Ionocaloric refrigeration cycle

Tunable Electrochemical Entropy through Solvent Ordering by a Supramolecular Host

An aqueous electrochemically controlled host-guest encapsulation system demonstrates a large and synthetically tunable redox entropy change. Electrochemical entropy is the basis for thermally regenerative electrochemical cycles (TRECs), which utilize reversible electrochemical processes with large molar entropy changes for thermogalvanic waste-heat harvesting and electrochemical cooling, among other potential applications. A supramolecular host-guest system demonstrates a molar entropy change of 4 times that of the state-of-the-art aqueous TREC electrolyte potassium ferricyanide. Upon encapsulation of a guest, water molecules that structurally resemble amorphous ice are displaced from the host cavity, leveraging a change in the degrees of freedom and ordering of the solvent rather than the solvation of the redox-active species to increase entropy. The synthetic tunability of the host allows rational optimization of the system's ΔS, showing a range of -51 to -101 cal mol-1 K-1 (-2.2 to -4.4 mV K-1) depending on ligand and metal vertex modifications, demonstrating the potential for rational design of high-entropy electrolytes and a new strategy to overcome theoretical limits on ion solvation reorganization entropy.

Multifunctional composite coatings with hydrophobic, UV-resistant, anti-oxidative, and photothermal performance for healthcare

Personal protective textiles have attracted extensive interest since Corona Virus Disease 2019 has broken out. Moreover, developing eco-friendly, multifunctional waterproof, and breathable surface is of great importance but still faces enormous challenges. Notably, good hydrophobicity and breathability are necessary for protective textiles, especially protective clothing and face masks for healthcare. Herein, the multifunctional composite coatings with good UV-resistant, anti-oxidative, hydrophobic, breathable, and photothermal performance has been rapidly created to meet protective requirements. First, the gallic acid and chitosan polymer was coated onto the cotton fabric surface. Subsequently, the modified silica sol was anchored on the coated cotton fabric surface. The successful fabrication of composite coatings was verified by RGB values obtained from the smartphone and K/S value. The present work is an advance for realizing textile hydrophobicity by utilizing fluorine-free materials, compared with the surface hydrophobicity fabricated with conventional fluorinated materials. The surface free energy has been reduced from 84.2 to27.6 mJ/m2 so that the modified cotton fabric could repel the ethylene glycol, hydrochloric acid, and sodium hydroxide solutions, respectively. Besides, the composite coatings possesses lower adhesion to deionized water. After 70 cycles of the sandpaper abrasion, the fluorine-free hydrophobic coatings still exhibits good hydrophobicity with WCA of 124.6 ± 0.9°, with overcoming the intrinsic drawback of the poor abrasion resistance of hydrophobic surfaces. Briefly, the present work may provide a universal strategy for rapidly creating advanced protective coatings to meet personal healthcare, and a novel method for detecting RGB values of composite coatings by smartphone.

High-performance multimode elastocaloric cooling system

Developing zero-global warming potential refrigerants has emerged as one area that helps address global climate change concerns. Various high-efficiency caloric cooling techniques meet this goal, but scaling them up to technologically meaningful performance remains challenging. We have developed an elastocaloric cooling system with a maximum cooling power of 260 watts and a maximum temperature span of 22.5 kelvin. These values are among the highest reported for any caloric cooling system. Its key feature is the compression of fatigue-resistant elastocaloric nitinol (NiTi) tubes configured in a versatile multimode heat exchange architecture, which allows the harnessing of both high delivered cooling power and large temperature spans. Our system shows that elastocaloric cooling, which only emerged 8 years ago, is a promising direction for commercializing caloric cooling.

Cool it, with a pinch of salt

Melting a solvent with a salt and then desalinating it enables a reversible cooling cycle.