Dual-Functional Aligned and Interconnected Graphite Nanoplatelet Networks for Accelerating Solar Thermal Energy Harvesting and Storage within Phase Change Materials.

Solar thermal energy conversion and storage within phase change materials (PCMs) can overcome solar radiation intermittency to enable continuous operation of many heating-related processes. However, the energy-harvesting performance of current storage systems is always limited by low efficiencies in either solar thermal energy conversion or thermal transport within PCMs. Although PCM-based nanocomposites can address one or both of these issues, achieving high-performance composites with simultaneously enhanced photothermal performance and thermal transport capacity remains challenging. Here, we demonstrate that dual-functional aligned and interconnected graphite nanoplatelet networks (AIGNNs) yield the synergistic enhancement of interfacial photothermal conversion and thermal transport within PCMs to accelerate the solar thermal energy harvesting and storage. The AIGNNs include the naked part as the three-dimensional optical absorber and the incorporated part as thermally conductive pathways within PCMs. First, a phase change composite composed of the AIGNNs and the solid-solid PCM of polyhydric alcohol is synthesized using a facile three-step method, and shows 400% thermal conductivity enhancement for per 1 wt % graphite loading compared to pristine PCMs. After the elaborate surface treatment, a small part of the graphite networks is in situ exposed as the 3D optical absorber to boost the surface full-spectrum sunlight absorptivity up to 95%. This dual function design takes full advantage of the integrated AIGNNs in terms of both photothermal conversion and thermal transport capacities, superior to the traditional coating-enhanced photothermal conversion. This work offers a promising route to accelerating solar thermal energy harvesting and storage within PCMs.

Near-Zero-Energy Smart Battery Thermal Management Enabled by Sorption Energy Harvesting from Air.

Effective battery thermal management (BTM) is critical to ensure fast charging/discharging, safe, and efficient operation of batteries by regulating their working temperatures within an optimal range. However, the existing BTM methods not only are limited by a large space, weight, and energy consumption but also hardly overcome the contradiction of battery cooling at high temperatures and battery heating at low temperatures. Here we propose a near-zero-energy smart battery thermal management (SBTM) strategy for both passive heating and cooling based on sorption energy harvesting from air. The sorption-induced reversible thermal effects due to metal-organic framework water vapor desorption/sorption automatically enable battery cooling and heating depending on the local battery temperature. We demonstrate that a self-adaptive SBTM device with MIL-101(Cr)@carbon foam can control the battery temperature below 45 °C, even at high charge/discharge rates in hot environments, and realize self-preheating to ∼15 °C in cold environments, with an increase in the battery capacity of 9.2%. Our approach offers a promising route to achieving compact, liquid-free, high-energy/power-density, low-energy consumption, and self-adaptive smart thermal management for thermo-related devices.

Efficient Solar-Driven Water Harvesting from Arid Air with Metal-Organic Frameworks Modified by Hygroscopic Salt.

Freshwater scarcity is a global challenge threatening human survival, especially for people living in arid regions. Sorption-based atmospheric water harvesting (AWH) is an appealing way to solve this problem. However, the state-of-the-art AWH technologies have poor water harvesting performance in arid climates owing to the low water sorption capacity of common sorbents under low humidity conditions. We report a high-performance composite sorbent for efficient water harvesting from arid air by confining hygroscopic salt in a metal-organic framework matrix (LiCl@MIL-101(Cr)). The composite sorbent shows 0.77 g g-1 water sorption capacity at 1.2 kPa vapor pressure (30 % relative humidity at 30 °C) by integrating the multi-step sorption processes of salt chemisorption, deliquescence, and solution absorption. A highly efficient AWH prototype is demonstrated with LiCl@MIL-101(Cr) that can enable the harvesting of 0.45-0.7 kg water per kilogram of material under laboratory and outdoor ambient conditions powered by natural sunlight without optical concentration and additional energy input.

High-Performance Thermally Conductive Phase Change Composites by Large-Size Oriented Graphite Sheets for Scalable Thermal Energy Harvesting.

Efficient thermal energy harvesting using phase-change materials (PCMs) has great potential for cost-effective thermal management and energy storage applications. However, the low thermal conductivity of PCMs (KPCM ) is a long-standing bottleneck for high-power-density energy harvesting. Although PCM-based nanocomposites with an enhanced thermal conductivity can address this issue, achieving a higher K (>10 W m-1 K-1 ) at filler loadings below 50 wt% remains challenging. A strategy for synthesizing highly thermally conductive phase-change composites (PCCs) by compression-induced construction of large aligned graphite sheets inside PCCs is demonstrated. The millimeter-sized graphite sheet consists of lateral van-der-Waals-bonded and oriented graphite nanoplatelets at the micro/nanoscale, which together with a thin PCM layer between the sheets synergistically enhance KPCM in the range of 4.4-35.0 W m-1 K-1 at graphite loadings below 40.0 wt%. The resulting PCCs also demonstrate homogeneity, no leakage, and superior phase change behavior, which can be easily engineered into devices for efficient thermal energy harvesting by coordinating the sheet orientation with the thermal transport direction. This method offers a promising route to high-power-density and low-cost applications of PCMs in large-scale thermal energy storage, thermal management of electronics, etc.