It remains difficult to understand the surface of solid acid catalysts at the molecular level, despite their importance for industrial catalytic applications. A sulfated zirconium-based metal-organic framework, MOF-808-SO4, has previously been shown to be a strong solid Brønsted acid material. In this report, we probe the origin of its acidity through an array of spectroscopic, crystallographic, and computational characterization techniques. The strongest Brønsted acid site is shown to consist of a specific arrangement of adsorbed water and sulfate moieties on the zirconium clusters. When a water molecule adsorbs to one zirconium atom, it participates in a hydrogen bond with a sulfate moiety that is chelated to a neighboring zirconium atom; this motif in turn results in the presence of a strongly acidic proton. On dehydration, the material loses its acidity. The hydrated sulfated MOF exhibits good catalytic performance for the dimerization of isobutene (2-methyl-1-propene), achieving 100% selectivity for C8 products with good conversion efficiency. The chemistry at the surface of solid acid catalysts is of vital importance for industrial catalytic applications, yet a precise molecular picture of these surfaces remains elusive. Attempts to obtain a clear view of the Brønsted acid sites in solid acids such as sulfated zirconia have resulted in multiple proposed models, in part due to the difficulty in characterizing the structure of this

High-voltage layered lithium- and manganese-rich (LMR) oxides have the potential to dramatically enhance the energy density of current Li-ion energy storage systems. However, these materials are currently not used commonly; one reason is their inability to maintain a consistent voltage profile (voltage fade) during electrochemical cycling. This report rationalizes the cause of this voltage fade by providing evidence of layered to spinel (LS) structural evolution pathways in the host Li1.2Mn0.55Ni0.15Co0.1O2 oxide. By employing neutron powder diffraction, we show that LS structural rearrangement in the LMR oxide occurs through a tetrahedral cation intermediate via the following: (i) diffusion of lithium atoms from octahedral to tetrahedral sites of the lithium layer [(LiLioct → LiLitet] which is followed by the dispersal of the lithium ions from the adjacent octahedral site of the metal layer to the tetrahedral sites of lithium layer [LiTMoct → LiLitet]; (ii) migration of Mn from the octahedral sites of the transition-metal layer to the “permanent” octahedral site of lithium layer via tetrahedral site of lithium layer [MnTMoct → MnLitet → MnLioct)]. These findings open the door to potential routes to mitigate this “atomic restructuring” in the high-voltage LMR composite oxide by manipulating their composition/structure for practical use in high-energy-density lithium-ion batteries.

The large-voltage hysteresis remains one of the biggest barriers to optimizing Li/Na-ion cathodes using lattice anionic redox reaction, despite their very high energy density and relative low cost. Very recently, a layered sodium cathode Na2Mn3O7 (or Na4/7Mn6/7□1/7O2, □ is vacancy) was reported to have reversible lattice oxygen redox with much suppressed voltage hysteresis. However, the structural and electronic structural origin of this small-voltage hysteresis has not been well understood. In this article, through systematic studies using ex situ/in situ electron paramagnetic resonance and X-ray diffraction, we demonstrate that the exceptional small-voltage hysteresis (<50 mV) between charge and discharge curves is rooted in the well-maintained oxygen stacking sequence in the absence of irreversible gliding of oxygen layers and cation migration from the transition-metal layers. In addition, we further identify that the 4.2 V charge/discharge plateau is associated with a zero-strain (de)­intercalation process of Na+ ions from distorted octahedral sites, while the 4.5 V plateau is linked to a reversible shrink/expansion process of the manganese-site vacancy during (de)­intercalation of Na+ ions at distorted prismatic sites. It is expected that these findings will inspire further exploration of new cathode materials that can achieve both high energy density and efficiency by using lattice anionic redox.

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An in situ variable-temperature neutron diffraction study of Li3PS4 reveals the structure and Li-ion diffusion pathways (via MEM and BVEL calculations) of the high temperature fast-ion conductor, α-Li3PS4, (Ea = 0.22 eV), and compares them to those of other polymorphs and the Si-substituted phase.