Spin-state modulation boosts *OOH intermediate generation for Ni-Co3O4 catalyst in electro-Fenton like process

Abstract

The electronic structure of metal oxides plays an important role in determining their catalytic activity, but how to regulate this structure to overcome inherent limitations in electron transfer efficiency and spin state configuration remains a significant challenge. Herein, we designed a Ni-doped Co₃O₄ nanorod, where Ni occupied at the octahedral site can effectively facilitate the spin-state transition of Co³⁺ from a low-spin to a high-spin state, inducing an electronic structure reconstruction in Co₃O₄. This not only increases the e_g filling of Co³⁺ but also generates additional electronic states, benefiting water purification process. As expected, the obtained Ni-Co₃O₄-4 catalyst exhibits excellent catalytic performance in electro-Fenton like (EF-like) system, achieving a ciprofloxacin (CIP) removal efficiency of 94.3 %, with a rate constant (k) 1.69 times higher than that of Co₃O₄. In situ Raman spectra confirmed that the charge rearrangement between Ni and Co₃O₄ facilitated the formation of the key *OOH intermediate, promoting the production of superoxide radicals (·O₂^–). Additionally, the developed Ni-Co₃O₄-4 system can operate continuously for 600 min in a continuous-flow reactor. This work deepens the comprehensive understanding of the relationship between electrocatalytic activity and the spin configuration of Co ions, offering an effective design strategy for spinel compound catalysts aimed at environmental remediation.