Progress of Capillary Flow-Related Hydrovoltaic Technology: Mechanisms and Device Applications

Capillary flow-related hydrovoltaic technology is an emerging research field for sustainable electricity generation. Despite great progress in the last decade, the mechanisms behind electricity generation remain unclear. In this review, we provide an overview of the current proposed mechanisms for electricity generation induced by water evaporation and moisture absorption. We explore key mechanisms, including streaming potential, ion concentration gradient, microbial electricity, ionovoltaic effect, pseudo-streaming, evaporating potential, and upstream proton diffusion. Each offers distinct insights and faces specific challenges that require further study. Unlike previous reviews, we focus specifically on the detailed mechanistic understanding of capillary flow-related electricity generation and highlight the interplay of different mechanisms. Additionally, we identify critical gaps in current research, particularly the need for empirical validation through advanced characterization techniques, such as spectroscopy, microscopy, and electrochemical analysis. Moreover, we discuss the practical applications of capillary flow-related hydrovoltaic technology in energy harvesting systems and self-powered sensors, highlighting its potential to convert water evaporation and environmental moisture into sustainable energy. We believe this review can serve as a starting point for further efforts aimed at addressing these challenges, thus paving the way for the commercialization of this technology and its contribution to sustainable development goals.