The CCC value can be perceived as the ratio between the non-catalytic acid-base CO2 consumption rate and the rate of catalytic alkalinity production. It is experimentally easily accessible and reveals the nature of the prevalent anion crossing the membrane in an uniquely intuitive way: For CCC=0 there is pure OH -transfer, for CCC=1 pure CO 3 2-crossover, and for CCC=2 pure 𝐻CO 3 2-crossover. A number of the kinetic electrolyzer performance parameters in Supplementary Table can be expressed in terms of the CCC.