Mild pH-decoupling ARFB the center chamber. NaCl solution is cycled in this center compartment between the two membranes, and pH sensors were inserted in all three chambers' electrolyte tanks for real-time pH monitoring. To counteract any remaining proton/hydroxide crossover processes, the posolyte and negolyte tanks were also connected to a bipolar membrane sub-cell (BPM sub-cell) for in situ pH recovery. By reducing the posolyte and oxidizing the negolyte in a BPM cell, water can dissociate into protons and hydroxides, generating acid and base for recovery. This BPM sub-cell could be small, relative to the main cell, and only operate at intervals as controlled by valve gates, as illustrated.