Large-Scale Production of Flexible, High-Voltage Hydroelectric Films Based on Solid Oxides

Abstract

Spontaneous electricity generation through water evaporation is becoming a hot research area. However, low power output, limited material availability, and unscalable fabrication largely hinder its wide applications. Here, we report scalable painting and blade coating approaches for the mass production of flexible hydroelectric films (HEFs) based on solid oxides (e.g., Al2O3), which are of tolerance to mechanical deformation and are compatible with three-dimensional diverse configuration. The electricity power is generated continuously and can last for more than 10 days in ambient conditions. A single HEF unit is capable of supplying an output voltage of more than 2.5 V and even up to 4.5 V at specific conditions. The accumulative energy output can be tuned conveniently by means of series/parallel connections or size control to meet the practical needs of commercial electronics. A family of solid oxides has been verified to have the ability for water evaporation-induced electricity generation, which offers considerable room for the development of high-performance energy-supplying devices.

Rational Design of MOF‐Based Hybrid Nanomaterials for Directly Harvesting Electric Energy from Water Evaporation

“…It is reported that the UIO‐66 synthesized with the acid modulator (e.g., acetic acid) possesses numerous defects due to missing of organic linkers, resulting in unsaturated coordination of the Zr clusters [ 29,32 ] and subsequently the positively charged surface of UIO‐66. [ 33 ] Similar to the previously reported materials with positively charged surface, [ 13–16 ] since there are negatively charged OH − ions in water, EDLs with the excess OH − ions can form in the capillary channels. Therefore, when the water molecules move through the capillary channels driven by the water evaporation, the collective movement of negatively charged OH − ions results in a high electric potential at the bottom electrode and a low electric potential at the top electrode (Figure 3a).…”

“…It has been recently found that the natural water evaporation can generate a continuous output of electric energy on a porous carbon black film. [ 6 ] However, this research field is still at infancy stage, and only a few materials, including carbon‐based materials [ 6–12 ] and several metal oxides (hydroxides), [ 13–16 ] have been demonstrated to show such capability. Therefore, it is highly desired to further develop other suitable materials in this emerging field of clean energy harvesting.…”

“…First, capillary channels can be formed by the material, and thus water molecules can move in the channels driven by the evaporation process. [ 6,13,14 ] Second, the surface of material possesses high zeta potential, resulting in high concentration of counterions within the EDLs. [ 10,15 ]…”

Evaporating Potential

“…The streaming potential, a classic electrokinetic phenomenon in which an electric voltage can be generated when an electrolyte is driven through a narrow channel under a pressure gradient 15,16 , plays an important role in previous experiments of evaporation induced electricity 3,4,[6][7][8][9][10][11][12][13][14] . The dashed lines in Fig.…”

“…Harvesting energy from liquid evaporation has significant potential for green energy owing to the ubiquity of evaporation 1,2,5 . Evaporation has been widely used to drive microfluidic flow within porous films to generate electric power 3,4,[6][7][8][9][10][11][12][13][14] mainly based on the classic streaming potential effect 15,16 . However, the interactions between materials and evaporating molecules have been rarely investigated.…”