Octahedral molecular sieves (OMS) are built of transition metal-oxygen octahedra that delimit sub-nanoscale cavities. Compared to other microporous solids, OMS exhibit larger versatility in properties, provided by various redox states and magnetic behaviors of transition metals. Hence, OMS offer opportunities in electrochemical energy harnessing devices, including batteries, electrochemical capacitors and electrochromic systems, provided two conditions are met: fast exchange of ions in the micropores and stability upon exchange. Here we unveil a novel OMS hexagonal polymorph of tungsten oxide called h’-WO3, built of (WO6)6 tunnel cavities. h’-WO3 is prepared by a one-step soft chemistry aqueous route leading to the hydrogen bronze h’-H0.07WO3. Gentle heating results in h’-WO3 with framework retention. The material exhibits an unusual combination of 1-dimensional crystal structure and 2-dimensional nanostructure that enhances and fastens proton (de)insertion for stable electrochromic devices. This discovery paves the way to a new family of mixed valence functional materials with tunable behaviors.

An aqueous synthetic route at 95 °C is developed to reach selectively three scarcely reported vanadium oxyhydroxides. Häggite VO(OH), Duttonite VO(OH), and Gain's hydrate VO(HO) are obtained as nanowires, nanorods, and nanoribbons, with sizes 1 order of magnitude smaller than previously reported. X-ray absorption spectroscopy provides evidence that vanadium in these phases is V. Combined with FTIR, XRD, and electron microscopy, it yields the first insights into formation mechanisms, especially for Häggite and Gain's hydrate. This study opens the way for further investigations of the properties of novel V (oxyhydr)oxides nanostructures.

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Size tuning for MoO2 nanoparticles is demonstrated for the first time over a wide range 2–100 nm, through a colloidal route into water. A nucleation‐growth mechanism based on oriented attachment is evidenced to rationalize the impact of two simple synthetic levers: reactant ratio and temperature. The smallest non‐aggregated crystalline MoO2 nanoparticles are reported, with specific surface area reaching 86 m2 g−1. Size and morphology control, along with the ability to produce, non‐aggregated ultra‐small MoO2 particles are important for a wide range of applications, such as catalysis and energy storage. To exemplify the importance of size tuning, the impact of downscaling on the electrochemical properties in Li‐ion batteries is investigated.