Photo-assisted high-entropy metal-organic framework glass with embedded nanocrystals for LiO₂ batteries

A high-entropy metal-organic framework (MOF) glass with embedded nanocrystals is developed as a photocathode for LiO₂ batteries. The synthesis combines five metals (Zn, Co, Fe, Ni, Cu) with 2-methylimidazole to form a crystalline high-entropy ZIF precursor, followed by melt-quenching and controlled Ar/H₂ reduction to generate a homogeneous glass matrix containing in-situ formed metallic nanocrystals (10-12 nm). X-ray diffraction, selected area electron diffraction, differential scanning calorimetry, and extended X-ray absorption fine structure confirm the amorphous structure with preserved short-range coordination. X-ray photoelectron spectroscopy (XPS) and X-ray absorption near edge structure reveal partial reduction of Co and Cu to metallic states alongside mixed-valence Fe and Ni species. Ultraviolet-visible and Tauc's plots give a bandgap of 2.5 eV for HZH3, with the valence band maximum at 2.1 eV. Under visible-light illumination, the optimized cathode delivers a specific capacity exceeding 25,000 mAh g^-1, with a charge voltage of 2.50 V and an overpotential gap of only 0.05 V, and the cell maintains stable cycling for 1800 h without voltage degradation. Cyclic voltammetry shows an anodic peak of 1.40 mA cm^-2 at 3.5 V. UV-Vis spectra confirm efficient superoxide and Li₂O₂ generation under light. XPS and Fourier-transform infrared after cycling confirm complete Li₂O₂ reversibility and suppressed carbonate byproducts. The band alignment straddles the O₂/O₂^- and Li₂O₂/O₂ redox potentials, enabling photogenerated holes to directly oxidize Li₂O₂ and electrons to drive oxygen reduction reaction (ORR).