Typically, the intensity ratio of the characteristic peaks at ~460 and ~540 cm -1 , namely IB/IS, can be employed as an index to reflect the fraction of disorder. In Figure , both IB/IS of CoNiCuFe-PBA and CoNiCuFe-oxide are found to evolve along with the increasing potential applied to the working electrode. Nevertheless, there exist significant differences between the IB/IS of CoNiCuFe-PBA and CoNiCuFe-oxide. The values of IB/IS for the CoNiCuFe-PBA electrocatalyst are much higher than oxide, which is in accordance with the crystallinity calculated by XRD patterns (the inset in Figure ). What's more, the IB/IS of CoNiCuFe-PBA does not reduce with the decreasing potential, indicative of an increasing trend in the degree of order for CoNiCuFe-PBA with the increasing potential and the retained high degree of order after OER though the potential decreased. The IB/IS of CoNiCuFe-oxide was significantly lower than that of CoNiCuFe-PBA. Regardless of the higher structural disorder of oxide, it still exhibited the less MOOH active phase and thus a poor catalytic activity (Figure ). This is contradictory to the previous reports which held the point that high structural disorder could bring about enhanced OER performance. Both the lower formation potential and the increased Raman band intensity of the active M 3+ species in the CoNiCuFe-PBA catalyst disclosed by spectroscopic characterizations and electrochemical results suggest that the CoNiCuFe-PBA catalyst tends to undergo active phase transformation easily and formed a highly reactive MOOH layer in alkaline media. This revealed the abundance in oxidizable active sites of CoNiCuFe-PBA, which is conducive to the transition to MOOH active phase and thus exhibits more reactivity. By contrast, the formation of the MOOH active phase is a more sluggish process for the CoNiCuFe-Oxide during the OER and it does not exhibit a large amount of MOOH on the surface, leading to poor OER activity.