Hydrovoltaic Device Based On Silicon Nanowire Arrays

Very recently,hydrovoltaic technology is emerging as a novel renewable energy harvesting method relying on water evaporation or moisture absorption in nanomaterials to generate electricity,which shows tremendous potential for developing innovative energy-harvesting devices due to its low cost,performance tailoring and no mechanical energy input.The peak power density of hydrovoltaic device can be up to mW/cm2.However,most known devices cannot output constant electricity with high current density,severely hindering the potential application of hydrovoltaic technology.Here,we fabricated a novel hydrovoltaic device based on silicon nanowire arrays(SiNWs).According to scanning electron microscope,Fourier infrared spectrometer and Zeta potentiometer measurements,the surface charge of SiNWs can be ascribed to silicon hydroxyl(Si-OH)on silicon oxide.The resulting device can output constant electricity with an open-circuit voltage(Voc)of up to 400 mV and a short-circuit current density(Jsc)of over 55 μA/cm2,correspondingly,the maximum output power density is over 6μW/cm2.Besides,the affecting factors for SiNWs hydrovoltaic devices were explored,including graphite coverage ratio,length and surface charge density of SiNWs.We explore that the electricity-generating mechanism from SiNWs is mainly related to streaming potential through ion concentration-dependent and pH-dependent output voltage.Combined with excellent photovoltaic performance of crystal silicon,we try to integrate photovoltaic and hydrovoltaic effects in a SiNWs based device,which shows accumulated power density.The main work can be included in the following parts:1.The SiNWs were prepared from silicon wafers metal-assisted chemical etching process.An ultrathin SiO2 sheath covered the silicon nanowire can be characterized by scanning electron microscope,Fourier infrared spectrometer,and the negative charge in SiNWs originated from Si-OH was also revealed.Then,we fabricated and characterized sandwich structured SiNWs hydrovoltaic devices,resulting in the peak voltage of over 600 mV upon water capillary flowing into SiNWs.The affecting factors for this electrokinetic phenomenon are explored.Besides,we find that this hydrovoltaic device based on SiNWs can output constant electricity.2.The origin of constant electricity in SiNWs hydrovoltaic devices is fully characterized.At 65℃,SiNWs hydrovoltaic devices can output the Voc of 400 mV and Jsc of 55 μA/cm2.We revealed that the electricity should be related to carrier concentration gradient in silicon,which stemmed from internal water flow in nanochannels of nanostructured silicon.Protons in solution can induce electrons in silicon upon Coulomb interactions,resulting in electron concentration gradient.Besides,breathing sensor based on SiNWs with superior moisture sensitivity was demonstrated as a potential application.3.Combined with photovoltaic performance of crystal silicon,we explored the photovoltaic response of SiNWs hydrovoltaic devices in order to integrate photovoltaic and hydrovoltaic effect in one device.We measured the photovoltaic response and hydrovoltaic effect of SiNWs(with a resistance of 0.001-0.005 Ω·cm)under 1 sun illumination simultaneously,resulting in accumulated output voltage.The device can output constant electricity with an Voc of approximately 400 mV at room temperature.