Hydrogel‐Based Hydrovoltaic Power Generators: Mechanisms, Design Strategies, and Emerging Applications

Hydrogel‐based hydrovoltaic power generators (HHPGs) have emerged as a promising platform for sustainable energy harvesting by converting water‐related energy into electricity. Owing to their high water content, tunable ionic conductivity, and mechanical flexibility, hydrogels enable continuous ion transport and stable charge generation under various real‐world environments, whether driven by moisture, evaporation, or direct liquid flow. In this review, we first examine the fundamental mechanisms of hydrovoltaic energy conversion, breaking down the roles of ion diffusion, electrical double layer (EDL) effects, and electrochemical redox processes. We then discuss recent advances in design strategies for HHPGs, focusing on enhancing ion transport, interfacial charge separation, redox activity, device reusability, and hybrid energy harvesting. Furthermore, we summarize a wide range of applications, including wearable and on‐skin electronics, self‐powered smart systems, biomedical devices, and environmental remediation. Finally, we outline the remaining technical bottlenecks and offer critical perspectives for the development of high‐performance and scalable hydrovoltaic systems. This review provides a unified framework linking fundamental mechanisms, material design, and device performance, offering guidance for the advancement of next‐generation self‐powered technologies.