Boosting electrocatalytic performance of ZnFe2O4/CNT via synergy of CNT defect and oxygen vacancies

Spinel-type complex oxides are considered promising electrocatalysts, nevertheless, the mechanism of electrocatalytic reduction of O2 to generate H2O2 and to activate H2O2 still needs to be further explored. In this work, the dependence of selectivity of electrocatalytic O2 to generate H2O2 and the efficiency of activating H2O2 of defect sites in ZnFe2O4/CNT composites were investigated based on experimental data and characterization. Firstly, the ZnFe2O4/CNT composites were obtained by hydrothermal method combined with high-temperature calcination. Then phenol was used as a typical pollutant to evaluate its electrocatalytic performance. The results indicated that ZnFe2O4/CNT can degrade nearly 100% phenol of 20 mg/L and appears excellent TOC removal efficiency. Impedance experiments showed that the existence of CNT significantly promoted the electron transfer for ZnFe2O4/CNT. Raman spectroscopy and XPS analysis disclosed that the defect degree of CNT as well as oxygen vacancies of ZnFe2O4 in the ZnFe2O4/CNT composites were higher than those of the individual CNT and ZnFe2O4, greatly facilitating the adsorption of O2. Consequently, more O2 was reduced electrocatalytically to H2O2 via the 2e process. Free radical quenching experiments and Fenton experiments showed that homogeneous and heterogeneous activation jointly promoted the conversion of H2O2 to ·OH. This work provides a strategy for the design of efficient electrocatalysts with spinel structures.