Constant Electricity Generation in Nanostructured Silicon via Evaporation-driven Water Flow.

Very recently, hydrovoltaic technology is emerging as a novel renewable energy harvesting method through carefully controlling the interaction between water and solid surface, which dramatically extends the capability to harvest water energy. However, the urgent issue restricting its device performance is poor carrier transport properties of the solid surface if large charged interface is considered simultaneously. Here, a hydrovoltaic device based on silicon nanowire arrays (SiNWs), which provide large charged surface/volume ratio and excellent carrier transport properties simultaneously, yields sustained electricity via carrier concentration gradient induced by evaporation-induced water flow inside nanochannels. And a device can yield direct current with a short-circuit current density of over 55 muA/cm 2 , which is three orders larger than previous reported analogous device (approximately 40 nA/cm 2 ). In addition, this device exhibits a constant output power density of over 6 muW/cm 2 and an open-circuit voltage of up to 400 mV, which enables it to easily drive a commercial light emitting diode. We also demonstrate the potential application of this electrokinetic phenomenon by using it to create a breathing sensor. Through changing ion concentration in water, length and surface charge of SiNWs, we propose the mechanism of harvesting energy through water flow in SiNWs. Our findings reveal that the generated energy should be mainly correlated with Debye screening effect and Coulomb interactions. Our finding may pave a way for developing innovative energy-harvesting devices from ubiquitous evaporation-driven internal water flow in nature with semiconductor material of silicon.