In Situ XAS Study on the Dynamic Structural Evolution of Metal-Organic Frameworks for Efficient Oxygen Evolution Electrocatalysis

Metal-organic frameworks (MOFs), featuring well-defined metal active sites and unique coordination environment, have recently emerged as ideal model catalysts for establishing precise structure-activity relationships in oxygen evolution reaction (OER). However, elucidating essential catalytic mechanisms responsible for dynamic reaction conditions remain challenging, primarily due to the complicated adsorption behavior and cross-step transfer of key adsorbates during OER. Herein, we propose a defect-driven stepwise activation strategy to meticulously control the adsorption behavior for defective Co-based MOF (termed D/CoFc-MOF) through tailoring the interplay between local coordination geometry and electronic configuration. Theoretical calculations, complemented by surface phase diagrams, demonstrate that reaction intermediates (OH*, O*, and OOH*) can be sequentially activated, thereby overcoming high reaction barrier induced by cross-step transfer. Operando attenuated total reflection Fourier transform infrared (ATR-FTIR) and Raman characterizations reveal that D/CoFc-MOF undergoes a unique stepwise activation during OER, progressing from FeOOH state to coexistence intermediate FeOOH/CoFeOOH state, and ultimately to active CoFeOOH phase, which markedly differs from conventional single-step surface phase conversion. However, a fundamental challenge lies in directly probing the real-time evolution of local coordination structure and electronic states of active sites under operational conditions, which is essential for establishing quantitative structure-activity relationships and accelerating the development of efficient MOF-based catalysts. In-situ X-ray absorption spectroscopy (XAS) offers a powerful approach to unravel (a) the stepwise structural transformation from pristine MOF structure to CoFeOOH, (b) the sequential activation and optimization of local coordination environment, and (c) the impact of defect-driven stepwise activation strategy on charge transfer and electronic interaction around active sites. This will provide fundamental insights into the design of catalysts prone to dynamic phase transitions.