Electrochemical Production of >1 M Acid and Base from Neutral Salt at High Current Density and Low Energy Demand

Consumption of acid and base drives chemical transformations underpinning industrial hydrometallurgical processes and many proposed carbon management technologies. Production of acid and base is the key driver of the energy demand, emissions, and waste generation of these processes. Generating acid and base electrochemically from salt solutions enables their production without stoichiometric waste using low-carbon power. However, conventional electrochemical approaches using ion-exchange membranes (IEMs) have an excessive energy demand, low productive current densities, and poor impurity tolerance. These shortcomings can be addressed by the diaphragm flow cell (DFC), which has a lower resistance and an improved impurity tolerance. Here we report an improved DFC design that produces a concentrated (1.1–1.5 M) acid and base from neutral salt at the lowest energy demand (0.051–0.067 kWh mol –1 ) and highest productive current densities (275–367 mA cm –2 ) reported to date at 70 °C, a realistic temperature for a scaled system. Using a continuum model, we show that the electrolyte residence time has a significant impact on current efficiency by controlling diffusive losses.