Imagine a device using an energy source the size of planet Earth, and offering nearly limitless electricity with no ecologically devastating mining required to get it. Science fiction? A lie from Big Battery? A fentanyl fantasy from the Energizer Bunny? No – it’s real, and it’s the ocean.
The device – a silicon semiconductor – operates autonomously to deliver stable current by controlling how ions and electrons move while using light and heat to evaporate seawater. And according to researchers at the School of Engineering in the Laboratory of Nanoscience for Energy Technology (LNET) at Switzerland’s École Polytechnique Fédérale de Lausanne (EPFL), the process opens the gateway to even more technology for ecologically safe energy collection.
In a paper published in the journal Nature Communications, team lead Giulia Tagliabue and researcher Tarique Anwar describe their “unified physical and experimental framework” for evaporation-driven hydrovoltaic systems that separates and controls interfacial (that is, inter-phase such as solid-to-liquid or liquid-to-gas) processes while using sunlight and heat to generate electricity.
The system builds on previous LNET work employing the hydrovoltaic effect, which allows collection of electricity while fluid streams over a nanodevice’s charged exterior, and uses the spaces among silicon nanopillars in a hexagonal array for evaporating the fluid. “Heat and light imbalances will always affect a hydrovoltaic device,” says Anwar, “but we have discovered how these can be leveraged to our advantage” by directing heat and light to control the ions in evaporating seawater, which is a limitless, eco-friendly resource.
A significant conceptual breakthrough was realizing that evaporation wasn’t the sole cause of increases electrical generation. Instead, because the LNET device is composed of a silicon semiconductor, heat increases the negative charge on the semiconductor’s surface while sunlight excites the electrons within it.
The results are massive. “Due to this surface charge effect,” says Tagliabue, “the addition of solar light and heat can enhance energy production by a factor of five. This natural effect has always existed, but we are the first to harness it.”
By employing a trio of layers in their evaporation generator for three separate processes – evaporation, ion transport, and electrical charge collection – Tagliabue and Anwar are able to analyze and calibrate processes and results at each stage. For instance, the middle layer conducting ions sits below the evaporating layer on top, while sitting above a dielectric (a substance that poorly conducts electricity but effectively stores it) array of silicon nanopillars. Such a design improves generation while also demonstrating how charge arises from heat and light induction, thereby boosting electrical output and ion migration.
The LNET innovation offers another major advantage for delivering continuous, autonomous power: durability. Heat and light degrade hydrovoltaic mechanisms, and that degradation is even worse in the highly corrosive environment of saltwater. But as Tagliabue says, because her device’s nanopillars are coated with an oxide layer to ensure stable performance under heat and light, they’re safe from “unwanted chemical reactions.”
If further iteration on LNET’s device is successful, Tagliabue and Anwar say they hope it will lead to hydrovoltaic devices that can power small, battery-free sensor networks wherever people can access sunlight, heat, and water. Such applications, they say, include not only environmental monitoring systems, but all devices connected to the Internet of Things, and current and future wearable technology. Clearly, a future in which access to electricity is free and mobile offers nearly incalculable benefits for humanity.
Source: EPFL
