In situ generation of NiFeOOH mitigates metal-organic framework degradation for ampere‑level oxygen evolution reaction and anion‑exchange membrane water electrolysis

Abstract

NiFe-based metal–organic frameworks (NiFe-MOFs) require reconstruction into metal (oxy)hydroxides to achieve oxygen evolution reaction (OER) activity. However, during the OER process, deep electrochemical reconstruction can lead to the degradation and structural collapse of the organic framework, thereby reducing the activity and stability of the electrocatalyst. Herein, we immerse the Ni-MOF precursor in a mixed salt solution of Ni 2+ and Fe 2+ to in-situ form NiFeOOH/Ni-MOF. In-situ electrochemical impedance spectroscopy (EIS) reveals that the formation of NiFeOOH significantly reduces the interfacial charge transfer resistance and enhances the OER interfacial kinetics. In-situ Raman spectroscopy indicates that NiFeOOH, as the OER active phase, significantly enhances the activity. Furthermore, in-situ / ex-situ Raman spectroscopy and X-ray photoelectron spectroscopy demonstrate that NiFeOOH can mitigate the degradation of the organic framework (O=C–O, C=C) in the MOF. After operating for 810 h at 1.0 A cm −2 , the organic framework is only partially degraded, thereby enhancing the structural stability of the electrocatalyst. As a result, NiFeOOH/Ni-MOF achieves OER stability for over 810 h at 1.0 A cm −2 and overall water splitting for over 1000 h at 1.5 A cm −2 . In 6.0 M KOH at 60 °C, it requires only 1.92 V to drive 1.0 A cm −2 (243.9 A g −1 ) and maintain anion exchange membrane water electrolysis (AEMWE) durability for 210 h.