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The cathodic reduction of anthraquinone in 85% H2SO4 at cathodes of glassy carbon or mercury has been investigated. Voltammetric curves exhibit two steps at +0.23 and +0.10 V vs. SHE. The limiting current densities show a ratio between 4:O via 1 : 1 to 1 : 3, depending on the experimental conditions. Experiments at the RRDE indicate two reoxidizable intermediates. -We derive a mechanism from our findings, involving the electrochemical formation of these intermediates, anthrasemiquinone AQH-and anthrahydroquinone AQH2. Both are subject to a bimolecular follow up reaction (disproportionation) to yield AQH2 and anthrone. The rate constants are estimated to be 2. lo3 and 3 . lo4 1 mol-' s-', respectively. Anthrone is the only reduction product which could be isolated.

Carbon Black / Electrochemistry / Slurry Electrode / Surfaces Slurry electrodes in 1 M H lP04 , made from carbon blacks with a specific surface ranging from 28 to 1475 m 2 g-t, were studied by cyclovoltammetry (5 mV S-I) at potentials between -0.1 V and +2.3 V vs. SHE. A large anodic peak and a small cathodic one is found, with an extreme peak separation (1.5 V) and with a charge ratio of 3: 1 to 5: 1. Charge transfer at the feeder is hindered by insulating surface layers on the carbon black. Part of the anodic peak is due to the irreversible oxidation of the solid. The initial curves are governed by the large capacity of the system. -This slurry electrode differs widely from that made with metal powders or hard graphite. The particles strongly adhere to the feeder and build up a porous system. The exchange with the dispersed particles is poor. In spite of this, the curves are reproducible, they reflect the specific surface and it is possible to recognize features with respect to the anodic oxidation of carbon black.

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