Autonomous energy scavenging from the ambient environment, or self-energy management, has attracted increasing attention because it could solve the energy problem of abundant Internet of things (IoT) devices. In recent years, several energy harvesters that generate electricity using water have been invented due to their simplicity, sustainability, and eco-friendliness. Until now, the devices have required periodic supplementation of water for continuous electricity generation, which hinders their practical use. Here, we built an artificial hydrological cycle in a transpiration-driven electrokinetic power generator (TEPG) to continuously and autonomously generate electric power. The TEPG, composed of carbon-coated cotton fabric, generates electricity by using a few drops of water (0.2 mL); the electric power originates from the potential difference in the asymmetrically wetted device and the pseudostreaming current. However, after only one hour, the TEPG stops generating electricity, as water inevitably evaporates from the device. For continuous self-operation, we utilized calcium chloride (CaCl₂), a typical deliquescent chemical, to collect water vapor from the surrounding environment and continuously supply water to the TEPG. In the range of 15–60% relative humidity (RH), CaCl₂ successfully compensates for the water loss by evaporation and maintains the electrical power generation in the closed system. In addition, CaCl₂ enhances the generated voltage (0.74 V) and current (22.5 μA) by supplying additional Ca²⁺ ions to the carbon surface and reducing the resistance of the device, respectively. The developed self-operating transpiration-driven electrokinetic power generator (STEPG) is stable enough to light a light-emitting diode (LED) for a week and charge a commercialized supercapacitor (5 F) to 1.6 V for 8 days.

The use of Ti ₃ C ₂ T _x MXenes/polyaniline composite tremendously improved the electrokinetic energy conversion efficiencies of nano-hydroelectric generators, demonstrating a power output sufficient to charge a commercial battery for the very first time.

The disposal of natural wastes has become a global problem and the use of lower-grade gums is very limited owing to their impurities as well as sticky nature. Rather than disposing these wastes, nanoporous carbon (nC) has instead been synthesized by carbonization and exfoliation. The synthesized nC exhibits a substantially high surface area along with abundant micro/mesopores. This desirable and useful nature of nC is well-suited for water-driven effective electrical energy conversion, which enables the fast evaporation of water via a capillary action through nanopores. Under asymmetric wetting in a water container and ambient conditions, the nC-based energy harvesters showed high capability of electricity production and reliable output generation, easily turning on a blue light-emitting diode (2.5 V and 20 mA) using a stored power source. In summary, many energy harvesters can be manufactured for the scale-up of electricity, and the suitability of regenerated carbon nanomaterials for green energy harvesting can contribute toward alleviating chronic environmental issues.