Voltammetry of [Re(DMPE)3]+ at Ionomer-Entrapped Composite-Modified Electrodes

Nafion 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, Nafion-entrapped sol−gel-derived silica (Nafion-silica) exhibited a sensitivity for [Re I (DMPE) 3 ] + ∼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 ∼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.