Estuaries, where freshwater rivers meet the salty sea, are ideal locations for activities such as birdwatching and kayaking. These areas also hold potential for sustainable energy generation through osmotic energy. Researchers in ACS Energy Letters have developed a semipermeable membrane that can harvest osmotic energy from salt gradients and convert it into electricity. The new design demonstrated an output power density over two times higher than commercial membranes in laboratory tests, showing promise for capturing renewable energy in areas with salt gradients.
Osmotic energy can be generated wherever there are salt gradients, but current technologies for capturing this energy have room for improvement. One method involves using reverse electrodialysis (RED) membranes, which function like a “salt battery” by generating electricity from pressure differences caused by the salt gradient. To increase the capturing power, the membrane needs to allow ions to flow easily across while maintaining low internal electrical resistance for efficient electron transport. The researchers, Dongdong Ye, Xingzhen Qin, and their colleagues, designed a semipermeable membrane using environmentally friendly materials to minimize internal resistance and maximize output power.
The researchers’ RED membrane prototype featured separate channels for ion transport and electron transport to enhance efficiency. They achieved this by incorporating a negatively charged cellulose hydrogel for ion transport and layers of an electrically conductive polymer called polyaniline for electron transport. Initial tests confirmed that the decoupled transport channels resulted in higher ion conductivity and lower resistivity compared to homogeneous membranes made from the same materials. The prototype demonstrated an output power density over two times higher than commercial RED membranes in a simulated estuary environment and maintained performance during 16 days of continuous operation underwater, showcasing its long-term stability.
In a final test, the team created a salt battery array using 20 of their RED membranes and generated enough electricity to power devices such as a calculator, LED light, and stopwatch individually. The findings of Ye, Qin, and their team expand the possibilities of using ecological materials to create RED membranes and improve osmotic energy-harvesting performance. These advancements make osmotic energy systems more feasible for real-world applications, offering a promising avenue for sustainable energy generation in areas with salt gradients.
The research conducted by Ye, Qin, and their team not only demonstrates the potential of osmotic energy as a renewable energy source but also highlights the importance of developing efficient technologies for capturing and converting this energy. By utilizing semipermeable membranes designed to maximize output power and minimize internal resistance, the researchers have laid the foundation for improved osmotic energy harvesting. The findings contribute to the ongoing efforts to enhance sustainable energy solutions and reduce dependence on traditional fossil fuels.
