A nanodevice developed at EPFL produces an autonomous, stable current from evaporating saltwater by using heat and light to control the movement of ions and electrons. Previously, researchers in the Laboratory of Nanoscience for Energy Technology (LNET) in EPFL's School of Engineering reported a platform for studying the hydrovoltaic (HV) effect—a phenomenon that allows electricity to be harvested when fluid is passed over the charged surface of a nanodevice. Their platform consisted of a hexagonal network of silicon nanopillars, the space between which created channels for evaporating fluid samples.

Now the LNET team, led by Giulia Tagliabue, has developed this platform into a hydrovoltaic system with a power output that matches or exceeds similar technologies—with a major advantage. Instead of relying on heat and light to simply boost evaporation, the EPFL system generates current by harnessing heat and light to control the movement of ions in evaporating saltwater, and the flow of electrons in the silicon nanodevice.

"Heat and light imbalances will always affect a hydrovoltaic device, but we have discovered how these can be leveraged to our advantage," explains LNET researcher Tarique Anwar.

With three distinct layers dedicated to evaporation, ion transport, and electrical charge collection, the nanodevice's decoupled design allows the scientists to observe and finely tune each step in the process. 

The researchers believe their innovation will accelerate the development of hydrovoltaic devices, which have great potential to power battery-free small sensor networks wherever water, heat, and sunlight are available. Examples include self-powered environmental monitoring systems, wearable devices, and internet-of-things applications.