The energy-dispersive X-ray spectroscopy (EDS) mapping images show a uniform distribution of elements with a slight increase in elemental O on the surface. To further corroborate the increased oxygen vacancies through Na-doping, the electrochemical oxygen intercalation in 1 and 2 was probed through cyclic voltammetry (CV) performed on a three-electrode system in oxygen saturated 1M KOH electrolyte environment. As illustrated in Figure , redox peaks appear as oxygen ions are inserted into and extracted from the accessible lattice vacancy sites. It is important to note that 2 shows positive-shifted redox peaks (marked by arrows) compared to 1, which is in harmony with the increased BE reflected by XPS. Furthermore, the linear sweep voltammetry (LSV) curve of 2 exhibits a low η of 270/390 mV (on NF) to yield current densities of 10/250 mA cm -2 (Figure and). This catalytic activity is much better than 1 and several other cathode materials deployed for water catalysis (Table ). As the reaction kinetics directly relates to the electrochemically active surface area, we also evaluated double-layer capacitance (Cdl) measurements to compare the electrochemically active surface areas of 1 and 2 (Figure ). The double-layer capacitance 2 (Cdl =1.63 mF cm -2 ) is higher than 1 (Cdl =1.25 mF cm -2 ), which suggests that the former possesses a relatively higher density of active sites for catalytic reactions, thus further boosting the OER activities.