Vertically aligned montmorillonite aerogel-encapsulated polyethylene glycol with directional heat transfer paths for efficient solar thermal energy harvesting and storage

The conversion and storage of photothermal energy using phase change materials(PCMs)represent an optimal approach for harnessing clean and sustainable solar energy.Herein,we encapsulated polyethylene glycol(PEG)in montmorillonite aerogels(3D-Mt)through vacuum impregnation to prepare 3D-Mt/PEG composite PCMs.When used as a support matrix,3D-Mt can effectively prevent PEG leakage and act as a flame-retardant barrier to reduce the flammability of PEG.Simultaneously,3D-Mt/PEG demonstrates outstanding shape retention,increased thermal energy storage density,and commendable thermal and chemical stability.The phase transition enthalpy of 3D-Mt/PEG can reach 167.53 J/g and remains stable even after 50 heating-cooling cycles.Furthermore,the vertical sheet-like structure of 3D-Mt establishes directional heat transport channels,facilitating efficient phonon transfer.This configuration results in highly anisotropic thermal conductivities that ensure swift thermal responses and efficient heat conduction.This study addresses the shortcomings of PCMs,including the issues of leakage and inadequate flame retardancy.It achieves the development and design of 3D-Mt/PEG with ultrahigh strength,superior flame retardancy,and directional heat transfer.Therefore,this work offers a design strategy for the preparation of high-performance composite PCMs.The 3D-Mt/PEG with vertically aligned and well-ordered array structure developed in this research shows great potential for thermal management and photothermal conversion applications.

Simulation and Optimization of Energy Efficiency and Total Enthalpy Analysis of Sand Based Packed Bed Solar Thermal Energy Storage

This study is focused on the simulation and optimization of packed-bed solar thermal energy storage by using sand as a storage material and hot-water is used as a heat transfer fluid and storage as well.The analysis has been done by using the COMSOL multi-physics software and used to compute an optimization charging time of the storage.Parameters that control this optimization are storage height,storage diameter,heat transfer fluid flow rate,and sand bed particle size.The result of COMSOL multi-physics optimized thermal storage has been validated with Taguchi method.Accordingly,the optimized parameters of storage are:storage height of 1.4m,storage diameter of 0.4 m,flow rate of 0.02 kg/s,and sand particle size 12 mm.Among these parameters,the storage diameter result is the highest influenced optimized parameter of the thermal storage fromthe ANOVA analysis.For nominal packed bed thermal storage,the charging time needed to attain about 520 K temperature is more than 3500 s,while it needs only about 2000 s for the optimized storage which is very significant difference.Average charging energy efficiency of the optimized is greater than the nominal and previous concrete-based storage by 13.7%,and 13.1%,respectively in the charging time of 2700 s.

Highly conductive solid-solid phase change composites and devices enhanced by aligned graphite networks for solar/electro-thermal energy storage

Phase change materials(PCMs)are widely considered as promising energy storage materials for solar/electro-thermal energy storage.Nevertheless,the inherent low thermal/electrical conductivities of most PCMs limit their energy conversion efficiencies,hindering their practical applications.Herein,we fabricate a highly thermally/electrically conductive solid-solid phase change composite(PCC)enabled by forming aligned graphite networks through pressing the mixture of the trimethylolethane and porous expanded graphite(EG).Experiments indicate that both the thermal and electrical conductivities of the PCC increase with increasing mass proportion of the EG because the aligned graphite networks establish highly conductive pathways.Meanwhile,the PCC4 sample with the EG proportion of 20wt%can achieve a high thermal conductivity of 12.82±0.38W·m^(-1)·K^(-1)and a high electrical conductivity of 4.11±0.02S·cm^(-1)in the lengthwise direction.Furthermore,a solar-thermal energy storage device incorporating the PCC4,a solar selective absorber,and a highly transparent glass is developed,which reaches a high solar-thermal efficiency of 77.30±2.71%under 3.0 suns.Moreover,the PCC4 can also reach a high electro-thermal efficiency of 91.62±3.52%at a low voltage of 3.6V,demonstrating its superior electro-thermal storage performance.Finally,stability experiments indicate that PCCs exhibit stabilized performance in prolonged TES operations.Overall,this work offers highly conductive and cost-effective PCCs,which are suitable for large-scale and efficient solar/electro-thermal energy storage.

Photoelectrochemical regeneration of all vanadium redox species for construction of a solar rechargeable flow cell

Energy storage is pivotal for the continuous utilization of solar energy suffering from the intermittency issue. Herein, we demonstrate a solar rechargeable flow cell（SRFC） based on photoelectrochemical regeneration of vanadium redox species for in-situ solar energy harvest and storage. In this device, TiO_2 and MWCNT/acetylene black（MWCNT/AB） composite are served as the photoanode and the counter electrode,respectively, with all vanadium redox couples, VO_2~＋/VO^（2＋）and VO^（2＋）/V^（3＋）, as solar energy storage media.Benefitting from solar energy, the cell can be photocharged under a bias as low as 0.1 V, which is much lower than the discharge voltage of ~0.5 V. Photocharged under the optimized condition, the cell delivers a discharge energy of 23.0 mWh/L with 67.4% input electric energy savings. This prototype work may inspire the rational design for cost-effective solar energy storage devices.

High Solar Energy Absorption and Human Body Radiation Reflection Janus Textile for Personal Thermal Management

A large of energy consumption is required for indoor and outdoor personal heating to ameliorate the comfortable and healthy conditions.Main personal thermal management strategy is to reflect mid-infrared human body radiation for human surface temperature(THS)regulation.We demonstrate a visible Janus light absorbent/reflective air-layer fabric(Janus A/R fabric)that can passively reflect radiative heating meanwhile can actively capture the solar energy.A series of azobenzene derivatives functionalized with alkyl tails are reported to co-harvest the solar and phase-change energy.The THS covered by Janus A/R fabric can be heated up to~3.7°C higher than that covered by air-layer fabric in cold environment(5°C).Besides,integrating the thermo-and photo-chromic properties is capable of monitoring comfort THS and residue energy storage enthalpy,respectively.According to the colour monitors,intermittent irradiation approach is proposed to prolong comfortable-THS holding time for managing energy efficiently.

Azobenzene/graphene hybrid for high-density solar thermal storage by optimizing molecular structure

A large capacity storing solar energy as latent heat in a close-cycle is essentially important for solar thermal fuels. This paper presents a solar thermal molecule model of a photo-isomerizable azobenzene(Azo) molecule covalently bound to graphene. The storage capacity of the Azo depending on isomerization enthalpy(ΔH) is calculated based on density functional theory. The result indicates that the ΔH of Azo molecules on the graphene can be tuned by electronic interaction, steric hindrance and molecular hydrogen bonds(H-bonds). Azo with the withdrawing group on the ortho-position of the free benzene shows a relatively high ΔH due to resonance effect. Moreover, the H-bonds on the trans-isomer largely increase ΔH because they stabilize the trans-isomer at a low energy. 2-hydroxy-4-carboxyl-2′,6′,-dimethylamino-Azo/graphene shows the maximum ΔH up to 1.871 e V(107.14 Wh kg^(-1)), which is 125.4% higher than Azo without functional groups. The Azo/graphene model can be used for developing high-density solar thermal storage materials by controlling molecular interaction.

Wide spectrum solar energy harvesting through an integrated photovoltaic and thermoelectric system

This paper proposes a power system concept that integrates photovoltaic （PV） and thermoelectric （TE） technologies to harvest solar energy from a wide spectral range. By introduction of the ＇spectrum beam splitting＇ technique, short wavelength solar radiation is converted directly into electricity in the PV cells, while the long wavelength segment of the spectrum is used to produce moderate to high temperature thermal energy, which then generates electricity in the TE device. To overcome the intermittent nature of solar radiation, the system is also coupled to a thermal energy storage unit. A systematic analysis of the integrated system is carried out, encompassing the system configuration, material properties, thermal management, and energy storage aspects. We have also attempted to optimize the integrated system. The results indicate that the system configuration and optimization are the most important factors for high overall efficiency.

Entire onion source-derived redox porous carbon electrodes towards efficient quasi-solid-state solar charged hybrid supercapacitor

Biomass-derived electrodes inherently containing redox-active species have gained extensive attention recently due to their availability,eco-friendliness,sustainability,and low cost.We report novel binder-free faradic surface redox onion-derived carbon positive electrode with nano regime particles by hydrothermal synthesis and Na^(+)and Cl^(−)ions diffused porous carbon negative electrode via a carbonization method.Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy confirmed the presence of oxidized sulfur and(N-6)pyridinic N-based redox groups inherently present in the as-prepared compounds.The electrochemical analysis of the positive electrode revealed its faradic redox type of energy storage mechanism with an excellent specific capacitance of 1805 Fg^(-1) at the current density of 3 Ag^(-1) as well as appreciable long-term cycling stability(76.8%retention after 10000 charge-discharge cycles).Meanwhile,the negative electrode exhibited a maximum specific capacitance of 373 Fg^(-1) at 1 Ag^(-1) with outstanding long-term cycling stability(100.7%retention after 10000 cycles).The fabricated polyvinyl alcohol-potassium hydroxide gel electrolyte-based quasi-solid-state hybrid supercapacitor(QHSC)delivered excellent energy density and power density of 19.94 Wh kg^(-1) and 374.99 W kg^(-1),respectively with an ultralong cyclic life(102.3% retention)over 10000 cycles.Furthermore,the QHSC was connected to a solar panel to store renewable energy.Solar charged QHSC effectively powered a speedometer,enlightening its potential application in advanced sustainable energy storage systems.

Effects of nanostructure on clean energy: big solutions gained from small features

The increasing energy consumption and environmental concerns have driven the development of costeffective, high-efficiency clean energy. Advanced functional nanomaterials and relevant nanotechnologies are playing a crucial role and showing promise in resolving some energy issues. In this view, we focus on recent advances of functional nanomaterials in clean energy applications, including solar energy conversion, water splitting, photodegradation, electrochemical energy conversion and storage, and thermoelectric conversion, which have attracted considerable interests in the regime of clean energy.

一种新型太阳能热电化学耦合甲烷重整制氢脱碳与太阳能储能方法

Hydrogen is widely regarded as a sustainable energy carrier with tremendous potential for low-carbon energy transition.Solar photovoltaic-driven water electrolysis(PV-E)is a clean and sustainable approach of hydrogen production,but with major barriers of high hydrogen production costs and limited capacity.Steam methane reforming(SMR),the state-of-the-art means of hydrogen production,has yet to overcome key obstacles of high reaction temperature and CO_(2)emission for sustainability.This work proposes a solar thermo-electrochemical SMR approach,in which solar-driven mid/low-temperature SMR is combined with electrochemical H_(2)separation and in-situ CO_(2)capture.The feasibility of this method is verified experimentally,achieving an average methane conversion of 96.8%at a dramatically reduced reforming temperature of 400-500℃.The underlying mechanisms of this method are revealed by an experimentally calibrated model,which is further employed to predict its performance for thermoelectrochemical hydrogen production.Simulation results show that a net solar-to-H_(2)efficiency of26.25%could be obtained at 500℃,which is over 11 percentage points higher than that of PV-E;the first-law thermodynamic efficiency reaches up to 63.27%correspondingly.The enhanced efficiency also leads to decreased fuel consumption and lower CO_(2)emission of the proposed solar-driven SMR system.Such complementary conversion of solar PV electricity,solar thermal energy,and low-carbon fuel provides a synergistic and efficient means of sustainable H_(2)production with potentially long-term solar energy storage on a vast scale.