Fig. 2: Design and performance of membrane-free acid-base-producing electrochemical cell.

A Ion transport schemes for three electrolytes. B Model and validation of CE at different current-to-flow ratios, which correspond to what the output concentrations would be if CE were 100%. The actual output concentrations are obtained by multiplying the value of the current-to-flow ratio on the x-axis by the corresponding CE value (Table S2). Error bars were calculated from the standard error of the data (n = 3). Error bars are rendered for all points, where not visible they are smaller than the marker. C Contributions of H⁺ and OH^– to the loss of CE as a function of the current-to-flow ratio. Note that 100% – sum of contributions = predicted CE. D E_ab and EE values for a range of j_tot at a constant Q = 0.1 mL min^–1. Error bars were calculated from the standard error of the data (n = 3). E Corresponding values for productive current density and output acid and base concentrations. Error bars were calculated from the standard error of the data (n = 3). F Cell voltage vs. time trace for a 35 h run at j_tot = 100 mA cm⁻² and Q = 0.1 mL min⁻¹ cm⁻² in mixed NaCl/ Na₂SO₄ electrolyte containing Mg and Si impurities. The cell was operated in reverse polarity for 60 s every 5 h. The average V_cell is 1.04 V. V_cell decays by 1-2 mV h^–1 (inset), but it is recovered by brief reverse polarization. Voltage data is not iR corrected.