Plug Flow: Generating Renewable Electricity with Water from Nature by Breaking the Limit of Debye Length

Abstract

Charge separation occurs spontaneously at the solid-liquid interface, forming an electric double layer. Previous methods, including streaming current, used to harvest the constantly separated charge in micron-sized and larger systems reported negligible power output due to the fundamental limit caused by the very short nanoscale Debye length. This study reports on the phenomenon that plug flow of water that falls naturally down a millimeter-sized tube generates electricity with a high efficiency of >10% and power density of ∼100 W/m2. This high power breaks the theoretical limit defined by the Debye length in macroscale channels. Plug flow generates 5 orders of magnitude more electricity than continuous flow (i.e., streaming current) and more than other technologies using falling water. Plug flow triggers a unique interfacial chemistry with large chemical potential of charge separation: the complete spatial separation of aqueous H+ and OH- ions without the electric double layer. Having macroscale channels enables the energy of water from nature (e.g., rain or rivers) to be harvested freely. The simple setup lights up multiple LEDs continuously, modifies surfaces, and performs chemical reactions. Plug flow via harvesting energy from nature is a source of renewable power with many advantages for achieving sustainable societies.