Fig. 2: BPM electrodialysis performance characteristics.

a Simulated BPM voltage vs. total current density (black line) as well as partial current density carried by major ions, including proton and hydroxide for water dissociation (blue line), Na⁺ (green line) and Cl⁻ (purple line), in the synthetic oceanwater. Black dots indicate the experimentally measured BPM voltage as a function of the applied current density, corrected for the ohmic resistance in the oceanwater. b Fractional current carried by H⁺ \(\left( {j_{{\mathrm{H}}^ + }}/j_{\mathrm{total}} \right)\), OH⁻ \(\left( {j_{{\mathrm{OH}}^ - }} /j_{\mathrm{total}}\right)\), Na⁺ \(\left( {j_{{\mathrm{Na}}^ + }} /j_{\mathrm{total}}\right)\) and Cl⁻ \(\left( {j_{{\mathrm{Cl}}^ - }} /j_{\mathrm{total}} \right)\) across the BPM as a function of the total current density (j_total). c Experimentally measured voltage-current density characteristics of the BPM electrodialysis cell using 0.5 M Na₂SO₄ electrode solution at a flow rate of 40 ml min⁻¹ (red dots), 0.4 M K₃/K₄[Fe(CN)₆] at a flow rate of 40 ml min⁻¹ (black dots) and 20 ml min⁻¹ (blue dots), 0.2 M K₃/K₄[Fe(CN)₆] at a flow rate of 40 ml min⁻¹ (green dots) and 20 ml min⁻¹ (purple dots). Dashed lines are used to guide the eye. d Experimentally measured (black dots) and calculated (lines) pH of the acidified stream as a function of applied current density for BPM electrodialysis cell with an electrode and membrane active area of 64 cm².