Energy harvesting from water's liquid–gas phase transition: mechanisms and structural designs

Abstract

Water phase transition-based energy harvesting has emerged as a promising branch of hydrovoltaic technology, offering substantial potential for sustainable energy generation. This review offers a systematic and thorough survey of the fundamental mechanisms, structural designs, integration strategies, and emerging applications of water phase transition energy generators (WPTEGs). It first elucidates four primary electricity generation mechanisms: ion concentration gradient diffusion, streaming potential, evaporating potential, and the ionovoltaic effect. Building on these fundamental principles, the review systematically examines four representative device architectures—basic, asymmetric, Janus, and heterojunction structures—analyzing their design characteristics and performance implications. Furthermore, it highlights applications of WPTEGs across diverse domains, including self-powered microsystems, hybrid energy harvesting systems, and advanced sensing applications, showcasing their practical versatility. Despite substantial progress, critical challenges persist in terms of power density, stability, and scalability. Accordingly, this review outlines current limitations and proposes prospective strategies to advance the development of high-performance, multifunctional WPTEG systems, aiming to meet the requirements of next-generation autonomous electronics and facilitate the widespread adoption of this innovative energy-harvesting technology.