Efficient solar-driven CO2-to-fuel conversion via Ni/MgAlO x @SiO2 nanocomposites at low temperature.

Solar-driven CO2-to-fuel conversion assisted by another major greenhouse gas CH4 is promising to concurrently tackle energy shortage and global warming problems. However, current techniques still suffer from drawbacks of low efficiency, poor stability, and low selectivity. Here, a novel nanocomposite composed of interconnected Ni/MgAlO x nanoflakes grown on SiO2 particles with excellent spatial confinement of active sites is proposed for direct solar-driven CO2-to-fuel conversion. An ultrahigh light-to-fuel efficiency up to 35.7%, high production rates of H2 (136.6 mmol min-1g- 1) and CO (148.2 mmol min-1g-1), excellent selectivity (H2/CO ratio of 0.92), and good stability are reported simultaneously. These outstanding performances are attributed to strong metal-support interactions, improved CO2 absorption and activation, and decreased apparent activation energy under direct light illumination. MgAlO x @SiO2 support helps to lower the activation energy of CH* oxidation to CHO* and improve the dissociation of CH4 to CH3* as confirmed by DFT calculations. Moreover, the lattice oxygen of MgAlO x participates in the reaction and contributes to the removal of carbon deposition. This work provides promising routes for the conversion of greenhouse gasses into industrially valuable syngas with high efficiency, high selectivity, and benign sustainability.

Ultrastable halide perovskite CsPbBr3 photoanodes achieved with electrocatalytic glassy-carbon and boron-doped diamond sheets.

Halide perovskites exhibit exceptional optoelectronic properties for photoelectrochemical production of solar fuels and chemicals but their instability in aqueous electrolytes hampers their application. Here we present ultrastable perovskite CsPbBr3-based photoanodes achieved with both multifunctional glassy carbon and boron-doped diamond sheets coated with Ni nanopyramids and NiFeOOH. These perovskite photoanodes achieve record operational stability in aqueous electrolytes, preserving 95% of their initial photocurrent density for 168 h of continuous operation with the glassy carbon sheets and 97% for 210 h with the boron-doped diamond sheets, due to the excellent mechanical and chemical stability of glassy carbon, boron-doped diamond, and nickel metal. Moreover, these photoanodes reach a low water-oxidation onset potential close to +0.4 VRHE and photocurrent densities close to 8 mA cm-2 at 1.23 VRHE, owing to the high conductivity of glassy carbon and boron-doped diamond and the catalytic activity of NiFeOOH. The applied catalytic, protective sheets employ only earth-abundant elements and straightforward fabrication methods, engineering a solution for the success of halide perovskites in stable photoelectrochemical cells.

Structural Heredity in Catalysis: CO2 Self-Selective CeO2 Nanocrystals for Efficient Photothermal CO2 Hydrogenation to Methane.

The chemical inertness of CO2 molecules makes their adsorption and activation on a catalyst surface one of the key challenges in recycling CO2 into chemical fuels. However, the traditional template synthesis and chemical modification strategies used to tackle this problem face severe structural collapse and modifier deactivation issues during the often-needed post-processing procedure. Herein, a CO2 self-selective hydrothermal growth strategy is proposed for the synthesis of CeO2 octahedral nanocrystals that participate in strong physicochemical interactions with CO2 molecules. The intense affinity for CO2 molecules persists during successive high-temperature treatments required for Ni deposition. This demonstrates the excellent structural heredity of the CO2 self-selective CeO2 nanocrystals, which leads to an outstanding photothermal CH4 productivity exceeding 9 mmol h-1 mcat -2 and an impressive selectivity of >99%. The excellent performance is correlated with the abundant oxygen vacancies and hydroxyl species on the CeO2 surface, which create many frustrated Lewis-pair active sites, and the strong interaction between Ni and CeO2 that promotes the dissociation of H2 molecules and the spillover of H atoms, thereby greatly benefitting the photothermal CO2 methanation reaction. This self-selective hydrothermal growth strategy represents a new pathway for the development of effective catalysts for targeted chemical reactions.

Revealing the stochastic kinetics evolution of photocatalytic CO2 reduction.

Investigating kinetic mechanisms to design efficient photocatalysts is critical for improving photocatalytic CO2 reduction, but the stochastic photo-physical/chemical properties of kinetics remain unclear. Herein, we propose a statistical study to discuss the stochastic feature evolution of photocatalytic systems. The uncertainties of light absorption, charge carrier migration, and surface reaction are described by nonparametric estimation methods in the proposed model, which includes the effect of operational and material parameters. The density distribution of surface electrons shifts from a skewed distribution to an approximate uniform distribution as incident photon density increases. The system temperature rising induces the rate-determining step of surface reactions to change from charge carrier kinetics to reactant activation processes. Benefiting from the synergistic optimization between the operational parameter and active site density, the electron-capturing probability of active sites is boosted from 0.06 to 0.17. The modified reaction kinetic equation is constructed based on the distribution function of charge carrier kinetics. Furthermore, the experimental photoactivity results are consistent with the statistical analysis, which proves the feasibility of the established model. The characterization tests show that the gap between testing activities and theoretical efficiency is caused by a mismatch between charge carrier supply and mass transfer. Our work unveils the stochastic features in photocatalytic CO2 reduction, offering a comprehensive analytical framework for photocatalytic system optimization.

A multi-process model for the photocatalytic reduction of CO2.

The photocatalytic conversion of CO2 to fuel and valuable carbon compounds is a feasible method for the large-scale reuse of CO2. However, it involves complex multi-processes and physical phenomena, limiting the enhanced performance of photocatalysis. Consequently, building a comprehensive model is necessary. Herein, we present a multi-process computational framework for simulating the whole photocatalytic CO2 reduction process. In this work, the physical and chemical properties of the catalysts were determined by density functional theory (DFT). Specifically, we employed a framework consisting of an optical absorption and carrier transport model to simulate the conversion process from photons to carriers, a micro-kinetic model to describe the surface catalytic reaction process, and a continuum transport model to calculate the mass transfer process between the solution and surface. Using this multiscale model, we simulated and analyzed the photocatalytic processes of rGO-MoS2/PPy (MoS2 and polymer polypyrrole on reduced graphene oxide). The simulation clarified the key factors affecting the catalyst activity and selectivity. Moreover, the energy loss in different processes was also clarified, which showed that the model can be a theoretical analysis tool for analyzing and improving the photocatalytic performance of materials.

Transcriptome analysis of tea (Camellia sinensis) leaves in response to ammonium starvation and recovery.

The tea plant is a kind of ammonium-preferring crop, but the mechanism whereby ammonium (NH4 +) regulate its growth is not well understood. The current study focused on the effects of NH4 + on tea plants. Transcriptomic analysis was performed to investigate the early- and late-stage NH4 + deprivation and resupply in tea plants shoots. Through short- and long-term NH4 + deficiency, the dynamic response to NH4 + stress was investigated. The most significant effects of NH4 + deficiency were found to be on photosynthesis and gene ontology (GO) enrichment varied with the length of NH4 + deprivation. Enriched KEGG pathways were also different when NH4 + was resupplied at different concentrations which may indicate reasons for tolerance of high NH4 + concentration. Using weighted gene co-expression network analysis (WGCNA), modules related to significant tea components, tea polyphenols and free amino acids, were identified. Hence, NH4 + could be regarded as a signaling molecule with the response of catechins shown to be higher than that of amino acids. The current work represents a comprehensive transcriptomic analysis of plant responses to NH4 + and reveals many potential genes regulated by NH4 + in tea plants. Such findings may lead to improvements in nitrogen efficiency of tea plants.

What Role Does the Incident Light Intensity Play in Photocatalytic Conversion of CO2 : Attenuation or Intensification?

Artificial photoreduction of CO2 is vital for the sustainable development of human beings via solar energy storage in stable chemicals. This process involves intricate light-matter interactions, but the role of incident light intensity in photocatalysis remains obscure. Herein, the influence of excitation intensity on charge kinetics and photocatalytic activity is investigated. Model photocatalysts include the pure graphitic carbon nitride (g-C3 N4 ) and g-C3 N4 loaded with noble/non-noble-metal cocatalysts (Ag, TiN, and CuO). It is found that the increase of light intensity does not always improve the electron utilization. Overly high excitation intensities cause charge carrier congestion and changes the recombination mechanism, which is called the light congestion effect. The electron transport channels can be established to mitigate the light-induced effect via the addition of cocatalyst, leading to a nonlinear growth in the reaction rate with increasing light intensity. From experiments and simulations, it is found that the light intensity and active site density should be collectively optimized for increasing the energy conversion efficiency. This work elucidates the effect of light intensity on photocatalytic CO2 reduction and emphasizes the synergistic relationship of matching the light intensity and the photocatalyst category. The study provides guidance for the design of efficient photocatalysts and the operation of photocatalytic systems.

Superior thermal-charging supercapacitors with bio-inspired electrodes of ultra-high surface areas.

High-performance thermally chargeable supercapacitors (TCS) greatly depend on the design of electrode materials. The unique features of succulents of absorbing water for sustaining their lives during long severe droughts imply that there exist vast spaces inside these plants, which inspires us of fabricating biomass-based electrodes by means of such succulents to develop highly efficient TCS. The optimized porous carbon prepared from succulents presents a high specific surface area of up to 3188 m2 g-1, resulting in the superior capability of accommodating a vast amount of ions and promising thermal charging performance. The TCS with this carbon electrode can generate an open-circuit voltage of 565 mV under a temperature difference of 50°C with a temperature coefficient as high as 11.1 mV K-1. This article provides a new method for the preparation of porous carbon from biomass for the TCS system.

Genome-wide identification, characterization, and expression analysis of the ammonium transporter gene family in tea plants (Camellia sinensis L.).

As a preferred nitrogen form, ammonium (NH4 + ) transport via specific transporters is particularly important for the growth and development of tea plants (Camellia sinensis L.). However, our understanding of the functions of the AMT family in tea plants is limited. We identified and named 16 putative AMT genes according to phylogenetic analysis. All CsAMT genes were divided into three groups, distributed on 12 chromosomes with only one segmental duplication repetition. The CsAMT genes showed different expression levels in different organs, and most of them were expressed mainly in the apical buds and roots. Complementation analysis of yeast mutants showed that CsAMTs restored the uptake of NH4 + . This study provides insights into the genome-wide distribution and spatial expression of AMT genes in tea plants.

Zinc ion thermal charging cell for low-grade heat conversion and energy storage.

Converting low-grade heat from environment into electricity shows great sustainability for mitigating the energy crisis and adjusting energy configurations. However, thermally rechargeable devices typically suffer from poor conversion efficiency when a semiconductor is employed. Breaking the convention of thermoelectric systems, we propose and demonstrate a new zinc ion thermal charging cell to generate electricity from low-grade heat via the thermo-extraction/insertion and thermodiffusion processes of insertion-type cathode (VO2-PC) and stripping/plating behaviour of Zn anode. Based on this strategy, an impressively high thermopower of ~12.5 mV K-1 and an excellent output power of 1.2 mW can be obtained. In addition, a high heat-to-current conversion efficiency of 0.95% (7.25% of Carnot efficiency) is achieved with a temperature difference of 45 K. This work, which demonstrates extraordinary energy conversion efficiency and adequate energy storage, will pave the way towards the construction of thermoelectric setups with attractive properties for high value-added utilization of low-grade heat.

Highly Selective Production of Ethanol Over Hierarchical Bi@Bi2 MoO6 Composite via Bicarbonate-Assisted Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction is a sustainable and inexpensive method to solve the energy crisis and the greenhouse effect. However, the major stumbling blocks such as poor product selectivity, low yield of the multi-carbon products, and serious recombination of electron-hole pairs hinder practical application of photocatalysts. Herein, a high-performance Bi@Bi2 MoO6 photocatalyst, Bi nanoparticles grown on the surface of Bi2 MoO6 nanosheets with oxygen vacancies, was fabricated via a simple solvothermal approach. Benefiting from the abundant active sites and effective separation of photogenerated carriers of Bi2 MoO6 nanosheets, and the localized surface plasmon resonance effect of Bi nanoparticles, the Bi@Bi2 MoO6 sample exhibited great photocatalytic CO2 reduction activity. Furthermore, adding NaHCO3 into the system not only significantly increased the C2 H5 OH generation rate but also enhanced the product selectivity. In the photocatalytic measurement (0.17 mol L-1 CO2 -saturated NaHCO3 solution), the highest formation rates of CO, CH3 OH, and C2 H5 OH were reached at 0.85, 0.59, and 17.93 µmol g-1 h-1 (≈92 % selectivity), respectively.

Lattice Boltzmann approach for near-field thermal radiation.

The lattice Boltzmann (LB) approach is presented for the near-field thermal radiation (including the contributions of the propagating and evanescent waves). The radiative transfer equations in the medium and on the interface are derived for the propagating and evanescent waves from the Maxwell equations, respectively. The Chapman-Enskog analysis is adopted to derive the LB model to recover the radiative transfer equation. The scattering parameter coefficient η is proposed to demonstrate the wave behavior of photons on the interface between medium and vacuum. The numerical tests are implemented to solve the near-field radiative heat transfer between two slabs by using the proposed LB approach. The accuracy of the LB model can be improved by increasing the resolution of the wave-number space. By comparing with the benchmark of analytical solutions, the proposed numerical approach enables computing the near-field thermal radiation with good accuracy and exhibits promising applications in dealing with complicated near-field thermal radiation processes.

Fabry-Perot-resonator-coupled metal pattern metamaterial for infrared suppression and radiative cooling.

The most intuitive approach for infrared stealth, namely, the indiscriminate suppression of thermal radiation, is often at the risk of overheating the target. Spectrally selective metamaterials may solve this problem by satisfying radiative cooling as well as infrared suppression. Therefore, we have designed and fabricated a broadband metamaterial by depositing a Fabry-Perot (F-P) resonator on top of a metal pattern. The composite structure has two absorption peaks, one originating from F-P resonance, the other from the magnetic resonance of the metal pattern, and they can be merged into the 5∼8 µm range through optimization. According to Kirchhoff's law, this results in high emissivity in the 5∼8 µm range (the best choice of nonatmospheric-window ranges) and low emissivity in the 3∼5 µm and 8∼14 µm ranges (the two atmospheric windows), satisfying both infrared suppression and radiative cooling. Energy dissipation distributions indicate apparent coupling of F-P resonance and magnetic resonance, but these two resonances are stronger at their respective intrinsic wavelengths. This paper reveals an alternative method for infrared suppression with radiative cooling, which is also meaningful in the design of broad/multiband absorbers.

Synergizing Photo-Thermal H2 and Photovoltaics into a Concentrated Sunlight Use.

Solar hydrogen and electricity are promising high energy-density renewable sources. Although photochemistry or photovoltaics are attractive routes, special challenge arises in sunlight conversion efficiency. To improve efficiency, various semiconductor materials have been proposed with selective sunlight absorption. Here, we reported a hybrid system synergizing photo-thermochemical hydrogen and photovoltaics, harvesting full-spectrum sunlight in a cascade manner. A simple suspension of Au-TiO2 in water/methanol serves as a spectrum selector, absorbing ultraviolet-visible and infrared energy for rapid photo-thermochemical hydrogen production. The transmitted visible and near-infrared energy fits the photovoltaic bandgap and retains the high efficiency of a commercial photovoltaic cell under different solar concentration values. The experimental design achieved an overall efficiency of 4.2% under 12 suns solar concentration. Furthermore, the results demonstrated a reduced energy loss in full-spectrum energy conversion into hydrogen and electricity. Such simple integration of photo-thermochemical hydrogen and photovoltaics would create a pathway toward cascading use of sunlight energy.

Selective Growth of Stacking Fault Free ⟨100⟩ Nanowires on a Polycrystalline Substrate for Energy Conversion Application.

Cubic semiconductor nanowires grown along ⟨100⟩ directions have been reported to be promising for optoelectronics and energy conversion applications, owing to their pure zinc-blende structure without any stacking fault. But, until date, only limited success has been achieved in growing ⟨100⟩ oriented nanowires. Here we report the selective growth of stacking fault free ⟨100⟩ nanowires on a commercial transparent conductive polycrystalline fluorine-doped SnO2 (FTO) glass substrate via a simple and cost-effective chemical vapor deposition (CVD) method. By means of crystallographic analysis and density functional theory calculation, we prove that the orientation relationship between the Au catalyst and the FTO substrate play a vital role in inducing the selective growth of ⟨100⟩ nanowires, which opens a new pathway for controlling the growth directions of nanowires via the elaborate selection of the catalyst and substrate couples during the vapor-solid-liquid (VLS) growth process. The ZnSe nanowires grown on the FTO substrate are further applied as a photoanode in photoelectrochemical (PEC) water splitting. It exhibits a higher photocurrent than the ZnSe nanowires do without preferential orientations on a Sn-doped In2O3 (ITO) glass substrate, which we believe to be correlated with the smooth transport of charge carriers in ZnSe ⟨100⟩ nanowires with pure zinc-blende structures, in distinct contrast with the severe electron scattering happened at the stacking faults in ZnSe nanowires on the ITO substrate, as well as the efficient charge transfer across the intensively interacting nanowire-substrate interfaces.

Full-spectrum light management by pseudo-disordered moth-eye structures for thin film solar cells.

In this paper, the role of pseudo-disordered moth-eye structures on the optical features for application to thin-film solar cells is investigated to realize the superior light management for the full-spectrum solar energy utilization, compared with some ordered structures. Without loss of generality, the c-Si thin film solar cell is taken as the example. The results demonstrate that the fluctuations introduced into the geometry parameters of moth-eye elements can lead to the remarkable absorption enhancement in the wavelength region of 0.3-1.1 µm and high transmission in the wavelength range of 1.1-2.5 µm. Two mechanisms including the increasing spectral density of modes and the intensive forescattering intensity are identified to be responsible for the absorption enhancement. In addition, the optical characteristics of the moth-eye surface with both disordered height and disordered diameter are insensitive to the incident angle.

Full-spectrum light management by pseudo-disordered moth-eye structures for thin film solar cells: erratum.

This erratum is presented to correct Fig. 11 in [Opt. Express25(16), A824 (2017)].

Full-spectrum volumetric solar thermal conversion via photonic nanofluids.

Volumetric solar thermal conversion is an emerging technique for a plethora of applications such as solar thermal power generation, desalination, and solar water splitting. However, achieving broadband solar thermal absorption via dilute nanofluids is still a daunting challenge. In this work, full-spectrum volumetric solar thermal conversion is demonstrated over a thin layer of the proposed 'photonic nanofluids'. The underlying mechanism is found to be the photonic superposition of core resonances, shell plasmons, and core-shell resonances at different wavelengths, whose coexistence is enabled by the broken symmetry of specially designed composite nanoparticles, i.e., Janus nanoparticles. The solar thermal conversion efficiency can be improved by 10.8% compared with core-shell nanofluids. The extinction coefficient of Janus dimers with various configurations is also investigated to unveil the effects of particle couplings. This work provides the possibility to achieve full-spectrum volumetric solar thermal conversion, and may have potential applications in efficient solar energy harvesting and utilization.

New Insight into the Angle Insensitivity of Ultrathin Planar Optical Absorbers for Broadband Solar Energy Harvesting.

Two challenging problems still remain for optical absorbers consisting of an ultrathin planar semiconductor film on top of an opaque metallic substrate. One is the angle-insensitive mechanism and the other is the system design needed for broadband solar energy harvesting. Here, first we theoretically demonstrates that the high refractive index, instead of the ultrathin feature as reported in previous studies, is the physical origin of the angle insensitivity for ultrathin planar optical absorbers. They exhibit omnidirectional resonance for TE polarization due to the high complex refractive index difference between the semiconductor and the air, while for TM polarization the angle insensitivity persists up to an incident angle related to the semiconductor refractive index. These findings were validated by fabricating and characterizing an 18 nm Ge/Ag absorber sample (representative of small band gap semiconductors for photovoltaic applications) and a 22 nm hematite/Ag sample (representative of large band gap semiconductors for photoelectrochemical applications). Then, we took advantage of angle insensitivity and designed a spectrum splitting configuration for broadband solar energy harvesting. The cascaded solar cell and unassisted solar water splitting systems have photovoltaic and photoelectrochemical cells that are also spectrum splitters, so an external spectrum splitting element is not needed.

Comprehensive design of omnidirectional high-performance perovskite solar cells.

The comprehensive design approach is established with coupled optical-electrical simulation for perovskite-based solar cell, which emerged as one of the most promising competitors to silicon solar cell for its low-cost fabrication and high PCE. The selection of structured surface, effect of geometry parameters, incident angle-dependence and polarization-sensitivity are considered in the simulation. The optical modeling is performed via the finite-difference time-domain method whilst the electrical properties are obtained by solving the coupled nonlinear equations of Poisson, continuity, and drift-diffusion equations. The optical and electrical performances of five different structured surfaces are compared to select a best structured surface for perovskite solar cell. The effects of the geometry parameters on the optical and electrical properties of the perovskite cell are analyzed. The results indicate that the light harvesting is obviously enhanced by the structured surface. The electrical performance can be remarkably improved due to the enhanced light harvesting of the designed best structured surface. The angle-dependence for s- and p-polarizations is investigated. The structured surface exhibits omnidirectional behavior and favorable polarization-insensitive feature within a wide incident angle range. Such a comprehensive design approach can highlight the potential of perovskite cell for power conversion in the full daylight.