Mechanochemical Solid-Solution Formation in Zeolitic Imidazole–Tetrazole Frameworks for Enhanced Oxygen Evolution Reaction

Exploring heterometallic architectures and uncoordinated nitrogen sites in zeolitic imidazole–tetrazole frameworks provides an unconventional route to enhancing electrocatalytic activity. Herein, we report a mechanochemical alloying approach that simultaneously induces metal–metal (Co–Zn) and ligand–ligand (imidazole–tetrazole) mixing to yield an amorphous solid solution, aZn0.5Co0.5ZI0.5T0.5F-8, from pristine ZnZTF-8 and CoZIF-8 under solvent-free conditions in an inert atmosphere (Ar). Subsequent methanol vapor exposure at 25 °C transforms this disordered phase into a crystalline analogue, cZn0.5Co0.5ZI0.5T0.5F-8. X-ray adsorption spectroscopy (EXAFS and XANES), inductively coupled plasma mass spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, and field emission scanning electron microscopy analyses confirm the coexistence of metal and ligand solid solution and defect-rich uncoordinated nitrogen sites in the amorphous phase. Owing to its higher density of active sites and degree of heterogeneity, aZn0.5Co0.5ZI0.5T0.5F-8 exhibits superior oxygen evolution reaction (OER) performance, featuring an overpotential of 338 mV and a Tafel slope of 94.8 mV dec–1 over parent frameworks. Furthermore, the origin of enhanced OER performance is validated using the computational hydrogen electrode approach in which the OER intermediates (*OH, *O, and *OOH) were evaluated on the optimized secondary building units of Zn0.5Co0.5ZI0.5T0.5F-8, as well as ZnZTF-8 and CoZIF-8. This work establishes mechanically induced simultaneous metal and ligand solid solution in MOFs as a sustainable and versatile strategy for engineering noncrystalline frameworks with exceptional electrocatalytic efficiency.