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, N-2,N- and NaBH4/N-2), respectively. With the aid of vast oxygen vacancies (O-v), cobalt at tetrahedral sites (Co2+(Th)) in spinel Co3O4 is diffused into interstitial octahedral sites (Oh) to form rocksalt CoO and ternary oxide CoFe2O4 has been induced to give the unique defective CoO/CoFe2O4 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.

Automated summary

In this study, three CoFe-bimetallic oxides with different compositions were prepared by thermal treating MOF precursors under different atmospheres. Defect engineering effectively tunes the electronic configuration, enhancing the electrocatalytic activity.