Desalination via chemical energy: An electrodialysis cell driven by spontaneous electrode reactions

Abstract

The form of the energy input for widely investigated desalination technologies include thermal energy (distillation), mechanical work (reverse osmosis) or electrical energy (electrodialysis and capacitive deionization). We here propose and characterize an electrodialysis-type desalination cell which is driven instead by spontaneous redox reactions occurring at electrodes. Thus, this system utilizes solely a chemical energy input to perform desalination, and requires no electricity input, instead producing electricity while desalinating. With our custom-built prototype system based on high performance zinc-bromine chemistry, we demonstrate the desalination of feedwater with an initial salinity of ~30g/L while simultaneously generating up to 23.5 kWh of electricity per m3 of desalted water. Further, we show our prototype cell can recover up to 85% of the input chemical energy as electricity during operation without needing a recovery device. The net energy usage, defined as chemical energy input minus electricity output, was measured to be 3.9 kWh/m3 when desalting to near-zero concentration at 2mA/cm2 with our first-generation cell. Our proposed concept decouples reactant production from its usage in the cell, and we show that this decoupling can potentially lead to net negative operating costs when low-cost reactants are employed.