Analysis of deposition and desorption processes of ion pairs using cyclic voltammetry with varied scan rates: Two-step formation of barium salt of chloranil anion radical on electrode surface

In order to investigate the adsorption and the desorption processes of the barium salts of 2,3,5,6-tetrachloro-1,4-benzoquinone anion radical (TCQ(.-) ), cyclic voltammetry was utilized with scan rates from 50 mV/s up to 100 V /s. As a result, together with the changes in the shape of one peak in the negative going scan, three kinds of characteristic oxidation peaks were obs erved in the reversed positive going scan depending on the scan rate. These peaks could be attributed to the oxidation of TCQ(.-), Ba(2+)TCQ(.-) and B a2+(TCQ(.-))(2) formed via the following equations. TCQ + e(-) --> TCPQ(.-) TCQ(.-) + Ba2+ --> Ba(2+)TCQ(.-) Ba2+ TCQ(.-) + TCQ(.-) --> Ba2+(TCQ(.-))(2) Namely, while TCQ(.-) can be detected at the faster scan rate of 100 V/s by depressing the consecutive reactions, the oxidation peal; of the intermedi ate Ba(2+)TCQ(.-) could be observed at the medium scan rates in the potenti al region negative to that of the final product, Ba2+(TCQ(.-))(2). This mea ns that Ba2+(TCQ(.-))(2) is formed through the two-step reactions, and that the final product, Ba2+(TCQ.-)(2), was stabilized on the electrode surface judging from its oxidation potential.