Defect‐Induced Atomic Arrangement in CoFe Bimetallic Heterostructures with Boosted Oxygen Evolution Activity

Three CoFe-bimetallic oxides with different compositions (termed as CoFeOx -A/N/H) are prepared by thermally treating metal-organic-framework (MOF) precursors under different atmospheres (air, N2, and NaBH4 /N2 ), respectively. With the aid of vast oxygen vacancies (Ov ), cobalt at tetrahedral sites (Co2+ (Th)) in spinel Co3 O4 is diffused into interstitial octahedral sites (Oh) to form rocksalt CoO and ternary oxide CoFe2 O4 has been induced to give the unique defective CoO/CoFe2 O4 heterostructure. The resultant CoFeOx -H exhibits superb electrocatalytic activity toward water oxidation: overpotential at 10 mA cm-2 is 192 mV, which is 122 mV smaller than that of CoFeOx -A. The smaller Tafel slope (42.53 mV dec-1 ) and higher turnover frequency (785.5 h-1 ) suggest fast reaction kinetics. X-ray absorption spectroscopy, ex situ characterizations, and theoretical calculations reveal that defect engineering effectively tunes the electronic configuration to a more active state, resulting in the greatly decreased binding energy of oxo intermediates, and consequently much lower catalytic overpotential. Moreover, the construction of hetero-interface in CoFeOx -H can provide rich active sites and promote efficient electron transfer. This work may shed light on a comprehensive understanding of the modulation of electron configuration of bimetallic oxides and inspire the smart design of high-performance electrocatalysts.