The working electrode was a glassy carbon (GC) disk embedded in Teflon (Pine Instruments) with a geometric surface area of 0.196 cm 2 . The GC electrode has been polished to a mirror finish with Al2O3 paste (particle size 0.05 µm, Buehler) on a polishing cloth (Buehler). After polishing, the electrode has been rinsed and ultrasonicated (Ultrasonic cleaner, ASonic) in Milli-Q/isopropanol mixture several times for 5 min. Once the GC electrode is prepared, 20 µL of 1 mg mL -1 fresh prepared water-based well-dispersed electrocatalyst ink was pipetted on the electrode completely covering it and dried under ambient conditions. After the drop had dried, 5 µL of Nafion solution (ElectroChem, 5 % aqueous solution) diluted in isopropanol