Interfacial Evaporation Synergistically Boosting Silicon Nanowires Arrays-based Hydrovoltaic Devices

The water cycle of the earth(evaporation,transportation,precipitation,and runoff)carries abundant energy.Currently,the utilization of this energy source mainly comes from the potential energy of water molecules-that is,the process of precipitation and runoff.However,this accounts for only a small portion of the enormous amount of energy that can be harnessed.In recent years,with the increasing understanding and development of solid-liquid interface phenomena and nanomaterials,widespread and miniaturized water energy harvesting devices have emerged,offering new possibilities for utilizing energy during the water cycle.Among them,the hydrovoltaic effect,which generates electricity by the evaporation of water molecules and their contact with micro/nano materials,has attracted many researchers due to its clean power generation and wide energy sources.After nearly a decade of development,hydrovoltaic technology has been developed based on carbon materials,organic polymer materials,biomass materials,and inorganic semiconductors.Inorganic semiconductor silicon nanowire(SiNW)arrays have become an excellent hydrovoltaic material due to their high-performance hydrovoltaic signal response,large specific surface area,high carrier transport properties,and ease of large-scale preparation.However,due to their small working area,poor electrode interface design,and slow water evaporation rate,they cannot generate sufficient power output for widespread commercial electronic devices.This thesis focuses on the above three main technical development limitations and optimizes the hydrovoltaic devices in terms of SiNWs device preparation,electrode selection,and interface evaporation coacceleration to improve their power output performance and explore their mechanism.The main contents are as follows:1.To address the problem of low current output of hydro voltaic devices,a large-area SiNW array device was prepared by designing a vertical back-to-back metal-assisted chemical etching(MACE)method based on capillary adhesion phenomenon.The SiNWs has the advantages of large specific surface area,high surface charge density,and rich storage that are easy to process.By efficiently bonding the wafer-scale silicon chips backto-back through capillary adhesion force between the solid-liquid interface,the operation pollution and transfer caused by the need for additional hydrophobic protection layers in traditional SiNW preparation are avoided,and the difficulty of large-area preparation of hydrovoltaic devices is overcome.The electrical properties and morphology were analyzed,and the SiNW array showed excellent electrical signal response,with uniformly distributed nanochannels and high surface charge density,and could maintain its structure stability in the environment for a long time.The six-inch SiNW array hydrovoltaic device prepared by this method can achieve an open-circuit voltage output of 0.46 V and a shortcircuit current signal output of 3.80 mA under room temperature and darkness,breaking the record of hydrovoltaic device output.2.In order to improve the effective evaporation area and the collection and transportation of charge carriers in hydrovoltaic devices,a high surface area conductive fabric electrode based on carbon nanotube immersion was constructed.By utilizing the high conductivity of carbon nanotubes(CNTs)and the hydrophilic and inherent porous of the fabric,the problem of ineffective collection of charge carriers generated by hydrovoltaic devices and hindering water molecule evaporation in traditional carbon paste printed electrodes was improved.The conductivity performance of the CNT fabric electrode and its promotion of hydrovoltaic devices were quantitatively measured by fourpoint probe and other electrical characterization techniques.The immersion frequency of the CNT fabric was optimized through scanning electron microscopy and contact angle tests,resulting in lower resistance and improved water evaporation rate,effectively collecting the charge carriers generated by hydrovoltaic devices and promoting water molecule evaporation.Meanwhile,based on the interface contact and energy band theory,a metal aluminum electrode was designed for the bottom electrode of SiNW array hydrovoltaic devices,improving the contact between the bottom electrode and the device and constructing a more favorable channel for charge carrier transportation.By selecting appropriate electrodes and optimizing the interface design,the performance of the hydrovoltaic device based on SiNW arrays was significantly improved,achieving an open circuit voltage of 0.65 V and a current density of 47.5 μA cm-2.3.Faced with the challenge of sluggish evaporation rates due to environmental heat for hydrovoltaic devices,we combined the concept of interfacial evaporation from solar evaporators and built a stable water supply structure for SiNW array hydrovoltaic devices by selectively coating carbon nanotube fabrics as electrodes.This promoted the output of hydrovoltaic signals.By designing a selectively coated CNT fabric electrode that can selfsupply water,the hydrovoltaic device can drive output by autonomously pumping water.Under the working environment of interfacial evaporation,it can achieve a water evaporation rate of 1.31 kg m-2 h-1 and complete desalination of seawater and dye wastewater.Furthermore,this highly efficient water evaporation rate greatly promoted the generation of hydrovoltaic signals.The open-circuit voltage of the device reached 0.81 V,and the short-circuit current density reached 108.0μA cm-2.In addition,we proposed a possible hydrovoltaic mechanism model that involves charge injection induced by environmental heat and evaporation motion through theoretical analysis of the solid-liquid interface.