Thermal‐Gradient‐Driven Hydrovoltaic Nanogenerators: Opportunities and Challenges for Advanced Energy Conversion

ABSTRACT The global energy crisis necessitates innovative approaches to harness ambient low‐grade energy. Hydrovoltaic technology, which generates electricity from water‐ nanomaterial interaction, is promising but limited by low power density and environmental intermittency. While previous reviews have focused on materials and isolated mechanisms, this review pioneers a comprehensive analysis of a strategic solution: the active integration of thermal gradients to govern and enhance hydrovoltaic phenomena. We systematically dissect the fundamental synergistic mechanisms—such as thermal‐osmosis and evaporation‐driven potential—that underpin this coupling. The review critically evaluates key advancements in material innovations (e.g., phase‐engineered 2D materials, functionalized carbon, hydrogels) and structural designs (e.g., 3D porous and asymmetric architectures) essential for optimizing thermal‐hydrovoltaic performance. Furthermore, we chart the expanded application landscape, from wearable electronics and self‐powered sensors to dual‐purpose electricity and freshwater production systems. Finally, we confront persistent challenges in material stability, scalability, and system integration, outlining a forward‐looking research roadmap focused on multi‐physics modeling and intelligent power management. This work also identifies the underexplored potential of high thermal gradients as a critical future direction. By transcending single‐source energy harvesting, integrated thermal‐gradient‐driven hydrovoltaics represents a transformative paradigm for sustainable, distributed power generation.