2 research outputs found
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Model-driven development of durable and scalable thermal energy storage materials for buildings
The energy impact of integrating phase change materials (PCMs) in buildings for thermal energy storage has been modeled by various whole-building simulation programs, demonstrating that PCM incorporation can reduce energy consumption, provide grid flexibility and resilience, and reduce CO2 emissions. The models assume that the PCMs are in perfect operating condition and underestimate the impact of actual phase change behavior (e.g., enthalpy curve shape) on thermal load shifting in practical deployment. In this paper, we bridge the gap between theory and practice when evaluating the energy impact of PCMs by using a model-driven approach to develop durable thermal energy storage materials with desired phase change properties. For ease of integration, we fabricate shape-stabilized PCMs (ss-PCMs) by encapsulating solid-liquid polyethylene glycol (PEG) consisting of different molecular weights within mesoporous magnesium oxide (MgO) matrices. Learning from the modeling results, we manipulate phase change properties such as peak melting temperature and temperature glide of PEG-MgO ss-PCMs during the synthesis process to achieve desired properties. As such, the energy density is maximized within the optimum operating temperature range, which is critical to boosting energy efficiency. Compared to a case with no PCM, a layer of PEG-MgO ss-PCM integrated into the wall provides a 50% reduction in the peak load and also exhibits a repeatable phase change behavior for up to 1000 thermal cycles without leakage, showing durability of this material. We also show that this lab-scale synthesis process is easy to be scaled up by 100 times for a demonstration of large-scale industrial production. The synthetic tunability of transition temperature of ss-PCMs also extends their applicability beyond buildings
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Identification of Exciton Complexes in Charge-Tunable Janus WSeS Monolayers.
Janus transition-metal dichalcogenide monolayers are artificial materials, where one plane of chalcogen atoms is replaced by chalcogen atoms of a different type. Theory predicts an in-built out-of-plane electric field, giving rise to long-lived, dipolar excitons, while preserving direct-bandgap optical transitions in a uniform potential landscape. Previous Janus studies had broad photoluminescence (>18 meV) spectra obfuscating their specific excitonic origin. Here, we identify the neutral and the negatively charged inter- and intravalley exciton transitions in Janus WSeS monolayers with ∼6 meV optical line widths. We integrate Janus monolayers into vertical heterostructures, allowing doping control. Magneto-optic measurements indicate that monolayer WSeS has a direct bandgap at the K points. Our results pave the way for applications such as nanoscale sensing, which relies on resolving excitonic energy shifts, and the development of Janus-based optoelectronic devices, which requires charge-state control and integration into vertical heterostructures