Aerogel-Directed Energy-Storage Films with Thermally Stimulant Multiresponsiveness

Novel protic ionic liquids-based phase change materials for high performance thermal energy storage systems

Phase change materials (PCMs) are an important class of innovative materials that considerably contribute to the effective use and conservation of solar energy and wasted heat in thermal energy storage systems (TES). The performance of TES can be improved by using environmentally friendly PCMs called ionic liquids (ILs) based on ethanolamines and fatty acids. The 2-hydroxyethylammonium, bis(2-hydroxyethyl)ammonium, and tris(2-hydroxyethyl)ammonium palmitate ILs, which function is in the temperature range of 30-100 °C and provide a safe and affordable capacity, are introduced in this study for the first time as PCMs. PCMs' chemical composition and microstructure were examined using fourier transformation infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM), respectively. DSC was used to evaluate the ILs' latent heat of fusion and specific heat capacity, while TGA was used to establish their thermal stability. Finally, a home-made device with a PCMs (synthesized ILs) container cell and a commercial thermoelectric generator device to record the real-time voltage (V) was used to convert thermal energy into electrical energy.

Aerogels Meet Phase Change Materials: Fundamentals, Advances, and Beyond

Benefiting from the inherent properties of ultralight weight, ultrahigh porosity, ultrahigh specific surface area, adjustable thermal/electrical conductivities, and mechanical flexibility, aerogels are considered ideal supporting alternatives to efficiently encapsulate phase change materials (PCMs) and rationalize phase transformation behaviors. The marriage of versatile aerogels and PCMs is a milestone in pioneering advanced multifunctional composite PCMs. Emerging aerogel-based composite PCMs with high energy storage density are accepted as a cutting-edge thermal energy storage (TES) concept, enabling advanced functionality of PCMs. Considering the lack of a timely and comprehensive review on aerogel-based composite PCMs, herein, we systematically retrospect the state-of-the-art advances of versatile aerogels for high-performance and multifunctional composite PCMs, with particular emphasis on advanced multiple functions, such as acoustic-thermal and solar-thermal-electricity energy conversion strategies, mechanical flexibility, flame retardancy, shape memory, intelligent grippers, and thermal infrared stealth. Emphasis is also given to the versatile roles of different aerogels in composite PCMs and the relationships between their architectures and thermophysical properties. This review also showcases the discovery of an interdisciplinary research field combining aerogels and 3D printing technology, which will contribute to pioneering cutting-edge PCMs. This review aims to arouse wider research interests among interdisciplinary fields and provide insightful guidance for the rational design of advanced multifunctional aerogel-based composite PCMs, thus facilitating the significant breakthroughs in both fundamental research and commercial applications.

Mechanically Tough and Regenerable Antibacterial Nanofibrillated Cellulose-Based Aerogels for Oil/Water Separation

Nanofibrillated cellulose (NFC)-based aerogels have been widely used for various applications. However, the disadvantages of poor structural stability, low mechanical toughness, and easy contamination by bacteria hinder their large-scale application. In this work, 3-(3'-acrylicacidpropylester)-5,5-dimethyl hydantoin (APDMH) was grafted on oxidized NFC (ONC) to prepare antibacterial poly(APDMH)-g-ONC (PAC). PAC and poly(ethyleneimine) (PEI) were chemically cross-linked using 3-glycidoxypropyltrimethox (GPTMS), aiming at constructing a PAC-g-PEI aerogel with multiple network structures. The mechanical behaviors of composite aerogel and oil/water separation performances under different conditions were investigated. PAC-g-PEI aerogel exhibits outstanding fatigue resistance (>50 cycles of compression) and superior elasticity (96.76% height recovery after five compression-release cycles at 50% strain). The obtained superhydrophilic and underwater-oleophobic properties endow the aerogel with excellent oil/water separation performances, achieving a satisfactory separation efficiency of over 99% and flux of over 9500 L·m^-2·h^-1. Furthermore, the chlorinated aerogel of PAC-g-PEI-Cl shows highly efficient and rechargeable antibacterial properties, can inactivate 6.72-log Escherichia coli and 6.60-log Staphylococcus aureus within 10 min, and can still kill all inoculated bacteria after 50 cycles. In addition, PAC-g-PEI-Cl aerogel can inhibit biofilm formation, making it a promising candidate for highly efficient oil/water separation applications in diverse harsh conditions.

Solid-Liquid Host-Guest Composites: The Marriage of Porous Solids and Functional Liquids

Composite materials can provide remarkable improvements over the individual constituents. Especially, with a liquid component introduced into a solid porous host, solid-liquid host-guest composites have recently come to the forefront with exceptional functions that promise them for a wealth of applications. Combining the unprecedented dynamic, transparent, omniphobic, self-healing, diffusive and adaptive nature of functional liquid with inherent solid host's property, solid-liquid host-guest composites can realize the ease of fabrication, long-term stability, and a broad spectrum of enhanced properties, which cannot be fully met by conventional solid-solid composites or liquid-liquid composites. This review presents the state-of-the-art progress in solid-liquid host-guest composites. Initially, the concept, classification, design strategy, as well as fabrication methods as a path forward to develop the composites are unraveled, and further it is elaborated on how the functionality of porous solid and functional liquid can be harnessed to create composites with a broad range of unique properties, especially, the optical, thermal, electric, mechanical, sorption, and separation properties. With these fascinating properties, a myriad of emerging applications such as optical devices, thermal management, electromagnetic-interference shielding, soft electronics, gas capture and release, and multiphase separations are touched upon, inspiring more frontier researches in materials science, interfacial chemistry, membrane science, engineering, and multidisciplinary. Finally, this review provides the perspective on the future directions of solid-liquid host-guest composites and assesses the challenges and opportunities ahead.

A Review of Composite Phase Change Materials Based on Porous Silica Nanomaterials for Latent Heat Storage Applications

Phase change materials (PCMs) can store thermal energy as latent heat through phase transitions. PCMs using the solid-liquid phase transition offer high 100-300 J g-1 enthalpy at constant temperature. However, pure compounds suffer from leakage, incongruent melting and crystallization, phase separation, and supercooling, which limit their heat storage capacity and reliability during multiple heating-cooling cycles. An appropriate approach to mitigating these drawbacks is the construction of composites as shape-stabilized phase change materials which retain their macroscopic solid shape even at temperatures above the melting point of the active heat storage compound. Shape-stabilized materials can be obtained by PCMs impregnation into porous matrices. Porous silica nanomaterials are promising matrices due to their high porosity and adsorption capacity, chemical and thermal stability and possibility of changing their structure through chemical synthesis. This review offers a first in-depth look at the various methods for obtaining composite PCMs using porous silica nanomaterials, their properties, and applications. The synthesis and properties of porous silica composites are presented based on the main classes of compounds which can act as heat storage materials (paraffins, fatty acids, polymers, small organic molecules, hydrated salts, molten salts and metals). The physico-chemical phenomena arising from the nanoconfinement of phase change materials into the silica pores are discussed from both theoretical and practical standpoints. The lessons learned so far in designing efficient composite PCMs using porous silica matrices are presented, as well as the future perspectives on improving the heat storage materials.

Nanoporous Boron Nitride Aerogel Film and Its Smart Composite with Phase Change Materials

With the advent of the 5G era, electronic systems have become more and more powerful, miniaturized, integrated ,and intelligent. The thermal management of electronic systems requires more efficiency and multiple functions for their practical applications, especially for the portable 5G electronic devices of the future, as the undesired heat can cause thermal discomfort or even thermal injury to people who use these electronic devices. Herein, two thermal management strategies based on boron nitride (BN) aerogel films have been proposed and demonstrated for portable devices. First, a flexible BN aerogel film with high porosity (>96%), large specific surface area (up to 982 m² g^-1), and controllable thickness (in the range from 50 to 200 μm) was fabricated via molecular precursor assembly, sublimation drying, and pyrolysis reaction in sequence. The resulting BN aerogel film individuals, serving as a thermal insulation protecting layer in portable electronics, can significantly reduce heat transfer from electronics to skin. Second, BN phase change composite films, made by dipping BN aerogel films into the melts of the organic phase change materials (e.g., paraffin), can effectively cool the portable electronics as the organic phase change materials filled in the aerogel matrix can serve as a smart thermal-regulator to absorb the undesired heat via solid-liquid phase transition. These two typical strategies of the flexible BN aerogel film-directed thermal management could assist in efforts to miniaturize, integrate, and intelligentialize portable 5G electronic devices in the future.

Phase Change Materials for Electro-Thermal Conversion and Storage: From Fundamental Understanding to Engineering Design

Advanced functional electro-thermal conversion phase change materials (PCMs) can efficiently manage the energy conversion from electrical energy to thermal energy, thereby playing a significant role in sustainable energy utilization. Considering the inherent insulating properties of pristine PCMs, electrically conductive supporting materials are widely used to encapsulate PCMs to prepare composite PCMs for electro-thermal conversion and storage. Herein, we comprehensively review the recent advances in different electro-thermal conversion PCMs, mainly including carbon-based PCMs (carbon nanotubes [CNTs], graphene, biomass-derived carbon, graphite, highly graphitized carbon, and metal organic frameworks [MOFs]-derived carbon) and MXene-based PCMs. This review aims to provide an in-depth understanding of the electrothermal conversion mechanism and the relationships between structure design (random and array-oriented structure or single and hybrid supporting materials) and electrothermal properties, thereby contributing profound theoretical and experimental bases for the construction of high-performance electro-thermal conversion PCMs. Finally, we highlight the current challenges and future prospects.