Unraveling the π-interaction of NiFe-based metal-organic frameworks with enhanced oxygen evolution: Optimizing
Mi Wang1, Yushan Chen1, Zebin Yu1
1State Key Laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures, School of Resources, Environment and Materials, Guangxi University, Nanning 530004, China.
Abstract:
Metal-organic frameworks (MOFs) with conjugation carboxylate ligands as electrocatalysts can significantly improve oxygen evolution reaction (OER), but the role of π-interaction on the reactive sites of OER is often neglected. We intend to unravel the mechanism of how π-interaction enhances OER performance. The results of Rietveld refinement, density functional theory (DFT) calculations, and in-situ Raman spectra show that π-interaction can efficiently modulate the local spin configuration of metal centers, facilitate γ-Ni1-xFexOOH active species with high-valence Ni sites modified by high-spin Fe, accelerate electron transfer, optimize the d-band center together with the beneficial rate-determining step of OER. NiFe-BPDC MOFs/NF with 0.8559 eV π-interaction energy generated γ-Ni1-xFexOOH in only 60 s at 1.4 V, demonstrating that π-interaction promotes the rapid generation of highly active reactive sites. Furthermore, the results of in-situ Raman and electron paramagnetic resonance (EPR) spectra reveal that the deprotonation and deoxygenation steps of OER are accompanied by changes in the oxidation state of metal ions and the generation of oxygen vacancies on the surface of catalysts. In addition, NiFe-BPDC MOFs/NF rapidly completes the deprotonation and deoxygenation steps, and it requires only 288 mV overpotential to reach 100 mA/cm2 with 100 h of stability, suggesting promising industrial application.
