A membrane-less Na ion battery-based CAPMIX cell for energy extraction using water salinity gradients

Abstract

“Salinity energy” stored as the salinity difference between sea water and fresh water is a large scale renewable resource that can be harvested and converted to electricity directly. In this study, a high performance membrane-less Na ion battery-based “capacitive mixing” cell (CAPMIX) was fabricated to extract the entropy energy from the water salinity gradient. The CAPMIX used copper hexacyanoferrate and silver as the electrodes in an aqueous electrolyte. A maximum working voltage of 0.65 V and a maximum power output of 2798 μW g⁻¹ was obtained, which is a significant improvement over previous reported results. This energy harvesting process does not seem to play any significant role in the natural process and no deleterious substances were added to the output stream; it is a completely environmentally friendly power source. The entropy energy extracting battery represents a novel electrochemical device and is also a promising technology in the development of renewable energy production.