Furthermore, in the Fe 2p XPS spectra (Figure ) of CoNiCuFe-Oxide, the Fe 2p peaks at binding energies of 712.82 eV and 725.87 eV were characteristic of Fe 3+ , while the peaks at 710.29 eV and 723.39 eV were characteristic of Fe 2+ , with satellite signals at 718.54 eV and 731.64 eV. However, there was no satellite peak for both the Fe 2p1/2 and 2p3/2 of CoNiCuFe-PBA, and the peaks centered at 723.809 eV and 710.181 eV can be ascribed to Fe 3+ , which displayed a remarkable shift to lower binding energy (Figure ). The unsaturated oxygen coordination leads to the decreased chemical states of Fe. High valence state active Fe intermediates have been found to be thermodynamically unstable under the OER conditions, which will leach out of the catalyst during the reaction and thus lead to the degradation of the OER activity over time. Accordingly, the lower valence state Fe cations in the CoNiCuFe-PBA (Figure ) are favorable to maintaining the cubic framework structure of the catalyst and provide considerably well stability under OER operation conditions. Generally, well-crystalline metal oxide catalysts have poor hydroxylation ability and therefore poor activity; oxide catalysts with poor crystallinity cannot possess a combination of excellent activity and stability. In this work, the low-valence Co or Ni of the CoNiCuFe-oxide lead to poor hydroxylation ability and thus poor activity; and it is difficult to maintain a good crystal structure due to its poorer crystallinity, resulting in its instability. In contrast, the initial crystalline CoNiCuFe-PBA catalyst with high-valence active Co or Ni ions can relieve the effects of OER oxidation currents to maintain crystalline states and orderliness, and also has good hydroxylation ability, giving rise to simultaneous high activity and durability.