The space-charge region at NiFe-MOF⊆LDH p-n junction by self-sacrificing LDH to boost oxygen evolution tandem with in-situ electro-Fenton

Abstract

The rational design of p-n heterojunction was highly desirable to optimize charge distribution at space-charge region, tailoring the adsorption free energy of intermediate matters, and to boost the oxygen evolution reaction (OER) and in situ electro-Fenton (EF) reaction. Herein, a self-sacrificing strategy has been employed to construct the NiFe-MOF⊆LDH nanosheet arrays on carbon cloth (CC), directly using NiFe-LDH as template. NiFe-MOF⊆LDH exhibited outperformed OER activity with a lower overpotential of 196 mV and smaller Tafel slope of 48 mV dec-1(η10). The conferred higher valence state for Ni3+ and the more carrier density to absorb more OH– ions confirmed by in-situ Raman and density functional theory (DFT) calculation endowed the excellent OER activity, which was expected to endow the self-oxygenation to support the following EF in this system without additional O2. An electrochemical flow reactor was designed for anodic OER and cathodic EF only at low voltage of 1.6 V. Typically, the in-situ H2O2 yield rate could achieve 27.4 mmol/h at cathodic ORR reaction, which was further activated by Fe2+/Fe3+ cycling for the heterogeneous Fenton reaction. This tandem reactor could remove 96% of ibuprofen (IBF) within 120 min with long-term cycle use. In a word, coupling the OER with EF in a flow reactor has possible application in the fields of sustainable energy and environmental remediation.