Estuaries represent potential sources of power — specifically, osmotic energy — that can be harnessed from the differences in the salt concentration between seawater and river water. Reverse electrodialysis (RED) membrane technology has typically been applied for this application, generating electricity from the pressure differences caused by the salt gradient.

Past research has indicated that improving both the flow of positively charged ions across the RED membrane and the efficiency of electron transport by suppressing internal electrical resistance would likely boost the amount of electricity captured. Researchers in China have pursued these avenues by designing a semipermeable membrane with environmentally friendly materials deliver reductions in internal resistance and maximize output power.

The layered-structured nanofluidic membrane fosters ion transport by embedding a negatively charged cellulose hydrogel between layers of electrically conductive polyaniline polymer to promote electron transport. These decoupled transport channels were demonstrated to yield higher ion conductivity and lower resistivity compared to homogenous membranes derived from the same materials.

When tested in a water tank to simulate an estuary environment, the prototype produced an output power density 2.34 times higher than a commercial RED membrane. Performance was maintained during 16 days of continuous operation, and a salt battery array composed of 20 of RED membranes generated enough electricity to individually power a calculator, LED light and stopwatch.

The study conducted by researchers from Guangxi University and Anhui Agricultural University is published in ACS Energy Letters

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