New concept to improve salinity energy harvesting by capacitive layers.

To effectively combat global warming, it is necessary to increase the use of clean renewable energy. Blue energy is a less-known source with enormous potential since it can be generated directly by mixing the fresh and the sea water. However, current processes for extracting this energy remain inefficient. Indeed, the existing approaches such as the reverse electrodialysis or the pressure retarded osmosis are still not economically viable. Hopes for nonselective nanoporous charged membranes designed to reduce the internal resistance of the cell seem to be in vain. Here we present a novel solution that involves increasing the potential of the membrane by attaching tailored capacitive layers negatively charged on the surface to adsorb ions. Such a configuration allows us to double the potential of the cell without modifying the global ohmic resistance and thus to multiply by 4 the recoverable power.

After a thorough study carried out to characterize the process and optimise of the energy consumption caused by the hydraulic pressure drop, we introduce a centimeter-scale device with only one membrane. We manage to harvest a power density of 5.4 W/m² using brines solutions, which makes the system economically viable.