Salt battery enhances osmotic energy capture from river-sea convergence

Salt battery enhances osmotic energy capture from river-sea convergence
by Simon Mansfield
Sydney, Australia (SPX) Apr 26, 2024
Estuaries, where freshwater rivers meet the sea, are not only ideal for birdwatching and kayaking but also serve as potential sources of renewable, "blue" osmotic energy. A recent study published in ACS Energy Letters highlights a breakthrough in this field, involving a semipermeable membrane designed to harvest osmotic energy from the salt gradients between these waters, effectively converting it into electrical power. The novel membrane demonstrated more than double the output power density compared to conventional commercial membranes in laboratory tests.

Osmotic energy harnessing, feasible anywhere salt gradients exist, has seen various technological approaches. A notable method utilizes a series of reverse electrodialysis (RED) membranes, described as a "salt battery," which generates electricity from the pressure disparities induced by the salt gradients. This process involves positively charged ions like sodium from seawater moving into freshwater, thus increasing membrane pressure. Optimizing this transfer and reducing internal electrical resistance are critical for enhancing energy capture.

Building on previous research, Dongdong Ye, Xingzhen Qin, and their colleagues developed a new semipermeable membrane using eco-friendly materials aimed at reducing internal resistance and maximizing energy output. Their approach involved creating decoupled channels within the membrane-one for ion transport made of negatively charged cellulose hydrogel, and another for electron transport consisting of an electrically conductive polymer, polyaniline.

Testing in a controlled environment simulating an estuary, the prototype achieved an output power density that was 2.34 times higher than that of a standard commercial RED membrane, with consistent performance over 16 days. Furthermore, when arranged into an array of 20 membranes, this setup successfully powered devices like a calculator, LED light, and stopwatch independently.

The researchers believe their innovative design opens new possibilities for using ecological materials in RED membranes and enhancing the efficiency of osmotic energy systems for practical applications.

Research Report:Decoupled Ionic and Electronic Pathways for Enhanced Osmotic Energy Harvesting