Electron self-exchange dynamics of hexacyanoferrate inredox polyether hybrid moltensalts containing polyether-tailed counterions

摘要

Hexacyanoferrate(III) is combined with a quatemary ammonium countercation consisting of triethylammonium connected to a poly(ethylene glycol) methyl ether (MW 350) “tail”, to form a highly viscous room-temperature redox polyether hybrid melt (e.g., a molten salt) in which the concentration of hexacyanoferrate centers is 0.82 M. Microelectrode voltammetry and potential step chronoamperometry in the undiluted melt give an apparent diffusion coefficient D_(App) = 2.5X10~(10) cm~2/s at 20 deg C that is interpreted as reflecting primarily the rate of electron self-exchange between Fe(IU and Fe(III) centers. A rate constant of k_(EX)= 1.1 x l0~5 M~(-1)s~(-1) is derived from this DAPP. and from its temperature dependence, an activation energy barrier of 30 kJ/mol. kEx is in good agreement with results in fluid solutions. At the same concentration (0.82 M). but in aqueous solution. the (potassium salt) hexacyanoferrate species displays a D_(APP) of 4 x 10-6 cm~2/s. which is interpreted as reflecting physical transport of the hexacyanoferrate species. Transport of the hexacyanoferrate species is enormously “plasticized in aqueous medium as opposed to the highly viscous polyether melt. Electronic spectra and ionic conductivity of the hybrid redox polyether melt are also reported.