Atomic-scale engineering of cation vacancies in two-dimensional unilamellar metal oxide nanosheets for electricity generation from water evaporation

Water evaporation-induced electricity generation, as an emerging energy harvesting technology, has recently attracted extensive attention owing to its ability to harvest electricity directly from the natural water evaporation process. However, the crucial issue that has restricted its practical applications is the low power density and conversion efficiency presented thus far, which generally originated from the weak water-solid interaction between evaporation-induced water flow and nanostructured materials. Exploration of a regulatory approach that can enhance water-solid interaction at an atomic level is highly demanded. Herein, we propose the Ti vacancy engineering at the atomic scale in two-dimensional (2D) unilamellar titanium oxide (Ti_1−δO₂) nanosheets for efficient water evaporation-induced electricity generation. 2D Ti_0.87O₂ and Ti_0.91O₂ nanosheets with precisely controlled concentrations of Ti atomic vacancies are rationally designed. The water flow passes through the 2D gallery of nanosheets while the Ti atomic vacancies can effectively enhance the water-solid interaction between Ti_1−δO₂ nanosheets and water flow during the water evaporation process for electricity generation. As a result, a stable open-circuit voltage of ∼1.32 V for the hydrovoltaic device made of Ti_0.87O₂ nanosheets can be maintained for more than 250 h, outperforming those for the commercial TiO₂ and Ti_0.91O₂ nanosheets. This work indicates a promising way to utilize defective 2D materials for hydrovoltaic technology.