CHARGE-TRANSPORT IN FROZEN TETRAALKYLAMMONIUM FLUORIDE HYDRATES CONTAINING A 1 1 MIXTURE OF K3FE(CN)(6) AND K4FE(CN)(6)/

Charge transport in frozen tetraalkylammonium fluoride hydrates (CH3)( 4)NF . 4H(2)O and (C4H9)(4)NF . 32H(2)O, containing a 1:1 mixture of K 3Fe(CN)(6) and K4Fe(CN)(6), has been studied by impedance spectroscopy , cyclic voltammetry and potential step chronoamperometry at temperatu res 60-80 K below the melting point of electrolytes. Generally, the bu lk conductivity of both electrolytes containing redox active ions incr eases substantially in comparison with that of pure electrolytes. The shape of slow scan cyclic voltammograms obtained in frozen electrolyte is different from that obtained in liquid, and depends on temperature and scan rate. The apparent diffusion coefficient of redox active ion s in (CH3)(4)NF . 4H(2)O does not change substantially at temperatures around the electrolyte melting point. The activation energy of charge transport in this electrolyte is twice as large in frozen as in liqui d electrolyte, being about 0.7 and 0.35 eV respectively. It has been c oncluded that, at temperatures close to the melting point of frozen el ectrolyte, this process occurs rather by physical diffusion than by el ectron hopping. The shape of current response obtained from potential step experiments in frozen electrolyte is different from that expected for semi-infinite diffusion towards a planar electrode. The reasons f or this phenomenon are discussed.