Low-dimensional nanostructures offer a host of intriguing properties which are distinct from those of the bulk material, owing to size-confinement effects and amplified surface areas. Here, we report on the scalable, bottom-up synthesis of ultrathin coordination polymer nanosheets via surfactant-mediated synthesis and subsequent exfoliation. Layers of a two-dimensional (2D) zinc coordination polymer are self-assembled in the interlamellar space of a reverse microemulsion mesophase into stacks of nanosheets interleaved with cethyltrimethylammonium bromide (CTAB) at regular intervals, thus giving rise to a lamellar hybrid mesostructure with a lattice period of ~8 nm and an underlying highly crystalline substructure. The basic structural motif is composed of 2D acetato-benzimidazolato-zinc layers of tetrahedrally coordinated zinc joined together by anionic acetate and benzimidazolate ligands. The hierarchical structure was studied by PXRD, TEM, EDX, EELS, AFM, and solid-state NMR spectroscopy, revealing a high level of order on both the atomic and mesoscale, suggesting fairly strong interactions along the organic-inorganic hybrid interface. Exfoliation of the hybrid material in organic solvents such as THF and chloroform yields sheet- and belt-like nanostructures with lateral sizes between 10's and 100's of nanometers and a height of about 10 nm measured by AFM, which precisely maps the basal spacing of the lamellar mesostructure; further exfoliation results in nanobelts with minimum sizes around 4 nm. Finally, the sheetlike nanostructures behave as morphological chameleons, transforming into highly regular multiwalled coordination polymer nanotubes upon treatment with organic solvents.

The rational design of hydrogen evolution reaction (HER) electrocatalysts which are competitive with platinum is an outstanding challenge to make power-to-gas technologies economically viable. Here, we introduce the delafossites PdCrO 2 , PdCoO 2 and PtCoO 2 as a new family of electrocatalysts for the HER in acidic media. We show that in PdCoO 2 the inherently strained Pd metal sublattice acts as a pseudomorphic template for the growth of a strained (by +2.3%) Pd rich capping layer under reductive conditions. The surface modification continuously improves the electrocatalytic activity by simultaneously increasing the exchange current density j 0 from 2 to 5 mA/cm² geo and by reducing the Tafel slope down to 38 mV/decade, leading to overpotentials 10 < 15 mV for 10 mA/cm² geo , superior to bulk platinum. The greatly improved activity is attributed to the in-situ stabilization of a β-palladium hydride phase with drastically enhanced surface catalytic properties with respect to pure or nanostructured palladium. These findings illustrate how operando induced electrodissolution can be used as a top-down design concept for rational surface and property engineering through the strainstabilized formation of catalytically active phases.

SnTiO 3 was successfully synthesized for the first time in bulk form by soft chemistry. STEM and Rietveld refinement show that SnTiO 3 adopts a structure similar to the archetypical ilmenite-type structure, forming a honeycomb lattice of edge-sharing TiO 6 -octahedra, which are decorated with Sn 2+ . Given the formation of a van der Waals gap between the individual layers and hence close energetic minima of different stacking types, SnTiO 3 forms multiple stacking orders and twinning domains that we describe by systematic DIFFaX-simulations. The structure is governed by the tin lone pairs, which influence the stacking of the layers as well as local distortions observed by EELS and NMR, potentially leading to a wide range of applications.