High-energy storage performance in lead-free (1-x)BaTiO3-xBi(Zn0.5Ti0.5)O3 relaxor ceramics for temperature stability applications

In this paper, we prepared lead-free (1-x)BaTiO₃-xBi(Zn_0.5Ti_0.5)O₃ (x=0.04, 0.08, 0.10, and 0.14) ceramics by a conventional solid-state reaction technique. Pure perovskite structures and dense microstructures were demonstrated for all the compositions. Interestingly, it was found that the sintering temperature tended to decrease with increasing the Bi(Zn_0.5Ti_0.5)O₃ content. It should be stressed that a low sintering temperature of 1050 °C was utilized for the composition of x=0.14. Moreover, the dielectric permittivity-temperature curve became more flat and the relaxor degree became stronger with the augment in Bi(Zn_0.5Ti_0.5)O₃ content. We also conducted a detailed study on the energy storage performance for all the compositions from 25 °C to 180 °C.We found that relatively temperature-stable energy storage performance could be obtained in the compositions with x=0.08, 0.10 and 0.14 regardless of the evolution of dielectric constant during the test temperature range. In particular, due to a higher field of 12 MV m⁻¹, the discharge energy storage densities of x=0.14 could reach 0.81 J cm⁻³, 0.80 J cm⁻³, 0.78 J cm⁻³, 0.72 J cm⁻³, and 0.67 J cm⁻³ with high efficiencies of 94%, 92%, 94%, 88% and 77% at 25 °C, 50 °C, 100 °C, 150 °C, and 180 °C, respectively. All these results demonstrate the (1-x)BaTiO₃-xBi(Zn_0.5Ti_0.5)O₃ ceramics are quite promising for temperature-stable energy storage applications.     

Nanoconfinement of LiBH4·NH3 towards enhanced hydrogen generation

Successful synthesis of LiBH₄·NH₃ confined in nanoporous silicon dioxide (LiBH₄·NH₃@SiO₂) was achieved via a new “ammonia-deliquescence” method, which avoids the involvement of any solvents during the process of synthesis. Compared to the pure LiBH₄·NH₃, the confined LiBH₄·NH₃@SiO₂ exhibited significantly improved dehydrogenation properties, which not only suppressed the emission of NH₃, but also decreased the onset dehydrogenation temperature to 60 °C, thus leading to an enhanced conversion of NH₃ to H₂. In the temperature range of 60–300 °C, the mole ratio of H₂ release for the confined LiBH₄·NH₃@SiO₂ is 85 mol % of the total gas evolved, compared to 2.66 mol % for the pristine LiBH₄·NH₃. Isothermal dehydrogenation results showed that the LiBH₄·NH₃@SiO₂ is able to release about 1.26, 2.09, and 2.35 equiv. of hydrogen, at 150 °C, 200 °C, and 250 °C, respectively. From analysis of the Fourier transform infrared, Raman, and nuclear magnetic resonance spectra of the confined LiBH₄·NH₃@SiO₂ sample heated to various temperatures, as well as its dehydrogenation product under NH₃ atmosphere, it is proposed that the improved dehydrogenation of LiBH₄·NH₃@SiO₂ is mainly attributable to two crucial factors resulting from the nanoconfinement: (1) stabilization of the NH₃ in the nanopores of SiO₂, and (2) enhanced combination of LiBH₄ and NH₃ groups, leading to fast dehydrogenation at low temperature.     

Measurement of Micro Kinetics of Hydrogenation in Liquid Phase Using Raman Spectroscopy

Hydrogenation of liquid organic hydrogen carriers is usually carried out in liquid phase. To measure the kinetics of this hydrogenation, an experimental setup using in situ Raman spectroscopy for analysis of the reaction mixture is proposed. With this setup it is possible to perform hydrogenation reactions at temperatures of up to 573 K and pressures up to 25 MPa. For validation of the experimental setup the hydrogenation of 1‐octene was measured in liquid phase. The reaction progress can be monitored in detail by Raman spectroscopy. To determine kinetic parameters from the experimental data, two modeling approaches were applied: a classic kinetic model and a thermodynamic kinetic model. The results were compared to literature data.     

High‐temperature latent heat storage technology to utilize exergy of solar heat and industrial exhaust heat

Latent heat storage (LHS) using phase change materials is quite attractive for utilization of the exergy of solar energy and industrial exhaust heat because of its high‐heat storage capacity, heat storage and supply at constant temperature, and repeatable utilization without degradation. In this article, general LHS technology is outlined, and then recent advances in the uses of LHS for high‐temperature applications (over 100 °C) are discussed, with respect to each type of phase change material (e.g., sugar alcohol, molten salt, and alloy). The prospects of future LHS systems are discussed from a principle of exergy recuperation. In addition, the technologies to minimize exergy loss in the future LHS system are discussed on the basis of the thermodynamic analysis by ‘thermodynamic compass’. Copyright © 2016 John Wiley & Sons, Ltd.     

An overview of the environmental,economic, and material developments of the solar and wind sources coupled with the energy storage systems

There is a constant growth in energy consumption and consequently energy generation around the world. During the recent decades, renewable energy sources took heed of scientists and policy makers as a remedy for substituting traditional sources. Wind and photovoltaic (PV) are the least reliable sources because of their dependence on wind speed and irradiance and therefore their intermittent nature. Energy storage systems are usually coupled with these sources to increase the reliability of the hybrid system. Environmental effects are one of the biggest concerns associated with the renewable energy sources. This study summarizes the last and most important environmental and economic analysis of a grid‐connected hybrid network consisting of wind turbine, PV panels, and energy storage systems. Focusing on environmental aspects, this paper reviews land efficiency, shaded analysis of wind turbines and PV panels, greenhouse gas emission, wastes of wind turbine and PV panels' components, fossil fuel consumption, wildlife, sensitive ecosystems, health benefits, and so on. A cost analysis of the energy generated by a hybrid system has been discussed. Furthermore, this study reviews the latest technologies for materials that have been used for solar PV manufacturing. This paper can help to make a right decision considering all aspects of installing a hybrid system. Copyright © 2017 John Wiley & Sons, Ltd.     

Power-to-Gas integration in the Transition towards Future Urban Energy Systems

Temperature levels play a key role in the thermal energy demand of urban contexts affecting their associated primary energy consumption and Renewable Energy Fraction. A Smart Heating strategy accounts for those supply features requiring new solutions to be effectively renewable and to solve the RES capacity firming. Power-to-Gas (P2G) is the way to decarbonize the energy supply chain as fraction of Hybrid fuels, combination of fossil ones and Renewable Hydrogen, as immediate responsive storage solution. While, Power-To-Heat is conceived as the strategy to modernize the high and medium temperature heating systems by electricity-driven machines to switch from Fuel-to-Heat to Electricity-to-Heat solutions. The authors investigated on different urban energy scenarios at RES share increase from 25% up to 50% in the energy mix to highlight strengths and weaknesses of the P2G applications. Primary Energy Consumption was chosen as the objective function. Three Reference Cities were chosen as reference scenarios. Moreover, the analytical models of P2G was designed and implemented in the reference energy system. The results of the twelve scenarios, four for each Reference City were evaluated in terms of amount of Renewable Heat delivered. Finally, the interaction between P2G and renewable heat production was evaluated.     

The phase transformations and cycling performance of copper-tin alloy anode materials synthesized by sputtering

A sputtering technique was adopted to synthesize Sn-Cu thin film electrodes. Island Sn particles were obtained on the copper foil. Cu₆Sn₅ was spontaneously generated at the interface between Sn and Cu foil. To further improve the cycling stability, Cu source was introduced to increase the formation of Cu₆Sn₅ and to serve as a buffer during cycling. Moreover, the phase and elemental ratio of Sn and Cu varied in the synthesized electrode by alternately adjusting sputtering time for Sn and Cu. The cell synthesized by sputtering Sn for 5 min and Cu for 9 s alternately exhibited the best cycling stability. The 1st charge capacity of cell was 635 mA hg⁻¹, and the 1st efficiency was even higher than 97%. The capacity remained higher than 500 mA hg⁻¹ after 15 cycles. The phase transformation of cell was investigated through voltage profile, CV curve and in situ XRD analysis. The in situ XRD analysis confirmed that Cu₆Sn₅ could react with lithium directly without the presence of Li₂CuSn during cycling. The reaction mechanism of Cu₆Sn₅ with lithium during cycling was demonstrated to be an alloying process, and the structure of Cu₆Sn₅ was thus a low-temperature monoclinic phase.     

Chemisorption,physisorption and hysteresis during hydrogen storage in carbon nanotubes

The question of chemisorption versus physisorption during hydrogen storage in carbon nanotubes (CNTs) is addressed experimentally. We utilize a powerful measurement technique based on a magnetic suspension balance coupled with a residual gas analyzer, and report new data for hydrogen sorption at pressures of up to 100 bar at 25 °C. The measured sorption capacity is less than 0.2 wt.%, and there is hysteresis in the sorption isotherms when multi-walled CNTs are exposed to hydrogen after pretreatment at elevated temperatures. The cause of the hysteresis is then studied, and is shown to be due to a combination of weak sorption – physisorption – and strong sorption – chemisorption – in the CNTs. Analysis of the experimental data enables us to calculate separately the individual hydrogen physisorption and chemisorption isotherms in CNTs that, to our knowledge, are reported for the first time here. The maximum measured hydrogen physisorption and chemisorption are 0.13 wt.% and 0.058 wt.%, respectively.     

Iodide substitution in lithium borohydride, LiBH4-LiI

The new concept, anion substitution, is explored for possible improvement of hydrogen storage properties in the system LiBH₄-LiI. The structural chemistry and the substitution mechanism are analyzed using Rietveld refinement of in situ synchrotron radiation powder X-ray diffraction (SR-PXD) data, attenuated total reflectance infrared spectroscopy (ATR-IR), differential scanning calorimetry (DSC) and Sieverts measurements. Anion substitution is observed as formation of two solid solutions of Li(BH₄)_1−xI_x, which merge into one upon heating. The solid solutions have hexagonal structures (space group P6₃mc) similar to the structures of h-LiBH₄ and β-LiI. The solid solutions have iodide contents in the range ∼0-62 mol% and are stable from below room temperature to the melting point at 330 °C. Thus the stability of the solid solutions is higher as compared to that of the orthorhombic and hexagonal polymorphs of LiBH₄ and α- and β-LiI. Furthermore, the rehydrogenation properties of the iodide substituted solid solution Li(BH₄)_1−xI_x, measured by the Sieverts method, are improved as compared to those of LiBH₄. After four cycles of hydrogen release and uptake the Li(BH₄)_1−xI_x solid solution maintains 68% of the calculated hydrogen storage capacity in contrast to LiBH₄, which maintains only 25% of the storage capacity after two cycles under identical conditions.