In-situ grown MOF-on-MOF heterojunction cathode boosting efficient metal redox cycling for enhanced electro-Fenton processes

To address metal-ion leaching and insufficient electrical conductivity that hinder H 2 O 2 activation in electro-Fenton cathodes, a binder-free CoNi-MOF-74@ZIF-67 MOF-on-MOF heterostructure was in situ grown on nickel (Ni) foam, with carbon nanotubes (CNTs) forming a conductive network and suppressing metal leaching. The heterojunction induced a built-in electric field from CoNi-MOF-74 toward ZIF-67, improving tetracycline (TC) degradation by 32.0% and doubling the degradation rate compared with pristine CoNi-MOF-74, with an electrical energy consumption (EE/O) of only 0.3 kWh/m 3 . Although ·OH was the dominant radical, oxygen vacancies at the heterointerface increase the ·O 2 − contribution. After ten cycles, TC degradation remained above 90%, and Co(III) was efficiently reduced for sustained H 2 O 2 activation. Average leaching amounts were 0.128 mg/L for Co and 0.063 mg/L for Ni, with a batch metal loss below 0.5%. The MOF-on-MOF architecture provides efficient internal electron channels for sustained metal reduction, while the binder-free nature further reduces electron-transport barriers. The CoNi-MOF-74@ZIF-67-C/Ni cathode demonstrated considerable promise for industrial applications.