Electricity Generation From Ambient Water Evaporation in the Absence of Sunlight via PVA‐Based Porous Hydrogels

Abstract In the current era where electronics and technologies are getting smaller in size, off‐grid and battery‐free features are getting increasingly sought after. This motivates innovation in ambient energy harvesting from light, heat, and mechanical sources. Among these technologies, hydrovoltaics has emerged as a promising source of electricity by harvesting energy from ubiquitous water evaporation. However, the power densities of hydrovoltaics are so far limited to the order of hundreds of mW cm⁻ 2 . In this work, a porous polyvinyl alcohol (PVA) hydrogel in combination with a thermoelectric generator (TEG) is devised to directly capture energy from water evaporation. It is found that under moderate environmental conditions with relative humidity (RH) of 40%, temperature of 26 °C, and mild wind speed of 2.8 m s −1 , a temperature gradient (ΔT TEG ) of ≈2 °C is established across the TEG. This gives rise to 1.71 mW of power output, which is equivalent to 1.02 W m −2 power density. This is more than 3 fold higher than traditional hydrovoltaics. This work opens a pathway for further investigation into scavenging electricity from water evaporation.