The geometric surface area of each WE and CE was 0.84 cm 2 , and the volume of the 3DPEC flow cell was approximately 1.6 cm 3 . An activation procedure was carried out by electrochemical saponification in 1 M NaOH during ten polarisation cycles at a constant scan rate of 100 mV/s, from -1.4 to 1.2 V .