Unraveling the Synergistic Effect of Heteroatomic Substitution andVacancy Engineering in CoFe2O4for Superior Electrocatalysis Performance

Metal ion substitution and anion exchange are twoeffective strategies for regulating the electronic and geometric structureof spinel. However, the optimal location of foreign metallic cations andthe exact role of these metals and anions remain elusive. Herein,CoFe2O4-based hollow nanospheres with outstanding oxygenevolution reaction activity are prepared by Cr3+substitution and S2-exchange. X-ray absorption spectra and theoretical calculations revealthat Cr3+can be precisely doped into octahedral (Oh) Fe sites andsimultaneously induce Co vacancy, which can activate adjacenttetrahedral (Td) Fe3+. Furthermore, S2-exchange results in structuredistortion of Td-Fe due to compressive strain effect. The change in thelocal geometry of Td-Fe causes the*OOH intermediate to deviatefrom they-axis plane, thus enhancing the adsorption of the*OOH.The Co vacancy and S2-exchange can adjust the geometric and electronic structure of Td-Fe, thus activating the inert Td-Fe andimproving the electrochemical performance.

Automated summary

In this study, CoFe2O4-based hollow nanospheres with outstanding oxygen evolution reaction activity were prepared by Cr3+ substitution and S2-exchange. Cr3+ can be precisely doped into octahedral Fe sites and simultaneously induce Co vacancy, activating adjacent tetrahedral Fe3+. S2-exchange results in structuredistortion of tetrahedral Fe due to compressive strain effect, enhancing the adsorption of *OOH. The Co vacancy and S2-exchange can adjust the geometric and electronic structure of tetrahedral Fe, improving the electrochemical performance.