Voltammetry of [Re(DMPE)3]+ at ionomer-entrapped composite-modified electrodes

Nation or sodium poly(styrenesulfonate) (NaPSS) entrapped in either sol-gel-derived silica or cross-linked poly(vinyl alcohol) (PVA) composite coatings on spectroscopic graphite electrodes were investigated electrochemically with [Re-I(DMPE)(3)](+), where DMPE = 1,2-bis(dimethylphosphino)ethane. Among these composite coatings, Naftion-entrapped sol-gel-derived silica (Nafion-silica) exhibited a sensitivity for [Re-I(DMPE)(3)](+) similar to 4 times higher than that of NaPSS-entrapped sol-gel-derived silica or NaPSS-entrapped PVA. When Nafion was entrapped in cross-linked PVA matrix, however, the voltammetric response was found to be only similar to 14% of that of Nafion and Nafion-silica composite coatings. Dispersing Nafion in sol-gel-derived silica matrix improves the slow diffusion of [Re-I(DMPE)(3)](+) in Nafion, thus leading to a higher sensitivity than Nafion in a shorter preconcentration time. Such a Nafion-silica composite is promising for both electrochemical and spectroelectrochemical sensing of [Re-I(DMPE)(3)](+). It was also found that increasing the high potential of a cyclic voltammetric scan greatly reduces the amount of [Re-II(DMPE)(3)](2+) available for reduction in the reverse potential scan, suggesting that the electrochemically generated [Re-II(DMPE)(3)](2+) was consumed in the more positive potential region.