Studies in hydrogen overpotential the effect of catalytic poisons at platinized platinum and nickel

Abstract

The effect of As (as As2O3 in HCl) on H overpotential set up at platinized platinum electrodes has been examined. The effect of the presence in solution of traces of As2O3, CO, CS 2, KCN and PtCl4 on the rate of the hydrogen evolution reaction at a Ni cathode has been determined. Negative deviations from the Tafel equation at higher current densities were not observed in pure solutions but were produced by the presence of traces of poison (As2O3). At high (0.1 M) concentration of As2O3 a limiting current occurs at about 3 × 10-3 A/cm.2 in N aqueous HC1 solution. The variation of hydrogen overpotential with time at constant c.d. is negligible at platinized platinum and Ni electrodes in the absence of impurities but is considerable, erratic and of long duration in the presence of traces of impurities. This variation in impure solution can be considerably reduced by pre-electrolysis of the solutions used. Impurities at concentrations of the order of 10-10 mole/1, affect the rate of the hydrogen evolution reaction on Ni cathodes at a given overpotential. The effect of these poisons is experimentally analogous in a number of respects to poison effects in heterogeneous catalysis.