Compact Electrolytic Hydrocapacitor for Direct Harvesting and Storing Energy from Water Droplet Achieving High Voltage

Abstract

As a renewable and low‐carbon emission energy source, water‐droplet‐based devices are attracting increasing interest. However, the uncertain mechanistic explanation, output shortage, and lack of storability remain huge barriers to their large‐scale applications. Herein, a compact quasi‐solid‐state electrolytic hydrocapacitor (HC_elect) is successfully designed and fabricated with dual‐function of self‐charging and storage by employing novel bilayer graphene oxide/graphite flake composite films symmetrically sandwiched by poly(vinyl alcohol)–phosphoric acid electrolyte. The sandwich‐like HC_elect can achieve a high‐level and repetitive self‐generation voltage of 0.94 V for over a month under a small‐scale water droplet. A possible model is proposed to explain the operating principle in detail based on the capillarity, ion diffusion, and streaming potential mechanisms. Simultaneously, the generated energy is continuously stored for ≈2.1 h due to water evaporation. In addition, unlimited output extension can be realized by integrating hydrocapacitors in an array for powering commercial devices. Interestingly, it is ascertained that prolonged finger touches on the HC_elect can produce a high voltage. Therefore, this novel hydrocapacitor has notable potential applications in small portable and wearable devices owing to its compactness, low cost, environmental friendliness, safety, and flexibility, thereby providing a design idea for new innovative electronic devices.