Humidity-driven energy harvesting systems: mechanisms, materials, challenges, and future directions

Abstract

The continuous advancement in low-power electronics, wearable devices, and autonomous sensing platforms has increased the demand for energy harvesting technologies capable of extracting power from ambient energy sources. Among these sources, atmospheric humidity has recently emerged as a promising source for micro-scale power generation, as ambient moisture gradients can drive ion transport in hygroscopic materials to produce electrical output for low-power electronics and self-powered sensors. Recently, the systems like moisture-enabled electric generators (MEGs), hygroelectric converters, and evaporation-induced energy harvesters have shown the capability to transform water vapor or humidity gradients into usable electrical energy, utilizing environmentally friendly materials and via passive operation. This review presents a comprehensive overview of the fundamental mechanisms, materials, and device architectures that define humidity-driven energy harvesting technologies. Current methods are categorized according to their operational principles, such as ionic diffusion, surface charge modulation, and evaporation-driven flow. Key material systems, including carbon-based films, hydrogels, metal oxides, and bio-inspired composites, are examined for their performance, durability, and scalability. The discussion also includes the integration of these harvesting systems with energy storage components as a means to achieve fully autonomous and self-sufficient power platforms. This review focuses on applications in wearable technology, environmental monitoring, and the Internet of Things (IoT) to emphasize the potential impact of humidity-powered systems in practical situations. Finally, the current limitations in power output, environmental sensitivity, and fabrication complexity are critically examined, and future research directions are suggested. This review aims to summarize emerging knowledge in this field and promote the advancement of next-generation humidity-enabled energy technologies for decentralized and sustainable energies.