Hydrogels and Hydrogel-Derived Materials for Energy and Water Sustainability

Abstract

Energy and water are of fundamental importance for our modern society, and advanced technologies on sustainable energy storage and conversion as well as water resource management are in the focus of intensive research worldwide. Beyond their traditional biological applications, hydrogels are emerging as an appealing materials platform for energy-and water-related applications owing to their attractive and tailorable physiochemical properties. In this review, we highlight the highly tunable synthesis of various hydrogels, involving key synthetic elements such as monomer/polymer building blocks, cross-linkers, and functional additives, and discuss how hydrogels can be employed as precursors and templates for architecting three-dimensional frameworks of electrochemically active materials. We then present an in-depth discussion of the structure−property relationships of hydrogel materials based on fundamental gelation chemistry, ultimately targeting properties such as enhanced ionic/electronic conductivities, mechanical strength, flexibility, stimuli-responsiveness, and desirable swelling behavior. The unique interconnected porous structures of hydrogels enable fast charge/mass transport while offering large surface areas, and the polymer−water interactions can be regulated to achieve desirable water retention, absorption, and evaporation within hydrogels. Such structurederived properties are also intimately coordinated to realize multifunctionality and stability for different target devices. The plethora of stimulating examples is expounded with a focus on batteries, supercapacitors, electrocatalysts, solar water purification, and atmospheric water harvesting, which showcase the unprecedented technological potential enabled by hydrogels and hydrogel-derived materials. Finally, we study the challenges and potential ways of tackling them to reveal the underlying mechanisms and transform the current development of hydrogel materials into sustainable energy and water technologies.

Topology‐Controlled Hydration of Polymer Network in Hydrogels for Solar‐Driven Wastewater Treatment

“…In recent years, solar‐driven water purification technology based on vapor/steam generation has attracted tremendous attention due to the potential to alleviate water scarcity by producing clean water without extra power input. [ 8–10 ] In this context, various photothermal materials with high solar absorption such as plasmonic nanoparticles, [ 11,12 ] carbon materials, [ 13–18 ] and semiconductors [ 19 ] have been developed to improve the solar vapor generation (SVG). Nevertheless, to reduce the loss of obtained solar energy is another significant pedestal for efficient SVG.…”

Recent advances in polysaccharide‐based hydrogels for synthesis and applications

“…Agglomerations of nanoparticles decreased the surface area and the conductivity path. [ 4 ] It should be noted that hydrogels could be used as templates for inorganic frameworks. For example, hierarchical oxygen‐enriched porous carbon materials were synthesized by carbonizing the biopolymer composite consisting of sodium alginate and bacterial cellulose, as well as KOH activation at different temperature.…”

“…They find a broad spectrum of applications in biomedical, [ 1 ] self‐healing, [ 2 ] sensory, [ 3 ] energy, and water sustainability fields. [ 4 ] These hydrophilic polymer networks can be produced via in situ physical and/or chemical crosslinking. Generally, chemical crosslinking can be achieved using redox‐, thermal‐, photo‐, or radiation‐initiated free radical polymerization.…”

Enzyme-Regulated Healable Polymeric Hydrogels

“…The enzyme-regulated healable polymeric hydrogels are synthesized from either monomers or polymers (i.e., building blocks) via noncovalent and/or covalent bonds. 78 In the hydrogels, enzymes usually act as special assisting additives to regulate the synthesis, degradation, and/or self-healing of the hydrogels, but they are usually stably immobilized in the polymer networks based on covalent bonds or supramolecular interactions. For example, glucose oxidase (GOX) was immobilized in the polymer networks based on the metal–ligand interactions between the cobalt ions and the histidine functional groups on GOX in our previous study.…”