The enhancement of non-Faradaic charge and energy density stored by ionic electrolytes in nanostructured electrodes is an intriguing issue of great practical importance for energy storage in electric double layer capacitors. On the basis of extensive molecular dynamics simulations of various carbon-based nanoporous electrodes and room temperature ionic liquid (RTIL) electrolytes, we identify atomistic mechanisms and correlations between electrode/electrolyte structures that lead to capacitance enhancement. In the symmetric electrode setup with nanopores having atomically smooth walls, most RTILs showed up to 50% capacitance increase compared to infinitely wide pore. Extensive simulations using asymmetric electrodes and pores with atomically rough surfaces demonstrated that tuning of electrode nanostructure could lead to further substantial capacitance enhancement. Therefore, the capacitance in nanoporous electrodes can be increased due to a combination of two effects: (i) the screening of ionic interactions by nanopore walls upon electrolyte nanoconfinement, and (ii) the optimization of nanopore structure (volume, surface roughness) to take into account the asymmetry between cation and anion chemical structures.

The structural properties of electrolytes consisting of solutions of ionic liquids in a polar solvent at charged electrode surfaces are investigated using classical atomistic simulations. The studied electrolytes consisted of tetraethylammonium tetrafluoroborate (NEt4-BF4), 1-ethyl-3-methylimidazolium tetrafluoroborate (c2mim-BF4) and 1-octyl-3-methylimidazolium tetrafluoroborate (c8mim-BF4) salts dissolved in acetonitrile solvent. We discuss the influence of electrolyte concentration, chemical structure of the ionic salt, temperature, conducting versus semiconducting nature of the electrode, electrode geometry and surface roughness on the electric double layer structure and capacitance and compare these properties with those obtained for pure room temperature ionic liquids. We show that electrolytes consisting of solutions of ions can behave quite differently from pure ionic liquid electrolytes.

There has in recent years been considerable research into the use of metallocene catalysts of the type [Cp 2 ZrMe] + for propene polymerization, 1 and it is generally accepted that initiation and propagation involve alkene coordination to the vacant site to give [Cp 2 Zr(Me)(η 2 -propene)] + . Following a series of 1,2-insertions, chain transfer follows -hydrogen migration to release a polymer with a terminal vinylidene end group (eq 1). 1 However, attempts are still being made to detect and characterize alkyl alkene intermediates of the type [Cp 2 Zr(Me)(η 2 -alkene)] + , which are generally quite short-lived because of their pronounced proclivity to undergo insertion and which therefore have never been observed. 2 Indeed, the only d 0 zirconocene-alkene complexes which are known are chelated complexes in which the coordinated alkene is also tethered to the metal via a heteroatom, 2a-d and the complexes [Cp 2 Zr(C 6 F 5 )(alkene)] + and [Cp 2 Zr(OBu t )(alkene)] + (alkene ) 1-alkenes, allyltrimethylsilane, vinylferrocene, tert-butyl vinyl ether) in which migratory insertion cannot occur. 2e,f There is also considerable interest in related observations that some propene polymerization processes are affected adversely by slow degradation of catalysts to dormant species. It is thought that active catalysts can convert to unreactive allylic species of the type [Cp 2 Zr(η 3 -allyl)] + via transfer of a methyl hydrogen atom from a coordinated propene to a polymeryl or hydride ligand. 3 Alternatively, compounds of the type [Cp 2 ZrMe] + are found to react slowly with vinylidene compounds CH 2 dCMeR to form methane and cationic allylic complexes [Cp 2 Zr(η 3 -CH 2 C(R)CH 2 )] + , 3d,4 and it has been suggested that polypropene-containing vinylidene end groups CH 2 dCMe∼P (P ) polymeryl) (eq 1) may react in the same way (eq 2) rather than just behaving as spectators of the polymerization process. 4c,e As part of an ongoing study of the nature of dormant species during alkene polymerization processes, 5 we are investigating reactions of [Cp 2 ZrMe] + with, e.g., 2,4-dimethyl-1-pentene, a model compound for propene macromonomers containing vinylidene end groups. We report here that [Cp 2 ZrMe] + does indeed react with 2,4-dimethyl-1-pentene to form methane and an allyl complex, [Cp 2 -Zr(η 3 -CH 2 C(CH 2 CHMe 2 )CH 2 )] + , but the reaction involves the unprecedented η 1 -vinylidene or near η 1 -vinylidene intermediate [Cp 2 Zr(Me)(η 1 -CH 2 CMeCH 2 CHMe 2 )] + , detected by low-temperature one-and two-dimensional (1D and 2D) 1 H NMR spectroscopy. As an unanticipated corollary, the existence of the η 1 -vinylidene complex suggests an alternative and possibly general route to allylic species, one which has not heretofore been considered.In a typical experiment Cp 2 ZrMe(µ-Me)B(C 6 F 5 ) 3 , generated by reacting Cp 2 ZrMe 2 with 1.1 equiv of B(C 6 F 5 ) 3 , was reacted with 1.5 equiv of 2,4-dimethyl-1-pentene in C 6 D 5 Cl at 21°C; the reaction was monitored by 1 H NMR spectroscopy over several hours. During the course of...

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