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Register a new userEfficient Solar-driven Steam Generation Enabled by An Ultra-black Paint
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Solar-driven interfacial steam generation for desalination has attracted broad attention. However, a significant challenge still remains for achieving a higher evaporation rate and high water quality, together with a cost-effective and easy-to-manufacture device to provide a feasible solar-driven steam generation system. In this study, a novel ultra-black paint, Black 3.0, serving as a perfect solar absorber is introduced into the hot-pressed melamine foam networks, allowing us to construct an ultra-black (99% absorptance in the solar region) and self-floating evaporation device. The high performing features of effective solar absorptance and salt-rejection capability contribute to a high-to-date evaporation rate of freshwater at 2.48 kg m-2 h-1 under one sun (1 kW m-2). This interfacial solar evaporator has a daily drinkable water yield of 2.8 kg m-2 even in cloudy winter weather and maintains stability in water with a wide range of acidity and alkalinity (pH 1~14). These features will enable the construction of a facilely fabricated, robust, highly-efficient, and cost-effective solar steam generation system for freshwater production.
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The reversible heat in lithium-ion batteries (LIBs) due to entropy change is fundamentally important for understanding the chemical reactions in LIBs and developing proper thermal management strategies. However, the direct measurements of reversible heat are challenging due to the limited temperature resolution of applied thermometry. In this work, by developing an ultra-sensitive thermometry with a differential AC bridge using two thermistors, the noise-equivalent temperature resolution we achieve (10 uK) is several orders of magnitude higher than previous thermometry applied on LIBs. We directly observe reversible heat absorption of a LIR2032 coin cell during charging with negligible irreversible heat generation and a linear relation between heat generations and discharging currents. The cell entropy changes determined from the reversible heat agree excellently with those measured from temperature dependent open circuit voltage. Moreover, it is found that the large reversible entropy change can cancel out the irreversible entropy generation at a charging rate as large as C/3.7 and produce a zero-heat-dissipation LIB during charging. Our work significantly contributes to fundamental understanding of the entropy changes and heat generations of the chemical reactions in LIBs, and reveals that reversible heat absorption can be an effective way to cool LIBs during charging.
Solution-processed quantum dots (QDs) have a high potential for fabricating low cost, flexible and large-scale solar energy harvesting devices. It has recently been demonstrated that hybrid devices employing a single monovalent cation perovskite solution for PbS QD surface passivation exhibit enhanced photovoltaic performance when compared to standard ligand passivation. Herein we demonstrate that the use of a triple cation Cs0.05(MA0.17FA0.83)0.95Pb(I0.9Br0.1)3 perovskite composition for surface passivation of the quantum dots results in highly efficient solar cells, which maintain 96 % of their initial performance after 1200h shelf storage. We confirm perovskite shell formation around the PbS nanocrystals by a range of spectroscopic techniques as well as high-resolution transmission electron microscopy. We find that the triple cation shell results in a favorable energetic alignment to the core of the dot, resulting in reduced recombination due to charge confinement without limiting transport in the active layer. Consequently, photovoltaic devices fabricated via a single-step film deposition reached a maximum AM1.5G power conversion efficiency of 11.3 % surpassing most previous reports of PbS solar cells employing perovskite passivation.
Many efforts have been dedicated to improve the solar steam generation by using a bi-layer structure. In this paper, a two-dimensional mathematical model describing the water evaporation in a bi-layer structure is firstly established and then the finite element method is used to simulate the effects of different influence factors on the evaporation rate. Results turn out that: besides the high solar energy absorptivity of the first-layer, an optimum porosity of the second-layer porous material should be applied and the optimum porosity is about 0.45 in this work. This optimum porosity is determined by the balance between the positive effect of the lowering effective thermal conductivity of the second layer and the negative effect of the reduced vapor diffusivity in the second layer when the porosity is decreased. The influence of the thermal conductivity of the second-layer porous material is negligible because the effective thermal conductivity of the second layer is determined by the porosity while a larger porosity means more water in the second layer. The ambient air velocity could greatly enhance the evaporation rate, and the evaporation rate will decrease linearly with the increase of the air relative humidity. This study is expected to supply some information for developing a more effective bi-layer solar steam generation system.
Interface constitutes a significant volume fraction in nanocomposites, and it requires the ability to tune and tailor interfaces to tap the full potential of nanocomposites. However, the development and optimization of nanocomposites is currently restricted by the limited exploration and utilization of interfaces at different length scales. In this research, we have designed and introduced a relatively large-scale vertical interphase into carbon nanocomposites, in which the dielectric response and dispersion features in microwave frequency range are successfully adjusted. A remarkable relaxation process has been observed in vertical-interphase nanocomposites, showing sensitivity to both filler loading and the discrepancy in polarization ability across the interphase. Together with our analyses on dielectric spectra and relaxation processes, it is suggested that the intrinsic effect of vertical interphase lies in its ability to constrain and localize heterogeneous charges under external fields. Following this logic, systematic research is presented in this article affording to realize tunable frequency-dependent dielectric functionality by means of vertical interphase engineering. Overall, this study provides a novel method to utilize interfacial effects rationally. The research approach demonstrated here has great potential in developing microwave dielectric nanocomposites and devices with targeted or unique performance such as tunable broadband absorbers.
The bi-layered structure has drawn a wide interest due to its good performance in solar steam generation. In this work, we firstly develop a calculation model which could give a good prediction of experimental results. Then, this model is applied to numerically study the effects of the depth of the liquid water, the temperature of the ambient air, the temperature of the liquid water, the porosity and the thermal conductivity of the second-layer porous material on the evaporation efficiency. Results show that when the depth of the liquid water is large enough, the thermal insulation at the bottom of the liquid water is not needed. There is a linear dependence of the evaporation efficiency on the temperature of the ambient air or/and the temperature of the liquid water, and an equation has been given to describe this phenomenon in the text. Compared to the temperature of the ambient air, the temperature of the liquid water could have a much larger effect on the evaporation efficiency. The effective thermal conductivity of the second layer, which could impose important effect on the evaporation efficiency, mainly depends on the porosity rather than the thermal conductivity of the second-layer porous material. Thus, we do not need to take into consideration of the thermal conductivity when selecting second-layer materials. This study is expected to provide some information for designing a high-evaporation-performance bi-layered system.
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