Comparative Study of Borohydride Oxidation, at Polycrystalline and Nanostructured Copper Electrodes
The oxidation of NaBH4 on copper electrodes was studied by cyclic voltammetry at different scan rates and concentrations of NaBH4. Figure 1 shows cyclic voltammograms obtained in a 3M NaOH + 1M NaBH4 aqueous solution of a polycrystalline Cu electrode (curve a) and copper nanoparticles (curves b and c). Curve c shows the study in the absence of borohydride. The experiments started at -1.2 V vs. Ag/AgCl towards positive potential values at a potential sweep scan rate of 100 mVs-1. In these curves, five anodic peaks can be observed, namely peak A1, assigned to the formation of an intermediary due to the hydrolysis of borohydride , peak A2 corresponds to the formation of Cu2O (Cu I), peak A3 corresponds to subsequent oxidation in CuO (Cu II), peak A4 corresponds to a parallel reaction forming Cu(OH)2 (Cu II), and finally, peak A5 results from both the formation of Cu (III) and the borohydride oxidation BH4 . Shift in the potentials associated to the peaks A3, A4 and A5 can be observed when compared the voltammogram on the nanostructurated electrode with the PCE. As far as the borohydride oxidation is concerned, the oxidation starts at +0.3 V vs.Ag/AgCl with copper nanoparticles, while in the PCE the value is +0.4 V. A possible correlation between particle size and reactivity will be explored.
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