EPFL Nanodevice Generates Electricity Autonomously from Evaporating Saltwater

An EPFL-developed nanodevice produces an autonomous and stable electrical current from evaporating saltwater by utilizing heat and light to regulate the movement of ions and electrons.

Background

In 2024, researchers at EPFL's Laboratory of Nanoscience for Energy Technology (LNET) reported a platform for studying the hydrovoltaic (HV) effect. This phenomenon allows electricity to be harvested when fluid passes over a nanodevice's charged surface. Their initial platform consisted of a hexagonal network of silicon nanopillars, creating channels for evaporating fluid samples.

New Development

The LNET team, led by Giulia Tagliabue, has evolved this platform into a hydrovoltaic system that matches or exceeds the power output of similar technologies. This 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, rather than merely boosting evaporation. LNET researcher Tarique Anwar noted that heat and light imbalances can be leveraged.

Device Design and Mechanism

The nanodevice features a decoupled design with three distinct layers for evaporation, ion transport, and electrical charge collection, allowing for observation and fine-tuning. The research was published in Nature Communications.

When light photons excite electrons within the silicon semiconductor, heat enhances negative charges on its surface. Simultaneously, heat-driven evaporation in a saltwater layer above the nanodevice causes ions to shift, creating separations between positive and negative charges. This charge separation at the liquid-solid interface generates an electric field that drives the excited electrons through a connected circuit, producing electricity.

According to Tagliabue, this surface charge effect, combined with solar light and heat, can enhance energy production by a factor of five, a natural phenomenon now harnessed by the team.

Performance and Future Outlook

The system demonstrates excellent voltage (1 V) and power density (0.25 W/m²). It offers continuous, autonomous electricity generation. Unlike some HV devices where performance enhancement via heat and light can lead to material degradation, this device's nanopillars are coated with an oxide layer to ensure stable performance and protection against chemical reactions. The team developed a model to explain observations and optimize power output by adjusting nanopillar structure and salt concentration. Ongoing work involves developing real-time probing tools and experimenting with heat and light input via a solar simulator.

The researchers anticipate that this innovation will accelerate the development of hydrovoltaic devices, which could power battery-free small sensor networks, environmental monitoring systems, wearable devices, and internet-of-things applications in environments with water, heat, and sunlight.