Unlocking the Potential of ZIF-67 as an Efficient Electrocatalyst for the Oxygen Reduction Reaction

Zeolitic imidazolate frameworks (ZIFs) are widely explored as precursors for constructing electrocatalysts for the oxygen reduction reaction (ORR). However, most studies convert these frameworks into metal-nitrogen-carbon (M-N-C) catalysts via pyrolysis, a process that often compromises their structure integrity and coordination precision. Herein, it is demonstrated that ZIF-67 can serve directly as a highly-active molecular catalyst for ORR. By applying ball-milling to enhance cobalt sites exposure, the optimized ZIF-67 exhibits exceptional ORR activity in alkaline media. Combined spectroscopic and theoretical analyses reveal that this remarkable activity stems from coordinatively unsaturated Co-N4-x sites, which transform into Co-N4-x(OH) moieties under reaction conditions, thereby facilitating oxygen adsorption and activation. Furthermore, mild thermal treatment (<= 500 degrees C) enhances the proportion of Co-N4-x sites up to 48%, as confirmed by X-ray absorption spectroscopy, achieving ORR activity rivals or even exceeds conventional pyrolyzed M-N-C catalysts. This study unlocks the potential of ZIFs as active molecular electrocatalysts upon mild thermal treatment, providing a scalable and efficient strategy for optimizing ZIFs for catalytic applications while preserving their structural precision.