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

The use of acid and base to drive chemical transformations underpins industrial hydrometallurgical processes and many proposed carbon management technologies. The production of the acid and base are key drivers of the energy demand, emissions, and waste generation of these processes. Generating acid and base electrochemically from salt solutions enables the use of low-carbon power and avoids stoichiometric salt waste. However, conventional electrochemical approaches that use ion exchange membranes (IEMs) have excessive energy demand, low productive current densities, and poor impurity tolerance. These shortcomings can be addressed by using a diaphragm flow cell (DFC), which has lower resistance than IEM-based systems and improved impurity tolerance. Here we report an improved design for the DFC that incorporates mesh spacers in the electrolyte compartments to reduce the residence time of the electrolyte and rigidify the compartments. This cell produces 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 while operating 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.