Moisture‐Enabled Electricity Generation: From Physics and Materials to Self‐Powered Applications

Abstract

Ongoing efforts to develop this energy have led to the creation of a variety of novel technologies based on photovoltaic, [12,13] piezoelectric, [14,15] triboelectric, [16,17] and thermoelectric principles. [18,19] Devices based on these technologies are readily incorporated into self-powered, battery-free electronic systems. This also acts to eliminate the harm to the environment caused by the use of conventional batteries. [20,21] As recyclable resource, water is not only indispensable to life but also constitutes the largest energy carrier on Earth (Figure 1a). As 71% of the Earth's surface is covered by water and 35% of solar energy incident on the Earth is absorbed by water, petawatts of energy are received in this way. [22] As the water resource is clean and sustainable, the energy contained in even a small fraction of the water on Earth can meet the current global energy demand if this energy can be efficiently harvested. Terrestrial water exists in vapor and liquid form including moisture, rain, clouds, lakes, rivers, and oceans. It also forms the basis for biological systems. Even though there is a long history of electricity generation from running water, most technologies only utilize the gravitational and kinetic energy in liquid water. [23] Such systems are inherently incompatible with the development of self-powered devices. The development of nanomaterials has enabled technology for the extraction of electrical energy from moisture, leading to The exploration of the utilization of sustainable, green energy represents one way in which it is possible to ameliorate the growing threat of the global environmental issues and the crisis in energy. Moisture, which is ubiquitous on Earth, contains a vast reservoir of low-grade energy in the form of gaseous water molecules and water droplets. It has now been found that a number of functionalized materials can generate electricity directly from their interaction with moisture. This suggests that electrical energy can be harvested from atmospheric moisture and enables the creation of a new range of self-powered devices. Herein, the basic mechanisms of moisture-induced electricity generation are discussed, the recent advances in materials (including carbon nanoparticles, graphene materials, metal oxide nanomaterials, biofibers, and polymers) for harvesting electrical energy from moisture are summarized, and some strategies for improving energy conversion efficiency and output power in these devices are provided. The potential applications of moisture electrical generators in self-powered electronics, healthcare, security, information storage, artificial intelligence, and Internet-of-things are also discussed. Some remaining challenges are also considered, together with a number of suggestions for potential new developments of this emerging technology.

Full-Self-Powered Humidity Sensor Based on Electrochemical Aluminum–Water Reaction

“…These interferences may manifest as a reading offset or may result in noise and erratic readings. Additionally, the hydrovoltaic effect might come into play and increase the voltage level, apart from RF interferences [ 22 , 23 ]. A set of experiments was conducted in order to analyze the contribution of possible concurrent processes on the sensor’s output.…”

“…Another mechanism for energy harvesting from the interaction between solid surface and water is the hydrovoltaic effect [ 22 , 23 , 45 ]. Devices whose working mechanism is based on the hydrovoltaic principle generate electricity if at least one of the following conditions is fulfilled: the presence of diffusion as a consequence of concentration gradient, fluid flow (waving, streaming, pressure or gradient-induced), or gradient in ion concentration as a consequence of nonequilibrium in water desorption from its surface [ 23 ].…”

“…The full understanding of the underlying process required micro- and nanotesting of the sensor’s surface using the following methods: micro-Fourier transform infrared spectroscopy (µ-FTIR), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), electrochemical impedance spectroscopy (EIS), and X-ray diffraction (XRD) [ 21 ]. We also considered possible concurrent processes such as the hydrovoltaic effect [ 22 , 23 ] and radiofrequency harvesting [ 12 ].…”

New Material and New Concepts Improve Hygroelectric Generator Output

“…Several research groups verified the possibility to collect energy from water moisture but often using graphene oxide [3] and various experimental arrangements, supported by different concepts and theoretical arguments, such as the moisture adsorption and diffusion processes. Nevertheless, the reported output power and voltage are still low, ranging from 10 −8 to 10 −3 W and < 0.5 V, respectively [4].Here, we present new scalable higroelectricity devices with unprecedented outputs, whose design guidelines follow new thermodynamic arguments valid for an open, multiphase, and non-electroneutral system. Thus, water ions adsorb on the electrodes following the Bronsted acid-basic properties of the surface: negative ions (OH -) adsorb in acidic oxide metal, and positive ions (H + ) adsorb in base oxide metal.…”

“…Several research groups verified the possibility to collect energy from water moisture but often using graphene oxide [3] and various experimental arrangements, supported by different concepts and theoretical arguments, such as the moisture adsorption and diffusion processes. Nevertheless, the reported output power and voltage are still low, ranging from 10 −8 to 10 −3 W and < 0.5 V, respectively [4].…”