To get better insights into OER kinetics, the Tafel slopes of the cathodes was obtained from steady-state polarization curve. Figure manifests that Tafel slope of 2 (67.5 mV dec -1 ) is lower than 1 (72.2 mV dec -1 ) and benchmark IrO2 (86 mV dec -1 ). The lower Tafel slope value of 2 indicates that the Na + substitution into DRX matrix plays a vital role in promoting the electrochemical OER kinetics, thus improving the intrinsic catalytic activity.