The middle chamber was circulated with 2 M NaCl solution sandwiched by E620K as CEM and Selemion DSV-N as AEM. 3 layers of carbon papers (SGL 39AA) baked at 400 °C overnight were used in each half-cell. For the Fe(Bhmbpy)3 -DBEAQ cell, conditions were similar but supporting electrolytes were changed into KCl.