Fig. 4. Effect of (a-b) pyrolysis temperature, (c-d) urea dosage and (e-f) Fe/Co ratio on the OER electrocatalytic activity of CoFe-CoxN@NC by LSV measurement and its corresponding Tafel slop
The stability of electrocatalyst was another key feature in practical applications. The stability of CoFe-CoxN@NC for OER was evaluated by the chronopotentiometri measurement recorded at a constant current density of 10 mA·cm−2, as show in Fig. 5. After the continuous test for 80000 s, the overpotential of CoFe-CoxN@NC kept well-maintained, of which just increased by about 20 mV. The TEM images, TEM-mapping images and XRD pattern (Fig. S11-12) of CoFe-Co5.47N@NC catalyst after stability test indicated that the structure and morphology of the catalyst remains unchanged. From the electrocatalytic performance above, the catalytic activity and stability of CoFe-CoxN@NC for OER was mainly attributed to the active sites of CoFe-Co5.47N heterogeneous structure encapsulated by the graphic carbon layers and embedded in the nitrogen-doped lignin-derived shell-core carbon material.