A novel class of metal organic frameworks (MOFs) has been synthesized from Cu-acetate and dicarboxylic acids using liquid phase epitaxy. The SURMOF-2 isoreticular series exhibits P4 symmetry, for the longest linker a channel-size of 3 × 3 nm2 is obtained, one of the largest values reported for any MOF so far. High quality, ab-initio electronic structure calculations confirm the stability of a regular packing of (Cu++)2- carboxylate paddle-wheel planes with P4 symmetry and reveal, that the SURMOF-2 structures are in fact metastable, with a fairly large activation barrier for the transition to the bulk MOF-2 structures exhibiting a lower, twofold (P2 or C2) symmetry. The theoretical calculations also allow identifying the mechanism for the low-temperature epitaxial growth process and to explain, why a synthesis of this highly interesting, new class of high-symmetry, metastable MOFs is not possible using the conventional solvothermal process.

We present a technique for extracting Raman intensities from ab initio molecular dynamics (MD) simulations at high temperature. The method is applied to the highly anharmonic case of dense hydrogen up to 500 K for pressures ranging from 180 to 300 GPa. On heating or pressurizing we find first-order phase transitions under the experimental conditions of the phase III-IV boundary. At even higher pressures, close to 350 GPa, we find a second phase transformation to the previously proposed Cmca-4. Our method enables, for the first time, a direct comparison of Raman vibrons between theory and experiment at finite temperature. This turns out to provide excellent discrimination between subtly different structures found in MD. We find candidate structures whose Raman spectra are in good agreement with experiment. The new phase obtained in hightemperature simulations adopts a dynamic, simple hexagonal structure with three layer types: freely rotating hydrogen molecules, static hexagonal trimers, and rotating hexagonal trimers. We show that previously calculated structures for phase IV are inconsistent with experiment, and their appearance in simulation is due to finite-size effects.

The polymer binders used in most lithium-ion batteries (LIBs) serve only a structural role, but there are exciting opportunities to increase performance by using polymers with combined electronic and ionic conductivity. To this end, here we examine dihexyl-substituted poly­(3,4-propylenedioxythiophene) (PProDOT-Hx2) as an electrochemically stable π-conjugated polymer that becomes electrically conductive (up to 0.1 S cm–1) upon electrochemical doping in the potential range of 3.2 to 4.5 V (vs Li/Li+). Because this family of polymers is easy to functionalize, can be effectively fabricated into electrodes, and shows mixed electronic and ionic conductivity, PProDOT-Hx2 shows promise for replacing the insulating polyvinylidene fluoride (PVDF) commonly used in commercial LIBs. A combined experimental and theoretical study is presented here to establish the fundamental mixed ionic and electronic conductivity of PProDOT-Hx2. Electrochemical kinetics and electron spin resonance are first used to verify that the polymer can be readily electrochemically doped and is chemically stable in a potential range of interest for most cathode materials. A novel impedance method is then used to directly follow the evolution of both the electronic and ionic conductivity as a function of potential. Both values increase with electrochemical doping and stay high across the potential range of interest. A combination of optical ellipsometry and grazing incidence wide angle X-ray scattering is used to characterize both solvent swelling and structural changes that occur during electrochemical doping. These experimental results are used to calibrate molecular dynamics simulations, which show improved ionic conductivity upon solvent swelling. Simulations further attribute the improved ionic conductivity of PProDOT-Hx2 to its open morphology and the increased solvation is possible because of the oxygen-containing propylenedioxythiophene backbone. Finally, the performance of PProDOT-Hx2 as a conductive binder for the well-known cathode LiNi0.8Co0.15Al0.05O2 relative to PVDF is presented. PProDOT-Hx2-based cells display a fivefold increase in capacity at high rates of discharge compared to PVDF-based electrodes at high rates and also show improved long-term cycling stability. The increased rate capability and cycling stability demonstrate the benefits of using binders such as PProDOT-Hx2, which show good electronic and ionic conductivity, combined with electrochemical stability over the potential range for standard cathode operation.