Emerging Materials for Water-Enabled Electricity Generation

Abstract

Water is one of the most abundant natural resources on Earth, which has attracted huge research interest in the field of energy harvesting and conversion, because of its environmental friendliness and easy access. Through precise regulation of functional materials and elaborate design of the solid/liquid interface, the interactions between water molecules and functional materials enable the generation of considerable electricity, giving researchers an alternative to extract renewable energy from water. In this Perspective, we will systematically discuss the water-enabled electricity generation (WEG) technologies, based on the interactions between functional materials and water. We mainly classify the WEGs into three types: mechanical-to-electric WEG, thermal-toelectric WEG, and chemical-to-electric WEG, according to the energy source of input water and the mode of energy conversion. For each type of WEG, the basic working principles for generating electricity are outlined, accompanied by a summary and comparison of system structures, working types, and performance characteristics. Recent significant progress in terms of the development of functional materials and the design of devices are emphasized. Efficient strategies involving a deep understanding of the solid/liquid interface and the structure of electric double layer, kinetics of ions adsorption, migration and diffusion or combination thereof, are also discussed. Then, we survey nascent fields promising to advance the development of WEGs, particularly in the area of self-powered and wearable electronics. The general requirements for developing next-generation functional materials for high-performance WEGs are further concluded, as well as standards for WEG's performance testing. The scientific and technological challenges and opportunities of WEG are finally addressed for future studies and practical applications.

Ionic Hydrogel for Efficient and Scalable Moisture‐Electric Generation

“…[7][8][9][10][11] In principle, MEGs convert considerable chemical potential energy released by gas-liquid moisture migration in air into useful electric power by constructing oxygen gradient conformation in graphene oxide or water gradient in homogenous polymer films and proteins. [1,12,13] Many methods have been attempted to improve their output performance, including asymmetrical structure, [14,15] chemical modification, [16,17] interface mediation, [18] heterogeneous system, [9] sunlight-coordinated moisture-electricity, [19] and new materials. [20,21] Since 2015, Qu et al has pioneered the work from graphene-based MEGs [22,23] with instantaneous output signal, followed by polymer-based MEGs with continuous power generation.…”

Water evaporation–induced electricity with Geobacter sulfurreducens biofilms

“…The utilization of water energy by human beings stems from early hydroelectric power, which mainly uses the kinetic energy of a large amount of flowing water and is limited by geographical location, hydrological conditions, and high infrastructure cost ( 2 , 3 ). In recent years, a variety of energy conversion modes related to water flow, waves, drops, moisture, and water evaporation have been proposed on the basis of the concept of the “hydrovoltaic effect” ( 2 , 4 , 5 ), providing more ways to harvest water energy. Among these approaches, the water evaporation–induced electricity generator (WEG) produces electricity directly from the water evaporation process, which is attracting attention because of its highly spontaneous and continuous electricity generation ( 2 , 6 ).…”

Water‐Enabled Electricity Generation: A Perspective

“…Despite the ubiquitous presence of water, opportunities for waterenabled electricity generation has been usually overlooked. [17,18] The possibilities for electricity generation are facilitated by the electrification of water in response to changes in phase but experiments directed toward the harvesting of this charge to generate electrical power from atmospheric water vapor have been only recently been reported. [11,15] Since graphene oxide (GO) can generate electricity when exposed to moisture, this material has attracted much attention as a power source in a variety of practical applications.…”

“…This has led to the incorporation of water-enabled electrical generators (WEEGs) in novel self-powered, battery-free electronic and monitoring/diagnostic systems in health care, the internet of things (IoTs), the environment, security and information applications, and artificial intelligence. [11,18,32] There is no doubt that additional practical applications for WEEGs in these and other scenarios will boost the development of user-friendly, environmentally sustainable devices.…”