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

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 degrees C, and mild wind speed of 2.8 m s-1, a temperature gradient (Delta TTEG) of approximate to 2 degrees 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.