Salinity Gradient Energy : Current Membrane Development and Challenges for Reverse Electrodialysis System

Salinity gradient power generation has huge potential to generate clean energy from mixing water streams of different salinities. Reverse electrodialysis (RED) is an emerging membrane-based energy conversion technique that drives such energy sources to electricity. In RED, the transport of ions in selective ion exchange membranes (IEMs) is employed for power generation. As a key component in RED power generation, the development and optimization of IEM are crucial for sustainable energy conversion from salinity gradients. Recently, the demand for high quality membranes that are designed uniquely for superb power performance is increasing. This review evaluated commercially available IEMs, currently available state-of-the-art RED membranes, and their key physical and electrochemical properties (e.g., resistance, permselectivity, and swelling). The crucial role of the membrane properties in salinity gradient power generation and their interconnected relationship are discussed through the RED system. This review highlights the importance of IEM development for effective energy harvesting from salinity gradients and provides a better understanding of the dominant factors in RED that directly determine the power performance. The use of proper membranes will expedite the wide-spread application of RED as the next promising renewable energy technology.