Low-Cost Hygroelectric Devices Enable Continuous Onboard Trickle Charging for Small Electric Vehicles

Hygroelectric materials generate electrical power by harnessing the interaction between ambient water vapor and the surface of the material, exploiting the inherent polarity of water molecules—specifically, the negative and positive charge components on the oxygen and hydrogen atoms, respectively. Hygroelectric devices, also known as humidity electric generators, incorporate molecular structures that function analogously to capacitor plates, producing current upon collision with water molecules. Although the power output of individual devices is modest, stacking lightweight materials in multiple layers can significantly enhance overall performance. In this study, aluminum foil served as the anode, while either copper foil or conductive fabric was employed as the cathode. A gel composed of table salt and sodium alginate was positioned between the electrodes. Various parameters were investigated to optimize power generation, including the incorporation of conductive graphite, thermal treatment (baking), and adjustments to the salt-to-sodium alginate ratio. A 1.2 kg power supply, integrating printed circuit boards and hygroelectric devices, was fabricated and successfully mounted on a 0.5 kg remote control car. This power supply delivered 108 mW at 90% efficiency, enabling the trickle charging of four AA batteries to full capacity over five days. On average, the fabricated hygroelectric devices generated 1.2 ± 0.2 mW over a 14-day period, with a mean output voltage of 55 ± 0.10 V and an average current of 2.1 ± 0.4 A. A higher salt ratio, not baking the devices, and a copper cathode all resulted in significantly higher power outputs. With further optimization of device weight, fabrication parameters, and power output, it is feasible that more energy-intensive applications could be directly supported. Moreover, substantial potential exists for enhancing the base design through the use of advanced materials and novel chemical combinations. Notably, the current devices utilize readily available, minimally processed materials and do not produce toxic waste after use, underscoring their sustainability and practical viability.