The Co-N-C was initially deposited on glassy carbon (GC) electrode to evaluate its OER activity. An activation process was observed during consecutive cyclic voltammetry (CV) scans (Fig. ). Both chronoamperometry and chronopotentiometry could also be employed to activate the catalytic material (Fig. ), but chronopotentiometry led to better activity (Fig. ). Carbon-cloth (CC) electrode was adopted in order to further improve the catalytic performance due to its higher surface area and better conductivity. After activation (Fig. ), Co-N-C on CC exhibited an overpotential of 321 mV to reach 10 mA/cm 2 , with a Tafel slope of 40 mV/dec (Fig. ; Fig. ). Measurements on multiple samples resulted in good data reproducibility on both GC and CC electrodes (Fig. , Table ). To evaluate the stability of the catalyst, accelerated degradation measurements were performed using continuous fast CV scans. The polarization curve of the catalyst obtained after 3000 CVs exhibited a negligible increase in overpotential (4 mV) for 10 mA/cm 2 compared to the initial curve, indicating excellent stability (Fig. ). Moreover, a galvanostatic measurement was conducted at a current density of 10 mA/cm 2 . No significant overpotential increase was observed during 16 h of electrolysis (Fig. ). The Faradaic efficiency of OER was determined as 98%, implying almost all of the current was in charge of catalytic water oxidation (Fig. ).