From plant transpiration to hydrovoltaics: distributed energy harvesting driven by water evaporation

Evaporation continuously converts absorbed solar heat into the kinetic motion of water molecules, creating a ubiquitous driving force that remains largely untapped for direct electricity generation. In plants, this process is harnessed through transpiration, where capillary flow and sustained negative pressure drive long-range water transport without moving parts. Inspired by this natural hydraulic engine, transpiration-inspired hydrovoltaics (TIH) have emerged as solid-state material platforms that convert evaporation-driven water transport into electrical output through interfacial electrokinetic processes. In this review, we introduce a unified physical framework for TIH by explicitly connecting the physics of plant transpiration to evaporation-driven electricity harvesting in engineered porous media. We summarize the governing principles of water ascent in trees, including capillarity, water-potential gradients and cohesion-tension stability, and map these concepts onto synthetic TIH architectures built from hydrophilic micro- and nanofluidic networks. We critically examine the proposed electricity-generation mechanisms in TIH, including classical streaming potentials on insulating substrates, pseudo-streaming in conductive porous networks and ionovoltaic coupling in semiconducting channels. We systematically elucidate how geometry, pore microarchitecture, surface chemistry, electrical conductivity and environmental conditions such as humidity, temperature and airflow jointly govern device performance. By benchmarking TIH against decades of quantitative insight from plant hydraulics, we identify key trade-offs, unresolved mechanistic questions, and actionable design opportunities for robust, scalable evaporation-driven power generation and self-powered sensing. Together, these perspectives position TIH as a promising platform for distributed energy harvesting at the water-energy nexus.