Researchers at the Swiss Federal Institute of Technology in Lausanne (EPFL) have built a nanodevice that converts boiling saltwater into usable electricity by harnessing heat and sunlight simultaneously. The device, which pairs a specially engineered evaporation surface with a silicon nanopillar array, generates roughly 1 volt of open-circuit voltage and about 0.25 watts per square meter of power density in dilute saltwater. The result represents a new approach to harvesting energy from one of the planet’s most abundant resources: warm, salty water.
How the Nanodevice Splits Heat and Light
Most solar-evaporation systems use photothermal materials to speed up water vaporization, a strategy explored extensively in research on interfacial evaporation and absorber design for clean water production. Those systems focus on turning sunlight into heat to boil water faster, primarily for desalination. The EPFL team took a different path. Instead of treating heat and light as a single input, their evaporation-driven hydrovoltaic (EDHV) architecture separates the two forces and assigns each a distinct role in generating voltage.
The device uses a decoupled evaporating top interface paired with a bottom layer of silicon-dielectric nanopillars, as described in a peer-reviewed paper published in Nature Communications. The top layer handles evaporation, while the nanopillar array below manages charge dynamics. Heat drives thermodiffusion, the movement of ions along a temperature gradient, while sunlight contributes a photovoltaic effect at the silicon surface. By combining these two mechanisms rather than relying on one alone, the system reaches approximately 1 V open-circuit voltage and roughly 0.25 W/m2 power density at about 0.1 M salt concentration. A preprint version of the framework confirms these same figures and offers additional detail on how thermodiffusion and photovoltaic contributions were unified into a single device concept.
Why Saltwater Concentration Matters
A persistent problem for hydrovoltaic devices is that their performance shifts dramatically depending on how salty the water is. Seawater, brackish groundwater, and industrial brine all present different ionic environments, and a device tuned for one concentration often fails at another. The EPFL group addressed this in earlier peer-reviewed work showing that surface charge and ion mobility create multiple open-circuit voltage peaks across a range of salinities. That finding demonstrated the silicon nanopillar platform could operate not just in dilute solutions but also at high salinity levels closer to actual seawater.
This salinity-dependent behavior is not a quirk but a design feature. By controlling the geometry and surface chemistry of the nanopillars, the researchers can shift the voltage peaks to match target salt concentrations. A preprint on optimization provides additional methodological detail and helps reconstruct the research timeline, showing that these salinity findings preceded and informed the later heat-and-light device. The practical implication is significant: a single device architecture could, in theory, be tuned for different water sources without a complete redesign, from coastal desalination intake to inland brackish wells.
The Physics Behind Thermal Voltage in Nanochannels
The idea that heat alone can push ions through nanoscale channels and generate voltage is not new, but the scale of the effect has only recently been measured with precision. Research published in Physical Review Letters established that thermal gradients at charged nanoscale interfaces produce giant thermoelectric responses driven by water’s excess enthalpy. When a temperature difference exists across a nanochannel lined with charged surfaces, ions redistribute unevenly, creating a measurable electrical potential. This effect is far stronger in confined nanoscale geometries than in bulk water, which is why the silicon nanopillar architecture matters so much.
The EPFL device exploits this physics directly. The nanopillar array creates thousands of tiny charged channels where heat-driven ion movement generates voltage. Adding sunlight on top of the thermal gradient amplifies the output because the silicon surface also produces photogenerated charge carriers. The two effects, thermodiffusion and photovoltaics, do not merely coexist; instead, they reinforce each other. Reviews of photothermal absorbers for solar water vaporization have catalogued many approaches to coupling light and heat for evaporation, but few have attempted to extract electricity from the process itself. The EPFL system does both, turning what is normally waste heat in a desalination setup into a secondary energy source.
Scaling Challenges and the Desalination Connection
The numbers are real but modest. At 0.25 W/m2, the device produces far less power per unit area than a conventional silicon solar panel, which typically delivers 150 to 200 W/m2. That comparison, however, misses the point. The EDHV system is not designed to replace rooftop solar. Its value lies in harvesting energy from thermal waste streams that currently go unused, particularly in solar desalination plants where large volumes of hot saltwater are already being processed. If the device can be integrated into the exhaust side of a desalination system, it could recover energy from heat that would otherwise dissipate, offsetting some of the plant’s electricity consumption.
No published data yet addresses long-term durability of the nanopillar array under continuous exposure to hot brine, salt fouling, or fluctuating sunlight. The peer-reviewed results demonstrate proof of concept under controlled laboratory conditions, and the salinity optimization work shows the platform can handle a range of ionic environments. But translating a lab prototype into a field-ready module requires answers on mechanical robustness, cleaning strategies, and performance under real-world temperature swings. The path from a few square centimeters of active area in a test cell to square meters of rugged hardware in a coastal facility will likely involve redesigning supports, encapsulation, and flow management while preserving the delicate nanoscale features that make the device work.
From Laboratory Curiosity to Hybrid Energy Systems
Despite these hurdles, the EPFL nanodevice points toward a broader category of hybrid systems that treat evaporation not only as a means of purifying water but also as a source of electrical work. In regions where sunlight is abundant and grid power is expensive or unreliable, solar-driven desalination is already attractive for producing drinking water. Embedding EDHV modules into such plants could add a trickle of on-site electricity generation, potentially powering sensors, control electronics, or small pumps without drawing from the main grid. Over time, incremental efficiency gains in both the thermal and electrical pathways could make this dual-use approach more compelling than standalone desalination or conventional photovoltaics alone.
More broadly, the research underscores how much untapped potential lies in low-grade heat and salinity gradients that are currently written off as waste. Industrial cooling ponds, power plant discharge channels, and even warm coastal lagoons all host the kind of conditions (moderate temperature differences, ionic solutions, and available sunlight) that the EDHV architecture is designed to exploit. While the present device is optimized for controlled salt concentrations and specific thermal gradients, the underlying principles of thermodiffusion in nanochannels and photovoltaic enhancement could inspire a new generation of materials and geometries tailored to diverse environments. As those concepts move from theory to practice, boiling saltwater might become not just a challenge for desalination engineers, but a quiet contributor to the renewable energy mix.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
