Interfacial Regulation Enables Spatially Selective Evaporation for High-Performance Wood-Based Hydrovoltaic Systems

Evaporation-driven hydrovoltaic generators show promise for sustainable low-grade energy harvesting, yet their efficiency is fundamentally hindered by reduced water transport under rising capillary pathways and charge accumulation at fully exposed evaporation interfaces. To address these challenges, we developed a structural design strategy based on spatially selective evaporation. Natural wood was used as the substrate, where partial removal of the cell wall components created low-resistance, highly ordered channels for stable directional water transport. Innovatively, poly(vinyl alcohol) was gradient-impregnated into the lower section to confine lateral evaporation precisely. This strategy directed water and ions toward the top evaporation interface, thereby achieving a more uniform charge distribution and enhancing the power output. Simultaneously, carbon black was loaded onto the wood surface to establish an efficient electronic conduction network. The optimized single hydrovoltaic device achieved significantly improved electrical output with an increased open-circuit voltage from 0.4 to 0.9 V and a high short-circuit current of 10 μA. The as-fabricated hydrovoltaic device enabled a peak power density of 1.85 μW cm –3 with stable long-term discharge over 100 h. This study presents a novel approach to advancing efficient and stable biomass-based hydrovoltaic technology through the innovative regulation of evaporation-induced structures.