Recent Manganese Oxide Octahedral Molecular Sieves (OMS–2) with Isomorphically Substituted Cationic Dopants and Their Catalytic Applications

Structure-Property Interplay Within Microporous Manganese Dioxide Tunnels For Sustainable Energy Storage

Tunnel-structured manganese dioxides (MnO2 ), also known as octahedral molecule sieves (OMS), are widely studied in geochemistry, deionization, energy storage and (electro)catalysis. These functionalities originate from their characteristic sub-nanoscale tunnel framework, which, with a high degree of structural polymorphism and rich surface chemistry, can reversibly absorb and transport various ions. An intensive understanding of their structure-property relationship is prerequisite for functionality optimization, which has been recently approached by implementation of advanced (in situ) characterizations providing significant atomistic sciences. This review will thus timely cover recent advancements related to OMS and their energy storage applications, with a focus on the atomistic insights pioneered by researchers including our group: the origins of structural polymorphism and heterogeneity, the evolution of faceted OMS crystals and its effect on electrocatalysis, the ion transport/storage properties and their implication for processing OMS. These studies represent a clear rational behind recent endeavors investigating the historically applied OMS materials, the summary of which is expected to deepen the scientific understandings and guide material engineering for functionality control.

Self-assembly of random networks of zirconium-doped manganese oxide nanoribbons and poly(3,4-ethylenedioxythiophene) flakes at the water/chloroform interface

Owing to their magnificent chemical and physical properties, transition metal-based heterostructures are potential materials for applications ranging from point-of-care diagnostics to sustainable energy technologies. The cryptomelane-type octahedral molecular sieves (K-OMS-2) are extensively studied porous materials with a hollandite (2 × 2 tunnel of dimensions 4.6 × 4.6 Å2) structure susceptible to the isovalent substitution of metal cations at the framework of MnO6 octahedral chains. Here we report a facile in situ synthesis of framework-level zirconium (Zr)-doped K-OMS-2 nanoribbons in poly(3,4-ethylenedioxythiophene) (PEDOT) nanoflakes at a water/chloroform interface at ambient conditions. An oxidant system of KMnO4 and ZrOCl2·8H2O initiated the polymerisation at temperatures ranging from 5° to 50 °C. The lattice distortions arising from the framework-level substitution of Mn4+ by Zr4+ in the K-OMS-2 structure were evidenced with powder X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and N2 adsorption-desorption studies. Transmission electron microscopic and mapping images confirmed that PEDOT/Zr-K-OMS-2 comprises a highly crystalline random network of two-dimensional PEDOT flakes and Zr-doped K-OMS-2 nanoribbons. In this regard, the proposed interfacial strategy affirms an in situ method for the morphological tuning of heterostructures on polymer supports at low temperatures.