Outflow geometry for electrochemical desalination cells

•Novel outflow geometry applied to electrochemical desalination.•Desalination cell is analytically, computationally, and experimentally characterized.•Charge efficiency, energy efficiency, and throughput of the system are studied.•Lowest energy consumption facilitated by balanced advection and diffusion. Electrochemical desalination approaches continue to gain in application. Here, we introduce an electrochemical desalination system utilizing a novel flow geometry with symmetric, porous Ag/AgCl electrodes. The system takes advantage of advection to continuously deliver input solution to the surface of the electrodes and reduce depletion that limits throughput and energy efficiency of many desalination systems. We explore the system behavior using steady-state analytical and transient numerical models along with experimental characterization of a small (1 cm2 active area) cell. Desalination performance is explored in terms of degree of separation, throughput, charge efficiency, and energy usage. Optimal flowrate corresponding to minimum energy per mole of salt removed is found based on steady state models when advective separation and system resistive loss is balanced. As an example, for idealized flow, with 65% removal and 50% recovery from a 50 mM NaCl solution, system energy usage at optimum velocity is predicted to be 16.5x the thermodynamic minimum. A gradual tradeoff between energy efficiency and cell throughput exists, potentially allowing vastly higher superficial velocities (e.g., > 0.1 mm/s) and more compact systems than comparable techniques such as reverse osmosis. At example experimental operating conditions, the test cell provides 83% removal of NaCl from a 50 mM input solution at 0.32 V cell voltage with 50% recovery. [Display omitted]