X/TEMPO-mediated nanoporosity engineering of wood for high-performance hydrovoltaic energy harvesting

The increasing global demand for renewable and sustainable energy has driven growing interest in hydrovoltaic energy generators (HEGs), which harvest electricity from naturally occurring water without relying on extensive infrastructure. Wood, with its anisotropic and hierarchical porous architecture, provides efficient pathways for water transport and ion migration, making it an attractive and sustainable platform for HEG applications. However, conventional wood-based evaporation-driven generators predominantly rely on streaming-potential effects arising from microscale fluid flow, while the contribution of surface-charge regulation and nanoscale transport within the wood cell walls remains limited. In this study, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidation is employed to increase the density of carboxyl functional groups and, upon sufficiently prolonged oxidation, induce the formation of nanoscale pores within the wood cell walls, thereby strengthening interfacial charge interactions and facilitating ion transport under evaporation-driven water flow. As a result, the optimized TEMPO-treated wood (TW) delivers a maximum open-circuit voltage of 303.6 mV with a corresponding power density of 0.34 μW cm−2. These results highlight the effectiveness of cell-wall-level chemical and structural engineering in enhancing hydrovoltaic performance, providing new insights for the development of scalable and sustainable wood-based energy harvesting systems.