorption; (ii) adsorption; (iii) gas-separation membranes; and (iv) cryogenic distillation. The resulting streams with high CO2 concentrations are transported and stored in geological formations. However, these methodologies, known as carbon capture and storage (CCS) technologies, are considered as short-term solutions, as there are still concerns about the environmental sustainability of these processes.
A promising technology is the biological capture of CO2 using microalgae. These microorganisms can fix CO2 using solar energy with efficiency ten times greater than terrestrial plants. Moreover, the capture process using microalgae has the following advantages: (i) being an environmental sustainable method; (ii) using directly the solar energy; and (iii) co-producing high added value materials based on biomass, such as human food, animal feed mainly for aquaculture, cosmetics, medical drugs, fertilizers, biomolecules for specific applications and biofuels. Approaches for making CO2 fixation by microalgae economically competitive in comparison with CCS methodologies are discussed, which includes the type of bioreactors, the key process parameters, the gaseous effluents and wastewater treatment, the harvesting methods and the products extracted by microalgal biomass.
Within the context of achieving low carbon shipping by 2050, high hopes are placed on alternative marine fuels in addition to a large number of technological and operational measures. A technological ...review has been carried out in this paper to determine the most promising alternative marine fuels considering the simultaneous reduction of sulphur oxides, nitrogen oxides and carbon dioxide emissions as well as sustainability. Firstly, potential alternative marine fuel options have been summarized based on a review of published literature. Then, key physicochemical properties, feedstocks, production processes, transportation and storage factors, and end uses of zero carbon or carbon-neutral fuels have been analyzed. Finally, a qualitative ranking of the potential of different marine fuel options is presented based on a multi-dimensional decision-making framework. It was found that zero carbon synthetic fuels including hydrogen and ammonia accompanied by clean production could play a vital role in domestic and short sea shipping, though current costs and infrastructure are not commercially feasible. Methanol (fossil/renewable) appears likely to be the most promising alternative fuel for global shipping instead of other carbon-neutral biofuels such as renewable natural gas, bioethanol, biogenic dimethyl ether and biodiesels, which may be feasible for domestic and short sea shipping depending on local practices. It should be highlighted that marine fuel substitution is a prolonged process. Accordingly, consensus-building and action-adopting in the maritime community as early as possible is important to anchor expectations and achieve the goals of clean maritime transportation.
•Renewable methanol appears to be the most promising fuel option for global shipping.•Potential of hydrogen and ammonia is mainly in domestic and short sea shipping.•Prospects of alternative marine fuels significantly depend on the world energy mix.
A supermassive black hole, obscured by cosmic dust, powers the nearby active galaxy NGC 1068. Neutrinos, which rarely interact with matter, could provide information on the galaxy’s active core. We ...searched for neutrino emission from astrophysical objects using data recorded with the IceCube neutrino detector between 2011 and 2020. The positions of 110 known gamma-ray sources were individually searched for neutrino detections above atmospheric and cosmic backgrounds. We found that NGC 1068 has an excess of
79
−
20
+
22
neutrinos at tera–electron volt energies, with a global significance of 4.2σ, which we interpret as associated with the active galaxy. The flux of high-energy neutrinos that we measured from NGC 1068 is more than an order of magnitude higher than the upper limit on emissions of tera–electron volt gamma rays from this source.
Nearby active galaxy emits neutrinos
Observations have shown a diffuse background of high-energy neutrinos, which is known to be of extragalactic origin. However, it has been difficult to identify individual sources that contribute to this background. The IceCube Collaboration reanalyzed the arrival directions of astrophysical neutrinos and then searched for point sources (see the Perspective by Murase). They identified evidence for neutrino emission from NGC 1068 (also known as Messier 77), a nearby active galaxy. Its properties are quite different from TXS 0506+056, which was found to be a neutrino source in 2018, leading the investigators to suggest that there might be more than one population contributing to the neutrino background. —KTS
The arrival directions of astrophysical neutrinos indicate point source neutrino emission from NGC 1068.
PDF
