Fig. 1: Evaporation-driven hydrovoltaic device architecture, mechanisms, and materials.
a Schematic representation of the hydrovoltaic device featuring a top evaporating electrode surface and a bottom array of SiNPs immersed in water. The top and bottom components do not physically contact but are electrochemically connected through the water. The inset displays the three effects contributing to the device’s performance. i A side view of the evaporating surface with the liquid meniscus and the thermal gradient across the liquid layer. ii An intermediate electrolyte layer and thermally tuned chemical equilibrium at the bottom nanostructures, resulting in a higher surface charge at increased temperatures. iii photoactive nanostructure-electrolyte interface depicting the enhanced surface charge under irradiation due to electron-hole pair generation. CB conduction band, VB valence band, EF Fermi level. b Scanning electron microscopy (SEM) image of the SiNPs array. (left) Top view, and (right) cross-sectional view. c Scanning transmission electron microscopy (STEM) image of a single NP. The cross-sectional cut of a single NP reveals the presence of a silicon core and Al2O3 shell. Intensity mapping was performed in the rectangular region (see Fig. S1). d TEM-EDX image of the NP displaying the elemental maps of aluminum, silicon, and oxygen. e (Top) A detailed view of the interface potential and free space charge in the silicon and electrolyte mediated by the oxide layer. The total potential is the sum of the potential difference in the space charge layer of silicon \((\Delta {\Phi }_{{SC}})\), the oxide layer \((\Delta {\Phi }_{{ox}})\), and the double layer \((\Delta {\Phi }_{{DL}})\) of the electrolyte (bottom), as well as the free charge profile in the respective regions and the corresponding equivalent capacitance.
