Electricity Generation from Phase Transitions between Liquid and Gaseous Water

Abstract The ubiquitous and spontaneous phase transitions between liquid and gaseous water contain substantial energy that can be harvested by emerging hydrovoltaic technologies, including evaporation‐induced generators (EIGs) and moisture‐induced generators (MIGs). Featuring the virtues of ubiquity, spontaneity, and direct current output, this emerging technology broadens the technical feasibility of harvesting energy from the natural water cycle, enabling self‐powered and sustainable electronics. Elaborated materials synthesis and innovative device design have been proposed to facilitate efficient water energy harvesting. However, some critical challenges in gaining insight into the mechanisms, power improvements, and practical applications are imperative to be overcome for this nascent yet impactful field. Herein, the evolution and advances of EIGs and MIGs are comprehensively summarized. The basic principles of phase transitions between liquid and gaseous water and the mechanisms of power generation are clarified. Then the current materials systems and strategies to further enhance the device performance are reviewed and thoroughly evaluated. The exemplary applications assembled in EIGs and MIGs are also outlined. Finally, the main challenges and future orientations of this burgeoning technology are presented.