Preparation of sol–gel TiO2/purified Na-bentonite composites and their photovoltaic application for natural dye-sensitized solar cells

The sol–gel TiO₂/purified natural clay electrodes having Ti:Si molar ratios of 95:5 and 90:10 were initially prepared, sensitized with natural red cabbage dye, and compared to the sol–gel TiO₂ electrode in terms of physicochemical characteristics and solar cell efficiency. The results showed that the increase in purified Na-bentonite content greatly increased the specific surface area and total pore volume of the prepared sol–gel TiO₂/purified Na-bentonite composites because the clay platelets prevented TiO₂ particle agglomeration. The sol–gel TiO₂/5 mol% Si purified Na-bentonite and sol–gel TiO₂/10 mol% Si purified Na-bentonite composites could increase the film thickness of solar cells without cracking when they were coated as a scattering layer on the TiO₂ semiconductor-based film, leading to increasing the efficiency of the natural dye-sensitized solar cells in this work.     

Thermodynamic evaluations of solar cooling cogeneration cycle using NaSCN–NH<Subscript>3</Subscript> mixture

The commercial refrigeration and air conditioning consumes more electric power for its operation. The solar vapor absorption refrigeration helps to minimize the electric power usage and it is renewable. Large size of solar collector area is required for producing the standalone power as well as cooling cycle. The integration of power and cooling cycle minimizes the number of components such as heat exchanger, separator and collector area. The main objective of the work is to integrate power and cooling for two outputs with single cycle using NaSCN–NH₃ as working fluid. The advantages of NaSCN–NH₃ are having high pressure and pure ammonia vapor at the exit of the generator. The integrated cycle is made by providing the turbine at the exit of the generator along with superheater. It has three pressures of generator, condensing and sink pressure, which is depending on separator and ambient temperature. At the separator temperature of 150°C with weak solution concentration of 0.30, it produces the cogeneration output of 284.80 kW with cycle and plant thermal efficiency of 0.49 and 0.20 respectively.     

Synthesis of π-A-porphyrins and their photoelectric performance for dye-sensitized solar cells

Three π-A-porphyrins containing long alkoxyl chains attached to the ortho position of phenyl ring and a phenyl carboxylate acid or acrylic acid at the meso position of porphyrin were synthesized. All compounds were characterized by ¹H NMR and mass spectrometry. Optical and electrochemical properties were also obtained. The photovoltaic properties of these π-A-porphyrins were examined for the first time and sensitizers N-1 and N-3 achieved comparable light to electricity conversion efficiencies: 3.94% for N-1 and 4.14% for N-3. However, preparation of N-1 required simple and cost-effective synthesis which made it a promising candidate for the future practical DSSC applications. The low efficiency conversion of N-2 was well explained by the amount of dye loading, IPCE and EIS.     

TiO2–Au plasmonic nanocomposite for enhanced dye-sensitized solar cell (DSSC) performance

Anatase TiO₂ nanoparticles dressed with gold nanoparticles were synthesized by hydrothermal process by using mixed precursor and controlled conditions. Diffused Reflectance Spectra (DRS) reveal that in addition to the expected TiO₂ interband absorption below 360 nm gold surface plasmon feature occurs near 564 nm. It is shown that the dye sensitized solar cells made using TiO₂–Au plasmonic nanocomposite yield superior performance with conversion efficiency (CE) of ～6% (no light harvesting), current density (J_SC) of ～13.2 mA/cm², open circuit voltage (V_oc) of ～0.74 V and fill factor (FF) 0.61; considerably better than that with only TiO₂ nanoparticles (CE ～ 5%, J_SC ～ 12.6 mA/cm², V_oc ～ 0.70 V, FF ～ 0.56).     

Fabrication and testing of a H2–O2 fuel cell using MoxRuySez

We report the results obtained in the preparation and characterization of Mo_xRu_ySe_z electrocatalysts for oxygen reduction reaction and the design, construction and characterization of a H₂–O₂ fuel cell using Mo_xRu_ySe_z. The catalysts were characterized with respect to their electrocatalytic properties. The fuel cell was designed and built with Mo_xRu_ySe_z supported on carbon as cathode, Pt supported on carbon as anode, and H₂SO₄ as the electrolyte. The fuel cell was tested at room temperature and atmospheric pressure. The H₂–O₂ cell showed an efficiency in the order of 30%.     

Influence of gamma radiation on spectral photosensitivity of (Si<Subscript>2</Subscript>)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript> (ZnSe)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solution

Increase of the photosensitivity of the pSi-n(Si₂)_{1 ? x} (ZnSe) _x (0 ≤ x ≤ 0.01) structure exposed to gamma radiation with photon energy E _ph ≥ 2.3 eV has been demonstrated. It is shown that irradiation with dose up to 10⁴ rad raises and radiation with dose up to 10⁵ rad reduces the forward current of the pSi-n(Si₂)_{1 ? x} (ZnSe) _x structure.     

Fabrication and investigation of ultravialet Au-Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cd<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>S-Mo-structures

For the first time fabricated and investigated the photovoltaic characteristics of Au-Zn _x Cd_1–x S-Mofilm structural injection photo detectors sensitive to narrow the ultraviolet region of the electromagnetic spectrum, based on polycrystalline Zn _x Cd_1–x S layers. It was found by adjusting the flow of ZnS and CdS coming to the surface Mo substrate can control the shape of the spectral sensitivity of the Au-Zn _x Cd_1–x S-Mo-film structural injection photo detectors. The results will allow to optimize the structure of photo detectors and solar cells based on polycrystalline thin film solar cells.     

Effect of gamma irradiation on photoconductivity and photosensitivity of Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> solid solutions

The results of studies of the structural feature and the effect of low-dose gamma irradiation (up to 105 rad) on the photoconductivity relaxation and the spectral photosensitivity of pSi-nSi_{1 − x} Sn _x (0 ≤ x ≤ 0.04) structures are described. It is shown that exposure to radiation leads to an increase in the relaxation time constant from 55 to 83 μs and an enhancement in the sensitivity of the structures in the short-wavelength emission spectrum, which is attributed to the radiation-stimulated gettering of crystal lattice defects localized in the near-boundaries regions between Si_{1 −x} Sn _x subcrystallites and Si_{1 − x} Sn _x -Sn and Si_{1 − x} Sn _x -SiO₂ phases.     

Which factors drive CO<Subscript>2</Subscript> emissions in EU-15? Decomposition and innovative accounting

This study breaks down carbon emissions into six effects within the 15 European Union countries group (EU-15) and analyses their evolution in four distinct periods: 1995–2000 (before European directive 2001/77/EC), 2001–2004 (after European directive 2001/77/EC and before Kyoto), 2005–2007 (after Kyoto implementation), and 2008–2010 (after Kyoto first stage), to determine which of them had more impact in the intensity of emissions. The complete decomposition technique was used to examine the carbon dioxide (CO₂) emissions and its components: carbon intensity (CI effect); changes in fossil fuels consumption towards total energy consumption (EM effect); changes in energy intensity effect (EG effect); the average renewable capacity productivity (GC effect); the change in capacity of renewable energy per capita (CP effect); and the change in population (P effect). It is shown that in the post Kyoto period there is an even greater differential in the negative changes in CO₂ emissions, which were caused by the negative contribution of the intensity variations of the effects EM, GC, CP and P that exceeded the positive changes occurred in CI and EG effects. It is also important to stress the fluctuations in CO₂ variations before and after Kyoto, turning positive changes to negative changes, especially in France, Italy and Spain, revealing the presence of heterogeneity. Moreover, the positive effect of renewable capacity per capita and the negative effect of renewable capacity productivity are the main factors influencing the reduction in CO₂ emissions during the Kyoto first stage. It is possible to infer from the results that one of the ways to reduce emissions intensity will be by increasing the renewable capacity and the productivity in energy generation and consequently through the reduction of the share of the consumption of fossil fuels.     

Effects of polysiloxane doping on transmittance and durability of sol–gel derived antireflective coatings for photovoltaic glass

Antireflective coatings with high transmittance and excellent durability were prepared by sol–gel process using tetraethyl orthosilicate as precursor. The base-catalyzed sol was modified by acid-catalyzed polysiloxane, and the effects of different doping ratio on the performance of films were studied. The properties including distribution of sol particles, UV–Vis absorbance, refractive index, film thickness and morphology were characterized by nano-particle size analyzer, spectrophotometer, ellipsometer, atomic force microscope (AFM), scanning electron microscopy (SEM) respectively. The results showed that the particle size in sols grew bigger, porosity of films was reduced, refractive index increased and undesirable decrease of the transmittance appeared with the increase of doped polysiloxane. Refractive index could be adjusted from 1.23 to 1.42 continuously by changing the doping ratio. Although the visible light transmittance of the film declined from 97.81% to 94.24% quickly when the doping ratio increased from 0% to 16%, the transmittance attenuation after outdoor exposure for 90 days reduced from 2.70% to 0.22% successfully, and the abrasive-resistance properties of the silica films improved remarkably. Take all factors into consideration, modified base catalyzed sol with 5 vol% doping ratio exhibits excellent properties including high transmittance, good durability and high abrasion-resistance.     

Synthesis of reduced graphene oxide–TiO2 nanoparticle composite systems and its application in hydrogen production

The utilization of solar energy for the conversion of water to hydrogen and oxygen has been considered to be an efficient strategy to solve crisis of energy and environment. Here, we report the synthesis of reduced graphene oxide–TiO₂ nanoparticle composite system through the photocatalytic reduction of graphite oxide using TiO₂ nanoparticles. Photoelectrochemical characterizations and hydrogen evolution measurements of these nanocomposites reveal that the presence of graphene enhances the photocurrent density and hydrogen generation rate. The optimum photocurrent density and hydrogen generation rate has been found to be 3.4 mA cm⁻² and 127.5 μmole cm⁻²h⁻¹ in 0.5 M Na₂SO₄ electrolyte solution under 1.5AM solar irradiance of white light with illumination intensity of 100 mW cm⁻². In graphene–TiO₂ nanocomposite, photogenerated electrons in TiO₂ are scavenged by graphene sheets and percolate to counter electrode to reduce H⁺ to molecular hydrogen thus increasing the performance of water-splitting reaction.     

Situation and measures of China’s CO<Subscript>2</Subscript> emission mitigation after the Paris Agreement

Global response to climate change has entered the phase of full implementation of the Paris Agreement. To control the global temperature rise below 2°C, all countries must make more efforts to reduce emission. China has combined its goal of emission reduction for combating climate change with its domestic sustainable development strategy to promote energy revolution and the transition of economic development to low-carbon patterns. Through reinforcing the commitment and action before 2020, the CO₂ intensity of GDP can decrease by more than 50% by 2020 compared with that of 2005, and the external commitment target of a 40%–45% decrease can be over fulfilled. Currently, under the new economic normal, China further strengthens the policy measure, vigorously saves energy, enhances energy use efficiency and the economic output benefit, and simultaneously develops new and renewable energy and accelerates energy structural decarbonization, so that the annual decrease rate of the CO₂ intensity of GDP keeps a high level of more than 4% and remains increasing. Thus, the decrease rate of the CO₂ intensity of GDP will exceed the GDP growth rate, and then CO₂ emission will peak around 2030. This will promote the fundamental turning of economic development mode, and lay a foundation for the establishment of a sustainable energy system with near-zero emissions and with new and renewable energy as the main body in the second half of this century. China implements the concept of green low-carbon development and accelerates the low carbon transition of energy and economy to achieve win-win results in economic growth and CO₂ emission mitigation, and these policies and actions will also provide experiences for many other developing countries. On the other hand, China will continue to play a positive and constructive leading role in the implementation of the Paris Agreement internationally, and promote the construction of new mechanisms of win-win cooperation, fairness and justice and common development for global climate governance. Moreover, China will make an effort to build a community of common destiny for mankind, promote pragmatic cooperation among countries, especially among developing countries, and take combating climate change as a new development opportunity for jointly moving toward climate-friendly low-carbon economic development path.     

Synthesis and performance of lithium vanadium phosphate as cathode materials for lithium ion batteries by a sol–gel method

Monoclinic lithium vanadium phosphate, Li₃V₂(PO₄)₃, was synthesized by a sol–gel method under Ar/H₂ (8% H₂) atmosphere. The influence of sintering temperatures on the synthesis of Li₃V₂(PO₄)₃ has been investigated using X-ray diffraction (XRD), SEM and electrochemical methods. XRD patterns show that the Li₃V₂(PO₄)₃ crystallinity with monoclinic structure increases with the sintering temperature from 700 to 800 °C and then decreases from 800 to 900 °C. SEM results indicate that the particle size of as-prepared samples increases with the sintering temperature increase and there is minor carbon particles on the surface of the sample particles, which are very useful to enhance the conductivity of Li₃V₂(PO₄)₃. Charge–discharge tests show the 800 °C-sample exhibits the highest initial discharge capacity of 131.2 mAh g⁻¹ at 10 mA g⁻¹ in the voltage range of 3.0–4.2 V with good capacity retention. CV experiment exhibits that there are three anodic peaks at 3.61, 3.70 and 4.11 V on lithium extraction as well as three cathodic peaks at 3.53, 3.61 and 4.00 V on lithium reinsertion at 0.02 mV s⁻¹ between 3.0 and 4.3 V. It is suggested that the optimal sintering temperature is 800 °C in order to obtain pure monoclinic Li₃V₂(PO₄)₃ with good electrochemical performance by the sol–gel method, and the monoclinic Li₃V₂(PO₄)₃ can be used as candidate cathode materials for lithium ion batteries.     

Effects on global CO<Subscript>2</Subscript> emissions when substituting LPG with bio-SNG as fuel in steel industry reheating furnaces—the impact of different perspectives on CO<Subscript>2</Subscript> assessment

The iron and steel industry is the second largest user of energy in the world industrial sector and is currently highly dependent on fossil fuels and electricity. Substituting fossil fuels with renewable energy in the iron and steel industry would make an important contribution to the efforts to reduce emissions of CO₂. However, different approaches to assessing CO₂ emissions from biomass and electricity use generate different results when evaluating how fuel substitution would affect global CO₂ emissions. This study analyses the effects on global CO₂ emissions when substituting liquefied petroleum gas with synthetic natural gas, produced through gasification of wood fuel, as a fuel in reheating furnaces at a scrap-based steel plant. The study shows that the choice of system perspective has a large impact on the results. When wood fuel is considered available for all potential users, a fuel switch would result in reduced global CO₂ emissions. However, applying a perspective where wood fuel is seen as a limited resource and alternative use of wood fuel is considered, a fuel switch could in some cases result in increased global CO₂ emissions. As an example, in one of the scenarios studied, a fuel switch would reduce global CO₂ emissions by 52 ktonnes/year if wood fuel is considered available for all potential users, while seeing wood fuel as a limited resource implies, in the same scenario, increased CO₂ emissions by 70 ktonnes/year. The choice of method for assessing electricity use also affects the results.     

Synthesis and electrochemical characterization of Li1.02Mg0.1Mn1.9O3.99S0.01 using sol–gel method

To improve the cycle performance of spinel LiMn₂O₄ as the positive electrode of 4 V lithium secondary batteries, the spinel oxysulfide Li_1.02Mg_0.1Mn_1.9O_3.99S_0.01 is synthesized by a sol–gel method using adipic acid as a chelating agent. The structural and electrochemical properties of the synthesized material are examined. Highly crystallized Li_1.02Mg_0.1Mn_1.9O_3.99S_0.01 is synthesized at 750°C in an oxygen atmosphere. Both cation and anion doping of spinel lithium manganese oxides are very effective for improving the cycle performance of lithium batteries.     

Preparation of CeO2 based nanocomposites for fuel cell electrolyte via sol–gel method

Abstract

A Ce_0·8Sm_0·2O_1·9 nanocomposite with potential for application as a fuel cell electrolyte was prepared via the sol–gel method. Nitrates and citric acid were respectively adopted as reactor and complexing agent to synthesise the composite. X-ray diffraction was used to investigate the influence of temperature and content of nitric acid on the purity and grain size of the CeO₂ phase. It was found that nanocrystals with 20 nm grain size can be obtained following heating for 4 h at 800°C and that addition of nitric acid improved the purity of the phase produced. A microscale model of the structural transformation from precursor gel to powder for the composite is proposed.     

The composition dependence of the effective thickness of the base layer in Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ga<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>P/GaP heterophotoconverters

The dependence between the composition of Al _x Ga_{1 − x} P heterophotoconverters and the effective thickness of their base layers was established. An empirical formula to estimate the effective thickness of a base layer as a function of the composition of solid-state solution (0 ≤ x ≤ 0.8) was proposed.     

Adipic acid assisted,sol–gel route for synthesis of LiCrxMn2−xO4 cathode material

Spinel LiMn₂O₄ and LiCr_xMn_2−xO₄ (x=0.00−0.20) have been synthesized by a soft chemistry method using adipic acid as the chelating agent. This technique offers better homogeneity, preferred surface morphology, reduced heat-treatment conditions, sub-micron sized particles, and better crystallinity. The synthesized spinel materials are characterized by X-ray diffraction, scanning electron microscopy, cyclic voltammetry, and charge–discharge testing. It is found that chromium substitution alleviates capacity fading in the 4-V region and improves the structural stability of LiMn₂O₄ spinel upon repeated cycling.