Intercalation and Conversion Reactions of Nanosized β‑MnO₂ Cathode in the Secondary Zn/MnO₂ Alkaline Battery

This work reports rechargeable Zn/β-MnO₂ alkaline batteries as promising stationary energy storage. Unlike commercial alkaline batteries with poor cyclic performance, the nanosized β-MnO₂ cathode in the mixture of LiOH and KOH electrolyte enables rechargeable reactions with high capacity. To unveil the underlying reaction mechanisms of nanosized β-MnO₂, we combine thermodynamic frameworks with experimental characterization, including electrochemistry, X-ray diffraction, and X-ray photoelectron spectroscopy. The results demonstrate a series of proton intercalation reaction (β-MnO₂ → γ-MnOOH) and two-phase conversion reactions (γ-MnOOH → Mn­(OH)₂ → λ-MnO₂) during the first cycle and Li and H cointercalation in the host structure of λ-MnO₂ spinel during the 100^th cycle. It is remarkable that the addition of Bi₂O₃ in the nanosized β-MnO₂ cathode exhibits outstanding capacity. After 100 dischargings, the battery demonstrates a capacity of 316 mA h g^–1. Our findings can serve in the tailored cathode design in high capacity and rechargeable Zn/β-MnO₂ alkaline batteries

Reusable Oxidation Catalysis Using Metal-Monocatecholato Species in a Robust Metal–Organic Framework

An isolated metal-monocatecholato moiety has been achieved in a highly robust metal–organic framework (MOF) by two fundamentally different postsynthetic strategies: postsynthetic deprotection (PSD) and postsynthetic exchange (PSE). Compared with PSD, PSE proved to be a more facile and efficient functionalization approach to access MOFs that could not be directly synthesized under solvothermal conditions. Metalation of the catechol functionality residing in the MOFs resulted in unprecedented Fe-monocatecholato and Cr-monocatecholato species, which were characterized by X-ray absorption spectroscopy, X-band electron paramagnetic resonance spectroscopy, and ⁵⁷Fe Mössbauer spectroscopy. The resulting materials are among the first examples of Zr­(IV)-based UiO MOFs (UiO = University of Oslo) with coordinatively unsaturated active metal centers. Importantly, the Cr-metalated MOFs are active and efficient catalysts for the oxidation of alcohols to ketones using a wide range of substrates. Catalysis could be achieved with very low metal loadings (0.5–1 mol %). Unlike zeolite-supported, Cr-exchange oxidation catalysts, the MOF-based catalysts reported here are completely recyclable and reusable, which may make them attractive catalysts for ‘green’ chemistry processes