electrolysis together with half-cell and overall-cell reactions can be written as 2H+ + 2e− →H2 (cathodic reaction) (1) H2O→2H+ + 1/2O2 + 2e− (anodic reaction) (2) H2O→H2 + 1/2O2 (overall reaction) (3) and are shown in Fig. 1a.