The reduction of carbonyl compounds at carbon electrodes in acidic water/methanol mixtures

The voltammetry of benzaldehyde in acidic methanol/water mixtures is shown to depend strongly on the cathode material. At pH 1, benzaldehyde always reduces in two 1e- steps and the first step is always reversible. On the other hand, the potential for the second reduction step varies strongly with cathode material; at vitreous carbon, the second step occurs at much more negative potential than at lead or mercury, giving much better resolution of the two reduction waves. In citrate buffer, pH 4, the first reduction step is shifted negative; as a result, at lead a single 2e- wave is seen but at vitreous carbon, two 1e- steps are still observed. These changes in voltammetry with cathode material are shown to be general for both aldehydes and ketones.