Exploring Structural Evolution Behaviors of Ligand‐Defect‐Rich Ferrocene‐Based Metal‐Organic Frameworks for Electrochemical Oxygen Evolution via Operando X‐Ray Absorption Spectroscopy

Abstract

AbstractMetal‐organic frameworks (MOFs) have exhibited encouraging catalytic activity for the oxygen evolution reaction (OER), a crucial process for water electrolysis to produce green hydrogen. Nonetheless, distinguishing the source of catalytic activity and establishing the structure‐composition‐property relationships of MOFs during OER processes remain challenging. Here, for the first time, operando X‐ray absorption spectroscopy (XAS) is utilized to monitor the structural evolution and identify the active components of ferrocene‐based MOFs (Ni‐Fc) for OER. Ligand‐defect‐rich Ni‐Fc is synthesized via the co‐deposition method. After electrochemical activation, Ni‐Fc exhibits superior electrocatalytic activity (228 mV at 10 mA cm−2 in 0.1 m KOH), which is highly competitive compared with state‐of‐the‐art electrocatalysts. Operando XAS analysis and ex‐situ characterizations reveal the structural reconstruction of Ni‐Fc into amorphous NiFe‐catalysts (a‐NiFe) during the activation process, and further into real catalytic phases (a‐NiFe‐C) under catalytic potential greater than 1.45 V (vs RHE). In catalytic phases, in‐situ formed deprotonated and oxygen‐defected Ni oxyhydroxide analogues act as catalytic sites, while Fe hydroxide analogues derived from ligands optimize the electronic structure of Ni sites for improving OER activity. Density functional theory (DFT) analysis indicates a reduced energy barrier in a‐NiFe‐C compared to pristine MOFs, supporting the improved catalytic activity of the latter.