To verify the valid activity of the CoNiCuFe-PBA catalyst under long-term OER operation, the chronopotentiometry (CP) measurements at a constant current density of 10 mA cm -2 were conducted, as shown in Figure . The potential of CoNiCuFe-PBA experienced a decline over time with a decrease of 6.7% at the end of the 12-h test, but there was a significant increase for the potential of CoNiCuFe-Oxide, proving the better stability of CoNiCuFe-PBA electrocatalysts in alkaline electrolytes. Moreover, the CoNiCuFe-PBA still maintained a higher catalytic activity than CoNiCuFe-Oxide after the CP stability test (Figure ), which evidences that it maintained the MOOH active phase.