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Combined solar concentration and carbon nanotube absorber for high performance solar thermoelectric generators
摘要： Solar thermoelectric generators (STEGs) is one of the most important technologies for solar energy conversion. However, the inefficiency due to coupling constraints such like low working temperature and dimensionless figure of merit of the thermoelectric materials, also known as material’s ZT value, has been hampering the development of STEGs for a time. Here we demonstrate a high performance STEG system combined with solar concentrators and carbon nanotubes (CNTs) absorber, which can greatly improve the solar-thermal conversion process. The proposed STEG system enables a peak efficiency of 4.3% with solar concentration of 78, and a maximum power of 11.2 W at 106× suns. The enhanced efficiency is ensured by the optimized system thermodynamics due to the combination of solar concentration devices and CNT based solar absorber. Our design provides a universal prototype of solar thermal energy recovery system for distributed energy harvesting and deep-space explorations.
关键词： Thermodynamics,Carbon nanotube,Solar concentration,Thermoelectricity,Energy harvesting
更新于2025-09-19 17:15:36
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Thermodynamic limits to energy conversion in solar thermal fuels
摘要： Solar thermal fuels (STFs) are an unconventional paradigm for solar energy conversion and storage which is attracting renewed attention. In this concept, a material absorbs sunlight and stores the energy chemically via an induced structural change, which can later be reversed to release the energy as heat. An example is the azobenzene molecule which has a cis-trans photoisomerization with these properties, and can be tuned by chemical substitution and attachment to templates such as carbon nanotubes, small molecules, or polymers. By analogy to the Shockley–Queisser limit for photovoltaics, we analyze the maximum attainable efficiency for STFs from fundamental thermodynamic considerations. Microscopic reversibility provides a bound on the quantum yield of photoisomerization due to fluorescence, regardless of details of photochemistry. We emphasize the importance of analyzing the free energy, not just enthalpy, of the metastable molecules, and find an efficiency limit for conversion to stored chemical energy equal to the Shockley–Queisser limit. STF candidates from a recent high-throughput search are analyzed in light of the efficiency limit.
关键词： energy storage,thermodynamics,solar energy conversion,photoisomerization
更新于2025-09-19 17:15:36
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Thermal Shock Synthesis of Metal Nanoclusters within On-the-fly Graphene Particles
摘要： Metal nanoclusters (1-10 nm) have drawn great attention due to their potential applications including energy storage, catalysis, nanomedicine and electronic devices. However, manufacturing ultra-small metal nanoparticles at high concentrations in an unaggregated state is not a solved problem. Here we report an aerosol-based thermal shock technique for in situ synthesis of well-dispersed metal nanoclusters in on-the-fly graphene aerosols. A rapid thermal shock to the graphene aerosol has been used to nucleate and grow the metal nanoclusters with subsequent quenching to freeze the newly formed nanoclusters in the graphene aerosol matrix. A characteristic time analysis comparison with experiment shows that the nanocluster formation is governed by nucleation and subsequent surface growth, and that the graphene retards coagulation, enabling unaggregrated metal nanoclusters. The method is generic, and we show the formation of sub-10 nm Ni, Co and Sn nanoclusters. This continuous aerosol-based thermal shock technique offers considerable potential for the scalable synthesis of well-dispersed and uniform metal nanoclusters stabilized within a host matrix. As an example of potential application, we demonstrate very favorable catalytic properties.
关键词： thermodynamics,in situ growth,growth mechanism,thermal shock synthesis,kinetics,metal nanoclusters
更新于2025-09-19 17:15:36
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Thermodynamic Implications of the Ligand Exchange with Alkylamines on the Surface of CdSe Quantum Dots: The Importance of Ligand-Ligand Interactions
摘要： Ligand exchange is a critical step for tuning the properties of quantum dots (QDs), as well as functionalization for wide applications. Previous studies have categorized X-, L- and Z-types of ligands and classified the ligand exchange process accordingly. Many works have investigated the influences of ligand exchange on the optical properties of QDs. To date, however, the thermodynamic implications of ligand exchange are not well understood, and the mechanisms of distinct effects of the ligands of the same type are unclear. To address these issues, ligand exchange reactions of the oleate-capped CdSe QDs with alkylamines of different carbon chain length, namely n-butylamine (C4Am), n-octylamine (C8Am), n-dodecylamine (C12Am), were investigated using 1H nuclear magnetic resonance (1H NMR) spectroscopy, fluorescence spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), et al. 1H NMR studies showed that the equilibrium constants (Keq) for the desorption of the Z-type ligand (cadmium oleate) from the surface of CdSe QDs, as promoted by the L-type ligands (alkylamines), were in the order of C4Am > C8Am > C12Am, presumably highlighting the small steric barrier of ligands with short carbon chain. In addition, the ligand exchange was studied by fluorescence titration at varied temperatures from a perspective of ligand adsorption following the desorption of cadmium oleate. The binding constants were in the order of magnitude of 103 M-1. A “Two-step Ligand Exchange (TSLE)” model was developed to describe the ligand desorption-adsorption process with thermodynamic perspectives. The increased length of the carbon chain brought not only increasing steric barrier but also increasing van der Waals interactions, exhibiting a double-edged sword effect in ligand exchange. The ligand exchange with C8Am contributed the most negative value of ΔH and ΔS since the van der Waals interactions between C8Am and neighboring ligands was stronger than that for C4Am, whereas its steric barrier was weaker than that of C12Am. These demonstrated the importance of ligand-ligand interactions, relatively less documented in the previous studies, besides the predominance of the nanocrystal-ligand interactions. UV-vis absorption spectroscopic and fluorescence lifetime studies further showed that the ligand exchange with all three alkylamines affected optical properties of CdSe QDs to some extent. Powder X-ray diffraction (XRD) and transmission electron microscopic (TEM) results showed that the ligand exchange process basically did not affect the crystal structure and core size of the CdSe QDs. Our work had proposed a conceivable mechanism for ligand exchange, elucidated the thermodynamic implications and provided a reasonable guidance for selection of suitable ligands.
关键词： Quantum dots,Ligand exchange,Thermodynamics,CdSe,Alkylamines
更新于2025-09-19 17:13:59
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Investigation of picosecond thermodynamics in a laser-produced plasma using Thomson scattering
摘要： The picosecond evolution of the plasma conditions in a laser-produced plasma was measured using a Thomson-scattering diagnostic. The picosecond resolved Thomson spectra was enabled by a pulse-front-tilt-compensated spectrometer. The Thomson spectra revealed a transition in the plasma conditions from an initially cold evolving plasma to a quasi-stationary equilibrium plasma. The equilibrium temperature was found to match the generalized heat equation’s predicted scaling Te ∝ n2/5 and Te ∝ I 1/5. The plasma evolution was compared to Raman gain bandwidth calculations and showed a time-dependent resonance detuning that would limit the transfer e?ciency of a Raman plasma ampli?er in the linear regime.
关键词： laser-produced plasma,Thomson scattering,picosecond thermodynamics,Raman plasma amplifier,plasma conditions
更新于2025-09-19 17:13:59
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Fundamentals of three-dimensional Yb-fiber Nd:YAG laser machining of structural bone
摘要： This work aims to understand the fundamental aspects of the laser-bone interaction in three-dimensional laser machining of the bone through an integrated experimental-computational approach. The study introduces 3-dimensional laser machining of bones through multi-laser passes and attempts to establish the dimensional control over the laser-machined cavity through a finite element method based multi-physics computational model. A continuous wave Yb-fiber Nd:YAG laser (λ = 1064 nm) was employed with laser fluences ranging from 5:31 J/mm2 to 25:46 J/mm2 generated in combination of laser power (400 W–700 W) and machining speed (50 mm/s–250 mm/s). In multi-laser pass machining, the optimum fill spacing of 0.2 mm was identified for higher machining rates with low deviation from linearity of machined edge (d = 9 μm). This resulted in high machining rates ranging from 16:49 + 0:2 mm3/s to 45:26 + 0:66 mm3/s for a given range of laser fluence. The optimization for machining efficiency and physical attributes of the machined cavity were comprehended through thermodynamics and kinetics of the laser interaction with the bone based on the computational model for varying laser processing parameters.
关键词： bone,kinetics,Yb-fiber Nd:YAG laser,laser machining,computational model,three-dimensional,thermodynamics
更新于2025-09-16 10:30:52
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Thermodynamics of Natural Pigment-Doped Ethanol under Monochromatic Laser Irradiation
摘要： A laser beam heats a mixture of ethanol and anthocyanins producing the effect of a reciprocating machine. This behaviour is analyzed in terms of the stable, metastable and unstable states of Landau and Lifschitz. Trying first with the van der Waals equation of state, with negative results because the system state is normally far from the critical state, a modified version, with van der Waals coefficients depending linearly on the temperature is proposed, based in the thermodynamic properties of ethanol at room and critical temperatures. The resulting theory allows us to understand the discontinuous results concerning the absorption of the laser beam in terms of a thermodynamic cycle and its frequency dependence on the laser light focus position. Slight changes in the experimental setup may enable the measurement of thermodynamic properties in metastable states.
关键词： Ethanol,van der Waals Equation,Laser Irradiation,Thermodynamics,Natural Pigments
更新于2025-09-16 10:30:52
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Controlled Fabrication of K2Ti8O17 Nanowires for Highly Efficient and Ultrafast Adsorption towards Methylene Blue
摘要： Advanced adsorbents need high adsorption rate and superior adsorption capability to clean up the organic methylene blue (MB) from wastewater. We prepared K2Ti8O17 nanowires grown along [0 1 0] direction with a one-step hydrothermal method. The K2Ti8O17 nanowires with tens of nanometers in diameter and tens of micrometers in length were achieved with smooth surfaces and twisted wire-like morphology. The K2Ti8O17 nanowires exhibit high uptake capacity of ～208.8 mg·g?1 in the MB removal under equilibrium pH = 7. The adsorption equilibriums of MB onto K2Ti8O17 adsorbent is achieved with 97% removal rate MB within only ~21 min, which is the shortest adsorption time among the recent reported inorganic adsorbents towards MB. The adsorption process has a good agreement with the well-known pseudo-second-order kinetic model (k2 = 0.2) and the Langmuir isotherm model. The FTIR measurements suggest that the adsorption can be assigned to the hydrogen bonding and electrostatic attraction between MB and K2Ti8O17. This ultrafast removal ability owns to the larger (0 2 0) interplanar spacing and zigzag surface structure of the nanowires, which provide abundant active adsorption sites. Thermodynamic parameters reflect the spontaneous, exothermic and feasible uptake of MB. Besides, K2Ti8O17 nanowires enjoy high adsorptive ability for chromium (VI) ions and photocatalytic removal towards NO. This work highlights the great significance of K2Ti8O17 nanowires as a low cast promising material used for adsorptive elimanation of organic contaminations in fast water purification on a large scale.
关键词： Hydrothermal synthesis,Tunnel-layered structure,Adsorption capability,K2Ti8O17 nanowires,Thermodynamics,Kinetics,Isotherms
更新于2025-09-16 10:30:52
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Formation Thermodynamics, Stability, and Decomposition Pathways of CsPbX <sub/>3</sub> (X = Cl, Br, I) Photovoltaic Materials
摘要： Standard enthalpies of formation of CsPbX3 (X = Cl, Br, I) perovskites from halides and from elements at 298 K were measured using solution calorimetry. Intrinsic and extrinsic stabilities of CsPbX3 halides were analyzed and compared with those of CH3NH3PbX3. The main difference between the stabilities of CsPbX3 and CH3NH3PbX3 halides was found to stem from the different chemical nature of cesium and methylammonium cations. Indeed, the enthalpies of formation of CsPbX3 from binary constituent halides, ?fH○hal, are only slightly more negative than those of CH3NH3PbX3. Small values of ?fH○hal imply that the entropic contribution to the Gibbs free energy of formation of CsPbX3 and CH3NH3PbX3 is significant and, hence, of utmost importance for understanding the intrinsic stability of these compounds and their analogs. Regarding the extrinsic stability, the presence of gaseous O2, H2O, and CO2 was shown to be crucial for the stability of the iodide, CsPbI3, for which several decomposition reactions, exergonic at 298 K, were identified. At the same time, chloride, CsPbCl3, and bromide, CsPbBr3, are much less sensitive to these chemical agents. However, liquid water should degrade all the CsPbX3 halides.
关键词： Plasmonics,Stability,Decomposition Pathways,Hybrid Materials,Thermodynamics,Magnetic,Photovoltaic Materials,CsPbX3,Optical
更新于2025-09-16 10:30:52
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Can Thermodynamics Guide Us to Make Better Solar Cells?
摘要： Thermodynamics has provided a powerful tool to study radiation and its conversion into useful work. Starting from the so-called Shockley’s paradox, this article discusses the thermodynamic view of fundamental losses to photovoltaic conversion, and how thermodynamics enters the charge-carrier transport in semiconductors and heat-exchange processes at p-n junctions. Turning to photon flows, considerations based on detailed balance and reciprocity provide a comprehensive picture of the voltage produced by the solar cell in the presence of nonradiative recombination. We shall use these tools to examine several topics under recent discussion, including photon recycling and hot-carrier conversion based on thermoelectricity.
关键词： thermodynamics,thermoelectricity,solar energy,Photovoltaic cells
更新于2025-09-12 10:27:22