Generalized Dynamic Junction Theory to Resolve the Mechanism of Direct Current Generation in Liquid-Solid Interfaces

TL;DR

This paper introduces a generalized dynamic junction theory explaining direct current generation in liquid-solid interfaces, emphasizing the role of dynamic versus static contact states and electron-hole separation under built-in fields.

Contribution

It extends the charge-discharge theory to include dynamic interfaces, providing a unified explanation for DC generation in liquid-solid systems.

Findings

Reversal of current explained by interface state changes

Dynamic interfaces generate DC via electron-hole separation

Generalized theory applies to various liquid-solid junctions

Abstract

Despite the unsettled mechanism of electricity generation from the continuous flow of liquids on a surface, the charge-discharge theory has been widely accepted for alternating current (AC) generation from a moving droplet. It has been recently extended to rationalize direct current (DC) generation across a droplet moving between two different materials. By designing a reconfigurable contact between a metal wire and a water droplet moving on graphene, we show that the charge-discharge theory cannot explain the reversal of current when water-metal interfaces switch from dynamic to static. All experiments can be described after we distinguish a dynamic from a static interface and generalize the photovoltaic-like effect to all dynamic junctions: excited electrons and holes in a moving interface will be separated and swept under the built-in electrical field, leading to a DC response. This generalized theory will lead to an understanding and the design of efficient electricity generation based on interfacial charge transfer.