An aluminum-air battery/hydrocapacitor-inspired hybrid device for energy conversion from micro water droplets

Abstract

Aluminum–air (Al–air) battery-inspired water-movement-based devices have emerged as promising candidates for green conversion because of their high specific energy and theoretical voltage. However, the self-corrosion of Al remains a huge barrier to hinder their large-scale applications. This study developed a novel hybrid device by merging an Al–air battery and a solid-state hydrocapacitor using a graphene sheet/carbon particles (GSCP) composite anode. A plant fiber layer separated the Al electrode from the poly(vinyl alcohol)/phosphoric acid electrolyte, which could greatly reduce Al self-corrosion. Additionally, the all-solid-state working condition of the device prevented negative leakage or undesirable deformation of the electrolyte when not in use. Moreover, the microporous GSCP electrode was synthesized through a green, cost-effective, and nonhazardous process by compositing exfoliated graphene with micro/nano-sized carbon particles processed from recovered spent battery parts. Remarkably, it could achieve a high-level open-circuit voltage of 1.5 V by simply dropping small-scale water droplets and daily repeating for over a month. Simultaneously, the stored energy was maintained for approximately 2.8 h due to water evaporation. Simply stacking cells in an array could amplify the output to power commercial devices. As a breakthrough, the device successfully operated as a human-breathing transducer. To explain the operational principle, a possible model based on the capillarity, ion diffusion, and streaming potential mechanisms was proposed and discussed comprehensively. This novel hybrid device provides considerable insight for future water-movement-based devices and small portable/wearable electronics and facilitates the development of green energy conversion systems.