CHRONOCOULOMETRY AT PLATINUM ELECTRODES IN NONAQUEOUS SOLVENTS AND KINETIC STUDIES IN ELECTROGENERATED CHEMILUMINESCENCE.

摘要

The nonideal behavior in chronocoulometry of nonaqueous systems involving platinum electrodes is mainly caused by the absorbed hydrogen in platinum. The net reaction complicating reductive electrochemistry is the transformation of the hydrogen atom to the hydride ion, involving phase transfer from the platinum lattice to the solution. Ideal behavior can be approached at low temperatures (ca. -40(DEGREES)), especially when care is taken in the preparation of the electrode surface. The results given here have general relevance to the continued use of platinum electrodes in electrochemistry.; The light emission mechanism of the 5,6,11,12-tetraphenylnaphthacene electrogenerated chemiluminescence (ECL) system is mixed ST-route with decreasing T-route fractions as temperature decreases. The decrease of T-route contributions at low temperatures is due to the increase of the ratio of singlet/triplet produced directly by electron transfer. The overall electron-transfer efficiency decreases with temperature decrease, and this effect is strongly dependent on the supporting electrolyte concentration, indicating the importance of radical-ion environments at the moment of electron transfer. The significance of these results is its link to the factors governing excitation yields in a process in which large amounts of energy is disposed.; The light transient shape of the 9,10-diphenylanthracene (DPA) system is greatly affected by the concentration and the types of the supporting electrolyte. In particular, there is a light shut-down effect in the presence of perchlorate. The kinetic behavior of the system also is affected by the electrogenerated hydride due to the reduction of DPA cation to DPA by hydride. Another effect of hydride on the light transient behavior is the formation of hyride reaction products which modify the ECL reaction zone structure. Cyclohexanone can be used as an effective hydride quencher, however, the presence of cyclohexanone also affects the transient behavior due to solvation with cations. A triplet induction effect was observed in the presence of cyclohexanone. The development of an effective hydride quencher or of new electrode material in the near future is essential to enable us to have clearer pictures of ECL processes.